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PDQ* SERIES
ACKERMANN
PDQ PHYSIOLOGY
BAKER, MURRAY
PDQ BIOCHEMISTRY
CORMACK
PDQ HISTOLOGY
DAVIDSON
PDQ MEDICAL GENETICS
JOHNSON
PDQ PHARMACOLOGY, 2/e
KERN
PDQ HEMATOLOGY
McKIBBON
PDQ EVIDENCE-BASED PRINCIPLES AND PRACTICE
NORMAN, STREINER
PDQ STATISTICS, 3/e
SCIUBBA, REGEZI, ROGERS
PDQ ORAL DISEASE: DIAGNOSIS AND TREATMENT
STREINER, NORMAN
PDQ EPIDEMIOLOGY, 2/e
*
PDQ (Pretty Darned Quick)
PDQ
HISTOLOGY
DAVID H. CORMACK, PHD
Professor Emeritus
Division of Anatomy, Department of Surgery
University of Toronto
Toronto, Ontario
with illustrations by
Monique Guilderson, BSc., MSc., BMC
2003
BC Decker Inc
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Notice: The authors and publisher have made every effort to ensure that the patient care recommended herein, including choice of drugs and drug dosages, is in accord with the accepted standard
and practice at the time of publication. However, since research and regulation constantly change
clinical standards, the reader is urged to check the product information sheet included in the package of each drug, which includes recommended doses, warnings, and contraindications. This is particularly important with new or infrequently used drugs. Any treatment regimen, particularly one
involving medication, involves inherent risk that must be weighed on a case-by-case basis against
the benefits anticipated. The reader is cautioned that the purpose of this book is to inform and
enlighten; the information contained herein is not intended as, and should not be employed as, a substitute for individual diagnosis and treatment.
Preface
I
t is my sincere hope that this short laboratory guide will turn
out to be a handy study aid for those histology students who, because of
inexperience, are nervous about becoming overwhelmed by too much histologic detail. In keeping with the approach taken by the other books in the
PDQ series, it deals only with basics, which it presents in a reasonably
rational manner. Because PDQ Histology focuses the reader’s attention on
the main structural features found in standard sections taken from the student’s slide box and emphasizes the particular combination of histologic criteria that characterizes each section, it represents a minireview of the distinctive microscopic features that permit histologic preparations of the
various tissues and organs of the body to be correctly identified. Included
on the accompanying CD-ROM are representative selections of review
questions, sample multiple-choice questions, and temporarily unidentified
test sections available for private assessment of the reader’s comprehension
and proficiency at appropriate stages in the course of study.
Along with a good slide box, microscope, labeled relevant photomicrographs, and the timely assistance of expert slide interpreters, histology
students generally appreciate being provided with a fairly nitty-gritty
approach to slide identification. PDQ Histology is designed to help beginners to make a productive start and then to keep them firmly on the rails.
To advance, students should, of course, endeavor to supplement their
knowledge base with further relevant information that they are receiving
from lectures, other textbooks, atlases, and recommended additional
sources. Before long, diligent students will find that they are able to compile other reliable recognition features of their own. By learning how to
rationalize test situation responses, they will soon be able to avoid flagrant
guesswork and with sufficient practice will attain self-confidence in microscopic identification of tissues.
David H. Cormack
January 2003
Contents
Preface, v
1
Introduction: Cells and Tissues, 1
2
Epithelial Tissue, 19
3
Connective Tissue, 35
4
Cartilage and Bone, 45
5
Blood and Myeloid and Lymphoid
Tissues, 61
6
Nervous Tissue, 83
7
Muscle, 99
8
Circulatory System, 109
9
Integumentary System, 119
10
Digestive System, 129
11
Respiratory System, 145
Contents
12
Urinary System, 155
13
Endocrine System, 169
14
Female Reproductive System, 185
15
Male Reproductive System, 201
Index, 214
vii
PDQ
Histology
1
Introduction: Cells and
Tissues
A
fundamental concept of body structure is that its interior
represents an intricate assembly of distinct body tissues. The constituent
cells of these tissues are so frail that they generally require the support of
extracellular matrix (ECM), but certain tissues have a minimal amount of
this component and others have an ECM that is represented by a fluid. The
least conspicuous tissue component at a microscopic level is a body fluid,
predominantly interstitial (tissue) fluid and, less commonly, blood plasma
or lymph. A profusion of functional cell products passes into these body fluids from the tissues, ranging from secreted matrix constituents and plasma
proteins to hormones and various other signaling molecules.
Histology is essentially the study of the body tissues. Although there
are only four basic tissues, some have variant and special subtypes, as
shown in Table 1–1. Organs and body parts are all constructed from these
four basic tissues and their subtypes. Histology also addresses the question
of how tissue cells carry out body processes at the cellular level. By describing major body functions in terms of the relevant tissues and their distinctive cell structure, it serves as a structural foundation for allied and
applied health sciences such as physiology, biochemistry, hematology, and
pathology.
1
2
PDQ HISTOLOGY
Table 1–1
Four Basic Tissues with Their Subtypes
Epithelial tissue
Epithelial membranes
Epithelial glands
Connective tissue
Loose (areolar) tissue
Nervous tissue
Muscle tissue
Skeletal muscle
Cardiac muscle
Smooth muscle
Dense ordinary (fibrous) tissue
Adipose (fat)
Cartilage
Bone
Blood cells
Myeloid tissue
Lymphoid tissue
MICROSCOPES
The chief tool at the histologist’s disposal is the light microscope (LM).
Providing two-staged magnification (Figure 1–1), the LM has as its basis (1)
an objective lens assembly and (2) an ocular (eyepiece) lens assembly. For
an eye unaided by any magnifying device, the minimal distance between
two adjacent points in a specimen that is necessary for these to be distinguishable as separate entities (ie, retinal resolution) is 0.2 mm. Magnifications up to 1,000, obtainable with the LM, enable small details up to
0.2 µm apart to be discerned, but because 0.2 µm is the LM’s absolute limit
of resolution, any further photographic enlargement exceeding 1,400 discloses no further details.
Another limitation of the LM is that incident light must pass through
the specimen viewed. Tissue slices (sections) or suitably thin alternative
preparations are therefore necessary. Also, appropriate histologic stains
(dyes) are required for most tissue components to be seen clearly, so the tissue is routinely fixed (killed and preserved with 4% aqueous formaldehyde
or some other protein coagulant) and processed further to permit its sectioning and enhance its staining. The necessary harsh treatment can cause
unintentional distortion that may complicate the interpretation of LM
appearance. An atypical histologic appearance may indicate inadequate fixation or excessive shrinkage during tissue processing.
Further information about the LM and some hints on how to get it to
perform properly may be found in the accompanying CD-ROM.
Chapter 1
Introduction: Cells and Tissues
3
Image on retina
Eyepiece lenses
Intermediate image
in optical path
Objective lenses
Section on stage
Condenser lenses
Lamp
Figure 1–1 Optical path of the light microscope.
When higher magnifications and better resolution are required, an electron microscope (EM) is used instead. The transmission electron microscope (TEM) operates in a manner similar to the LM but uses a beam of
electrons instead of incident light. The scanning electron microscope
(SEM) is somewhat different in design. When its narrow electron beam
tracks back and forth across a metallic or metal-coated surface, electrons
secondarily emitted or reflected from the metal are collected. The resulting
signal is processed to produce a three-dimensional-looking television image
(scan) of the scanned surface.
The usual kind of electron micrograph found in histology texts and
atlases (see Figure 1–5) is obtained with a TEM, which can provide magnifications up to 50,000 and resolve details that are 1 nm apart. This greater
resolution is achieved by using an electron beam instead of light. Resolution
is proportional to wavelength, and the wavelength of an electron beam is
over 1,000 times shorter than that of light. Resolution in scanning electron
micrographs, which are encountered less commonly in histology courses, is
generally limited to about 15 nm by the coating thickness, but SEM resolutions of 3 nm are technically possible.
4
PDQ HISTOLOGY
When EM sections of a tissue are viewed with the TEM following fixation with glutaraldehyde and appropriate staining with heavy metals, electrons pass unimpeded through areas where tissue components remain
unstained, whereas stained components scatter electrons out of the beam.
Through photographic reversal of the image on the viewing screen, electrondense components of the tissue accordingly appear black and electron-lucent
components appear white in the reversed prints (electron micrographs).
Although three-dimensional imaging of biologic surfaces is possible
with the SEM, routine photomicrographs and micrographs show tissues and
organs in section, so it is important to try to visualize the three-dimensional
structure of a living tissue or organ before it was fixed, distorted by tissue
preparation, sectioned, and stained.
INTERPRETING TISSUE SECTIONS
When confronted with histologic sections, beginning students often ask what
they are supposed to see. A generalized answer is either individual cells or
aggregates of cells forming some characteristic arrangement with the ECM.
Indeed, many organs and tissues are recognizable histologically by their distinctive arrangement of cells and ECM. Some detailed mental reconstruction
is generally necessary before histologic sections can be visualized in three
dimensions. An initial general impression to seek is whether the composition
of the tissue or organ is predominantly cellular (Figure 1–2) or predominantly ECM (Figure 1–3). Another useful clue is whether the structure seems
solid, perforated with spaces, or hollow. Preliminary observation under scanning power (30) or low power (100) generally provides helpful information before details are sought. Lower magnifications are often more informative than high ones, particularly for organ identification.
Chapter 1
Introduction: Cells and Tissues
Figure 1–2 Liver tissue made up chiefly of cells.
Extracellular
matrix
Cells
Figure 1–3 Elastic cartilage tissue made up chiefly of extracellular matrix.
5
6
PDQ HISTOLOGY
CELLS
The appearance of cells in LM sections of liver may be seen in Figure 1–4. The
central spherical nucleus houses the cell’s complement of chromosomes that
contain gene-bearing deoxyribonucleic acid (DNA). The darkly stained structure toward the nuclear center, the nucleolus, is the site of production of ribosomal RNA (rRNA). The other darkly stained material in the nucleus, heterochromatin (condensed chromatin), represents genetically inactive DNA that
is not being transcribed, that is, copied from DNA to RNA for protein synthesis. The outer part of the cell, its cytoplasm, derives energy through cell metabolism and synthesizes proteins. Few details of its internal structure are seen in
routine histologic sections because the cytoplasmic organelles are so small, so
the EM, with its higher resolution, is generally employed instead. The perimeter of each cell is sometimes difficult to discern in LM sections (see Figure 1–4),
generally because it lies at the wrong angle for good visibility. The cell membrane itself is not thick enough to be resolved in the LM.
Nucleus
Nucleolus
Cell boundary
Figure 1–4 Light microscopic appearance of hepatocytes.
Cytoplasm
Chapter 1
Introduction: Cells and Tissues
7
Figure 1–5 shows an example of cell and ECM appearance at the EM
level. The chief cytoplasmic organelles and their functions are summarized
in Table 1–2. For further information, see Web site links in the accompanying
CD-ROM.
Lysosome
Extracellular
matrix
Rough-surfaced
endoplasmic
reticulum
Nuclear envelope
Heterochromatin
Cell membrane
Figure 1–5 Electron microscopic appearance of chondrocytes and their associated extracellular matrix.
8
PDQ HISTOLOGY
Table 1–2
Main Components of Cytoplasm
Component
Cell membrane
Cytosol
Structure
Chief Functions
Fluid lipid bilayer with
integral and peripheral
proteins and cell coat
on external surface
Semifluid with minimal
internal support
Regulates molecular exchanges
with tissue fluid, responds to
signals
Contains soluble molecules and
cytoplasmic organelles and
inclusions
Synthesizes lipids and steroids,
segregates calcium in muscle
cells, metabolizes drugs and
glycogen in hepatocytes
Incorporates integral membrane
proteins, segregates
secretory and lysosomal
proteins in its lumen
Completes glycosylation of
glycoproteins, modifies and
sorts secretory products,
distributes secretory proteins
to secretory vesicles, sends
acid hydrolases to lysosomes
Convey secretory proteins from
Golgi apparatus to cell
surface
Smooth-surfaced
endoplasmic
reticulum
Branched tubular
system of smooth
intracellular membrane
Rough-surfaced
endoplasmic
reticulum
Parallel flat membranous
cisternae with bound
ribosomes
Golgi apparatus
Saucer-shaped stack
of flat smooth
membranous
saccules
Secretory vesicles
Spherical smooth
membranous saccules
containing secretory
proteins
Lysosomes
Small spherical smooth
membranous saccules
containing acid
hydrolases
Segregate destructive enzymes
for general use in
intracellular digestion
Mitochondria
Outer and inner limiting
membranes, cristae,
internal mitochondrial
matrix
Produce ATP through oxidative
phosphorylation
Ribosomes
Electron-dense
ribonucleoprotein
particles present as
subunits
Provide sites where amino acids
are assembled in the order
specified in mRNA sequences
Microtubules
Unbranched tubular
assemblies of tubulin
subunits, 25 nm in
diameter, single and
assembled into
centrioles, cilia, and
flagella
Provide support, guide
intracellular transport, provide
ciliary and flagellar motility
Continued
Chapter 1
Introduction: Cells and Tissues
9
Table 1–2 (Continued)
Main Components of Cytoplasm
Component
Structure
Chief Functions
Microfilaments
(equivalent to
thin filaments)
Actin-containing 7 nm rods
Interact with thick filaments
in contractions, support
microvilli
Thick filaments
Myosin-containing 12–16 nm
rods
Interact with microfilaments or
thin filaments in contractions
Intermediate
filaments
Heterogeneous class of
10 nm rods
Provide support, distribute
stresses
ATP = adenosine triphosphate; mRNA = messenger ribonucleic acid.
STAINS
A stain combination routinely used for histologic sections is hematoxylin and
eosin (H&E). Unless otherwise stated, the photomicrographs in this book
show sections that have been stained in this manner. Hematoxylin, a treederived dye combined with Al3+ ions, colors negatively charged components
blue or purple. Eosin is a negatively charged stain that colors positively charged
components pink or red. Basophilic components stain with hematoxylin (a
basic stain); acidophilic components stain with eosin (an acid stain). When a
blood stain is used, basophilic and acidophilic constituents stain equivalent
blue and pink colors. Periodic acid–Schiff (PAS) staining generates aldehyde
groups in glycoproteins and polysaccharides and discloses these as magenta or
purple dye complexes.
Tissue components staining blue in H&E sections
•
•
•
contain macromolecules having a net negative charge, for example,
DNA, RNA (nucleic acids are rich in PO43– groups);
have an affinity for hematoxylin because of its associated Al3+ ions;
include nuclear chromatin, nucleoli, and cytoplasmic ribosomes.
Tissue components staining pink in H&E sections
•
•
•
contain macromolecules having a net positive charge in the staining pH
range of 5 to 6, for example, fixed proteins with amino groups ionized
to –NH3+,
take up eosin because it has a negative charge, and
are in most cases proteins.
Tissue components staining magenta in PAS sections
•
•
may be secretory glycoproteins;
may be glycogen, a stored polysaccharide.
After H&E staining, why does the cell cytoplasm appear essentially pink
in Figure 1–6 and comparatively blue in Figure 1–7 and have areas of each
10
PDQ HISTOLOGY
Figure 1–6 Pink-stained cytoplasm in skeletal muscle fibers.
Osteoblasts
Figure 1–7 Blue-stained cytoplasm in osteoblasts.
color in Figure 1–8? What does this staining reveal about the particular
functions of each cell type?
The cytoplasm of muscle fibers (see Figure 1–6)
•
has a high concentration of structural proteins (actin, myosin, etc) that
are moderately acidophilic, and
Chapter 1
•
Introduction: Cells and Tissues
11
is functionally specialized for contraction.
The cytoplasm of osteoblasts (see Figure 1–7)
•
•
contains abundant ribosomes, and therefore basophilic RNA, bound to
its rough-surfaced endoplasmic reticulum (rER);
is functionally specialized for secretion (bone matrix constituents).
The cytoplasm of pancreatic acinar cells (see Figure 1–8)
•
•
•
contains abundant ribosomes, and therefore basophilic RNA, bound to
its rER;
contains abundant secretory vesicles with acidophilic secretory protein
content;
is functionally specialized for the synthesis and release of stored acidophilic secretory proteins (digestive enzymes).
Alternative staining can provide supplementary information. For example, the surface epithelium stained with H&E in Figure 1–9 exhibits round,
virtually colorless gaps containing some constituent with negligible affinity
for either stain. A PAS-stained section (Figure 1–10) discloses magentacolored mucus at these sites, indicating that the white gaps are goblet cells
Figure 1–8 Pink- and blue-stained cytoplasmic components in pancreatic acinar cells.
12
PDQ HISTOLOGY
Figure 1–9 Goblet cells in a hematoxylin and eosin–stained section of the small intestine.
Figure 1–10 Goblet cells in a periodic acid–Schiff–stained section of the small intestine.
Chapter 1
Introduction: Cells and Tissues
13
(glycoprotein-secreting surface epithelial cells). Special staining methods
are occasionally preferable, notably silver impregnation for nervous tissue
and immunohistochemical staining for specific proteins.
NUCLEAR APPEARANCE
Functional activity may be reflected in the appearance of the nucleus as well
as the cytoplasm. Cells that are actively synthesizing proteins, for example,
often exhibit a large nucleolus (see Figure 1–4) because they require an
abundance of the rRNA exclusively transcribed there.
It is equally important to be able to recognize mitotic (dividing) cells
because the proportion and LM appearance of dividing cells can have diagnostic value. Mitotic figures may be spotted under low magnification (Figure 1–11). At higher magnification, the individual rod-shaped chromosomes may be discernible (Figure 1–12).
Mitotic figures
Figure 1–11 Mitotic figures present in crypt bases of the small intestine.
14
PDQ HISTOLOGY
Anaphase
Figure 1–12 Mitotic figure seen in more detail (crypt of small intestine).
Chapter 1
Introduction: Cells and Tissues
The process of mitosis is summarized in Figure 1–13.
Polar microtubules form
between centriole pairs
Prophase
Chromosomes
become thread-like
Nuclear envelope
starts fragmenting
Metaphase
Kinetochore microtubules
form in mitotic spindle
Chromosomes (two
chromatids in each)
align in equatorial plane
Anaphase
Kinetochore microtubules
shorten
Spindle elongates due to
sliding between opposed
polar microtubules
Chromatids separate,
move toward poles
Nuclear envelope re-forms
Telophase
Daughter chromosomes
(formerly the chromatids)
segregate
Equatorial region
constricts
Residual microtubules
form midbody
Figure 1–13 The stages of mitosis.
15
16
PDQ HISTOLOGY
Appropriate preparation and special staining of isolated mitotic cells
allow specific identification of the chromosomes they contain (Figure
1–14). An assembled chromosome map obtained from a representative cell
is called a person’s karyotype.
Figure 1–14 Chromosomes isolated from a mitotic cell and stained to show their chromosome
bands.
Another important distinction that needs to be made is between mitotic
cells and dying cells. Sometimes both are present in the same field of view.
All stages of mitosis except early prophase are recognizable by the presence
of dark-staining chromosomes and the absence of an intact nuclear envelope (Figure 1–15). Dying or dead cells, on the other hand, exhibit terminal
disintegration of their nucleus (karyorrhexis), extreme condensation and
heavy (heterochromatic) staining of its chromatin (pkynosis), or unusually
pale heterochromatin staining (karolysis). Examples of these changes are
shown in Figure 1–16.
Chapter 1
Introduction: Cells and Tissues
Anaphase
Metaphase
Figure 1–15 Mitotic figures in dividing hepatoma cells.
Pyknosis
Karyorrhexis
Figure 1–16 Nuclear signs of cell death.
Karyolysis
17
18
PDQ HISTOLOGY
Finally, a few cell types, for example, osteoclasts (Figure 1–17) and
skeletal muscle fibers (see Figure 1–6), possess more than one nucleus. In
these cases, the multinucleate condition is a consequence of cell fusion.
Human erythrocytes (red blood cells) possess no nucleus because it is discarded at a late precursor stage.
Osteoclasts
Figure 1–17 Multiple nuclei in osteoclasts.
2
Epithelial Tissue
B
ody cavities are lined with extensive cellular sheets known as
epithelial membranes (epithelia). The body also has a protective epithelial
covering termed the epidermis. Epithelia are invaginated at certain sites,
extending into adjacent connective tissue as epithelial glands. Epithelial tissue accordingly consists of epithelial membranes and glands.
EPITHELIAL MEMBRANES
The constituent cells of epithelial membranes are clearly polarized in structure. Their free (luminal or apical) surface borders on the lumen of a body
compartment or the exterior of the body. A well-defined extracellular
matrix layer known as a basement membrane (basal lamina) attaches their
basal surface to adjacent connective tissue. This special matrix layer is
described in Chapter 3, “Connective Tissue.” The diverse functional roles of
epithelia include protection, absorption, secretion, transcellular transport,
restriction of diffusion, and provision of sensory function. Progressive cell
renewal through mitosis in basal layers of epithelia is their chief means of
maintaining structural integrity. Because epithelial tissue is entirely avascular, its cells typically obtain oxygen and nutrients by diffusion from capillaries of adjacent loose connective tissue.
Subtypes
Epithelial membranes are characterized by the number of constituent cell
layers and cell shape at their free surface (Table 2–1).
Typical examples of simple epithelia as they appear in hematoxylin and
eosin (H&E) sections are shown in Figures 2–1, 2–2, and 2–3.
19
20
PDQ HISTOLOGY
Table 2–1
Epithelial Membranes
Simple—a monolayer of cells
Squamous—flat shape
Cuboidal—short, roughly square in sections
Columnar—tall and narrow
Pseudostratified—all cells are attached to the basement membrane but some do not
reach the free surface, giving a false impression of stratification
Columnar
Ciliated columnar—commonly with goblet cells
Stratified—more than one layer of cells
Squamous—cuboidal basal cells, flat surface cells
Keratinized—flat keratinized cells on free surface
Nonkeratinized—flat nonkeratinized cells on free surface
Cuboidal—usually 2 layers, lines small ducts
Columnar—usually 2 layers, lines larger ducts
Transitional—bulging surface cells become flat if epithelium is stretched
Simple squamous
epithelium
Figure 2–1 Simple squamous epithelium.
Simple cuboidal epithelium
Figure 2–2 Simple cuboidal epithelium.
Chapter 2
Epithelial Tissue
21
Simple columnar epithelium
Figure 2–3 Simple columnar epithelium.
The pseudostratified epithelium lining the main airways (Figure 2–4)
possesses goblet cells and cilia that act together to trap and clear away any
inhaled suspended particles that settle. Cilia are hair-like motile cytoplasmic processes that project from the luminal surface of the epithelium. Using
the energy that they release from adenosine triphosphate, they continuously sweep a thin coating of mucus across the luminal surface. Cilia are
characterized by nine peripheral pairs of microtubules (doublets that can
actively slide past each other) and two central single microtubules (Figure
2–5). The mucus coating that is swept along by the cilia is produced by goblet cells (Figure 2–6) and underlying mixed (seromucous) glands.
22
PDQ HISTOLOGY
Cilia
Goblet cell
Figure 2–4 Ciliated pseudostratified columnar epithelium with goblet cells.
Figure 2–5 Electron micrograph of cilia.
Chapter 2
Epithelial Tissue
23
Figure 2–6 Electron micrograph of a goblet cell.
The chief stratified epithelia are shown in Figures 2–7, 2–8, and 2–9.
Cells approaching the surface of stratified squamous keratinizing epithelium become a layer of evaporation-resistant soft keratin termed the stratum corneum (Figure 2–7), whereas those of stratified squamous nonkeratinizing epithelium (Figure 2–8) remain nonkeratinized but still fairly
resistant to abrasion.
24
PDQ HISTOLOGY
Stratum corneum
Basal layer of epithelium
Figure 2–7 Stratified squamous keratinizing epithelium.
Figure 2–8 Stratified squamous nonkeratinizing epithelium.
Chapter 2
Epithelial Tissue
25
Transitional epithelium (see Figure 2–9), confined to the urinary tract,
is unique in that, for unknown reasons, some of the large football-shaped
cells on its luminal border are multinucleated and a few are polyploid, that
is, they contain more than one diploid set of chromosomes.
Multinucleated cell
Figure 2–9 Transitional epithelium.
Cell Junctions
Specialized sites known as cell junctions lie on the lateral and basal parts of
the epithelial cell membrane (Figure 2–10). Table 2–2 details their various
electron microscopic appearances and functions—essentially, cell-to-cell
sealing, cell attachment, and direct cell-to-cell communication.
26
PDQ HISTOLOGY
Continuous tight
junction
Adhesion belt
A
Desmosome
Gap junction
Hemidesmosome
Basement
membrane
B
C
Continuous tight
Adhesion belt
Desmosome
Gap
Figure 2–10 Epithelial cell junctions. A, Belt-shaped junctions on lateral surfaces. B, Circular
junctions on lateral and basal surfaces. C, Detailed structure of cell junctions.
Chapter 2
Epithelial Tissue
27
Table 2–2
Principal Cell Junctions
Junction
Structural Features
Function
Continuous tight
junction (zonula
occludens)
Circumferential band where
aligned integral membrane
proteins interlock and form
anastomosing ridges
By obstructing lateral
intercellular spaces,
these ridges limit
paracellular diffusion at
lateral cell borders
Adhesion belt
(zonula adherens)
Circumferential band where
linker glycoproteins extend
into the intercellular gap,
strongly bonding contiguous
cell membranes; anchors
the marginal band of
microfilaments
This junction maintains
strong cell-to-cell
adherence at the site
where the attached
marginal band
contracts
Desmosome
Circular area where strongly
bonding linker glycoproteins
form an electron-dense line
along midline of the gap;
electron-dense plaques
along desmosome’s lateral
borders anchor intermediate
(keratin) filaments
Tension in the attached
intermediate filaments
is resisted by the
rivet-like site of strong
cell-to-cell adherence
Hemidesmosome
Circular area on basal surface,
Tension in the attached
resembling half a desmosome,
intermediate filaments
where cell membrane, plaque,
is resisted by the
and anchored intermediate
rivet-like site of strong
filaments lie apposed to
anchorage to the ECM
basement membrane
Gap junction
Circular area containing tiny
spool-like assemblies
(connexons) of aligned
interlocking integral
membrane proteins;
connexons bridge the
intercellular gap and in
their open configuration
constitute walls of aqueous
channels
ECM = extracellular matrix.
By providing a route for
small molecules and
ions to diffuse directly
from one cell to another,
these channels permit
metabolic coupling and
direct cell-to-cell
communication
28
PDQ HISTOLOGY
EPITHELIAL GLANDS
Glands that release their secretion through a duct are classified as exocrine;
those that deliver it directly to the bloodstream are termed endocrine (see
Chapter 13, “Endocrine System”). The epithelial components of a gland (its
secretory units and ducts) are called its parenchyma; the connective tissue
components (loose connective tissue and fibrous capsule) are known as its
stroma. Exocrine gland classification is broadly based on the general structure and function of glands (Table 2–3).
Table 2–3
Exocrine Epithelial Glands
Structural Classification
Simple—unbranched duct system
Tubular —secretory unit is tubular and in some cases coiled
Acinar/alveolar—secretory unit is spherical/flask-shaped
Compound—branched duct system
Tubular
Acinar/alveolar
Functional Classification
Serous—produces a watery secretion that generally contains some protein
Mucous—produces mucus
Seromucous (mixed)—possesses separate serous and mucus-secreting cells
Other—eg, sebaceous glands producing an oily secretion (sebum) from
disintegrated lipid-laden cells
Chapter 2
Epithelial Tissue
29
In simple glands, the secretory portion is generally distinguishable from
the duct. In the example shown in Figure 2–11, a coiled simple tubular
sweat gland,
•
•
•
the pale-staining, low columnar epithelial cells are serous secretory cells,
the flat nuclei closely apposed to their basal border are those of contractile myoepithelial cells, and
the double layer of cuboidal epithelial cells with dark-staining nuclei are
duct cells.
Secretory portion
Duct
Figure 2–11 Simple tubular gland (eccrine sweat gland).
30
PDQ HISTOLOGY
In compound glands (Figure 2–12), stromal elements such as intralobular loose connective tissue, fibrous interlobular septa, and the fibrous capsule
are also recognizable. Intralobular ducts (see Figure 2–14) are the narrow
duct branches lying within lobules. Interlobular ducts are the slightly wider
branches extending along fibrous septa that delineate lobules. These ducts
collect the secretion from intralobular ducts. Hence, the parenchymal organization of a compound gland may be likened to a dormant bush-like tree:
•
•
•
•
rounded buds = secretory units
small twigs = intralobular ducts
branches = interlobular ducts
trunk = main duct
Building on this analogy, a heavy fall of snow covering the tree and filling all its crevices = stromal connective tissue.
Secretory unit
Interlobular duct
Fibrous interlobular
septum
Intralobular duct
Intralobular loose
connective tissue
Fibrous capsule
Figure 2–12 Organization of a compound gland.
Chapter 2
Epithelial Tissue
31
Serous secretory units (Figures 2–13 and 2–14) are readily distinguishable from mucous secretory units (Figures 2–13 and 2–15) by the following
criteria:
Serous cells
•
•
•
large spherical nucleus
basophilic cytoplasm at base
acidophilic secretory granules
Mucus-secreting cells
•
•
small flat dark-staining nucleus at base
essentially colorless in H&E sections because of their stored mucus
Mucous secretory units
Serous secretory units
Figure 2–13 Mixed (seromucous) gland showing mucous and serous secretory units.
32
PDQ HISTOLOGY
Both types of secretory unit may be found in the same gland (see Figures
2–13 and 2–15). The serous and mucous secretory cells of these mixed (seromucous) glands can lie in separate lobules (see Figure 2–13), a common
lobule (see Figure 2–15), or a common mixed secretory unit (Figure 2–16).
Serous secretory units
Intralobular duct
Figure 2–14 Serous gland showing serous secretory units and duct.
Mucous secretory unit
Serous secretory
unit
Serous cell in mixed
secretory unit
Figure 2–15 Mixed (seromucous) gland showing mucous, serous, and mixed secretory units.
Chapter 2
Epithelial Tissue
33
The serous and mucous cells of a mixed secretory unit release their secretions independently into the same central lumen. Arranged as a cap on one
side of the mucous unit, the serous cells in such a unit appear in sections as
a serous demilune. Whether this is apparent as a crescent-shaped area
depends on the plane of section.
Intralobular duct
Serous demilune
Figure 2–16 Mixed (seromucous) gland showing serous demilunes.
3
Connective Tissue
T
he three subtypes of connective tissue being considered in
this chapter are loose (areolar), dense ordinary (fibrous), and body fat (adipose). In contrast to the extracellular matrix (ECM) that represents the
principal constituent of the first two subtypes, the functionally important
constituent of adipose tissue is stored lipid.
INTERSTITIAL MATRIX
The ECM complex of connective tissue, known as the interstitial matrix, contains collagen fibers, elastic fibers, and an amorphous component known as
ground substance. Hard to distinguish in hematoxylin and eosin (H&E)stained sections, these intercellular fibers are recognizable in specially stained
tissue spreads (Figure 3–1). Representing strong bundles of nonbranching
collagen fibrils, collagen fibers can be fairly acidophilic, for example, at sites
where they are abundant. They provide substantial tensile strength. Branched,
comparatively narrow, straight elastic fibers provide elasticity. Incorporating
the protein elastin within a framework of unbranched microfibrils made of
glycoproteins called fibrillins, elastic fibers have little affinity for eosin and
require special stains (eg, orcein) for their presence to be evident. The finest
bundles of collagen fibrils (found, for example, in the liver and myeloid and
lymphoid tissues) branch owing to longitudinal bundle splitting. Demonstrable with silver stains, these bundles are called reticular fibers because they
constitute an intimate supporting network for cells. Whereas the coarse collagen fibers of connective tissue are assemblies of type I collagen, representing ~ 90% of the total collagen, reticular fibers are assemblies of type III collagen. Both collagen and elastic fibers become assembled interstitially from
their respective secreted precursor proteins, procollagen and tropoelastin.
The ground substance of connective tissue, essentially colorless in H&E
sections, is a hydrated gel containing proteoglycans, the glycosaminoglycan
hyaluronic acid, and glycoproteins. This gel plays a key role in nutrient and
waste diffusion because it sequesters tissue fluid in its aqueous channels.
35
36
PDQ HISTOLOGY
LOOSE CONNECTIVE TISSUE
In suitably stained loose connective tissue prepared as a flat spread (see Figure 3–1), it is possible to distinguish
•
•
•
•
•
capillaries (because it is a highly vascular tissue),
nuclei of the fibroblasts that secreted ECM macromolecules,
conspicuous mast cells full of histamine-containing secretory granules
wavy wide collagen fibers made up of fibrils, and
straight narrow elastic fibers.
It is important to realize that in such preparations, the entire thickness of
cells and fibers is seen.
Capillary
Fibroblast nucleus
Mast cell
Elastic fiber
Figure 3–1 Loose connective tissue spread (special stains).
Collagen fiber
Chapter 3
Connective Tissue
37
The H&E-stained loose connective tissue shown adjacent to stratified
epithelium in Figure 3–2 looks dissimilar from that in Figure 3–1 because
it has been sectioned. This is how it is usually seen. Its recognizable characteristics include the following:
•
•
abundant pink collagen fibers
numerous capillaries extending into projecting papillae that supply the
thick epithelium with nutrients
Epithelium
Loose connective tissue
Figure 3–2 Loose connective tissue in section (lamina propria of the esophagus).
38
PDQ HISTOLOGY
Along the interface between loose connective tissue and other tissues
such as epithelium, the ECM is organized into a thin sheet of binding
matrix called a basement membrane. At this site, laminin, an adhesive glycoprotein with a binding receptor in the cell membrane, is intimately associated with an interstitially assembled meshwork of type IV collagen. Other
interstitial glycoproteins and proteoglycans participate in binding the adjacent cells to the interstitial matrix. Basement membrane sites are periodic
acid–Schiff positive because of this high glycoprotein content (Figure 3–3).
At the electron microscopic level, a cross-section of the basement membrane appears as a thin fuzzy extracellular line of low electron density
(lamina densa) situated parallel and adjacent to the basal surface of the
attached cells.
Basement membrane
Figure 3–3 Basement membranes of renal tubules.
CONNECTIVE TISSUE CELLS
Table 3–1 lists the main characteristics of the cell types found in loose connective tissue. Because this tissue is involved in certain types of immune and
inflammatory responses, lymphocytes and neutrophils may also be encountered (see Chapter 5, “Blood and Myeloid and Lymphoid Tissues”).
Chapter 3
Connective Tissue
39
Table 3–1
Connective Tissue Cells
Cell Type
Structural Features
Chief Functions
Fibroblast
Spindle-shaped, basophilic
cytoplasm in secretory state
Plasma cell
Round with basophilic cytoplasm,
pale Golgi region, eccentric
nucleus with condensed
peripheral chromatin
Ovoid, eccentric kidney-shaped
nucleus sometimes hidden by
phagocytosed particles or
hemosiderin (hemoglobin
breakdown pigment)
Secretes fibrous and
amorphous interstitial
matrix constituents
Secretes immunoglobulin
Macrophage
Mast cell
Endothelial cell
Pericyte
Adipocyte
(fat cell)
Phagocytoses
microorganisms, foreign
particles, and cell debris;
processes antigens;
secretes complement
proteins and growth
factors
Ovoid, central ovoid nucleus
Releases histamine and
sometimes hidden by granule
other inflammatory
content, large metachromatic
mediators when triggered
secretory granules
by local trauma or antigen
cross-linking of surfacebound immunoglobulin E
Squamous epithelial lining cell
Regulates production of
of blood vessels and lymphatics
tissue fluid and fluid
exudate, regulates bloodtissue molecular
exchanges, releases
vasoactive mediators
(nitric oxide radical and
endothelin 1)
Irregularly shaped with long
Incompletely differentiated
cytoplasmic processes
cell persisting as a
wrapped around capillaries
potential source of new
and small venules
fibroblasts and smooth
muscle cells
Large and round, with small
Stores and mobilizes lipid
flat nucleus at periphery of
(long-term energy reserve)
large central lipid droplet
(which is extracted in tissue
processing)
40
PDQ HISTOLOGY
Fibroblasts are most readily recognizable at connective tissue sites where
they are actively secreting ECM macromolecules (Figure 3–4). Plasma cells,
derived from antigen-activated B lymphocytes, are recognizable by their
round shape, characteristic eccentric “clock-face” nucleus, cytoplasmic
basophilia, and pale negative Golgi region (Figures 3–4 and 3–5).
Plasma cells
Fibroblasts
Figure 3–4 Fibroblasts and plasma cells in loose connective tissue.
“Clock-face” nucleus
Golgi region
Figure 3–5 Plasma cells seen in more detail.
Chapter 3
Connective Tissue
41
Macrophages are readily identifiable if they contain phagocytosed particles, for example, a marker dye (Figure 3–6) or inhaled smoke-derived carbon particles. They are further characterized by having a kidney-shaped
nucleus.
Macrophages
Figure 3–6 Macrophages in loose connective tissue.
DENSE ORDINARY CONNECTIVE TISSUE
Compared with loose connective tissue, dense ordinary (fibrous) connective
tissue is substantially less vascular and its collagen bundles are much coarser
(Figures 3–7 and 3–8). Scattered between the type I collagen bundles are
nuclei of inactive fibroblasts (fibrocytes). Because the form of dense ordinary
(fibrous) connective tissue shown here is an interweaving arrangement of
wavy collagen bundles extending in almost every direction, it is described as
irregular. Tendons and ligaments are characterized by the regular form of
this tissue, where orderly arrays of essentially parallel collagen bundles are
oriented like cable wires along the direction of tension.
42
PDQ HISTOLOGY
Loose ordinary connective tissue
Dense ordinary connective tissue
Figure 3–7 Irregular dense ordinary connective tissue (reticular layer of dermis of thin skin).
Figure 3–8 Collagen bundles of irregular dense ordinary connective tissue.
Chapter 3
Connective Tissue
43
ADIPOSE TISSUE
In loose connective tissue, adipocytes (fat cells) may be found singly or in
small groups. In adipose (fat) tissue, adipocytes represent the predominant
cell type (Figure 3–9). The white spaces created by lipid extraction give this
tissue a distinctive “chicken wire” appearance. Besides storing lipid for
potential energy production, adipose tissue pads parts of the body and fills
some crevices. The widely distributed kind of adipose tissue shown in Figure 3–9, called white fat, is the principal site of lipid metabolism. The less
extensive kind, called brown fat because it contains an even greater abundance of mitochondrial cytochromes and blood capillaries, stores lipid as
multiple droplets and provides essential body heat, which is important in
newborn babies.
Figure 3–9 Adipocytes of white fat.
4
Cartilage and Bone
E
ach of the structurally specialized skeletal tissues cartilage and
bone is derived from mesenchyme, as are the other forms of connective tissue. Although both tissues are made up of extracellular matrix and cells,
cartilage is totally avascular, whereas bone tissue is highly vascular. Another
key difference is that cartilage can grow from within (interstitial growth)
through internal production of more matrix as well as grow externally by
adding more matrix to its outer surface (appositional growth), whereas
bone grows entirely through apposition to its surface. Functionally relevant
differences also exist in the composition of the matrix.
CARTILAGE
Essentially, hyaline cartilage (Figure 4–1) is designed to resist compression.
Approximately 75% of its wet weight is tissue fluid that provides a longdistance diffusion route for nutrients and oxygen to reach the chondrocytes
embedded in its avascular matrix. Other functionally important constituents of hyaline cartilage matrix are proteoglycan (chiefly present as
aggregates) and reinforcing fibrils composed of type II collagen. Chondrocytes occupy tiny spaces in the matrix (lacunae) that become visible because
the fixed cells shrink. When the chondrocytes of growing cartilages divide,
some lacunae remain closely associated as cell nests.
The common type of cartilage is more fully described as hyaline (glasslike). Articulating surfaces of bones are covered with a specialized form of
hyaline cartilage called articular cartilage (Figure 4–2). Besides hyaline cartilage, there are two other forms of cartilage, also avascular, known as elastic cartilage (Figures 4–3 and 4–4) and fibrocartilage (Figure 4–5). The
distribution of these reinforced forms of cartilage is more limited.
45
46
PDQ HISTOLOGY
Perichondrium
Matrix
Cell nests
Figure 4–1 Hyaline cartilage.
Articular cartilage
Subchondral bone
Figure 4–2 Articular cartilage.
Chapter 4
Cartilage and Bone
47
Typical features of hyaline cartilage (see Figure 4–1) include the following:
•
•
•
•
•
•
matrix slightly blue (or slightly pink)
peripheral fibrous perichondrium (irregular dense ordinary connective
tissue)
lacunae large and round, with shrunken chondrocytes, particularly in
its midregion
lacunae flatter near its periphery
some lacunae associated as cell nests
blood vessels absent
Articular cartilage (see Figure 4–2) has the following characteristics:
•
•
•
•
•
•
matrix pink, reflecting extent of type II collagen packing
no peripheral perichondrium (hence postnatal growth is entirely
interstitial)
lacunae near the articular surface are parallel and flat (sandwiched
between horizontal collagen fibrils)
in the midregion, some lacunae are arranged in longitudinal columns
(a feature in growing articular cartilages indicating chondrocyte
proliferation)
vascular subchondral bone supporting it appears more acidophilic
because it contains relatively more collagen
avascular
48
PDQ HISTOLOGY
The characteristics of elastic cartilage (see Figures 4–3 and 4–4; see also
Figure 1–3) are as follows:
•
•
•
matrix contains supplementary acidophilic elastic fibers that give the
matrix additional elastic properties (these fibers are more conspicuous
with an elastin stain, eg, in Figure 4–4)
resembles hyaline cartilage in other respects
found in the epiglottis and external ear
Figure 4–3 Elastic cartilage (hematoxylin and eosin stain).
Figure 4–4 Elastic cartilage (special elastin stain).
Chapter 4
Cartilage and Bone
49
Distinctive features of fibrocartilage (see Figure 4–5) are as follows:
•
•
•
•
matrix contains reinforcing pink-staining bundles of type I collagen
fibers that give the matrix extra tensile strength
round lacunae, containing round chondrocytes, are typically arranged
in straight rows
matrix is slightly blue between lacunae
found in tendon insertions, intervertebral disks, menisci, and pubic
symphysis
Figure 4–5 Fibrocartilage.
BONE
Bone matrix is heavily calcified (hydroxyapatite constitutes 70% of its wet
weight), and type I collagen constitutes approximately 90% of its organic
content, making it highly resistant to compression, tension, bending, and
twisting. In contrast, cartilage matrix stays largely uncalcified except during
long bone development and growth. Other important constituents of bone
matrix are (1) proteins that induce bone formation and promote matrix
calcification and (2) tissue fluid representing roughly 25% of its wet weight.
Because bone matrix is heavily calcified and has a comparatively low water
content, bone tissue requires short-range diffusion from blood capillaries;
hence, it is highly vascular. Numerous fine communicating channels called
canaliculi interconnect its lacunae (see Figures 4–16 and 4–17), conveying
tissue fluid that facilitates such diffusion.
50
PDQ HISTOLOGY
Bone Cells
Bone tissue forming in connective tissue membranes incorporates developing loose connective tissue that brings with it a capillary blood supply. In
this vascular environment, mesenchymal cells differentiate into osteoblasts
that start secreting the macromolecular constituents of bone matrix.
In intramembranously developing flat bones (Figure 4–6), basophilic
osteoblasts cover the surface of acidophilic bony trabeculae (beams), laying
down new matrix on the surface (appositional growth). Bone consisting of
anastomosing trabeculae like this is called cancellous bone.
Bony trabecula
Osteoblasts
Capillary
Figure 4–6 Cancellous bone developing in an intramembranous environment.
Osteoblasts show the cytoplasmic basophilia and pale negative Golgi
region characteristic of active protein secretion (Figure 4–7). Spindleshaped osteoprogenitor (osteogenic) cells are also present on the surface.
These progenitor cells persist as bipotential stem cells that give rise to
osteoblasts at well-vascularized sites but produce chondrocytes at avascular
sites. Osteocytes appear smaller and less rounded than osteoblasts and lie
within lacunae (see Figure 4–7).
Chapter 4
Cartilage and Bone
51
Osteoprogenitor cell
Endothelial cell of
blood vessel
Osteoblasts
Osteocyte
Figure 4–7 Osteoblasts and osteocytes of cancellous bone.
In addition to this bone-forming cell family, bone tissue contains large
multinucleated cells called osteoclasts that resorb bone matrix (Figures 4–8
and 4–9; see also Figure 1–17). Derived from blood monocytes, osteoclasts
are recognizable by their multiple nuclei, relative size, acidophilic cytoplasm, and resorptive ruffled border applied to a ragged matrix surface or
resorption bay (Howship’s lacuna). They decalcify and then partly digest the
adjacent matrix locally by secreting H+ ions and lysosomal hydrolases into
a sealed compartment of extracellular space under this border.
52
PDQ HISTOLOGY
Osteoclasts
Figure 4–8 Osteoclasts resorbing bone matrix.
Figure 4–9 Osteoclast seen in more detail.
Chapter 4
Cartilage and Bone
53
Bone matrix is subject to lifelong internal remodeling in which old or
weakened bone resorbed through osteoclast activity is immediately replaced
by new bone through osteoblast activity. Osteoporosis (ie, a decrease in the
body’s total bone mass) is a manifestation of inadequate compensation of
bone resorption by bone formation.
Growth of Long Bones
Development and postnatal growth of a long bone involves the progressive
bony replacement of a temporary cartilage model. This indirect process,
known as endochondral ossification, is more complicated than the
intramembranous ossification occurring directly in connective tissue membranes (see Figure 4–6). It is a consequence of vascularization of the model
and progressive encroachment into the cartilage by bone cells that lay down
layers of bone matrix by apposition on cartilage remnants.
The following zones may be recognized in the cartilaginous growth
plate (epiphyseal plate) present at either end of a child’s typical growing
long bone (Figure 4–10):
•
•
•
•
resting (reserve) cartilage—anchors epiphyseal plate to bony epiphysis;
chondrocytes randomly distributed
proliferating cartilage—replaces chondrocytes lost during ossification;
chondrocytes arranged as longitudinal stacks
maturing cartilage—hypertrophying (enlarging) chondrocytes initiate
calcification; chondrocytes large and pale staining
calcifying cartilage—calcium phosphate becomes deposited in matrix;
chondrocytes along diaphyseal border die; transverse partitions of lacunae disintegrate
Bone becomes deposited by apposition on the longitudinal partitions of
calcified cartilage extending as remnants from the diaphyseal border.
54
PDQ HISTOLOGY
Zones:
resting
proliferating
maturing
calcifying
Figure 4–10 Zones of an epiphyseal plate.
Bone Subtypes
Cancellous bone forming in the metaphysis under the epiphyseal plate (Figure 4–11) shows the following features:
•
•
•
light-staining wide vascular soft tissue spaces representing > 50% of its
volume
lamellae (layers) of dark pink bone matrix deposited on pale blue remnants of calcified cartilage
osteoblasts and osteoprogenitor cells on the bone surface
Adult cancellous bone (from iliac crest) is shown in Figure 4–12. The
pale tissue between the trabeculae is fat-storing (yellow) bone marrow. Cancellous bone (upper border of Figure 4–13) can give rise to dense (compact)
bone (lower third of Figure 4–13) through appositional thickening of its
trabeculae. The additional new lamellae diminish the former soft tissue
spaces to narrow haversian canals. Persisting cancellous bone nevertheless
provides necessary internal support in medullary cavities (see Figure 4–12).
Chapter 4
Figure 4–11 Cancellous bone developing endochondrally.
Figure 4–12 Cancellous bone (iliac crest).
Cartilage and Bone
55
56
PDQ HISTOLOGY
Figure 4–13 Dense bone forming from cancellous bone.
Dense (compact) bone (Figures 4–14 and 4–15) is characterized by the
following features:
•
•
•
•
•
•
filled-in soft tissue spaces representing only a small proportion of its
volume
cylindrical haversian systems (osteons), each having lamellae and osteocytes arranged concentrically around a central haversian canal
blood vessels in longitudinal haversian canals and radial Volkmann’s
canals
smooth inner and outer circumferential lamellae
external periosteum made up of an outer vascular dense ordinary connective tissue and a deeper population of osteoprogenitor cells
internal endosteum represented by a single layer of osteoprogenitor
cells that lines the medullary cavity and haversian canals
Chapter 4
Cartilage and Bone
57
Cancellous bone in
medullary cavity
Inner circumferential
lamellae
Haversian vessel in
a haversian canal
Blood vessel in a
Volkmann's canal
Periosteum
Interstitial lamellae
Haversian system (osteon)
Outer circumferential
lamellae
Figure 4–14 Organization of dense bone.
Figure 4–15 Dense bone.
58
PDQ HISTOLOGY
Several histologic features of dense bone, for example, haversian systems, bone canaliculi, and interstitial lamellae, are more recognizable in
ground sections (silver-stained transparent thin slices of undecalcified bone
matrix). Figure 4–16 shows some details of a haversian system. After parts
of a haversian system have been dismantled by osteoclasts during the course
of internal remodeling, the parts that are left behind constitute interstitial
lamellae (Figure 4–17).
Haversian canal
Osteocyte lacunae
interconnected by
canaliculi
Figure 4–16 Haversian system of dense bone (ground section, silver stain).
Lamellae of haversian
system
Interstitial lamellae
Figure 4–17 Interstitial lamellae of dense bone (ground section, silver stain).
Chapter 4
Cartilage and Bone
59
JOINT TISSUES
In sections of articulating synovial joints, it is possible to find articular cartilage (see Figure 4–2), fibrocartilage at tendon or ligament insertions into
cartilage (see Figure 4–5), epiphyseal plates if the bones are still growing
(see Figure 4–10), and the lining synovial membrane of the joint.
The synovial membrane (synovium), not regarded as an epithelial
membrane because it is made up of connective tissue cells trapped between
abundant interstitial fibers (both collagen and elastin), has three characteristic appearances. The vascular area shown at left in Figure 4–18 is typical
of an areolar region. Secretory cells (synovocytes) near its surface produce
the viscous glycoprotein and hyaluronic acid present in synovial fluid, the
lubricating fluid of the joint. The dense ordinary connective tissue shown
at the right in Figure 4–18 is a fibrous region with coarse collagen bundles
that are highly resistant to friction. The central fold of tissue in Figure 4–19
is an adipose region with synovocytes near its surface and underlying
grouped adipocytes that collectively serve as a cushion.
Areolar region
Fibrous region
Figure 4–18 Areolar and fibrous regions of synovium.
60
PDQ HISTOLOGY
Articular cartilage
Adipose region of synovium
Figure 4–19 Adipose region of synovium.
5
Blood and Myeloid and
Lymphoid Tissues
P
eripheral blood consists of plasma (ie, serum along with
fibrinogen and clotting factors) and formed elements, which are commonly
known as blood cells even though erythrocytes have no nucleus and
platelets are only cytoplasmic fragments. The total blood volume is about
5 L, with blood cells occupying roughly 45% of this volume. Blood cells are
produced by myeloid tissue and lymphoid tissue, the two hematopoietic
(hemopoietic) tissues.
BLOOD CELLS
The chief characteristics of the various kinds of circulating blood cells are
outlined in Table 5–1. In addition to erythrocytes (red blood cells) and
platelets, five different types of leukocytes (white blood cells) exist, each
having a characteristic appearance and distinctive functions. Erythrocytes
are more abundant than leukocytes in peripheral blood. The neutrophil is
the predominant type of leukocyte.
Individual blood cells are routinely observed in peripheral blood films
stained with suitable blood stains.
61
62
PDQ HISTOLOGY
Table 5–1
Blood Cells
Cell
Morphology and Staining
(Blood Stain)
Erythrocyte
Pink disk, without nucleus
Transports oxygen as
oxyhemoglobin
Platelet
Small blue fragment with central
purple granules and no nuclear
component
Platelet aggregates stop
blood loss from damaged
blood vessels
Chief Functions
Leukocytes
Neutrophil Pale with small mauve granules;
nucleus segmented (2–5 lobes)
Phagocytoses and destroys
bacteria
Eosinophil
Large red granules; nucleus bilobed
Destroys parasitic worms,
regulates local allergic
inflammation
Basophil
Large blue granules; nucleus
bilobed or segmented
Releases histamine and other
inflammatory mediators
when triggered by antigen
cross-linking of surfacebound immunoglobulin E
(systemic allergic response)
Lymphocyte Diameter small or large; cytoplasm
blue, without granules; nucleus
spherical
B and T cells mediating
immune responses
Monocyte
Phagocytoses debris;
circulating precursor of
macrophages and
osteoclasts
Diameter large; cytoplasm pale
blue, without granules; nucleus
shaped like a kidney or horseshoe
Chapter 5
Blood and Myeloid and Lymphoid Tissues
63
Erythrocytes and Platelets
Distinctive features of erythrocytes (Figure 5–1) are as follows:
•
•
•
•
biconcave disks, diameter 7 µm
middle third thinner and therefore paler
contain the oxygen-transporting protein hemoglobin
worn out and destroyed after 4 months in the circulation
Platelets (Figure 5–2) have the following characteristics:
•
•
•
•
biconvex disks, diameter 3 µm, dispersed or aggregated in blood films
irregular mass of purple granules at the center
derived through fragmentation of megakaryocytes
contain the vasoconstrictor serotonin and a potent growth factor
Figure 5–1 Erythrocytes.
Figure 5–2 Platelets.
64
PDQ HISTOLOGY
Granulocytes
Figure 5–3 Neutrophil.
Figure 5–4 Eosinophil.
Chapter 5
Blood and Myeloid and Lymphoid Tissues
65
Key features of neutrophils (Figure 5–3) include the following:
•
•
•
•
mauve granules, smaller and paler than those of eosinophils or basophils
distinctive segmented nucleus
presence at acutely inflamed sites
short life span (~ 3 days)
In sections, mature neutrophils are easily recognizable by their characteristic segmented nucleus with two to five lobes. Tissue sites where significant numbers of neutrophils lie external to blood vessels are sites of acute
inflammation.
Eosinophils (Figure 5–4) have the following characteristics:
•
•
•
conspicuous red granules and relatively large diameter
distinctive bilobed nucleus
found in loose connective tissue in local allergic responses
Distinctive features of basophils (Figure 5–5) are as follows:
•
•
large blue granules commonly obscuring bilobed or segmented nucleus
rarely encountered in blood films (~ 1% of the total leukocyte count)
66
PDQ HISTOLOGY
Figure 5–5 Basophil.
Nongranular Leukocytes
Small lymphocytes (Figure 5–6) are characterized by the following:
•
•
•
•
•
•
•
diameter close to that of erythrocytes
dark-staining spherical or slightly indented nucleus occupying most of
the cell’s volume
thin rim of blue cytoplasm
more T cells than B cells in peripheral blood
majority are long-lived T cells
recirculate from blood to lymph to blood, etc
found in (1) loose connective tissue at sites where antigen has entered
and (2) lymphoid tissues
Large lymphocytes (Figure 5–7) may be recognized by the following:
•
•
diameter approaching that of monocytes
similar in nuclear morphology and cytoplasmic color to the small lymphocyte but relatively more cytoplasm
Chapter 5
Figure 5–6 Small lymphocyte.
Figure 5–7 Large lymphocyte.
Blood and Myeloid and Lymphoid Tissues
67
68
PDQ HISTOLOGY
Typical monocytes (Figure 5–8) have the following:
•
•
•
a large diameter
a relatively large amount of pale blue cytoplasm
a large kidney-shaped nucleus
Figure 5–8 Monocyte.
MYELOID TISSUE
All types of blood cells except T lymphocytes are produced in myeloid tissue (red bone marrow). The intricate process of blood cell formation is
known as hematopoiesis. Hematopoietic cell populations include pluripotential self-renewing hematopoietic stem cells, hematopoietic progenitor
cells, and blood cell precursors. Respective properties, potentialities, and
acronyms have been assigned to these stem cells and progenitors, based in
large part on the types of blood cells they produce in tissue culture. In each
lineage, precursor stages can nevertheless be recognized directly with a light
microscope. Erythroid precursors, granulocytic precursors, and megakaryocytes (precursor cells of platelets) are examples of hematopoietic precursors that histology students may be asked to identify in myeloid tissue.
Chapter 5
Blood and Myeloid and Lymphoid Tissues
69
Erythroid Series
The erythroid precursors, with their various alternative names, are listed in
Table 5–2 following the sequence in which they are formed.
Table 5–2
Precursor Stages of Erythropoiesis
Proerythroblast (pronormoblast)
Basophilic erythroblast (basophilic normoblast)
Polychromatophilic erythroblast (early normoblast)
Normoblast (late normoblast; orthochromatophilic erythroblast)
Polychromatophilic erythrocyte (reticulocyte)
Erythrocyte (normocyte)
The erythroid precursors shown in Figures 5–9 to 5–13 are individually
identifiable in stained films of red bone marrow.
70
PDQ HISTOLOGY
Figure 5–9 Proerythroblast.
Figure 5–10 Basophilic erythroblast.
Figure 5–11 Polychromatophilic erythroblast.
Figure 5–12 Normoblast showing extrusion
of its nucleus.
Chapter 5
Blood and Myeloid and Lymphoid Tissues
71
Proerythroblasts (see Figure 5–9) are recognizable by the following:
•
•
•
large diameter
large spherical nucleus, sometimes with large nucleoli visible
abundant blue cytoplasm
Basophilic erythroblasts (see Figure 5–10) have the following characteristics:
•
•
•
•
diameter almost as large as that of proerythroblasts
spherical nucleus; chromatin now more condensed
blue cytoplasm
relatively abundant
Polychromatophilic erythroblasts (see Figure 5–11) are characterized by
the following:
•
•
•
•
slightly smaller diameter
spherical nucleus proportionately smaller; chromatin more condensed
and dark staining
bluish-pink cytoplasm (cytoplasmic ribonucleic acid [RNA] along with
newly synthesized hemoglobin)
final dividing stage in the erythroid series
Normoblasts (see Figure 5–12) have the following characteristics:
•
•
•
small diameter
dark-staining spherical nucleus, highly condensed and pyknotic,
becomes extruded from the cell
bluish-pink cytoplasm (becoming increasingly pink)
72
PDQ HISTOLOGY
At the polychromatophilic erythrocyte stage (see Figure 5–13),
•
•
•
•
the diameter is slightly larger than that of a mature erythrocyte;
the nucleus has been extruded;
compared with the color of mature erythrocytes, the cytoplasm still
looks a slightly bluish pink; and
the cell enters the circulation and after 2 days stains as a mature
erythrocyte.
The blue component of the characteristic cytoplasmic staining of erythroid
precursors is the RNA involved in globin synthesis. Its recognition is facilitated
by the use of special stains (new methylene blue or cresyl blue) that aggregate
and stain it, generally as a wreath-like network (Figure 5–14). Polychromatophilic erythrocytes stained this way are called reticulocytes. Cells lacking
such blue-stained particles represent mature erythrocytes (see Figure 5–14).
Mature erythrocyte
Polychromatophilic
erythrocyte
Figure 5–13 Polychromatophilic erythrocyte
Figure 5–14 Reticulocytes and mature
and mature erythrocyte.
erythrocyte.
Chapter 5
Blood and Myeloid and Lymphoid Tissues
73
Granulocytic Series
Table 5–3 lists the granulocytic precursors in the order of their formation.
Table 5–3
Precursor Stages of Granulopoiesis (Neutrophil Series)
Myeloblast
Promyelocyte
Myelocyte
Metamyelocyte
Band neutrophil
Neutrophil
The granulocytic precursors that are most readily identified in marrow
films are those with recognizable specific granules that are mauve, red, or
blue. Neutrophil precursors, characterized by mauve granules, predominate. The earliest precursors, myeloblasts and promyelocytes, are large cells
with spherical nuclei, sometimes with discernible large nucleoli. Promyelocytes also contain inconspicuous azurophilic (primary) granules. However,
because these two stages can have quite an ambiguous appearance, histology students are not often required to recognize them.
74
PDQ HISTOLOGY
Figure 5–15 Myelocyte (neutrophilic).
Figure 5–16 Metamyelocyte (neutrophilic).
Figure 5–17 Band neutrophil.
Chapter 5
Blood and Myeloid and Lymphoid Tissues
75
The neutrophilic myelocyte (Figure 5–15), the last dividing cell in the
neutrophilic series, may be recognized by the following:
•
•
•
diameter similar to that of the basophilic erythroblast
spherical or slightly indented nucleus with rather condensed chromatin
mauve specific (secondary) granules in addition to preexisting fine
azurophilic (primary) granules
The nucleus becomes more kidney shaped and condensed at the
metamyelocyte stage (Figure 5–16).
The band neutrophil (Figure 5–17) is a slightly immature neutrophil
that is nevertheless able to enter the peripheral blood. The highly condensed
nucleus is shaped like a band or horseshoe before it begins to segment.
Changes in the proportion of immature neutrophils to mature neutrophils
in the peripheral blood can be diagnostically indicative.
76
PDQ HISTOLOGY
Erythroid precursors
Granulocytic precursors
Figure 5–18 Bone marrow film.
Sinusoid
Megakaryocyte
Figure 5–19 Section of red bone marrow.
Megakaryocyte
Lipid droplet
Figure 5–20 Megakaryocyte in red bone marrow.
Chapter 5
Blood and Myeloid and Lymphoid Tissues
77
In bone marrow films (Figure 5–18), it is often possible to find erythroid precursors by looking for spherical nuclei and to find granulocytic
precursors (which are more numerous) by spotting their content of granules and/or elongating nucleus. Histologic organization of the tissue, however, is totally disrupted. Sections of myeloid tissue (Figures 5–19 and 5–20)
reveal further structural details in the tissue:
•
•
•
•
wide blood channels termed sinusoids
white empty-looking spaces representing lipid droplets in large fatstoring stromal cells
large megakaryocytes, some adjacent to sinusoids
an assortment of dividing and differentiating hematopoietic cells held
in a reticular fiber meshwork
Megakaryocytes (see Figure 5–19) have the following characteristics:
•
•
•
massive size
large multilobed nucleus that becomes increasingly polyploid as the cell
matures
copious cytoplasm that fragments into platelets at maturity
LYMPHOID TISSUE
Lymphoid tissue is characterized by an abundance of lymphocytes. Diffusely distributed below wet epithelial membranes and aggregated in the
tonsils, Peyer’s patches, and the appendix, it also constitutes a key component of the lymphoid organs, which are the thymus, lymph nodes, and
spleen. Because all of these locations except the thymus represent sites
where immune responses to antigen occur, they are often described as the
secondary lymphoid organs and tissues. The thymus is considered one of
the primary lymphoid organs because it is the site where T cells differentiate. The other primary lymphoid organ is bone marrow, the site where
mammalian B cells differentiate.
78
PDQ HISTOLOGY
Crypt
Lymphoid follicle
Mucous glands
Figure 5–21 Lingual tonsil.
Crypt
Lymphoid follicles
Figure 5–22 Palatine tonsil.
Chapter 5
Blood and Myeloid and Lymphoid Tissues
79
Tonsils are substantial aggregates of lymphoid follicles situated in the
pharynx (palatine tonsils), nasopharynx (pharyngeal tonsil), and tongue
(lingual tonsil).
The lingual tonsil (Figure 5–21) is recognized by the following:
•
•
•
•
conspicuous lymphoid follicles
overlying stratified squamous nonkeratinizing epithelium
underlying mucous glands
crypts kept clear of debris by secretion
The palatine tonsils (Figure 5–22) have the following characteristics:
•
•
•
•
•
large aggregates of lymphoid follicles
overlying stratified squamous nonkeratinizing epithelium
no underlying glands
deep crypts that commonly contain debris
more susceptible to infection
The palatine tonsils are the ones that are removed if they become chronically infected.
80
PDQ HISTOLOGY
Capsule
Subcapsular sinus
Medullary
sinus
Cortical lymphoid follicle
Figure 5–23 Lymph node.
Cortex
Medulla
Figure 5–24 Thymus.
Chapter 5
Blood and Myeloid and Lymphoid Tissues
81
Distinctive recognizable histologic features of lymph nodes (Figure
5–23) are the following:
•
•
•
•
•
afferent and efferent lymphatics
connective tissue capsule with subcapsular sinus
blue-staining cortex with lymphoid follicles and paracortical high
endothelial venules
antibody-secreting plasma cells present in medullary cords
pale lymph-containing medullary sinuses
The thymus (Figure 5–24) has the following characteristics:
•
•
•
•
incompletely lobulated appearance
dark blue-staining cortex packed with small lymphocytes (proliferating
and differentiating T cell progenitors)
cortical network of pale-staining thymic epithelial reticular cells (source
of thymic cytokines and hormones)
medullary pink spherical thymic (Hassall’s) corpuscles
82
PDQ HISTOLOGY
The spleen (Figure 5–25) has the following distinctive features:
•
•
•
•
connective tissue capsule with substantial inward projections (trabeculae)
blue areas (white pulp) containing abundant lymphocytes
close association between white pulp and splenic arterial blood vessels
(eg, the follicular arterioles found in its lymphoid follicles)
pink structural component (red pulp) with characteristic wide sinusoids and closely associated active macrophages
Capsule
Trabecula
Sinusoid
Red pulp
Figure 5–25 Spleen.
Lymphoid follicle with
central arteriole
6
Nervous Tissue
T
he nervous system is made up of nervous tissue with a certain amount of associated connective tissue. The neurons (nerve cells) of
the central nervous system (CNS) are chiefly supported by neuroglial cells
(glia), an ancillary population of heterogeneous cells that, in common with
neurons, are derived from neuroectoderm. Extending from the CNS is the
peripheral nervous system (PNS), consisting of the peripheral nerves, ganglia, and afferent and efferent nerve endings. A characteristic of the PNS is
that its nerve fibers, neuronal cell bodies, and associated glia are intimately
supported and strengthened by substantial wrappings of connective tissue.
Three concentric external connective tissue membranes collectively known
as the meninges similarly invest and protect the brain and spinal cord.
CENTRAL NERVOUS SYSTEM
The brain and spinal cord are both made up of two dissimilar arrangements
of nervous tissue termed gray matter and white matter. Gray matter is an
intimate assortment of neuronal and glial cell bodies embedded in an
entwined mass of nerve fibers (many without a myelin sheath) termed the
neuropil (see Figure 6–3). White matter is a more structured arrangement
of nerve fibers, many with myelin sheaths, along with their associated glia.
Neuronal cell bodies, on the other hand, are absent from white matter. The
two different arrangements are more easily recognized in sections of spinal
cord and cerebellum than in sections of cerebral cortex. Myelin sheaths
invest and insulate fast-conducting axons. The axon is generally the neuron’s longest nerve fiber, and, in most cases, it propagates nerve impulses
away from the cell body (afferent neurons being an exception). Compared
with the axon, the dendrites are typically shorter, more branched, and
tapered, and their role is to receive nerve impulses. In hematoxylin and
eosin (H&E)-stained sections, it is rarely evident whether representative
unmyelinated nerve fibers are axons or dendrites.
83
84
PDQ HISTOLOGY
Anterior horn of
gray matter
White
matter
Posterior horn
of gray matter
Subarachnoid
space
Dura
Figure 6–1 Spinal cord.
Neuropil
Multipolar neurons in gray matter
Myelinated nerve fibers
in white matter
Pia
Figure 6–2 Gray matter and white matter of spinal cord.
Chapter 6
Nervous Tissue
85
Spinal Cord
The spinal cord (Figure 6–1) can be recognized by a combination of
distinctive features:
•
•
•
•
•
central H-shaped area of gray matter (anterior and posterior horns with
interconnecting gray commissures)
surrounding white matter (funiculi containing descending and ascending longitudinal tracts)
anterior median fissure and posterior median sulcus
spinal nerve roots in the subarachnoid space
surrounding meninges (dura mater, arachnoid membrane, and pia
mater)
At higher magnification (Figure 6–2), it may be seen that
•
•
•
•
multipolar neurons are present in the gray matter,
delicate ingrowths of the pia mater (innermost meningeal membrane)
bring a blood supply,
shrinkage artifact is common (particularly between neuronal cell bodies and the surrounding neuropil), and
white matter contains pale-looking myelin sheaths (myelin lipids are
extracted during processing) but lacks neuronal cell bodies.
86
PDQ HISTOLOGY
Dendrite
Neuropil
Nucleolus
in nucleus
Glial cell
nuclei
Axon
hillock
Capillaries
Figure 6–3 Multipolar neuron.
Synaptic vesicles in
axon
Dendrite
Figure 6–4 Electron micrograph of a chemical synapse.
Postsynaptic
thickening
Chapter 6
Nervous Tissue
87
Typical neurons (Figure 6–3) are characterized by the following features:
•
•
•
•
•
•
large diameter
asymmetric multipolar, pseudounipolar, or bipolar shape (multipolar
in this case)
intense cytoplasmic basophilia, typically patchy and indicative of
patches of rough-surfaced endoplasmic reticulum (Nissl bodies),
reflecting active protein synthesis for maintenance of long axon
axon hillock (site where axon is attached) is generally not basophilic
dendrites with basophilic cytoplasm as in cell body
pale-staining central nucleus with central large nucleolus (“owl’s eye”
nucleus) that also reflects active protein synthesis
Neuropil and blood capillaries may also be seen to advantage in this
photomicrograph.
The special sites on neurons where nerve impulses can be transmitted
from one cell to another are known as synapses. Chemical synapses (the
common type) release neurotransmitter into their synaptic cleft; electrical
synapses (uncommon) possess gap junctions that conduct impulses directly.
Typical features of an axodendritic directed chemical synapse seen in
the electron microscope (Figure 6–4) include synaptic vesicles containing
neurotransmitter and electron-dense material (variable in amount) on the
cytoplasmic surface of the postsynaptic membrane (postsynaptic thickening). In addition to chemical synapses, there are electrical synapses. These
are essentially gap junctions (see Figure 2–10, C) that permit direct conduction of nerve impulses.
88
PDQ HISTOLOGY
Pia
Neuronal cell
body
Figure 6–5 Cerebral cortex (hematoxylin and eosin stain).
Neuroglial
cell
Figure 6–6 Cerebral cortex (silver impregnation).
Capillary
Chapter 6
Nervous Tissue
89
Brain
In H&E sections of cerebral cortex (Figure 6–5), the following may be
found:
•
•
•
•
superficial gray matter with neurons arranged as a series of indistinct
laminae (layers)
neuronal cell bodies, the largest of which are pyramid shaped (pyramidal cells)
widely scattered nuclei of neuroglia and surrounding neuropil
blood capillaries supplying the necessary oxygen and nutrients
Silver or gold impregnation methods (Golgi preparations) selectively
reveal representative neurons and neuroglia (Figure 6–6). With special
staining, the extensively interlacing long cytoplasmic processes of astrocytes, the predominant type of glial cell, may be seen (Figure 6–7).
Figure 6–7 Fibrous astrocytes (special stain).
90
PDQ HISTOLOGY
Molecular layer
Granular layer
White matter
Figure 6–8 Cerebellum.
Granular layer
Purkinje cell
Figure 6–9 Purkinje cell of the cerebellum.
Molecular layer
Chapter 6
Nervous Tissue
91
The cerebellar cortex (Figure 6–8) may be recognized by the following
characteristics:
•
•
•
•
•
deeply folded appearance (fissures and sulci)
pink outer cortical layer of gray matter (molecular layer)
blue inner cortical layer of gray matter (granular layer)
flask-shaped neuronal cell bodies (Purkinje cells) scattered along the
interface between the outer and inner cortical layers
pink central medullary core of white matter
Characteristic features of Purkinje cells (Figure 6–9) include the
following:
•
•
•
large diameter
cytoplasmic basophilia (Nissl bodies) and nuclear morphology both
typical of neurons
extensively branching dendritic tree extending far into the molecular
layer
PERIPHERAL NERVOUS SYSTEM
The PNS is more strongly reinforced by abundant connective tissue. Furthermore, under the right conditions, peripheral nerves show considerable
potential for nerve fiber regeneration when they become damaged. Small
peripheral nerves may often be found in adventitial connective tissue of
organs or structures. Sensory cranial ganglia and spinal ganglia (see Figure
6–13) have a slightly different histologic appearance from autonomic ganglia (see Figure 6–14), but the difference is subtle.
92
PDQ HISTOLOGY
Epineurium
Fascicle
Endoneurium
Perineurium
Schwann cell
and myelin sheath
Axon
Figure 6–10 Organization of a peripheral nerve.
Perineurium surrounding
fascicle
Myelinated nerve fibers
Figure 6–11 Peripheral nerve (cross-section).
Chapter 6
Nervous Tissue
93
Peripheral Nerves
A moderate-sized peripheral nerve has the structural organization shown in
Figure 6–10. Its outermost fibrous connective tissue covering, not represented in small nerves, is termed its epineurium. Internal to this, fibrous
perineurium fills the crevices between nerve fiber bundles and surrounds
each bundle as a sheath. Inside the bundle, loose connective tissue known
as endoneurium lies between the individual nerve fibers.
Typical features of peripheral nerves cut in cross-section (Figure 6–11)
or longitudinal section (Figure 6–12) are as follows:
•
•
•
•
•
nerve fiber bundles (fascicles), each bundle surrounded with perineurium
nerve fibers, with or without white myelin sheaths (compare Figures
6–11 and 6–12)
endoneurium often difficult to discern
epineurium not represented except in large nerves
nuclei of Schwann cells, occasionally with nuclei of endoneurial fibroblasts
Perineurium surrounding
fascicle
Schwann cell nuclei
Figure 6–12 Fascicle of peripheral nerve (longitudinal section).
94
PDQ HISTOLOGY
Cell body of ganglion cell
Nuclei of capsule cells
Figure 6–13 Spinal ganglion.
Nuclei of capsule cells
Cell body of ganglion cell
Unmyelinated
nerve fibers
Figure 6–14 Autonomic ganglion (parasympathetic ganglion in pancreas).
Chapter 6
Nervous Tissue
95
Spinal Ganglia
A section of spinal (posterior root or dorsal root) ganglion (Figure 6–13) is
recognizable by the following:
•
•
•
pseudounipolar ganglion cells with large spherical cell bodies
ganglion cell nucleus central to the cell body, conspicuous large nucleolus and cytoplasmic basophilia (Nissl bodies) indicative of active protein synthesis
each ganglion cell body enclosed by a layer of comparatively small capsule cells (neuroglial cells)
AUTONOMIC NERVOUS SYSTEM
Viscera, exocrine glands, blood vessels, and smooth muscles have their functional activities regulated automatically by way of their autonomic innervation. Sympathetic and parasympathetic ganglia of the autonomic nervous
system (Figure 6–14) are both characterized by the following features:
•
•
•
large multipolar ganglion cells, cell bodies more irregular in shape because
of multiple dendrites but otherwise resembling spinal ganglion cells
ganglion cell nucleus more commonly eccentric in position
the population of small capsule cells associated with each ganglion cell
appears discontinuous rather than as a layer because of the neuron’s
multipolar shape
96
PDQ HISTOLOGY
Neural retina
Retinal pigment
epithelium
Figure 6–15 Position of the retina. Box indicates the site and orientation of Figures 6–16
and 6–17.
Neuroglial cells
Inner nuclear
layer
Outer plexiform layer
Nuclei and cell bodies
of photoreceptors
External limiting membrane
Outer and inner segments
of photoreceptors
Retinal pigment epithelium
(simple cuboidal; outermost)
Figure 6–16 Photoreceptive part of the retina.
Cone Rod
Chapter 6
Nervous Tissue
97
OPTIC RETINA
The functional importance of the retina (Figures 6–15, 6–16, and 6–17—a
toluidine blue–stained semithin section) is that it is uniquely provided with
photoreceptors. Some essential features by which retinal sections may be
identified are as follows:
•
•
•
•
•
•
•
inner multilayered neural retina (photoreceptors, other retinal neurons,
optic nerve fibers)
outer single-layered retinal pigment epithelium (RPE) (a simple
cuboidal melanin-containing epithelium)
outer and inner segments of photoreceptors (rods and cones) adjacent
to RPE
a band of photoreceptor nuclei adjacent to the layer containing the
inner segments
a wide band containing nuclei of other retinal neurons and tall columnar supporting neuroglia
inner layers (not shown) containing fewer nuclei and more nerve fibers
optic nerve fibers forming the superficial retinal layer that lines most of
the vitreous cavity of the eye
Figure 6–17 Outer part of the retina.
7
Muscle
M
uscles are described histologically as consisting of muscle cells associated with moderate to large amounts of connective tissue.
Each of the three muscle types—skeletal, cardiac, and smooth—has distinctive features. When seen with a microscope, skeletal muscle (responsible
for voluntary movements) and cardiac muscle (involuntary heart muscle)
show striations. Smooth muscle (involuntary muscle of viscera and
contractile vessels) lacks striations.
Detailed descriptions of muscle cells commonly use terms that would
benefit from some initial explanation. In the case of skeletal or smooth
muscle, the term muscle fiber is often used as a synonym for muscle cell. In
cardiac muscle, however, it means a row of individual cells joined end to
end. Myofibrils, present in skeletal and cardiac muscle but not smooth muscle, are thread-like organized arrangements of thick and thin filaments. Filaments of all three classes (thick, thin, and intermediate) are present in all
three types of muscle cells. The underlying structural basis for all terminology is summarized in Figure 7–1.
SKELETAL MUSCLE
As in peripheral nerves, skeletal muscle fibers are arranged in bundles (fascicles), with fibrous perimysium surrounding each bundle (see Figures 7–1
and 7–2). The muscle is enclosed as a whole by fibrous epimysium, and delicate endomysium lies between the muscle fibers.
99
100
PDQ HISTOLOGY
Epimysium
Perimysium
Fascicle
Endomysium
Endomysium
Skeletal muscle
fiber
Myofibril
Thin and thick
filaments
Figure 7–1 Organization of a skeletal muscle.
Chapter 7
Skeletal muscle fibers
in fascicle
Perimysium
Figure 7–2 Skeletal muscle at low magnification.
Endomysium
Muscle
101
102
PDQ HISTOLOGY
Nucleus of capillary
endothelial cell
Nuclei of
muscle fibers
Capillary
endothelial cell
Figure 7–3 Skeletal muscle fibers in cross-section.
Myofibrils
Skeletal muscle fiber
containing myofibrils
Chapter 7
Muscle
103
The robust perimysial sheaths of skeletal muscle fascicles are recognizable in cross-sections of skeletal muscle, particularly at very low magnifications (see Figure 7–2). With more magnification, it is evident that skeletal
muscle fibers are multinucleated (as a result of fusion of myoblasts, their
precursor cells), and their nuclei lie in the peripheral cytoplasm (Figure
7–3). The interior portion of the muscle fibers appears closely packed with
myofibrils (the “breaks” between them are fixation artifact). The distinctive
multinucleated appearance of skeletal muscle fibers becomes more apparent in longitudinal sections (Figure 7–4).
Striations
Under optimal viewing conditions (or after special staining), transverse
striations may also be seen on the myofibrils: dark-staining A bands and
light-staining I bands. These bands seem to extend across the entire muscle
fiber because striations of myofibrils are aligned transversely across the
fiber. Scattered fibroblast nuclei or capillary endothelial nuclei (see Figure
7–3) can sometimes be found in the pale-staining endomysium separating
the muscle fibers.
Nuclei of a skeletal
muscle fiber
Striations
Figure 7–4 Skeletal muscle fibers in longitudinal section, showing striations.
104
PDQ HISTOLOGY
Sarcomeres
A distinctive arrangement of thick and thin filaments known as the sarcomere (Figure 7–5) is repeated along myofibrils in the form of an extended
linear series. The sarcomere is considered the basic contractile module of
skeletal and cardiac muscle. The thin filaments, which contain actin, troponin, and tropomyosin, are anchored to Z lines made of α-actinin. The
thick filaments, which contain myosin, are centrally interconnected in the
transverse plane by a narrow M line containing myomesin. A bands contain
both thick and thin filaments. I bands do not include any thick filaments. H
bands do not include any thin filaments. During contraction, the H band
disappears and the I bands shorten because the thin filaments are pulled farther into the A band, and this decreases the distance between the Z lines at
the ends of the sarcomere.
I
A
I
Z
H
Z
M
Relaxed
Contracted
Figure 7–5 Sarcomere, showing its bands and the arrangement of thin and thick filaments.
CARDIAC MUSCLE
Although cardiac muscle resembles skeletal muscle in certain respects, cardiac muscle is involuntary and has fibers made up of individual cardiac
muscle cells, each with one or two central nuclei. Distinctive structures
called intercalated disks attach these muscle cells to each other, forming
fibers that show a certain amount of branching. Hence, two key histologic
features of cardiac muscle fibers are their limited anastomosis and their distinctive assembly pattern incorporating separate cardiac muscle cells with
intercalated disks between them (Figure 7–6). A delicate endomysium occupies the spaces between cardiac muscle fibers, but epimysium and perimysium, characteristic of skeletal muscle, are unrepresented. Unlike skeletal
muscle, which can regenerate new muscle fibers from satellite (myosatellite)
cells situated at the periphery of its muscle fibers, cardiac muscle is characterized by a negligible inherent potential for regeneration. If it dies, it is
replaced by fibrous scar tissue.
Chapter 7
Muscle
105
Intercalated disks (see Figure 7–6) are not evident at the light microscopic level unless special stains are used. Electron microscopy reveals that
they are specialized for attachment and electrical conduction. They traverse
the muscle fiber in a step-like manner at the level of Z lines. Their distinctive features are as follows:
•
•
•
extensive interdigitation of cell borders
exclusive site of gap junctions that allow free ion movement (direct electrical conduction)
transverse adhering junctions (two types) that anchor (1) thin filaments
and (2) intermediate filaments
Fascia adherens
junction
Desmosome-like
junction
Intermediate
filaments
Gap
junction
Thick
filament
Thin
filament
Z line
Figure 7–6 Part of an intercalated disk, showing the component junctions and associated
filaments.
106
PDQ HISTOLOGY
Central nuclei
Peripheral myofibrils
in muscle fibers
Endomysial
capillary
Figure 7–7 Cardiac muscle in cross-section.
Branched muscle fibers
Endomysial capillaries
Central nuclei of muscle fibers
Figure 7–8 Cardiac muscle in longitudinal section.
Chapter 7
Muscle
107
Cross-sections of cardiac muscle fibers (Figure 7–7) have these
characteristics:
•
•
•
•
a large diameter
a central nucleus
peripheral myofibrils
highly vascular associated endomysium
In longitudinal sections (Figure 7–8), muscle fiber branching may also
be seen, together with striations at higher magnifications. Intercalated disks
are not usually identifiable at this magnification in hematoxylin and
eosin–stained sections.
SMOOTH MUSCLE
The appearance of smooth muscle fibers cut in cross- and longitudinal section may be seen in Figure 7–9. Smooth muscle fibers (commonly called
smooth muscle cells) may be recognized by the following:
•
•
•
•
•
•
small diameter compared with other types of muscle fiber
arranged as muscle coats, layers, or bundles
surrounding sheaths of loose connective tissue
central nucleus
absence of the discrete myofibrils and aligned striations that characterize skeletal and cardiac muscle
distinctive pleating of the nucleus in contracted and partly contracted
muscle fibers (compare Figures 7–10 and 7–11)
Other features of smooth muscle include gap junctional coupling (basis
of excitation spread through direct conduction, as in cardiac muscle) and
postnatal potential for mitosis and supplemental derivation from pericytes.
Figure 7–9 Smooth muscle in cross-section (left) and longitudinal section (right).
108
PDQ HISTOLOGY
Figure 7–10 Smooth muscle fibers in the relaxed state.
Pleated nuclei
Figure 7–11 Smooth muscle fibers in the contracted state.
8
Circulatory System
C
irculatory system is a broadly inclusive term for (1) the
heart and the various types of blood vessels characterizing the blood circulatory system and (2) the lymph-collecting vessels of the lymphatic system.
Components of the circulatory system are conventionally described as being
made up of three concentric layers known as tunicae—the tunica intima,
tunica media, and tunica adventitia—but the borders between these layers
are hard to distinguish in certain cases. In general, the tunica intima is a
loose connective tissue layer with endothelium, a characteristic simple
squamous lining epithelium, anchored to it by underlying basement membrane. The intimal lining layer of the heart is known as the endocardium,
and heart valves are sheet-like inward extensions of this layer. Deep in the
endocardium lie specialized impulse-conducting cardiac muscle fibers
(Purkinje fibers) belonging to the impulse-conducting system of the heart.
In arterial vessels, the intima is characterized by an additional substantial
layer of fenestrated elastin called the internal elastic lamina. The tunica
media of vessels and myocardium of the heart, the middle layer of their
walls, consist primarily of muscle cells—smooth muscle in most vessels and
cardiac muscle in the heart. The total amount of muscle present, however,
is consistent with the component’s function: abundant in the heart, meager
in venules, and unrepresented in capillaries. The outermost region of the
wall, the tunica adventitia, is a layer of loose connective tissue that in the
great veins also contains substantial bundles of smooth muscle. The tunica
adventitia—particularly that of veins—and also the outer region of the
media of some vessels are nourished by vasa vasorum (small nutritive vessels). The equivalent cardiac layer is the epicardium, consisting of fibrous
connective tissue and the overlying visceral layer of serous pericardium.
Lymphatic vessels share this wall structure, but the layers of the wall are
harder to distinguish. The component vessels of the blood circulatory and
lymphatic systems are listed in Table 8–1. In light microscopic sections,
metarterioles resemble arterioles and lymphatic capillaries may be difficult
to recognize and distinguish with confidence from blood capillaries.
The main features of blood vessel wall structure are shown in Figure 8–1.
109
110
PDQ HISTOLOGY
Table 8–1
Blood Circulatory and Lymphatic Vessels
Blood circulatory system
Elastic arteries (aorta)
Distributing (muscular) arteries
Arterioles and metarterioles
Capillaries
Venules
Small- and medium-sized veins
Large collecting veins (vena cava)
Lymphatic system
Lymphatics and lymphatic ducts
Lymphatic capillaries
Subendothelial layer
(intima)
Elastin
(laminae, fibers)
Internal
elastic
lamina Smooth muscle
(media)
Smooth
muscle
(media)
Aorta
Smooth muscle
in adventitia
Vena cava
External
elastic
lamina
Distributing artery
Smooth muscle
(media)
Vein
Arteriole
Smooth muscle
(media)
Venule
(large)
Figure 8–1 Comparative composition of the walls of blood vessels.
Chapter 8
111
Circulatory System
ELASTIC ARTERIES
Distinctive wall features of the aorta, which is an elastic artery (Figure 8–2;
see also Figure 8–1), are as follows:
•
•
•
•
•
•
•
•
marked overall thickness
substantial content of elastin (maintains diastolic blood pressure)
uniformly laminated appearance of the very wide media (rows of dark
pink smooth muscle cells separated by pale pink elastic laminae)
relatively thick intima compared with intima of a muscular artery
(endothelium with substantial subendothelial layer containing elastin,
smooth muscle cells, and some fibroblasts)
somewhat indistinct border between intima and media
even more indistinct internal and external laminae
vasa vasorum in adventitia, penetrating outer part of media
together with muscular (distributing) arteries, a site of development of
atherosclerotic plaques
Intima
Media
Figure 8–2 Aorta.
Adventitia
112
PDQ HISTOLOGY
Artery
Vein
Figure 8–3 Distributing artery and vein (hematoxylin and eosin stain).
Endothelium
Internal elastic lamina
Figure 8–4 Distributing artery (toluidine blue stain).
Smooth muscle cells
Chapter 8
Circulatory System
113
DISTRIBUTING ARTERIES
Also known as muscular arteries, distributing arteries (Figures 8–3 and 8–4;
see also Figure 8–1) may be recognized by the following:
•
•
•
•
•
substantial wall thickness compared with vein but thinner than aortic
wall
very thin intima compared with aorta (endothelium and underlying
internal elastic lamina)
wavy pale-staining internal elastic lamina (demonstrated to advantage
by toluidine blue staining; see Figure 8–4)
wide media containing dark pink smooth muscle cells circularly
arranged (regulates blood flow)
distinct border between muscular media and substantial connective tissue adventitia
VEINS
Features of the accompanying veins (see Figures 8–1 and 8–3) include the
following:
•
•
•
•
•
•
relatively thin walls (lower venous pressure)
media generally thinner, less distinct, and less muscular (except in
superficial leg veins)
adventitia fairly thick relative to other layers
internal elastic lamina unrecognizable
intimal flap valves, rarely seen in sections
degenerative changes in their wall components can lead to dilatation
(varicose veins)
The inferior vena cava (see Figure 8–1) has some additional characteristics:
•
•
•
wide lumen
fairly thin media compared with adventitia
thick contractile adventitia containing longitudinal bundles of smooth
muscle
114
PDQ HISTOLOGY
Endothelium
Smooth muscle cells
Figure 8–5 Arteriole.
Arteriole
Venules
Figure 8–6 Arteriole, venules, and capillaries.
Capillaries
Chapter 8
Circulatory System
115
SMALL BLOOD VESSELS
The features by which arterioles (Figures 8–5 and 8–6; see also Figure 8–1)
may be recognized include the following:
•
•
•
•
•
small overall diameter (< 100 µm)
thick walled relative to lumen (ie, wall thickness almost comparable
with luminal diameter)
distinct media made up of only one or two layers of circularly arranged
smooth muscle cells
internal elastic lamina generally discernible except in the smallest arterioles (see Figure 8–6)
indistinct border between media and adjacent thin adventitia
Venules may often be found in the vicinity of their companion arterioles (see Figure 8–6). They are characterized by the following:
•
•
•
•
small diameter generally between that of arterioles and capillaries
very thin walls
barely recognizable smooth muscle cells in media (unrepresented in
small venules)
allowing leukocytes and fluid exudate to escape at sites of acute
inflammation
Blood capillaries are distinguishable from arterioles and venules by
their small luminal diameter (see Figure 8–6). However, few details are discernible without the electron microscope.
116
PDQ HISTOLOGY
Pericyte
Erythrocyte
Endothelial
cell
Figure 8–7 Electron micrograph of a capillary.
Figure 8–8 Lymphatic.
Chapter 8
Circulatory System
117
Typical blood capillaries (Figure 8–7) have the following characteristics:
•
•
•
•
small diameter (8–10 µm, only slightly larger than an erythrocyte; see
Figure 8–7)
very thin endothelial lining (continuous or fenestrated)
associated pericytes
no media
LYMPHATIC VESSELS
Lymphatics (Figure 8–8) may be recognized through any combination of
the following:
•
•
•
•
•
•
uniform pink staining of the lymph protein in their lumen
presence of lymphocytes (without other blood cells) in their lumen
relatively wide lumen (appropriately scaled down in lymphatic capillaries)
very thin walls, occasionally showing recognizable smooth muscle cells
in larger lymphatics
poorly organized or skimpy appearance of walls
proximity to lymphoid organs (eg, lymph nodes)
Lymphatic capillaries differ from blood capillaries in the following
respects:
•
•
•
•
•
slightly wider lumen
blind ending
incomplete endothelial basement membrane
basal border of endothelium anchored to adjacent collagen fibers
pericytes absent
9
Integumentary System
T
he integumentary system consists of the skin and various types of skin appendages (Table 9–1). Each kind of skin is constructed
from two tissue components: epidermis, a stratified squamous keratinizing
epithelium derived from ectoderm, and dermis, its connective tissue layer
derived from mesoderm. The term hypodermis denotes the subcutaneous
adipose layer found immediately under the dermis. The skin-associated
glands, hairs, and nails (ie, all skin appendages) are entirely epidermal
derivatives.
In thick skin, which covers the palms of the hands, soles of the feet, and
the flexor surface of digits, epidermis is almost half as thick as the dermis,
whereas in the thin skin covering the remainder of the body, epidermal
thickness is only about one-fifth of the dermal thickness (Figures 9–1 and
9–2). The terminology is based on the thickness of the epidermis, not the
total thickness of the skin. Unless understood, this can be quite confusing
because thin skin has a greater total thickness than thick skin! One reason
Table 9–1
Integumentary System
Skin
Epidermis
Dermis
Epidermal skin appendages
Hairs
Nails
Sebaceous glands
Sweat glands
Eccrine type
Apocrine type
119
120
PDQ HISTOLOGY
B
A
Stratum corneum
Stratum lucidum
Stratum granulosum
Stratum spinosum
Stratum
germinativum
Papillary layer
of dermis
Reticular layer of dermis
Blood vessel
Sweat gland
Pacinian
corpuscle
Subcutaneous
fat
Figure 9–1 A, Organization of thick skin. B, Details of the epidermis.
Hair
Papillary layer
of dermis
Sebaceous gland
Arrector pili muscle
Sweat gland
Reticular layer
of dermis
Root sheath of
hair follicle
Connective tissue
papilla
Subcutaneous fat
Figure 9–2 Organization of thin skin.
Chapter 9
Integumentary System
121
for making a distinction between two types of skin is that certain structural
differences exist, notably the presence of friction ridges and protective
thickened stratum corneum in thick skin and the presence of hair follicles
and sebaceous glands in thin skin.
Because epidermis is an avascular epithelium, it must receive nutrients
from capillaries in the underlying papillary layer of dermis. Progressive displacement of its keratinocytes toward the surface isolates them from this
source, so they die and flake off. The turnover time for keratinocytes to
reach the skin surface from the stratum germinativum is almost 1 month.
The deep parts of certain skin appendages (namely, the growing region
of hair follicles and the secretory portion of most sweat glands) extend
down from the dermis into the subcutaneous tissue (see Figures 9–2 and
9–7). Encapsulated pressure-sensitive sensory nerve endings resembling
onions (pacinian corpuscles) may also be found in this adipose layer, particularly in sections of thick skin (Figure 9–3).
THICK SKIN AND THIN SKIN CHARACTERISTICS
The following generalizations apply to thick skin (see Figure 9–1):
•
•
•
•
•
five distinguishable epidermal layers (germinativum, spinosum, granulosum, lucidum, corneum)
thick stratum corneum
dermal papillae arranged on double (secondary) dermal ridges under
friction ridges
no hair follicles or sebaceous glands
eccrine sweat glands opening onto friction ridges
General features of thin skin (see Figure 9-2) include the following:
•
•
•
•
•
•
four distinguishable epidermal layers (germinativum, spinosum, granulosum, corneum)
thin stratum corneum
dermal papillae randomly arranged
hair follicles with associated flask-shaped sebaceous glands
eccrine and apocrine sweat glands (apocrine glands, limited to pubic,
perineal, and axillary areas and breasts, open into hair follicles)
nail plates in nail grooves
122
PDQ HISTOLOGY
Corneum
Sweat gland
Adipose tissue
Pacinian corpuscle
Figure 9–3 Thick skin at low magnification.
Corneum
Granulosum
Spinosum
Papillary layer
of dermis
Duct of sweat gland
Reticular layer
of dermis
Sweat gland
Figure 9–4 Thick skin seen in more detail.
Chapter 9
Integumentary System
123
Seen under low power, sections of thick skin (see Figure 9–3) are recognizable by the following:
•
•
•
•
thick stratum corneum
total depth (epidermis + dermis down as far as subcutaneous fat)
smaller than in thin skin
hair follicles and sebaceous glands absent (note that thorough lowpower searching of the entire section is mandatory for certainty about
this)
pacinian corpuscles also present in this particular case (compatible with
its being thick skin but does not rule out thin skin)
Increased magnifications of thick skin (Figure 9–4) disclose the following:
•
•
•
•
epidermal layers (notably, spinosum, granulosum, and thick corneum)
vascular dermal papillae (part of the papillary layer of dermis)
comparatively coarse collagen bundles indicative of the reticular layer of
dermis (beneath the papillary layer)
eccrine sweat glands, with their duct portion extending up through the
dermis and their secretory portion situated in the subcutaneous adipose
tissue
124
PDQ HISTOLOGY
Corneum
Granulosum
Spinosum
Papillary layer
of dermis
Reticular layer
of dermis
Figure 9–5 Thin skin at low magnification.
Stratum granulosum
Melanin in stratum germinativum
Figure 9–6 Epidermis of thin skin seen in more detail.
Chapter 9
Integumentary System
125
Sections of thin skin (Figures 9–5 and 9–6) typically show the following:
•
•
•
•
relatively thin epidermis
recognizable germinativum, spinosum, and corneum; granulosum
usually somewhat indistinct, and lucidum is not represented
relatively thin stratum corneum
melanin mostly confined to deep layers of the epidermis in lightskinned races (variable in amount; synthesized by neural crest–derived
epidermal melanocytes and acquired by keratinocytes through
phagocytosis)
In histology tests, students are generally expected to state whether the
skin being identified is thick or thin.
HAIR FOLLICLES
Although sections of thin skin may happen to include isolated small portions of hair follicles and/or their associated sebaceous glands, this is often
not the case. These particular skin appendages are more easily observed in
sections of the scalp, where the hair follicles are more tightly packed and
there are numerous oblique or longitudinal cuts to look at.
126
PDQ HISTOLOGY
The scalp is an area of thin skin uniquely characterized by a dense population of hair follicles (Figure 9–7). Readily identifiable features include
the following:
•
•
•
•
hair follicles containing growing hairs, extending down into subcutaneous tissue
follicle-associated, flask-shaped sebaceous glands (produce sebum
through disintegration of their lipid-laden cells)
arrector pili muscles (smooth muscles that give sebaceous glands a
squeeze and make hairs “stand up on end”)
representative parts of hairs and hair follicles, composite drawings of
which are shown in Figure 9–8
It is seldom expected that students will memorize every microscopic
detail of these structures. Recognition of the following components could
be considered challenging enough:
•
•
•
•
•
connective tissue papilla (nourishes the growth zone)
matrix region of the hair (the growth zone)
cortex and medulla of hair (medulla unrepresented in some types of hair)
internal and external root sheaths
connective tissue sheath (external to root sheath)
Arrector
pili muscles
Sebaceous
glands
Adipose
tissue
Papilla of
hair follicle
Blood
vessel
Figure 9–7 Scalp.
Chapter 9
Integumentary System
127
Sebaceous
gland
Cortex
of hair
Medulla
of hair
Connective tissue
sheath
External root sheath
Internal root sheath
Stratum
germinativum
Trichohyalin
granules
B.
Arrector pili
muscle
Hair matrix
Connective
tissue papilla
A.
Figure 9–8 Organization of a hair follicle. A, Longitudinal section. B, Cross-section at the level
indicated in A.
128
PDQ HISTOLOGY
SWEAT GLANDS
Two types of sweat gland exist, termed eccrine and apocrine.
Eccrine Type
The widely distributed, ordinary kind of sweat gland (eccrine sweat gland;
Figure 9–9), represented in both thick and thin types of skin, shows the following features:
•
•
•
•
•
•
simple tubular gland
irregularly coiled secretory portion
helically winding straighter duct portion
embedded in loose connective tissue
secretory portion with single layer of pale-staining low columnar serous
secretory cells
duct portion with double layer of cuboidal epithelial cells, characterized
by dark-staining nuclei
Apocrine Type
Largely resembling eccrine sweat glands in their histologic appearance,
apocrine sweat glands open into hair follicles instead of opening directly
onto the skin surface. Also, their secretory portion is rather large in comparison with their duct portion. The postpubertal secretory product of
apocrine sweat glands can undergo bacterial degradation, giving rise to
body odors. Sweat glands of the apocrine type are found chiefly in the
armpits and the pubic and perineal areas.
Duct
Figure 9–9 Eccrine sweat gland.
Secretory portion
10
Digestive System
The digestive system,
represented by the tubular gastrointestinal tract (gut) and its various accessory digestive glands (Table 10–1),
is endoderm derived. The duct portions of its many accessory glands open
directly into the gut lumen. An obvious general histologic feature of the
tract is its regional specialization for nutrient processing, digestion, and
absorption. Even though constituent regions share a common wall structure
based on four concentric layers (Figure 10–1), additional features indicating specific functions allow each part to be recognized individually. Thus,
absorptive villi (finger-like projections) are found in the small intestine but
not elsewhere. Lymphoid tissue is more conspicuous in the ileum (Peyer’s
patches) and appendix than it is elsewhere. A mixed population of simple
columnar absorptive epithelial cells and mucus-secreting goblet cells characterizes the intestine but not the esophagus or stomach.
Special arrangements are needed for continuous renewal of the lining
epithelial cells because they are subject to abrasion and exposure to acid or
damaging enzymes. In the intestine, the epithelial stem cells are protected
by being situated deep in crypts extending below the luminal surface. Gastric epithelial cells are renewed every 4 to 6 days and villous epithelial cells
are renewed every 5 to 6 days. Rapid epithelial turnover and secretion of
protective mucus by gastric epithelium, goblet cells, and mucous glands are
key mechanisms in maintaining an uninterrupted epithelial barrier between
gut contents and the internal environment of the body.
Table 10–1
Digestive System
Oral cavity
Esophagus
Stomach
Fundus
Pylorus
Duodenum
Jejunum
Ileum
Appendix
Colon
Accessory glands
Salivary glands
Pancreas
Liver
129
130
PDQ HISTOLOGY
Serosa or
adventitia
Outer layer
(longitudinal)
Inner layer
(circular)
Muscularis
externa
Submucosa with
submucosal glands
Muscularis mucosae
(circular)
Mucosa
Lamina propria
Epithelium
Figure 10–1 Layers of the gastrointestinal tract.
Epithelium
Muscularis mucosae
Lamina propria
Submucosa
Muscularis externa
Figure 10–2 Esophagus.
Chapter 10
Digestive System
131
WALL ORGANIZATION
The four layers of the gut wall (see Figure 10–1) are as follows:
•
•
•
•
mucosa made up of epithelium (lining and glandular invaginations, eg,
gastric pits, crypts of Lieberkühn), lamina propria (loose connective
tissue extending into villi), and muscularis mucosae (smooth muscle
regulating size and independent movement of luminal folds)
submucosa (loose connective tissue extending into rugae and plicae;
contains medium-sized blood vessels and submucosal autonomic nerve
plexus; site of mucous glands in the duodenum and esophagus)
muscularis externa (major smooth muscle layers involved in peristalsis;
inner circular and outer longitudinal layers; contains myenteric autonomic nerve plexus)
serosa or adventitia (covering of simple squamous visceral peritoneum =
serosa; connective tissue attachment, eg, to abdominal wall = adventitia)
ESOPHAGUS
Sections of esophagus (Figure 10–2) may be identified by the following
criteria:
•
•
•
•
•
four wall layers evident
stratified squamous nonkeratinizing epithelial lining, resistant to
abrasion
muscularis mucosae comparatively substantial in the lower part
thick muscularis externa made of skeletal muscle in the upper third,
smooth muscle in the lower third, and both types of muscle in the middle third
adventitia instead of a serosa
132
PDQ HISTOLOGY
Gastric pit
Mucus-secreting simple
columnar epithelium
Chief cells
Parietal cells
Figure 10–3 Fundic region of the stomach.
Mucus-secreting simple
columnar epithelium
Pyloric gland
Gastric pit
Lamina propria
Figure 10–4 Pyloric region of the stomach.
Muscularis mucosae
Chapter 10
Digestive System
133
STOMACH
Two representative parts of the stomach are shown here: the body of the
stomach (designated the fundic region) and the pyloric region.
The fundic region (Figure 10–3) may be recognized by the following:
•
•
•
•
•
pale-staining mucus-secreting simple columnar surface epithelium
(without goblet cells)
the same epithelium dipping down into the lamina propria as gastric
pits (foveolae)
long fundic glands extending down through the lamina propria from
the pits, their bases reaching down to the substantial muscularis
mucosae
fundic glands containing pink parietal cells (which produce hydrochloric acid and secrete intrinsic factor, a glycoprotein required for vitamin
B 12 absorption), purple chief cells (which secrete pepsinogen and
lipase), enteroendocrine cells (which secrete hormones), and mucussecreting cells
large mucosal folds with submucosal cores (rugae)
Some additional features by which the pyloric region (Figure 10–4) may
be identified:
•
•
mucus-secreting pyloric glands, resembling mucus-secreting surface
epithelium (demonstrated here to advantage by periodic acid–Schiff
staining, which colors glycoproteins magenta)
muscularis externa thickened at the pyloric sphincter
134
PDQ HISTOLOGY
Villus
Surface
epithelium
Crypt
Lamina
propria
Muscularis
mucosae
Crypt
Figure 10–5 Organization of a villus and crypts.
Goblet cells
Absorptive cells
Enteroendocrine
cell
Paneth cells
Figure 10–6 Crypt of the small intestine.
Chapter 10
Digestive System
135
SMALL INTESTINE
In the small intestine, the total absorptive area is increased by folds, villi,
and microvilli on the absorptive luminal surface of epithelial cells. Situated
between villi projecting into the lumen are crypts, straight simple tubular
mucosal glands invaginated into the lamina propria (Figure 10–5). Without
a clear understanding that in contrast to villi, which are tissue extensions
surrounded by luminal space, crypts are invaginations with a central space
and surrounding tissue, it can be difficult to tell which is which in sections.
In general, isolated profiles surrounded by space (the “tissue islands” seen
on the luminal border in Figure 10–7) are villi, and those extending into
solid tissue are crypts.
In the lower part of crypts (Figure 10–6) it is possible to find the
following:
•
•
•
•
•
basal epithelial stem cells called crypt base columnar cells
undifferentiated dividing epithelial cells
mucus-secreting goblet cells
Paneth cells, characterized by large acidophilic secretory granules that
contain an antibacterial enzyme (lysozyme)
enteroendocrine cells of many kinds that secrete a variety of gastrointestinal hormones
136
PDQ HISTOLOGY
Villi
Muscularis
mucosae
Submucosal
mucous glands
Muscularis
externa
Figure 10–7 Duodenum.
Villi
Crypts
Submucosal
lymphoid follices
Muscularis
externa
Figure 10–8 Ileum.
Chapter 10
Digestive System
137
Distinctive features of the duodenum (Figure 10–7) are the following:
•
•
relatively wide villi (seen in various planes of section) with crypts in the
lamina propria
conspicuous large mucus-secreting (Brunner’s) glands in submucosa,
generally extending through muscularis mucosae into lamina propria
(major source of protective alkaline mucus)
The ileum (Figure 10–8) is recognizable by the following:
•
•
•
narrower villi compared with duodenum
absence of large submucosal glands
conspicuous large aggregates of confluent lymphoid follicles (Peyer’s
patches) in submucosa, extending through muscularis mucosae into
lamina propria and raising surface epithelium between villi
The jejunum has the villi, crypts, and basic wall structure typical of the
small intestine but lacks conspicuous submucosal glands and lymphoid
follicles.
138
PDQ HISTOLOGY
Crypt
Lamina propria
Muscularis
mucosae
Figure 10–9 Large intestine.
Crypts
Submucosal
lymphoid follices
Figure 10–10 Appendix.
Muscularis mucosae
Muscularis externa
Chapter 10
Digestive System
139
LARGE INTESTINE
Distinguishing characteristics of the large intestine in general (Figure 10–9)
include the following:
•
•
•
absence of villi (often difficult to establish firmly unless a large area can
be searched for evidence of the “tissue islands” that would indicate villi)
higher proportion of goblet cells relative to columnar absorptive epithelial cells
relatively long straight crypts containing numerous goblet cells along
with a few enteroendocrine cells
Sections of the appendix (Figure 10–10) are additionally characterized by
the following:
•
•
relatively small irregularly shaped lumen
conspicuous confluent masses of lymphoid follicles in submucosa,
extending into lamina propria (enlarged appearance in children)
SEROUS ACCESSORY GLANDS
A few microscopic similarities exist between the parotid (a salivary gland of
the serous type) and the pancreas (another example of a compound serous
accessory digestive gland).
140
PDQ HISTOLOGY
Serous
secretory units
Intralobular
ducts
Figure 10–11 Parotid.
Intralobular duct
Islet
Centro-acinar cell
Figure 10–12 Pancreas.
Chapter 10
Digestive System
141
The parotid (Figure 10–11) shows the following features:
•
•
•
thick fibrous capsule, substantial septa, and obvious lobular organization
relatively numerous intralobular ducts, lined with simple cuboidal or
simple columnar epithelium
typical serous secretory units (acini)
In contrast, the pancreas (Figures 10–12 and 10–13) has the following:
•
•
•
•
•
•
a flimsy investing sheath of loose connective tissue
relatively thin and delicate septa
large main and accessory ducts, both supported by substantial amounts
of fibrous connective tissue
relatively few intralobular ducts (mostly with simple cuboidal or even
lower epithelium; see Figure 10–13)
central pale-staining centroacinar cells (proximal duct cells) included in
some of its serous acini, depending on their plane of section
irregularly shaped islets of Langerhans (pancreatic islets, the diffuse
endocrine component of this gland)
Acinus
Figure 10–13 Intralobular duct of the pancreas.
Intralobular duct
142
PDQ HISTOLOGY
Portal area
Central vein
Figure 10–14 Liver.
Central vein
Hepatocytes
Sinusoids
Figure 10–15 Central part of a liver lobule.
Chapter 10
Digestive System
143
LIVER
Histologic sections of the liver, the largest compound gland of all, appear
characteristically sponge-like. At low magnification (Figure 10–14), it is
possible to distinguish the following:
•
•
•
•
portal areas containing a wide portal vein, hepatic artery or arteriole,
bile duct (with characteristic simple cuboidal epithelium), and commonly also a lymphatic
wide central veins
roughly hexagonal liver lobules, with portal areas indicating their
periphery and central veins indicating their middle
irregularly anastomosing rows of hepatocytes arranged in a radial pattern that converges on the central vein
Further details seen with additional magnification (Figure 10–15)
include the following:
•
•
•
anastomosing radiating rows of hepatocytes (representing cross-sections
of widely perforated plates having a thickness of a single hepatocyte)
thin-walled venous sinusoids (ie, pale-looking blood channels between
these rows that convey the blood delivered by the hepatic artery and
portal vein of a portal area toward a central vein)
cytologic details of hepatocytes
144
PDQ HISTOLOGY
The liver acinus, an essentially functional concept, is not strictly recognizable in routine histologic sections. However, its central axis is represented by an arteriolar branch of the hepatic artery, along with an accompanying venular branch of the portal vein, extending along a border of a
lobule from a portal area (Figure 10–16). Its periphery is partly indicated by
the central veins on either side of this axis. Visualized in three dimensions,
the liver acinus resembles a hard-boiled egg lying on its side. Pursuing this
analogy, the highest concentrations of blood-borne nutrients and oxygen
reach the yolk area (termed zone 1). The lowest nutrient and oxygen levels
are found in the outer part of the egg white (termed zone 3).
1
2
3
Central vein
Hepatic artery
Portal vein
Portal
area
Figure 10–16 Organization of a liver acinus.
11
Respiratory System
E
xtending posteriorly from the nasal cavities and
nasopharynx and descending into the thorax are the constituent parts of the
respiratory system (Table 11–1). This system is conventionally subdivided
into (1) its conducting portion, which extends as far as the terminal bronchioles, and (2) its respiratory portion, which continues to the alveoli. A dichotomously branching system of airways, the tracheobronchial tree, cleans and
conducts the incoming air and also provides the exit route. Most of the lining
layer is ciliated pseudostratified columnar epithelium with goblet cells, which
is specialized to produce and propel a particle-trapping coating of mucus. The
respiratory portion of the system lying distal to this represents the essential
site of gas exchange. Beyond respiratory bronchioles, its structural components (alveolar ducts, alveolar sacs, and alveoli) represent air spaces separated
by intervening walls. A functionally important component of the tracheobronchial tree, visceral pleura, and interalveolar walls is elastin, the passive
recoil of which is the chief factor expelling air in expiration. Besides providing a simple squamous mesothelial (serosal) gliding surface with underlying
(subserosal) dense fibroelastic tissue, the visceral pleura contains a plexus of
pulmonary lymphatics draining, by way of interlobular septal lymphatics,
toward the hilum of the lung. Another functionally important constituent of
the respiratory portion is its extensive population of alveolar macrophages.
When these phagocytes engulf inhaled particles settling beyond the mucus
coating of the airways, they subsequently become trapped in the mucus layer
and are swept along with it toward the pharynx.
Table 11–1
Respiratory System
Nasal cavities and nasopharynx
Bronchioles
Larynx and epiglottis
Alveolar ducts and alveoli
Trachea
Pleura
Bronchi
145
146
PDQ HISTOLOGY
Pseudostratified
epithelium
Mixed submucosal
glands
Cartilage
Fibrous perichondrium
Figure 11–1 Trachea.
Cartilage
Mixed submucosal
gland
Figure 11–2 Bronchus.
Chapter 11
Respiratory System
147
TRACHEA AND BRONCHI
Sections of the trachea (Figure 11–1) may be recognized by the following:
•
•
•
•
•
C-shaped hyaline cartilages (keeping this major airway open when the
neck is bent)
ciliated pseudostratified columnar epithelium with goblet cells (responsible for maintaining ascending mucus coating)
mixed submucosal glands (providing supplementary watery mucus)
smooth (trachealis) muscle (interconnecting posterior ends of C-shaped
cartilages)
dense fibroelastic perichondrium (extending as cartilage interconnections)
Sections of the intrapulmonary bronchi (Figure 11–2) appear fairly
similar to those of the trachea, except that their
•
•
•
•
lumen is smaller than that of the trachea,
supporting cartilages are more irregular in shape,
mixed submucosal glands are smaller than those of the trachea, and
adventitia is attached to the surrounding lung tissue.
Crisscrossing smooth muscle bundles lie in the submucosal connective
tissue between the epithelium and the cartilage, but because they follow helical courses, they are not always easy to recognize.
148
PDQ HISTOLOGY
Smooth muscle
Ciliated pseudostratified
columnar epithelium
Figure 11–3 Large bronchiole.
Simple cuboidal epithelium
Figure 11–4 Small bronchiole.
Chapter 11
Respiratory System
149
BRONCHIOLES
Larger bronchioles such as a preterminal bronchiole (Figure 11–3) have the
following characteristics:
•
•
•
•
•
•
luminal diameter < 1 mm
smooth muscle arranged as helical bundles crisscrossing deep to the
elastic lamina propria (excessive tonus of this muscle can lead to expiratory difficulties in asthmatic patients)
ciliated pseudostratified columnar epithelium with goblet cells (continuation of the “mucociliary escalator”)
adventitia attached to surrounding lung tissue (bronchiolar walls pulled
outward by tension in interalveolar walls when alveoli inflate)
flexible walls unsupported by cartilages
submucosal glands are absent
Additional features of the smaller bronchioles (Figure 11–4) are as follows:
•
•
•
•
decreased total wall thickness and smaller luminal diameter
smooth muscle even less conspicuous
simple cuboidal epithelium, with some cells nonciliated
no goblet cells
150
PDQ HISTOLOGY
Alveolar duct
Alveolar sac
Respiratory bronchiole
Figure 11–5 Respiratory bronchiole.
Alveolar sac
Respiratory
bronchiole
Alveoli
Alveolar ducts
Figure 11–6 Respiratory bronchiole leading into alveolar ducts.
Chapter 11
Respiratory System
151
RESPIRATORY BRONCHIOLES AND ALVEOLAR AIR SPACES
Respiratory bronchioles represent the last few orders of branching of the
tracheobronchial tree. It is usually easier to recognize them from their distal position in the dichotomously branching air passages (Figure 11–5) than
from the small numbers of alveoli extending from their walls. Alveolar ducts
(Figure 11–6; see also Figure 11–5) are essentially cylindrical air spaces
extending distally from the ends of the final order of respiratory bronchioles. The more distal alveolar sacs represent compound air spaces that are
smaller than alveolar ducts yet larger than alveoli. Their perimeters consist
of bubble-like alveoli that bulge out from the sac (see Figures 11–5 and
11–6). The ultimate structural and functional unit of gas exchange, the alveolus, is recognizable in lung sections as the smallest white-looking intrapulmonary air space. Most of the very cellular tissue lying between air
spaces in this section represents juxtaposed walls of collapsed alveoli
because it is a section of collapsed lung.
152
PDQ HISTOLOGY
Alveolar sac
Alveolus
Capillary in
interalveolar wall
Figure 11–7 Alveolar sacs.
Alveolar macrophage
Type II
Type I
pneumocyte pneumocyte
Figure 11–8 Cell types in the interalveolar wall.
Erythrocytes in
alveolar capillary
Chapter 11
Respiratory System
153
Additional histologic features of the respiratory portion appearing to
advantage in sections of expanded lung (Figures 11–7 and 11–8) include the
following:
•
•
•
•
•
•
thin interalveolar walls (septa)
pulmonary blood capillaries (lymphatics present in the bronchovascular connective tissue but not the interalveolar walls)
flat squamous epithelial cells (type I pneumocytes) lining the alveoli,
recognizable by their flat nuclei
rounded secretory epithelial cells (type II pneumocytes) secreting
pulmonary surfactant, recognizable by their slightly foamy-looking
cytoplasm
rounded alveolar macrophages, recognizable by their content of phagocytosed particles (particularly in smokers’ lungs) but generally hard to
distinguish from type II pneumocytes in light microscopic sections
unless their position is superficial
elastic fibers (demonstrable in interalveolar walls when a special elastin
stain is used)
154
PDQ HISTOLOGY
Interalveolar walls are essentially sandwich-like in construction (Figure
11–9):
•
•
•
•
•
type I pneumocytes, with occasional interposed type II pneumocytes,
constitute the slices of bread;
a continuous basement membrane underlying these two types of
epithelial cells represents the butter;
a flat plexus of anastomosing pulmonary capillaries (ie, rolled-up
endothelial cells with their surrounding basement membrane) represents a major part of the filling;
an extensible supportive framework of interstitial fibers (elastic and
reticular) represents another part of the filling;
motile alveolar macrophages, scattered over the alveolar surfaces, correspond to crumbs adhering to the flat outer surfaces of the sandwich.
Alveolar
macrophage
Basement
membrane
Type I
pneumocyte
Type II
pneumocyte
Endothelial lining
cell of capillary
Figure 11–9 Organization of the interalveolar wall.
Interstitial
fibers
12
Urinary System
R
epresented by the kidneys, ureters, urinary bladder, and
urethra, the urinary system is responsible for producing and storing urine.
Internal organization is most complex in the kidneys; the other components
are all characterized by a central lumen and an appropriate wall structure.
KIDNEYS
The kidneys are largely composed of structural and functional units termed
nephrons that form urinary filtrate continuously from circulating blood
plasma and then concentrate, process, and deliver it to the collecting duct
system. The histologic basis for distinguishing the renal cortex from the
renal medulla is the route taken by the various parts of the nephron and the
collecting tubules and ducts into which it empties. The renal cortex represents the unique site of the renal corpuscle (the proximal filtration unit),
convoluted segments of the nephron (its proximal and distal convoluted
tubules), and medullary rays (ray-like cortical areas containing straight segments of several nephrons along with cortical collecting tubules). The renal
medulla is characterized by its content of straight segments of nephrons
(thick- and thin-walled parts of loops of Henle) and associated straight
medullary collecting tubules that merge and drain into main collecting
ducts opening onto the renal papillae at the hilum of the kidney. Each conical medullary pyramid, with its covering cap of cortex, represents a kidney
lobe. The human kidney is regarded as multilobar because it contains up to
18 lobes. Between kidney lobes, renal cortex extends down into the renal
medulla as renal columns. A convenient way to substantiate the position of
the corticomedullary boundary is to look for arcuate vessels fanning out
distally from the interlobar blood vessels at this level like the ribs of an
umbrella.
155
156
PDQ HISTOLOGY
Interlobular blood vessels
Cortical labyrinth
Renal corpuscles
Figure 12–1 Renal cortex.
Interlobular blood vessels
Medullary ray
Figure 12–2 Lobule of renal cortex.
Chapter 12
Urinary System
157
Some distinctive histologic features of the renal cortex (Figure 12–1) are
as follows:
•
•
•
•
•
renal corpuscles scattered throughout the cortex
cortical labyrinth (multiple cuts through proximal and distal convoluted tubules)
interlobular blood vessels, afferent and efferent arterioles
medullary rays (predominantly longitudinal cuts through straight
tubules resembling the medullary tubules)
fibrous external capsule may be included in the section, immediately
adjacent to outer cortex (not shown)
The following additional features characterize the cortical lobule (Figure
12–2):
•
•
the lateral borders of the lobule are indicated by the positions of the
interlobular blood vessels (interlobular arteries or veins);
the central core of the lobule is made up of longitudinal or oblique cuts
through parallel straight tubules, that is, it is a medullary ray.
Although cortical lobules are recognizable in favorable planes of section, they are not always easy to discern.
158
PDQ HISTOLOGY
Figure 12–3 Renal medulla.
Proximal convoluted
tubule
Renal corpuscle
Glomerulus
Site of juxtaglomerular
apparatus
Afferent arteriole
Distal convoluted
tubule
Collecting
duct
Loop of Henle
Figure 12–4 Parts of the nephron with associated collecting tubules.
Chapter 12
Urinary System
159
Sections of the renal medulla (Figure 12–3) typically contain longitudinal or oblique cuts of
•
•
•
•
thick- and thin-walled parts of loops of Henle,
medullary collecting tubules and papillary ducts (main collecting ducts),
long straight capillaries known as vasa recta, and
traces of loose connective tissue (comprising the site of an interstitial
osmotic gradient).
Each nephron is made up of a renal corpuscle, proximal convoluted
tubule, loop of Henle, and distal convoluted tubule (Figure 12–4). The component segments of the nephron have distinctive histologic appearances
and are readily distinguishable where they have been cut in cross-section
(see Figure 12–9).
160
PDQ HISTOLOGY
Renal corpuscle
Arterioles
Figure 12–5 Renal corpuscles.
Vascular pole
Capsular space
Podocyte
Glomerular
capillary
Glomerular
basement membrane
Proximal convoluted
tubule (tubular pole)
Parietal (capsular)
epithelium
Figure 12–6 Renal corpuscle seen in more detail.
Chapter 12
Urinary System
161
Renal Corpuscle
The blood being filtered by renal corpuscles comes from their afferent arteriole and leaves by way of their efferent arteriole (Figure 12–5). It is seldom
possible to tell whether a given arteriole lying in close association with a
renal corpuscle is afferent or efferent. Even though the glomerulusassociated end of the afferent arteriole is characterized by the presence of
juxtaglomerular (JG) cells in its media (see Figure 12–7), these periodic
acid–Schiff (PAS)-positive secretory cells are present in small numbers and
therefore difficult to find.
Distinctive features by which renal corpuscles (Figure 12–6) may be
recognized are as follows:
•
•
•
•
•
•
•
parietal (capsular) epithelium—a simple squamous epithelium with a
supporting basement membrane that appears to advantage in PASstained sections
visceral (glomerular) epithelium—represented by scattered cell bodies
and nuclei of podocytes (the pedicels or foot processes of which are
attached to the glomerular basement membrane)
central tuft of glomerular capillaries
glomerular basement membrane (the renal filtration barrier component that minimizes exit of plasma macromolecules), also appearing to
advantage in PAS-stained sections
capsular space into which urinary filtrate passes
vascular pole (representing the joint attachment site of the afferent and
efferent arterioles)
tubular pole (representing the proximal end of the proximal convoluted
tubule)
162
PDQ HISTOLOGY
Efferent
arteriole
Blood from
glomerulus
Afferent
arteriole
Blood to
glomerulus
JG cells
Lacis cells
Distal
convoluted
tubule
Macula
densa
Urinary filtrate to
collecting tubule
Figure 12–7 Organization of the juxtaglomerular apparatus (see Figure 12–4 for its orientation).
Medullary ray
Figure 12–8 Medullary ray.
Chapter 12
Urinary System
163
Juxtaglomerular Apparatus
JG cells are the principal effector component of the juxtaglomerular apparatus (Figure 12–7), the major features of which are as follows:
•
•
•
•
its juxtaglomerular position—located where the distal convoluted
tubule lies in apposition to the afferent and efferent arterioles at the vascular pole of the renal corpuscle
granule-containing JG cells (modified smooth muscle cells) in media of
afferent arteriole, which respond to decreased stretch of the vessel wall
by releasing renin, the enzyme that produces angiotensin from its precursor; angiotensin raises blood pressure
apposed macula densa (densely nucleated spot in the epithelial wall of
the distal convoluted tubule), which detects falls in the sodium and
chloride contents of urinary filtrate and triggers renin release by JG
cells
lacis (extraglomerular mesangial) cells, interposed between macula
densa cells and JG cells and presumed to be involved in cell-to-cell
signaling
Renal Tubules
The following are readily recognizable characteristics of a medullary ray
(Figure 12–8):
•
•
•
flanked by a combination of cortical labyrinth and renal corpuscles
(indicative of renal cortex)
straight thick-walled parts of loops of Henle (segments of superficial
nephrons)
straight cortical collecting tubules (recognizable by the fact that the
lateral margins of their cuboidal epithelial lining cells are relatively
distinct)
164
PDQ HISTOLOGY
Proximal convoluted
Distal convoluted
Thin-walled loop of Henle
Collecting tubule
Figure 12–9 Renal tubules in cross-section.
Proximal convoluted tubule
Distal convoluted tubule
Figure 12–10 Proximal and distal convoluted tubules.
Chapter 12
Urinary System
165
In routine histologic sections, the straight tubules characterizing
medullary rays and the medulla are seldom totally represented as longitudinal sections. The various kidney tubules, however, are also individually
recognizable in cross- or oblique section (Figure 12–9). Cortical proximal
and distal convoluted tubules are commonly cut in these two planes.
Proximal and distal convoluted tubules (Figure 12–10) are typically distinguishable by the following criteria:
•
•
•
proximal convoluted tubule longer than distal convoluted tubule
(therefore seen with greater frequency in sections)
epithelial lining cells of the proximal convoluted tubule larger, pinker,
and wider than those of the distal convoluted tubule
epithelial lining cells of the proximal convoluted tubule characterized
by a distinct striated luminal border (abundant absorptive microvilli
with an associated thick PAS-positive cell coat), whereas those of the
distal convoluted tubule lack such a border
166
PDQ HISTOLOGY
Smooth muscle
Lamina propria
Transitional epithelium
Figure 12–11 Ureter.
Lamina propria
Transitional
epithelium
Smooth
muscle
bundles
Figure 12–12 Urinary bladder.
Chapter 12
Urinary System
167
URETERS
Sections of a ureter (Figure 12–11) typically show the following features:
•
•
•
•
•
tubular organization
distinctive stellate lumen
deeply folded transitional epithelial lining (exclusive to the urinary
tract)
fibroelastic lamina propria and adventitia (with resulting luminal
folding)
muscular coat made up of inner longitudinal and outer circular layers
of smooth muscle (reverse arrangement of that found in the digestive
tract)
URINARY BLADDER
The urinary bladder (Figure 12–12) may generally be recognized by the
following:
•
•
•
•
•
wall structure less distinctly organized (sac-like, not tubular)
transitional lining epithelium (indicative of urinary tract)
comparatively shallow mucosal folds
fibroelastic lamina propria and adventitia
smooth muscle layers, the respective orientations of which are hard to
distinguish
13
Endocrine System
T
he glands generally included in histology courses as representative of the endocrine system are listed in Table 13–1 (the ovaries are
described in Chapter 14, “Female Reproductive System,” and the testes in
Chapter 15, “Male Reproductive System”). In contrast to epithelial glands of
the exocrine type, the endocrine glands are not provided with any ducts.
Instead, their target cell-specific secretory products (hormones) pass
directly into capillaries, enabling these products to reach their target cells by
way of the bloodstream. Each hormone (or its precursor) is synthesized
continuously. Many hormones then become stored in the cytoplasm until
their release is suitably triggered. Thyroid and steroid hormones, however,
are lipid soluble; hence, they diffuse out of secretory cells as soon as they are
made. Whereas the water-soluble hormones bind to specific hormone
receptors on the surface of their target cells, thyroid and steroid hormones
diffuse into cells and bind to specific intracellular receptor proteins in their
target cells. The complexes thus formed specifically promote the transcription of appropriate genes. The secretory cells of most endocrine glands are
arranged as anastomosing cords, columns, or clumps lying adjacent to wide
fenestrated capillaries and supported by a fibrous capsule and connective
tissue trabeculae.
Table 13–1
Endocrine Organs
Pituitary
Anterior lobe
Posterior lobe
Adrenal
Cortex
Thyroid
Parathyroids
Pancreatic islets
Ovaries
Testes
Medulla
169
170
PDQ HISTOLOGY
Infundibular stalk
Anterior lobe
Pars intermedia
Posterior lobe
Figure 13–1 Parts of the pituitary.
Anterior lobe
Posterior lobe
Figure 13–2 Pituitary seen under scanning power.
Chapter 13
Endocrine System
171
PITUITARY
The pituitary (hypophysis) is a relatively small endocrine gland, roughly
ovoid in shape, that is connected to the hypothalamus by its infundibular
stalk (Figure 13–1). Functionally and histologically, the anterior and posterior
lobes of the pituitary are dissimilar. Situated between these lobes is the pars
intermedia, poorly represented in the human pituitary and hard to recognize
except for a few colloid-filled cysts with negligible functional significance. The
anterior and posterior lobes may both be represented in vertical or horizontal planes of section. Secretory epithelial cells of the anterior lobe, a derivative of the oral ectoderm, secrete the hormones listed in Table 13–2. Hypothalamic hormones regulating the release of these hormones are included in
this table. The posterior lobe (pars nervosa), derived from a downgrowth of
the brain (the floor of the third ventricle), is entirely composed of nervous tissue. It is the exclusive site of release of two hypothalamic peptide hormones:
oxytocin and vasopressin (antidiuretic hormone [ADH]).
In a horizontal section of the pituitary (Figure 13–2), the anterior larger
lobe, with its brightly stained secretory epithelial cells, is readily distinguishable from the pale-staining nervous tissue that characterizes the posterior lobe.
Table 13–2
Anterior Pituitary Hormones
Hormones
Release-Regulating Hormones
(Hypothalamic)
Adrenocorticotropic
Corticotropin releasing
Follicle stimulating
Gonadotropin releasing
Growth
Growth hormone releasing
Growth hormone inhibiting
(somatostatin)
Luteinizing
Gonadotropin releasing
Melanocyte stimulating
None established
Prolactin
Prolactin releasing
Prolactin inhibiting (dopamine)
Thyroid stimulating
Thyrotropin releasing
172
PDQ HISTOLOGY
Posterior lobe
Anterior lobe
Figure 13–3 Anterior and posterior pituitary.
Acidophils
Basophils
Figure 13–4 Anterior pituitary.
Fenestrated capillary
Chromophobes
Chapter 13
Endocrine System
173
Juxtaposition of a mass of nervous tissue (representing the posterior lobe)
and a large mixed population of brightly stained secretory epithelial cells, somewhat haphazard in arrangement and without ducts (representing the anterior
lobe), is reliably indicative of the pituitary gland (Figure 13–3). The pars intermedia may or may not be discernible, depending mainly on the plane of section.
The posterior lobe contains the following:
•
•
•
hypothalamohypophyseal tracts of pale-staining unmyelinated axons
belonging to neurosecretory neurons situated in the supraoptic and
paraventricular nuclei of the hypothalamus (the major respective
sources of ADH and oxytocin)
small pale-staining neuroglia (pituicytes) represented by their darkstaining nuclei
capillaries of the fenestrated type, into which ADH and oxytocin are
released from axon terminals of the neurosecretory neurons
Characteristic features of the anterior pituitary, suitably stained (eg,
with Gomori’s stain) to show its acidophils and basophils and viewed at
higher magnification (Figure 13–4), are as follows:
•
•
•
•
groups of chromophils of two main kinds—red-staining acidophils and
blue-staining basophils
groups of chromophobes—unstained, smaller, quiescent, or degranulated secretory cells
no ducts
abundant wide capillaries of the fenestrated type
The various pituitary acidophils and basophils, together with the hormones they secrete, are listed in Table 13–3.
Table 13–3
Anterior Pituitary Hormone Sources
Cells and Cytoplasmic Staining
Secreted Hormones
Somatotrophs (acidophil)
Mammotrophs (acidophil)
Mammosomatotrophs (acidophil)
Corticotrophs (basophil)
Growth hormone
Prolactin
Prolaction and growth hormone
Adrenocorticotropic hormone (and
putative source of melanocytestimulating hormone)
Adrenocorticotropic hormone and
thyroid-stimulating hormone
Adrenocorticotropic hormone,
follicle-stimulating hormone, and
luteinizing hormone
Thyroid-stimulating hormone
Follicle-stimulating hormone and
luteinizing hormone
Corticothyrotrophs (basophil)
Corticogonadotrophs (basophil)
Thyrotrophs (basophil)
Gonadotrophs (basophil)
174
PDQ HISTOLOGY
Capsule
Zona
glomerulosa
Zona
fasciculata
Fenestrated
capillary
Zona
reticularis
Medullary
chromaffin
cells
Figure 13–5 Organization of an adrenal gland.
Zona reticularis
Capsule
Medulla
Figure 13–6 Adrenal seen under scanning power.
Chapter 13
Endocrine System
175
ADRENALS
The adrenals (suprarenals) are distinctively shaped endocrine glands
attached to the superomedial borders of the kidneys. Each adrenal gland has
a mesoderm-derived cortex with a neural crest–derived medulla that is
functionally separate. Compared with the medulla, the cortex is more elaborate in organization (Figure 13–5).
The following steroid hormones are produced by the adrenal cortex
(adrenocorticosteroids):
•
•
aldosterone, secreted by the cells in the glomerulosa (outermost zone of
the adrenal cortex)
cortisol and weak androgens, secreted jointly by the cells in the fasciculata and reticularis (middle and innermost zones of the adrenal cortex)
The following catecholamine hormones are produced by the adrenal
medulla:
•
•
epinephrine, secreted by many of the medullary chromaffin cells
norepinephrine, secreted by the remainder of the medullary chromaffin cells
Features generally permitting sections of the adrenals to be recognized
under scanning power (Figure 13–6) include the following:
•
•
•
•
characteristically folded, essentially triangular outline (indicating the
overall shape of the capsule)
bright-staining zona reticularis, demarcating the border between the
cortex and the medulla
paler-staining zona fasciculata, external to zona reticularis
relatively uniform-looking pale pink medulla with large medullary
veins that commonly have the appearance of wide empty spaces
176
PDQ HISTOLOGY
Capsule
Zona glomerulosa
Zona fasciculata
Zona reticularis
Medulla
Figure 13–7 Adrenal cortex.
Capsule
Glomerulosa
Fasciculata
Reticularis
Medulla
Figure 13–8 Adrenal cortex seen in more detail.
Chapter 13
Endocrine System
177
Working inward, further features of adrenal sections that may be distinguished at higher magnification (Figures 13–7 and 13–8) are as follows:
•
•
•
•
•
fibroelastic thick external capsule
narrow outer zone containing spherical clusters of small purple secretory cells, with closely associated fenestrated capillaries—the zona
glomerulosa of the adrenal cortex
wide middle zone containing radial columns, approximately one cell
thick, of larger pink secretory cells, with closely associated long straight
fenestrated capillaries—the zona fasciculata of the adrenal cortex
narrow inner zone containing anastomosing cords of small, pale purple
secretory cells arranged as a network, with closely associated fenestrated
capillaries—the zona reticularis of the adrenal cortex
central mass of slightly larger, relatively pale-staining, round cells that
include chromaffin cells of two types (either epinephrine secreting or
norepinephrine secreting) and occasional basophilic sympathetic ganglion cells, together with wide branches of the medullary vein and fenestrated capillaries—the adrenal medulla
178
PDQ HISTOLOGY
Figure 13–9 Thyroid (hematoxylin and eosin stain).
Figure 13–10 Thyroid (periodic acid–Schiff stain).
Chapter 13
Endocrine System
179
THYROID
The bilobed thyroid gland, lying anterior and lateral to the trachea just inferior to the larynx, incorporates two independent populations of hormonesecreting cells. The thyroid follicular epithelial cells, derived from endoderm, produce thyroid hormone (thyroxine plus triiodothyronine). The
parafollicular (C) cells, derived from neural crest, produce calcitonin.
A characteristic histologic feature of the thyroid gland is the thyroid
follicle, a cyst-like spherical structure lined by simple cuboidal thyroid
follicular epithelial cells and filled with extracellular thyroglobulin, the
macromolecular stored precursor of thyroid hormone (Figure 13–9).
Thyroglobulin is demonstrated to advantage by periodic acid–Schiff staining
(Figure 13–10) because it is a glycoprotein. On release through exocytosis
from the epithelial lining cells of the follicle, the secreted thyroglobulin
becomes iodinated extracellularly. It is subsequently ingested by these cells
and submitted to intracellular proteolysis, releasing thyroid hormone.
An outer fascial sheath surrounds the external connective tissue capsule
of the thyroid. The minimal connective tissue stroma is profusely supplied
with fenestrated capillaries.
180
PDQ HISTOLOGY
Follicular
epithelial cell
Figure 13–11 Thyroid follicle.
Parafollicular
cell
Follicular
epithelial cell
Figure 13–12 Parafollicular cells of the thyroid.
Chapter 13
Endocrine System
181
Seen here at higher magnification, thyroid follicular epithelial cells constitute a simple cuboidal epithelium bordering on the stored thyroglobulin (Figure 13–11). In a less active thyroid, these cells can appear low columnar (Figure 13–12). In the course of tissue processing, the thyroid tends to undergo
uneven shrinkage, accounting for the wide split extending from the bottom left
to the upper right in Figure 13–11 and the majority of empty-looking “spaces”
and thyroglobulin “bubbles” commonly seen in thyroid sections.
The slightly larger round cells with central nuclei that lie between follicles (see Figure 13–12) are parafollicular (C) cells. These cells lie internal
to the follicular basement membrane but do not border on the thyroglobulin
(Figure 13–13). They release calcitonin into adjacent fenestrated capillaries.
Parafollicular
cells
Basement
membrane
Thyroid
follicle
Figure 13–13 Position of parafollicular cells in the thyroid.
182
PDQ HISTOLOGY
Oxyphil cells
Chief cells
Figure 13–14 Parathyroid.
Acinus
Figure 13–15 Pancreatic islet.
Islet
Chapter 13
Endocrine System
183
PARATHYROIDS
Distinctive features of the parathyroids (Figure 13–14), the small endoderm-derived endocrine glands lying on the posterior surface of the thyroid
that secrete parathyroid hormone, are as follows:
•
•
•
•
large areas of relatively small round chief cells with an intensely stained small
central nucleus, representing the cells that secrete parathyroid hormone
smaller groups of larger, pinker cells with a fairly similar nucleus
(oxyphil cells) that first appear at puberty and are assumed to represent
retired or nonsecreting chief cells
numerous fenestrated capillaries
no ducts
PANCREATIC ISLETS
Pancreatic islets (islets of Langerhans), representing the diffuse endodermderived endocrine component of the pancreas (Figure 13–15), may be recognized by the following:
•
•
•
proximity to serous acini (a readily recognizable pancreatic exocrine
component)
relatively pale staining of the cytoplasm of their constituent cells in
hematoxylin and eosin–stained sections
irregular shape, size, and distribution of the islets
A (α) cells producing glucagon can be distinguished from B (β) cells
producing insulin by specially devised staining methods (eg, Gomori). Also
present are D (δ) cells secreting somatostatin, F cells secreting pancreatic
polypeptide, and fenestrated capillaries.
14
Female Reproductive System
T
his chapter deals with the parts of the female reproductive
system listed in Table 14–1 and describes how the histologic appearance of
some of them is affected by physiologic variation in the ovarian steroid hormone levels. From the age of puberty until menopause, the ovaries constitute the exclusive site of cyclic maturation of ovarian follicles, monthly
release of the secondary oocyte formed at the time of ovulation, and phasic
secretion of ovarian hormones. The secondary oocyte liberated in the course
of ovulation enters a uterine tube, where it may become fertilized. Peristaltic
waves of contraction, produced by smooth muscle of the tubal wall, convey
the liberated germ cell to the uterine body. The blastocyst developing from
a fertilized ovum generally implants in the endometrium (uterine mucosa)
at some posterior site. Estrogen and progesterone, the ovarian steroid hormones, are essential for appropriate growth and functional activity of the
endometrium, myometrium (uterine smooth muscle), cervical mucous
glands, and breast and also affect the cytologic appearance of the vagina.
OVARIES
The ovarian cortex is characterized by its distinctive content of ovarian
follicles representing various stages of maturation, embedded in a swirlylooking stroma. Just under the simple cuboidal covering epithelium lies a
relatively fibrous layer termed the tunica albuginea. The ovarian medulla
contains similar fibroblast-like stromal cells and is the site of substantial
ovarian blood vessels, some of which are fairly convoluted.
Table 14–1
Female Reproductive System
Ovaries
Vagina
Uterus
Breast
Uterine tubes (fallopian tubes)
185
186
PDQ HISTOLOGY
Early secondary
follicle
Corpus albicans
Primordial
follicle
Primary
follicle
Corpus
luteum
Cortex
Atretic follicle
Secondary
follicle
Medulla
Simple
cuboidal
epithelium
Theca
Mature follicle
Figure 14–1 Maturation stages of ovarian follicles.
Figure 14–2 Primary ovarian follicles.
Chapter 14
Female Reproductive System
187
The histologic appearance of the ovaries depends on both the species
represented and the current menstrual phase at the time of fixation. Composite drawings showing the maturation stages of ovarian follicles (Figure
14–1) are based on all of their possible histologic appearances. Only a representative selection is found in any given section. Furthermore, mature
follicles may appear surprisingly large after they accumulate follicular fluid,
and several follicles may be found to be approaching full maturity if, as is
often the case, the ovary was obtained from some animal that produces litters rather than single offspring. All stages except the corpus luteum are
generally present during the proliferative (estrogenic, follicular) phase. The
corpus luteum appears as an added feature in the secretory (progestational,
progravid) phase and, in particular, in the first trimester of a pregnancy,
when it becomes very large. Follicles may degenerate (undergo atresia) at
any stage in their maturation. Atretic and ruptured (ovulated) follicles
become replaced by a long-lasting fibrous scar called a corpus albicans.
The early stages of ovarian follicular maturation resulting from ovarian
stimulation by follicle-stimulating hormone (FSH) (Figure 14–2) are classified according to the histologic appearance of the ovarian follicular (granulosa) cells surrounding the primary oocyte:
•
•
•
•
primordial follicles—single layer of low cuboidal (almost squamous)
unstimulated follicular cells
primary follicles—two or more layers of cuboidal to columnar follicular cells but no antrum
secondary follicles—many layers of columnar follicular cells with
antrum containing follicular fluid
mature (tertiary, graafian) follicle—cyst-like structure with primary
oocyte attached to follicular wall at cumulus oophorus; surrounding
stroma constitutes theca
188
PDQ HISTOLOGY
Figure 14–3 Atretic ovarian follicles.
Theca
Cumulus oophorus
Figure 14–4 Mature ovarian follicles.
Antrum
Zona pellucida
Chapter 14
Female Reproductive System
189
Microscopic signs of follicular atresia (Figure 14–3) include the following:
•
•
•
loss, disorganized arrangement, or morphologic deterioration of the
follicular cells
degenerative changes of the primary oocyte, for example, loss of its
zona pellucida (external glycoprotein covering), loss of nuclear staining,
indications of nuclear disruption, invasion of the follicle by leukocytes,
such as neutrophils
presence of fibroblasts but not scar tissue inside the follicle
Mature follicles (Figure 14–4) show the following features:
•
•
•
•
•
•
•
substantial size and spherical shape
sizable antrum filled with follicular fluid
numerous follicular epithelial (granulosa) cells (producing estrogen)
vascular theca interna (releases the androgen substrate used in estrogen
production)
fibrous theca externa
cumulus oophorus containing primary oocyte
substantial pink zona pellucida present on oocyte surface
190
PDQ HISTOLOGY
Corpus albicans
Figure 14–5 Corpus albicans.
Theca lutein cells
Granulosa lutein cells
Figure 14–6 Corpus luteum.
Chapter 14
Female Reproductive System
191
A corpus albicans (Figure 14–5) may generally be recognized by its
•
•
•
essentially round to ovoid shape and rather irregular periphery merging with the stroma,
pink hyalinized collagen content, and
residual fibroblast nuclei (also showing that scarring has occurred).
Histologic features of a corpus luteum (Figure 14–6) include the
following:
•
•
•
•
•
•
during the first part of the secretory phase of a menstrual cycle: a diameter similar to or smaller than that of a ripening ovarian follicle
during the first trimester of a pregnancy: a large diameter (generally
peaking at about half the ovarian volume)
relatively pale-staining granulosa lutein cells (producing both estrogen
and progesterone)
slightly smaller and pinker theca lutein cells (producing additional
progesterone and the androgen substrate used in estrogen production)
connective tissue septa, extending into its interior from the theca and
giving it a somewhat “lobular” appearance
persisting remnants of the intrafollicular blood clot formed at ovulation
192
PDQ HISTOLOGY
Endometrial
glands
Spiral
arteries
Early proliferative
Late proliferative
Late secretory
Figure 14–7 Endometrium at representative phases of the menstrual cycle.
Endometrium
Myometrium
Figure 14–8 Uterine body.
Chapter 14
Female Reproductive System
193
UTERUS, ENDOMETRIUM, AND MENSTRUAL CYCLE
The histologic appearance of the endometrium reflects cyclical variation in
the circulating levels of estrogen and progesterone (Figure 14–7). Following
4 to 5 days of partial endometrial loss (the menstrual phase of the cycle),
rising estrogen levels from FSH-stimulated follicular granulosa cells promote mitosis and endometrial regeneration (proliferative, estrogenic, or
follicular phase). After ovulation, rising progesterone and estrogen levels
from luteinizing hormone– and FSH-stimulated granulosa lutein cells promote hypertrophy and secretory activity of endometrial glands in preparation for implantation (secretory, progestational, or progravid phase). Subsequent fall of the progesterone and estrogen levels leads to ischemic
necrosis of the endometrium (ischemic phase).
Sections of the uterine body (Figure 14–8) may be recognized by the
following:
•
•
•
•
“hollow pear” shape, with wide central lumen
substantial mucosa termed the endometrium, characterized by simple
tubular glands that appear straight at this menstrual phase
thick multilayered muscular wall termed the myometrium (uterine
smooth muscle)
thin external serosa
194
PDQ HISTOLOGY
Straight
endometrial glands
Figure 14–9 Proliferative endometrium.
Sacculated
endometrial glands
Figure 14–10 Secretory endometrium.
Chapter 14
Female Reproductive System
195
Endometrium observed fairly late in the proliferative phase (Figure
14–9) may be recognized by the following:
•
•
•
•
simple columnar lining epithelium
predominantly straight or slightly tortuous long endometrial glands
deeply invaginated into a relatively cellular lamina propria
a few mitotic figures in the glandular epithelium or lamina propria
underlying smooth muscle (myometrium)
Endometrium that is approaching the end of the secretory phase (Figure 14–10) typically shows the following additional features:
•
•
•
•
hypertrophy and sacculation of the endometrial glands (giving grazing
sections a “ladder-like” appearance)
pale-stained glandular secretory cells with a “ragged” luminal border
indicative of glycogen secretion
empty-looking spaces in the lamina propria, representing sites of intercellular accumulation of tissue fluid (edema spaces)
elongated spiral arteries in the lamina propria
196
PDQ HISTOLOGY
Lamina propria
Smooth muscle
Ciliated simple
columnar epithelium
Figure 14–11 Uterine tube.
Stratified squamous
nonkeratinizing epithelium
Lamina propria
Figure 14–12 Vagina.
Chapter 14
Female Reproductive System
197
UTERINE TUBE
Sections through the ampullary region of a uterine tube (Figure 14–11)
may be recognized by the following:
•
•
•
•
•
elaborately folded mucosa characterized by substantial primary, secondary, and tertiary folds
loose ordinary connective tissue (lamina propria) extending into each
fold
simple columnar lining epithelium, predominantly ciliated, with scattered groups of nonciliated secretory cells
fairly substantial muscular wall consisting of an inner circular layer and
an outer longitudinal layer of smooth muscle
external serosal covering
Care should be taken not to misidentify a section of this part of a uterine tube as a section of seminal vesicle bearing a superficial resemblance to
it (see Figure 15–9).
VAGINA
Histologic features of the vagina (Figure 14–12) are as follows:
•
•
•
•
substantial stratified squamous nonkeratinizing lining epithelium characterized by pale staining owing to its content of stored glycogen and
lipid (estrogen effect)
thick, vascular fibroelastic lamina propria containing numerous small
veins and venules
smooth muscle coat consisting of inner circular and outer longitudinal
bundles
fibrous adventitia
198
PDQ HISTOLOGY
Intralobular connective
tissue
Intralobular ducts
Interlobular connective tissue
Figure 14–13 Resting breast.
Interlobular connective tissue
Intralobular connective tissue
Figure 14–14 Lobule of resting breast.
Chapter 14
Female Reproductive System
199
BREAST
Breast tissue that is not currently lactating is commonly described as resting breast. At low magnification (Figure 14–13), resting breast is recognizable by the following criteria:
•
•
small groups of ducts showing a somewhat scattered distribution indicative of spherical lobules (permitting their distinction from sweat glands)
a relatively fibrous kind of connective tissue around the lobules that has
a variable content of adipocytes (not shown)
Additional features confirmed at higher magnification (Figure 14–14)
are as follows:
•
•
•
epithelial lining of some larger ducts consists of two layers of cuboidal
cells; smaller ducts lined with a single layer
no secretory component (unlike sweat glands or lactating breast)
intralobular connective tissue—relatively cellular; interlobular connective tissue—relatively fibrous
200
PDQ HISTOLOGY
Distinctive histologic features are acquired by the lactating breast
(Figure 14–15) in the second half of a pregnancy and lasting until the end
of breast-feeding:
•
•
distended, rounded lobules separated by septa of fibrous interlobular
connective tissue
numerous pale-staining secretory alveoli variably filled with extracellular secretion (colostrum until about the end of the first postnatal week
and then milk)
In the first half of a pregnancy, high estrogen levels induce a proliferative response in the ductal epithelium, bringing about further development
of the ducts and formation of the secretory alveoli. In the second half, rising additional levels of progesterone, acting in concert with prolactin and a
number of other hormones, ensure full breast differentiation and elicit
secretory activity of the alveoli.
Intralobular duct
Secretory
alveoli
Fibrous interlobular
connective tissue
Figure 14–15 Lactating breast.
15
Male Reproductive System
T
he parts of the male reproductive system considered in this
chapter are listed in Table 15–1. Beginning at the age of puberty, spermatozoa are produced from spermatogonial stem cells on an ongoing basis as
synchronously developing clones. This process of spermatogenesis occurs in
the seminiferous epithelium of the seminiferous tubules of each testis. The
other important function of the testis is testosterone secretion by its interstitial (Leydig) cells. From the seminiferous tubules, spermatozoa pass into
a ductus epididymis, a storage compartment where spermatozoa begin to
mature and become motile. On each side, a long muscular-walled tube, the
ductus deferens, conveys motile spermatozoa through the inguinal canal
and pelvic cavity to its site of junction with the proximal end of a seminal
vesicle, an accessory gland that contributes nutritive fluid secretion to
semen. The prostate, the other major accessory gland, similarly contributes
prostatic fluid to semen. The anatomic position of the prostate, surrounding the urethra at the base of the urinary bladder, is potentially of clinical
importance because constrictive prostatic enlargement (benign or malignant) is a common condition in aging men. On each side, the ejaculatory
duct leading from the junction between a ductus deferens and a seminal
vesicle traverses the prostate inferiorly and opens into the prostatic urethra.
Distally, the spongy part of the urethra terminates at the glans penis.
Table 15–1
Male Reproductive System
Testes
Epididymides
Ducti deferentes
Seminal vesicles
Prostate
Penis
201
202
PDQ HISTOLOGY
Ductus
deferens
Rete
testis
Tunica
albuginea
Ductuli
efferentes
Ductus
epididymis
Seminiferous
tubule
Figure 15–1 Organization of the testis and epididymis.
Mesothelium
Tunica
albuginea
Seminiferous
tubules
Figure 15–2 Testis.
Chapter 15
Male Reproductive System
203
TESTES
Each testis (Figure 15–1) is an ovoid structure enclosed by a capsule-like
tunica albuginea. Fibrous septa extend inward and subdivide the interior
incompletely into lobules, each of which contains up to four tightly packed
seminiferous tubules. The two ends of each looped seminiferous tubule
open through the rete testis and ductuli efferentes of the mediastinum testis
into the long convoluted ductus epididymis extending from the head of the
epididymis to its tail.
In sections of testis observed at low magnification, the thick tunica
albuginea and numerous component seminiferous tubules are readily identifiable (Figure 15–2). The external surface is covered with squamous peritoneal mesothelium (tunica vaginalis testis). Scattered small groups of
interstitial (Leydig) cells may be discerned in the connective tissue stroma
lying between the tubules.
204
PDQ HISTOLOGY
Spermatid
Spermatozoon
Primary
spermatocyte
Sertoli cell
Loose connective
tissue
Myoid cell
Basement
membrane
Spermatogonium
Figure 15–3 Seminiferous tubule.
Sertoli cell
Spermatozoa
Figure 15–4 Seminiferous tubule.
Spermatid
Spermatogonium
Chapter 15
Male Reproductive System
205
Seminiferous Tubules
The wall of a seminiferous tubule (Figure 15–3) is made up of (1) a single
layer of tall columnar epithelial cells called Sertoli cells and (2) a diverse
population of quiescent, dividing, and differentiating germ cell progenitors
representing the various stages of spermatogenesis. Occupying pockets in
the sides of Sertoli cells, the progenitor cells are so abundant that the Sertoli cells appear to be widely separated from each other in sections. At some
level, however, all of these constitutive epithelial cells stay laterally interconnected by continuous tight junctions that seal off the adluminal differentiation compartment from the basal stem cell compartment. Adjacent to
the basement membrane at the basal end of the Sertoli cells is an investing
layer of loose connective tissue containing contractile flat myoid cells.
Seminiferous tubules observed at an appropriate magnification (Figure
15–4) commonly show various combinations of the following characteristics:
•
•
•
•
•
•
smooth, round perimeter (basement membrane with associated connective tissue and myoid cells)
fairly large nuclei, with an ovoid or almost pyramidal shape and radial
orientation, representing Sertoli cells (which respond to folliclestimulating hormone by secreting androgen-binding protein)
fairly substantial rounded cells, with a spherical-to-ovoid central
nucleus, that lie in the basal stem cell compartment immediately internal to the basement membrane of the seminiferous tubule (spermatogonia = spermatogenic stem cells)
round dividing cells containing condensed chromosomes (predominantly spermatogonia and primary spermatocytes)
spermatids that are transforming into spermatozoa as they approach
the luminal border
formed spermatozoa awaiting release from the luminal border of Sertoli cells
206
PDQ HISTOLOGY
Mitochondrion
Golgi
apparatus
1.
Centriole
2.
Forming
flagellum
3.
Residual
cytoplasm
(discarded)
Forming
acrosome
Head
cap
4.
Flagellum
Mitochondrial
sheath
Figure 15–5 Principal stages of spermiogenesis.
Interstitial (Leydig) cells
Figure 15–6 Interstitial (Leydig) cells of testis.
Chapter 15
Male Reproductive System
207
Spermiogenesis
Based on electron microscopic observations, key stages in spermiogenesis
(spermatozoal production from the preceding stage, spermatids) are as
follows:
•
•
•
•
•
•
•
morphologic transformation of haploid spermatids with no further cell
division (Figure 15–5)
approximation of the Golgi apparatus to the anterior pole of the nucleus
spreading of the acrosomal vesicle (a Golgi saccule) over the anterior
pole of the nucleus, formation of the acrosome and head cap (site of
penetration enzymes)
caudal migration of the centriole pair
nuclear elongation and further chromatin condensation
flagellar growth from the distal centriole (which then disappears)
mitochondrial aggregation and helical rearrangement in proximal
axoneme as the mitochondrial sheath (middle piece)
Interstitial (Leydig) Cells
Testicular interstitial (Leydig) cells (Figure 15–6) possess the following
characteristics:
•
•
•
•
•
interstitial position (small groups in stroma between seminiferous
tubules)
relatively large diameter and central round-to-ovoid, pale-staining
nucleus
pale cytoplasmic staining reflecting cholesterol content (stored steroid
precursor)
proximity to blood capillaries and lymphatic capillaries
respond to luteinizing hormone by secreting testosterone
208
PDQ HISTOLOGY
Figure 15–7 Ductus epididymis.
Lamina propria
Pseudostratified
columnar epithelium
Figure 15–8 Ductus deferens.
Smooth muscle
Chapter 15
Male Reproductive System
209
EFFERENT TESTICULAR DUCTS
Distinctive features of the ductus epididymis (Figure 15–7) are as follows:
•
•
•
•
stored spermatozoa in lumen
pseudostratified columnar epithelium with stereocilia (immotile
groups of long microvilli)
surrounding thin circular layer of smooth muscle
supportive connective tissue stroma
A section of a ductus deferens, also widely known as a vas deferens (Figure 15–8), is recognizable by the following:
•
•
•
•
•
small corrugated lumen with low longitudinal mucosal folds
pseudostratified columnar epithelium with stereocilia
fibroelastic lamina propria
remarkably substantial muscular wall consisting of a longitudinal inner
layer, circular middle layer, and longitudinal outer layer of smooth muscle (propels through peristalsis during emission)
connective tissue adventitia
210
PDQ HISTOLOGY
Figure 15–9 Seminal vesicle.
Fibromuscular stroma
Figure 15–10 Prostate.
Chapter 15
Male Reproductive System
211
SEMINAL VESICLES
The histologic characteristics of a seminal vesicle (Figure 15–9) are as follows:
•
•
•
•
•
multiple cuts through a single tortuous tubular secretory diverticulum
that is folded into a fairly compact mass
wide, fluid-filled lumen containing an elaborate arrangement of thin
folds of fibroelastic lamina propria covered with secretory epithelium
(different in appearance from the folds found in the ampulla of a uterine tube; see Figure 14–11)
dark-staining pseudostratified columnar or simple columnar secretory
epithelium
thick muscular wall consisting of inner circular and outer longitudinal
smooth muscle
connective tissue adventitia binding tubular convolutions together
PROSTATE
Distinctive histologic features of the prostate (Figure 15–10) are as follows:
•
•
•
•
many lobules (compound tubuloalveolar gland)
characteristic extensive folding of the secretory epithelium
purple-staining tall columnar secretory epithelium (pseudostratified or
simple)
fibroelastic lamina propria
212
PDQ HISTOLOGY
Secretory unit
Calcified concretion
Secretory
epithelium
Stromal smooth
muscle cells
Figure 15–11 Secretory unit of prostate.
Corpora cavernosa
Spongy urethra
Figure 15–12 Penis.
Tunica albuginea
Corpus spongiosum
Chapter 15
•
•
Male Reproductive System
213
distinctive fibromuscular capsule and stroma: smooth muscle cells—
deep pink, collagen fibers—lighter pink (Figure 15–11)
calcified concretions found in the lumen of some secretory units (variable in occurrence and more common in the prostate of aging men)
PENIS
Sections of the shaft of the penis (Figure 15–12) may be readily recognized
by the following criteria:
•
•
•
essentially ovoid outline, thin skin at periphery
paired corpora cavernosa, each enclosed by its fibrous sheath
(tunica albuginea)
ventral spongy urethra, lined with stratified (or pseudostratified)
columnar epithelium and surrounded by the corpus spongiosum
with its enclosing tunica albuginea
Index
Entries with f following a page
number indicate figures; entries
with t following a page number
indicate tables.
A bands, 103, 104, 104f
A cells, of pancreatic islets, 183
Acidophilic staining, 9, 10f
Acidophils, of pituitary, 172f,
173, 173t
Acinus, of liver, 144, 144f
Acrosome, 206f, 207
Adhesion belt, 26f, 27t
Adipocytes, 39t
Adipose tissue, 43, 43f
Adrenals, 174f, 175, 176f, 177
Adrenocorticosteroids, 175
Adrenocorticotropic hormone,
171t, 173t
Adventitia
of blood vessels, 109, 110f
of gut, 130f, 131
Afferent arteriole, of renal corpuscle, 158f, 161, 162f, 163
Aldosterone, 175
Alveolar ducts, 150f, 151
Alveolar macrophages, 145, 152f,
153, 154f
Alveolar sacs, 150f, 151, 152f
Alveoli, of lungs, 150f, 151, 152f
Anaphase, 14f, 15f, 17f
Androgen-binding protein, 205
Angiotensin, 163
Antidiuretic hormone, 171
Aorta, 110f, 111, 111f
214
Apocrine sweat glands, 121, 128
Appendix, 138f, 139
Appositional growth, of cartilage
and bone, 45, 50
Arachnoid membrane, 85
Arector pili muscle, 126, 126f,
127f
Arteries
distributing, 110f, 112f, 113
elastic, 110, 111, 111f
muscular, 113
Arterioles, 110f, 114f, 115
afferent, of renal corpuscles,
158f, 161, 162f, 163
efferent, of renal corpuscles,
161, 162f
Articular cartilage, 45, 46f, 47,
60f
Astrocytes, 89, 89f
Atherosclerotic plaques, 111
Atresia, of ovarian follicles, 187,
188f, 189
Autonomic ganglia, 94f, 95
Autonomic nervous system, 95
Axon, 83, 92f
Band neutrophil, 73t, 74f
Basement membrane, 38, 38f
glomerular, 160f, 161
Basic tissues, 1, 2t
Basophilic erythroblasts, 69t,
70f, 71
Basophilic normoblast, 69t
Basophilic staining, 9, 10f
Basophils
Index
of blood, 62t, 65, 66f
of pituitary, 172f, 173, 173t
B cells, 66, 77
of pancreatic islets, 183
Bladder, urinary, 166f, 167
Blood cells, 61-68. See also under
individual types
B lymphocytes, 66, 77
Bone
cancellous, 50, 50f, 51f, 54, 55f
dense (compact), 56-58, 56f-58f
growth of, 53
Bone marrow, 68, 76f, 77
Bone matrix, 49
Brain, 89
Breast
lactating, 200, 200f
resting, 198f, 199
Bronchi, 146f, 147
Bronchioles, 148f, 149, 150f, 151
Brown fat, 43
Brunner’s glands, 137
Calcitonin, 179, 181
Canal, haversian, 56, 57f, 58f
Canaliculi, 49, 58, 58f
Cancellous bone, 50, 50f, 51f, 54,
55f
Capillaries, 114f, 116f, 117
Capsule cells, of ganglia, 94f, 95
Cardiac muscle, 104-107, 106f
Cartilage, 45-49, 46f
articular, 45, 46f, 47, 60f
elastic, 5f, 48, 48f
fibro-, 49, 49f
hyaline, 45-47, 46f
Cartilage matrix, 45, 46f, 47
Catecholamine hormones, 175
C cells, 181
Cell, microscopic appearance of,
6, 6f
Cell junctions, 25, 26f, 27t
Cell nests, 45, 46f
215
Cells. See under individual
names
Central nervous system, 83-91
Central veins, 142f, 143, 144f
Centroacinar cells, 140f, 141
Cerebellar cortex, 90f, 91
Cerebral cortex, 88f, 89
Chief cells
of fundic glands, 132f, 133
of parathyroid, 182f, 183
Chondrocytes, 7f, 45
Chromatids, 15f
Chromophils, 173
Chromophobes, 173
Chromosomes, 15f, 16, 16f
Cilia, 21, 22f
Circulatory system, 109-117
Collagen
fibers, 35, 36, 36f
types, 35, 38, 45
Collecting ducts, of kidney, 158f,
159, 164f
Compact bone. See Dense bone
Compound glands, 28t, 30, 30f
Cones, retinal, 96f, 97
Connective tissue, 35-42, 36f, 37f,
42f
dense ordinary, 41, 42f
loose, 36-41, 36f, 37f
Convoluted tubules, of kidney,
158f, 164f, 165
Corneum, of epidermis, 24f,
120f, 122f, 124f
Corpus albicans, 186f, 187, 190f,
191
Corpus luteum, 186f, 190f, 191
Corpuscles
Hassall’s (thymic), 81
renal, 155, 156f, 158f, 160f, 161
Corticogonadotrophs, 173t
Corticothyrotrophs, 173t
Corticotrophs, 173t
Cortisol, 175
216
PDQ HISTOLOGY
Crypts, intestinal, 134f, 135, 136f,
138f
Cytoplasm, main components
of, 8t-9t. See also Table 1-3 on
CD-ROM
Cytosol, 8t
D cells, of pancreatic islets, 183
Demilune, serous, 33, 33f
Dendrites, 83, 86f, 87
Dense bone, 56-58, 56f-58f
Dense ordinary connective
tissue, 41, 42f
Dermal papillae, 121
Dermis, 119, 120f, 122f, 124f
Desmosome, 26f, 27t
Digestive system, 129-144
Distal convoluted tubule, 158f,
164f, 165
Distributing arteries, 110f, 112f,
113
Dorsal root ganglia, 95
Ducts
alveolar, 150f, 151
collecting of kidney, 158f, 159,
164f
intralobular and interlobular,
30, 30f
papillary, 159
Ductus deferens, 208f, 209
Ductus epididymis, 208f, 209
Duodenum, 136f, 137
Dura mater, 84f, 85
Eccrine sweat glands, 121, 128,
128f
Efferent arteriole, of renal
corpuscle, 161, 162f
Elastic arteries, 110, 111, 111f
Elastic cartilage, 5f, 48, 48f
Elastic fibers, 35, 36f
Elastin, in lungs, 145, 153
Electron micrographs, 3, 4. See
also 7f, 22f, 23f, 116f
Electron microscope, 3
Endocardium, 109
Endochondral ossification, 53,
55f
Endocrine glands, 169-183, 169t.
See also under individual names
Endocrine system, 169-183
Endometrium, 192f, 193, 194f, 195
Endomysium, 99, 100f, 101f
Endoneurium, 92f, 93
Endoplasmic reticulum, 8t, 11
Endosteum, 56
Endothelial cells, 39t, 116f
Endothelium, 109, 112f, 114f
Enteroendocrine cells, 134f, 135
Eosin, 9
Eosinophils, 62t, 64f, 65
Epicardium, 109
Epidermis, 119, 120f, 121, 124f
Epididymis, 202f
Epimysium, 99, 100f
Epinephrine, 175, 177
Epineurium, 92f, 93
Epiphyseal plate, 53, 54f
Epithelial glands, 28-33, 28t,
29f-33f
Epithelial membranes, 19-25, 20t.
See also under individual types
Epithelium
pseudostratified, 20t, 21, 22f
retinal pigment, 96f, 97
simple, 20t, 20f, 21f
stratified, 20t, 23, 24f, 25f
stratified squamous, 23, 24f
transitional, 25, 25f
Erythroblasts
basophilic, 69t, 70f, 71
polychromatophilic, 69t, 70f, 71
Erythrocytes, 62t, 63, 63f
polychromatophilic, 69t, 72, 72f
Index
Erythroid (erythropoietic)
precursors, 69-72, 9t, 70f, 72f,
76f
Esophagus, 130f, 131
Estrogen, 185, 189, 191, 193, 200
Estrogenic phase, of menstrual
cycle, 192f, 193, 194f, 195
Exocrine glands, 28, 28t, 29f-33f
Extracellular matrix, 35, 38
Fallopian tubes. See Uterine tubes
Fasciculata, of adrenal cortex,
174f, 175, 176f, 177
Fat cell, 39t
Fat tissue, brown and white, 43
F cells, of pancreatic islets, 183
Female reproductive system,
185-200
Fibers
collagen, 35, 36, 36f
elastic, 35, 36f
Purkinje, 109
reticular, 35, 77
Fibrillins, 35
Fibroblasts, 39t, 40, 40f
Fibrocartilage, 49, 49f
Filaments
cytoplasmic, 9t
of muscle cells, 99, 100f, 104,
104f
Fixation, 2
Follicle-stimulating hormone,
187, 205
Follicles
hair, 125, 126, 126f, 127f
ovarian, 186f, 187, 188f, 189
primary, secondary, and
tertiary, 187
primordial, 186f, 187
Follicular atresia, 187, 188f, 189
Follicular epithelial cells, of
thyroid, 179, 180f, 181
217
Follicular phase, of menstrual
cycle, 192f, 193, 194f, 195
Foveolae, 133
Fundic region, of stomach, 132f,
133
Ganglia
autonomic, 94f, 95
spinal or posterior (dorsal)
root, 94f, 95
Ganglion cells, 94f, 95
Gap junction, 26f, 27t, 87, 105,
105f
Gastric pits, 132f, 133
Gastrointestinal tract, 129-139
Germinativum, of epidermis,
120f, 121, 124f
Gland(s)
adrenal, 174f, 175, 176f, 177
Brunner’s, 137
compound, 28t, 30, 30f
digestive accessory, 129t, 139
endocrine, 169-183, 169t. See
also under individual names
epithelial, 28-33, 28t, 29f-33f
exocrine, 28, 28t, 29f-33f
fundic, 132f, 133
mixed (seromucous), 32-33,
32f, 33f
parathyroid, 182f, 183
parotid, 140f, 141
pituitary, 170f, 171, 172f, 173
pyloric, 132f, 133
sebaceous, 126, 126f, 127
simple, 28t, 29, 29f
sweat, 121, 128, 128f
thyroid, 178f, 179, 180f, 181
Glia, 83, 86f, 88f
Glomerular basement membrane,
160f, 161
Glomerulosa, of adrenal cortex,
174f, 175, 176f, 177
218
PDQ HISTOLOGY
Glucagon, 183
Goblet cells, 21, 22f, 23f
Golgi apparatus, 8t, 40f
Gonadotrophs, 173t
Graafian follicles, 187
Granulocytes, 64. See also under
individual types
Granulocytic (granulopoietic)
precursors, 73, 73t, 76f
Granulosa cells, 189
Granulosa lutein cells, 190f, 191
Granulosum, of epidermis, 120f,
121, 122f, 124f
Gray matter, 83, 84f
Ground substance, of connective
tissue, 35
Growth hormone, 171t, 173t
Gut, 129-139
Hair follicles, 125, 126, 126f, 127f
Hassall’s corpuscles, 81
Haversian canal, 56, 57f, 58f
Haversian system, 56-58, 57f,
58f
H bands, 104, 104f
Head cap, 206f, 207
Hematopoiesis, 68
Hematoxylin, 9
Hemidesmosome, 26f, 27t
Henle, loop of, 158f, 159, 163, 164f
Histamine, 36, 39t
Hormone
adrenocorticotropic, 171t, 173t
antidiuretic, 171
follicle-stimulating, 187, 205
gastrointestinal, 133, 135
growth, 171t, 173t
luteinizing, 193, 207
parathyroid, 183
release-regulating
(hypothalamic), 171, 171t
thyroid, 179
thyroid-stimulating, 171t, 173t
Hormone receptors, 169
Howship’s lacunae, 51
Hyaline cartilage, 45-47, 46f
Hydrochloric acid, 133
Hydroxyapatite, 49
Hypodermis, 119
Hypophysis. See Pituitary
Hypothalamic release-regulating
hormones, 171, 171t
Hypothalamohypophysial tracts,
173
Hypothalamus, 173
I bands, 103, 104, 104f
Ileum, 136f, 137
Inferior vena cava, 110f, 113
Insulin, 183
Integumentary system, 119-128
Interalveolar walls, 152f, 153-154,
154f
Intercalated disks, 104, 105, 105f
Interlobular ducts, 30, 30f
Intermediate filaments, 9t, 27t,
105, 105f
Internal elastic lamina, 109, 110f,
112f
Interstitial cells, of testis, 203,
206f, 207
Interstitial growth, of cartilage,
45
Interstitial lamellae, 57f, 58, 58f
Interstitial matrix, 35
Intestine
large, 138f, 139
small, 135-137
Intima, of blood vessels, 109,
110f
Intralobular ducts, 30, 30f, 32f
Intramembranous ossification,
50, 50f
Intrinsic factor, 133
Index
Iodination, of thyroglobulin, 179
Ischemic phase, of menstrual
cycle, 193
Islets, pancreatic (of Langerhans),
140f, 141, 182f, 183
Jejunum, 137
JG cells, 161, 162f, 163
Junctions
cell, 25, 26f, 27t
gap, 26f, 27t
tight, 26f, 27t
Juxtaglomerular apparatus, 158f,
162f, 163
Juxtaglomerular cells, 161, 162f,
163
Karyolysis, 16, 17f
Karyorrhexis, 16, 17f
Karyotype, 16
Keratin, 23
Keratinocytes, 121
Kidneys, 155-165
lobule of, 156f, 157
Lacis cells, 163
Lactation. See Breast, lactating
Lacunae, 45, 49
Howship’s, 51
Lamina densa, 38
Lamina propria, of gut, 130f, 131
Laminin, 38
Langerhans, islets of, 140f, 141,
182f, 183
Large intestine, 138f, 139
Leukocytes, 62t. See also under
individual types
Leydig cells, 203, 206f, 207
Ligaments, 41
Light microscope, 2. See also in
Appendix on CD-ROM
Lingual tonsil, 78f, 79
219
Liver, 142f, 143, 144
acinus, 144, 144f
lobules of, 142f, 143
Loop of Henle, 158f, 159, 163, 164f
Loose connective tissue, 36-41,
36f, 37f
Lucidum, of epidermis, 120f, 121
Luteinizing hormone, 193, 207
Lymph nodes, 80f, 81
Lymphatic capillaries, 117
Lymphatics, 116f, 117
Lymphocytes, 62t, 66, 67f
Lymphoid organs, primary and
secondary, 77
Lymphoid tissue, 77-82
Lysosomes, 8t
Lysozyme, 135
Macrophages, 39t, 41, 41f
alveolar, 145, 152f, 153, 154f
Macula densa, 162f, 163
Male reproductive system,
201-213
Mammosomatotrophs, 173t
Mammotrophs, 173t
Mast cells, 36f, 39t
Matrix
of bone, 49
of cartilage, 45, 46f, 47
extracellular, 35, 38
interstitial, 35
Media, of blood vessels, 109, 110f
Medullary rays, 155, 156f, 157,
162f, 163
Megakaryocytes, 76f, 77
Melanin, 124f, 125
Melanocytes, 125
Membrane
arachnoid, 85
basement, 38, 38f
epithelial, 19-25, 20t. See also
under individual types
220
PDQ HISTOLOGY
synovial, 59, 59f, 60f
Meninges, 83, 85
Menstrual phase, 193
Mesangial cells, 163
Metamyelocytes, 73t, 74f
Metaphase, 15f
Microfilaments, 9t
Microscope
electron, 3
light, 2. See also in Appendix
on CD-ROM
Microtubules, 8t, 15f
Mitochondria, 8t
Mitosis, 15f
Mitotic figures, 13, 13f, 14f, 17f
Mixed glands, 32-33, 32f, 33f
M line, 104, 104f
Monocytes, 62t, 68, 68f
Mucosa, of gut, 130f, 131
Mucous secretory units, 31, 31f,
32f
Muscle
cardiac, 104-107, 106f
skeletal, 99-104, 100f-103f
smooth, 107, 107f, 108f
Muscular arteries, 113. See also
Distributing arteries
Muscularis externa, 130f, 131
Muscularis mucosae, 130f, 131
Myelin sheath, 83, 85, 92f, 93
Myeloblasts, 73t
Myelocytes, 73t, 74f
Myeloid tissue, 68-77, 76f
Myofibrils, 99, 100f, 102f, 103
Myoid cells, 204f, 205
Myosatellite cells, 104
Nephrons, 155, 158f, 159
Nerves, 91, 92f, 93, 93f
Nervous tissue, 83-95
Neuroglial cells, 83, 86f, 88f
Neurons, 83, 86f, 87
Neuropil, 83, 86f
Neutrophilic myelocytes, 74f, 75
Neutrophils, 62t, 64f, 65
band, 73t, 74f
Nissl bodies, 87, 91, 95
Norepinephrine, 175, 177
Normoblasts, 69t, 70f, 71
types of, 69t
Normocyte, 69t
Nucleolus, 6, 6f, 13
Nucleus, 13
Oocyte
primary, 187, 189
secondary, 185
Ossification
endochondral, 53, 55f
intramembranous, 50, 50f
Osteoblasts, 10f, 50, 51f
Osteoclasts, 18, 18f, 51, 52f
Osteocytes, 50, 51f
Osteon, 56, 57f
Osteoporosis, 53
Osteoprogenitor (osteogenic)
cells, 50, 51f
Ovarian follicles, 186f, 187, 188f,
189
Ovaries, 185-191
Oviduct. See Uterine tube
Oxyphil cells, 182f, 183
Oxytocin, 171
Pacinian corpuscles, 120f, 121,
122f
Palatine tonsils, 78f, 79
Pancreas, 140f, 141, 182f, 183
Pancreatic islets, 140f, 141, 182f,
183
Pancreatic polypeptide, 183
Paneth cells, 134f, 135
Papilla
dermal, 121
of hair, 126, 126f, 127f
Papillary ducts, 159
Index
Parafollicular cells, 179, 180f, 181
Parathyroid hormone, 183
Parathyroids, 182f, 183
Parenchyma, 30
Parietal cells, 132f, 133
Parotid gland, 140f, 141
Pars intermedia and pars nervosa, of pituitary, 171
Pedicels, 161
Penis, 212f, 213
Pepsinogen, 133
Pericytes, 39t, 117
Perimysium, 99, 100f, 101f, 103
Perineurium, 92f, 93
Periodic acid-Schiff staining, 9,
12f
Periosteum, 56, 57f
Peripheral nerves, 91, 92f, 93, 93f
Peripheral nervous system, 83,
91-95
Peyer’s patches, 137
Photoreceptors, 96f, 97
Pia mater, 84f, 85
Pituicytes, 173
Pituitary, 170f, 171, 172f, 173
Pituitary hormones, 171t, 173,
173t
Plasma, 61
Plasma cells, 39t, 40, 40f
Platelets, 62t, 63, 63f
Pleura, 145
Pneumocytes, 152f, 153, 154, 154f
Podocytes, 161
Polychromatophilic
erythroblasts, 69t, 70f, 71
Polychromatophilic erythrocytes,
69t, 72, 72f
Portal areas, 142f, 143, 144f
Posterior root ganglia, 95
Primary follicles, 186f, 187
Primary oocyte, 187, 189
Primordial follicles, 186f, 187
Proerythroblasts, 69t, 70f, 71
221
Progestational (progravid) phase,
of menstrual cycle, 187, 193
Progesterone, 185, 191, 193, 200
Prolactin, 171t, 173t, 200
Proliferative phase, of menstrual
cycle, 192f, 193, 194f, 195
Promyelocytes, 73t
Pronormoblast, 69t
Prophase, 15f
Prostate, 210f, 211, 212f, 213
Proximal convoluted tubule,
158f, 164f, 165
Pseudostratified epithelium, 20t,
21, 22f
Purkinje cells, 90f, 91
Purkinje fibers, 109
Pyknosis, 16, 17f
Pyloric region, of stomach, 132f,
133
Red pulp, of spleen, 82, 82f
Remodeling, of bone, 53
Renal columns, 155
Renal corpuscles, 155, 156f,
158f, 160f, 161
Renal cortex, 155, 156f, 157
Renal medulla, 155, 158f, 159,
165
Renin, 163
Resolution, 2, 3
Resorption, of bone, 51-53, 52f
Resorption bays, 51
Respiratory bronchioles, 150f,
151
Respiratory system, 145-154
Rete testis, 202f, 203
Reticular fibers, 35, 77
Reticularis, of adrenal cortex,
174f, 175, 176f, 177
Reticulocytes, 72, 72f
Retina, 96f, 97
Retinal pigment epithelium, 96f,
97
222
PDQ HISTOLOGY
Ribosomes, 8t, 11
Rods, retinal, 96f, 97
Root sheath, 126, 127f
Rugae, 133
Sarcomeres, 104, 104f
Satellite cells, 104
Scalp, 126, 126f
Scanning electron microscope, 3
Schwann cells, 92f, 93
Sebaceous glands, 126, 126f, 127f
Secondary follicles, 186f, 187
Secondary oocyte, 185
Secretory phase, of menstrual
cycle, 187, 192f, 193, 194f
Secretory units
mucous, 31, 31f, 32f
serous, 31, 31f, 32f
types of, 31-33, 31f-33f
Seminal vesicles, 210f, 211
Seminiferous tubules, 204f, 205
Seromucous glands, 32, 32f, 33f
Serosa, of gut, 130f, 131
Serotonin, 63
Serous demilune, 33, 33f
Serous secretory units, 31, 31f,
32f
Sertoli cells, 204f, 205
Serum, 61
Sheath(s)
of hair follicle, 126, 127f
mitochondrial, 206f, 207
myelin, 83, 85, 92f, 93
Simple epithelium, 20t, 20f, 21f
Simple glands, 28t, 29, 29f
Sinusoids
of bone marrow, 76f, 77
Sinusoids
of liver, 142f, 143
of spleen, 82, 82f
Skeletal muscle, 99-104, 100f-103f
Skin
appendages, 119t
thick, 119, 120f, 121, 122f, 123
thin, 119, 120f, 124f, 125
Small intestine, 135-137
Smooth muscle, 107, 107f, 108f
Somatostatin, 171t, 183
Somatotrophs, 173t
Spermatids, 204f, 205, 207
Spermatocytes, 204f, 205
Spermatogonia, 204f, 205
Spermatozoa, 204f, 205, 206f, 207
Spermiogenesis, 207
Spinal cord, 84f, 85
Spinal ganglia, 94f, 95
Spinosum, of epidermis, 120f,
121, 122f, 124f
Spleen, 82, 82f
Staining
acidophilic, 9, 10f
basophilic, 9, 10f
periodic acid-Schiff, 9, 12f
Stains, 9
Stereocilia, 209
Stomach, 132f, 133
Strata, of epidermis, 120f, 121
Stratified epithelium, 20t, 23, 24f,
25f
Stratified squamous epithelium,
23, 24f
Striations, of muscle fibers, 103,
103f
Stroma, 30
Subarachnoid space, 84f, 85
Submucosa, of gut, 130f, 131
Suprarenals. See Adrenals
Sweat glands, 121, 128, 128f
Synapses, 86f, 87
Synovial joints, 59
Synovial membrane (synovium),
59, 59f, 60f
Synovocytes, 59
System
circulatory, 109-117
digestive, 129-144
Index
endocrine, 169-183
female reproductive, 185-200
haversian, 56-58, 57f, 58f
integumentary, 119-128
male reproductive, 201-213
respiratory, 145-154
urinary, 155-167
T cells, 66, 77
Telophase, 15f
Tendons, 41
Tertiary follicles, 187
Testes, 202f, 203
Testosterone, 207
Theca interna and externa, 188f,
189
Theca lutein cells, 190f, 191
Thick filaments, 104, 104f, 105f
Thick skin, 119, 120f, 121, 122f,
123
Thin filaments, 104, 104f, 105f
Thin skin, 119, 120f, 124f, 125
Thymus, 80f, 81
Thyroglobulin, 179, 181
Thyroid gland, 178f, 179, 180f,
181
Thyroid hormone, 179
Thyroid-stimulating hormone,
171t, 173t
Thyrotrophs, 173t
Thyroxine, 179
Tight junction, 26f, 27t
Tissue
adipose (fat), 43, 43f
basic, 1, 2t
connective, 35-42, 36f, 37f, 42f
dense ordinary connective, 41,
42f
epithelial, 19-33
joint, 59
loose connective, 36-41, 36f,
37f
lymphoid, 77-82
223
myeloid, 68-77, 76f
nervous, 83-95
T lymphocytes, 66, 77
Tonsils, 78f, 79
Trabeculae, of bone, 50, 50f
Trachea, 146f, 147
Tracheobronchial tree, 145
Transitional epithelium, 25, 25f
Transmission electron
microscope, 3
Tubular pole, of renal corpuscle,
160f, 161
Tubules
cortical collecting, 163, 164f
proximal and distal
convoluted, 158f, 164f, 165
renal, 163, 164f
seminiferous, 204f, 205
Tunica adventitia, 109, 110f
Tunica albuginea
of ovary, 185
of testis, 202f, 203
Tunica intima, 109, 110f
Tunica media, 109, 110f
Ureters, 166f, 167
Urinary bladder, 166f, 167
Urinary system, 155-167
Uterine tube, 196f, 197
Uterus, 192f, 193
Vagina, 196f, 197
Varicose veins, 113
Vas deferens, 209
Vasa recta, 159
Vasa vasorum, 109
Vascular pole, of renal corpuscle,
160f, 161
Vasopressin, 171
Veins, 110f, 112f, 113
central, 142f, 143, 144f
Vena cava, 110f, 113
Venules, 110f, 114f, 115
Villi, 129, 134f, 135, 136f
224
PDQ HISTOLOGY
White fat, 43
White matter, 83, 84f
White pulp, of spleen, 82
Z line, 104, 104f, 105f
Zona pellucida, 188f, 189
Zones, of adrenal cortex, 174f,
175, 176f, 177
Zonula adherens, 26f, 27t
Zonula occludens, 26f, 27t