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Histology
(Tissues)
Anatomy & Physiology I
Chapter 4
Histology
Histology - study of tissues
Tissue - a collection of similar cells that group together to
perform a specialized function.
Tissue Classification
Four main groups of tissues
• Epithelial
• Connective
• Muscle
• Nervous tissue
Tissue Classification
Nervous tissue: Internal communication
• Brain, spinal cord, and nerves
Muscle tissue: Contracts to cause movement
• Muscles attached to bones (skeletal)
• Muscles of heart (cardiac)
• Muscles of walls of hollow organs (smooth)
Epithelial tissue: Forms boundaries between different
environments, protects, secretes, absorbs, filters
• Skin surface (epidermis)
• Lining of GI tract organs and other hollow organs
Connective tissue: Supports, protects, binds
other tissues together
• Bones
• Tendons
• Fat and other soft padding tissue
Epithelial Tissue

Forms a protective covering for the body

Is the main tissue of outer layer of skin

Forms membranes, ducts, and the lining of body
cavities and hollow organs

Layers of closely adhering cells

Flat sheet with upper surface exposed to the
environment or an internal body cavity

No blood vessels - underlying connective tissue
supplies oxygen

Rests on basement membrane - anchors epithelium
to connective tissue
Structure of Epithelial Tissue
Classification by shape
 Squamous – flat cells
 Cuboidal – cube shaped cells
 Columnar – tall, narrow cells
Classification by arrangement
 Simple – one layer of cells; all cell in contact with basement
membrane
 Stratified – two or more layers of cells
 Pseudostratified – one layer of cells but appears to be more
Simple vs. Stratified Epithelia

Simple epithelium
◦ allows diffusion and secretion of materials

Stratified epithelium
◦ protection in areas subject to wear and tear
(a)
Classes of
epithelium
Simple
(b)
Pseudostratified
columnar
Stratified
Cell
shapes
Squamous
Cuboidal
Columnar
Epithelial Tissue (Epithelium)
Two main types (by location):
1. Covering and lining epithelia

On external and internal surfaces
2. Glandular epithelia

Secretory tissue in glands
Overview of Epithelial Tissues

For each of the following types of epithelia,
note:
◦ Description
◦ Function
◦ Location
Simple Squamous Epithelium
Description: Single layer of flattened
cells with disc-shaped central nuclei
and sparse cytoplasm; the simplest
of the epithelia.
Air sacs of
lung tissue
Function: Allows passage of
materials by diffusion and filtration
in sites where protection is not
important; secretes lubricating
substances in serosae.
Nuclei of
squamous
epithelial
cells
Location: Kidney glomeruli; air sacs
of lungs; lining of heart, blood
vessels, and lymphatic vessels; lining
of ventral body cavity (serosae).
Photomicrograph: Simple squamous epithelium
forming part of the alveolar (air sac) walls (125x).
Epithelia: Simple Squamous

Two other locations
◦ Endothelium
 The lining of lymphatic vessels, blood vessels, and
heart
◦ Mesothelium
 The epithelium of serous membranes in the ventral
body cavity
Simple Cuboidal Epithelium
Description: Single layer of
cubelike cells with large,
spherical central nuclei.
Simple
cuboidal
epithelial
cells
Function: Secretion and
absorption.
Basement
membrane
Location: Kidney tubules;
ducts and secretory portions
of small glands; ovary surface.
Connective
tissue
Photomicrograph: Simple cuboidal
epithelium in kidney tubules (430x).
Simple Columnar Epithelium
Description: Single layer of tall cells
with round to oval nuclei; some cells
bear cilia; layer may contain mucussecreting unicellular glands (goblet cells).
Simple
columnar
epithelial
cell
Function: Absorption; secretion of
mucus, enzymes, and other substances;
ciliated type propels mucus (or
reproductive cells) by ciliary action.
Location: Nonciliated type lines most of
the digestive tract (stomach to anal canal),
gallbladder, and excretory ducts of some
glands; ciliated variety lines small
bronchi, uterine tubes, and some regions
of the uterus.
Basement
membrane
Photomicrograph: Simple columnar epithelium
of the stomach mucosa (860X).
Pseudostratified Columnar Epithelium
Description: Single layer of cells of
differing heights, some not reaching
the free surface; nuclei seen at
different levels; may contain mucussecreting cells and bear cilia.
Cilia
Mucus of
mucous cell
Function: Secretion, particularly of
mucus; propulsion of mucus by
ciliary action.
Pseudostratified
epithelial
layer
Location: Nonciliated type in male’s
sperm-carrying ducts and ducts of
large glands; ciliated variety lines
the trachea, most of the upper
respiratory tract.
Trachea
Photomicrograph: Pseudostratified ciliated
columnar epithelium lining the human trachea (570x).
Basement
membrane
Stratified Squamous Epithelium
Description: Thick membrane
composed of several cell layers;
basal cells are cuboidal or columnar
and metabolically active; surface
cells are flattened (squamous); in the
keratinized type, the surface cells are
full of keratin and dead; basal cells
are active in mitosis and produce the
cells of the more superficial layers.
Stratified
squamous
epithelium
Function: Protects underlying
tissues in areas subjected to abrasion.
Nuclei
Location: Nonkeratinized type forms
the moist linings of the esophagus,
mouth, and vagina; keratinized variety
forms the epidermis of the skin, a dry
membrane.
Basement
membrane
Connective
tissue
Photomicrograph: Stratified squamous epithelium
lining the esophagus (285x).
Stratified Epithelia
Stratified epithelium is found in tissues subject to wear and
tear; provides protection to underlying tissues; retards water
loss through skin; resists penetration by pathogenic
organisms
 range from 2 to 20 or more layers of cells
 some cells resting directly on others; only the deepest layer
attaches to the basement membrane
 three stratified epithelia are named for the shapes of their
surface cells
 most widespread epithelium in the body
 deepest layers undergo continuous mitosis

◦ their daughter cells push toward the surface and become flatter as
they migrate farther upward
◦ finally die and flake off – exfoliation or desquamation
Epithelia: Stratified Cuboidal
Quite rare in body
 Found in some sweat and mammary
glands
 Typically two cell layers thick

Epithelia: Stratified Columnar
Limited distribution in body
 Small amounts in pharynx, male urethra,
and lining some glandular ducts
 Also occurs at transition areas between
two other types of epithelia

Transitional epithelium
Description: Resembles both
stratified squamous and stratified
cuboidal; basal cells cuboidal or
columnar; surface cells dome
shaped or squamouslike, depending
on degree of organ stretch.
Transitional
epithelium
Function: Stretches readily and
permits distension of urinary organ
by contained urine.
Location: Lines the ureters, urinary
bladder, and part of the urethra.
Basement
membrane
Connective
tissue
Photomicrograph: Transitional epithelium lining the urinary
bladder, relaxed state (360X); note the bulbous, or rounded,
appearance of the cells at the surface; these cells flatten and
become elongated when the bladder is filled with urine.
Glandular Epithelia

A gland is an organ specialized to produce
a substance for use elsewhere in the body
or releases them for elimination from the
body

Classified by:
◦ Site of product release—endocrine or exocrine
◦ Relative number of cells forming the gland—
unicellular (e.g., goblet cells) or multicellular
Endocrine and Exocrine Glands

Glands are composed of epithelial tissue in a connective
tissue framework and capsule

exocrine glands - maintain their contact with
the body surface by way of a duct (epithelial tube
that conveys secretion to surface)
◦ sweat, mammary and tear glands

endocrine glands - lose their contact with the
surface and have no ducts
◦ hormones – secretion of endocrine glands
◦ secrete (hormones) directly into blood
◦ thyroid, adrenal and pituitary glands

some organs have both endocrine and exocrine
function (liver, gonads, pancreas)
Exocrine Glands
More numerous than endocrine glands
 Secrete products into ducts
 Secretions released onto body surfaces
(skin) or into body cavities
 Examples:

◦
◦
◦
◦
mucous glands
sweat glands
Oil glands
salivary glands
Exocrine Glands
 Single
cell
◦ Goblet cell (secretes mucus)
 The only important unicellular gland is the goblet cell
 Multiple
◦
◦
◦
◦
◦
cells
Simple Tubular (found in intestine)
Branched tubular (found in stomach)
Coiled tubular (sweat glands)
Saclike or alveolar (sebaceous glands)
Compound (salivary glands)
Microvilli
Secretory
vesicles
containing
mucin
Rough ER
Golgi
apparatus
Nucleus
Multicellular Exocrine Glands
Multicellular exocrine glands are
composed of a duct and a secretory unit
 Classified according to:

◦ Duct type (simple or compound)
◦ Structure of their secretory units (tubular,
alveolar, or tubuloalveolar)
Types of Exocrine Glands
Simple coiled tubular
Compound areolar
Compound tubuloareolar
Example: Sweat gland
Example: Pancreas
Key
Duct
Example: Mammary gland
Secretory unit
simple - unbranched duct
 compound - branched duct
 shape of gland

◦ tubular – duct and secretory portion have uniform diameter
◦ alveolar - secretory cells form dilated sac (alveolar or sacklike )
◦ tubuloalveolar - both tubular and alveolar portions
Multicellular Exocrine Glands
Tubular
secretory
structure
Alveolar
(saclike)
secretory
structure
Simple duct structure
Compound duct structure
(duct does not branch)
(duct branches)
Simple tubular
Simple branched
tubular
Example
Example
Compound tubular
Intestinal glands
Stomach (gastric)
glands
Duodenal glands of small intestine
Simple
alveolar
Simple branched
alveolar
Compound alveolar
Example
Example
Example
No important
example in humans
Sebaceous (oil)
glands
Mammary glands
Surface epithelium
Duct
Example
Secretory epithelium
Compound
tubuloalveolar
Example
Salivary glands
Methods of Secretion Merocrine Gland

merocrine glands (eccrine
glands) – have vesicles that
release their secretion by
exocytosis
◦ tear glands, pancreas, gastric
glands, and others

Exocytosis
Nucleus
Secretory
vesicle
Merocrine gland
apocrine glands – primarily
merocrine mode of secretion
◦ axillary sweat glands, mammary
glands
Methods of Secretion Holocrine Gland

holocrine glands – cells
accumulate a product and then
the entire cell disintegrates
◦ secretion a mixture of cell
fragments and synthesized
substance
◦ oil glands of scalp, glands of eyelids
(b) Holocrine gland
Connective Tissue Characteristics

cells usually occupy less space than the
extracellular material

most cells are not in direct contact with each
other
◦ separated by extracellular material

highly vascular – richly supplied with blood
vessels (except cartilage which is avascular)

most abundant, widely distributed, and
histologically variable of the primary tissues
Functions of Connective Tissue
binding of organs – tendons and ligaments
 support – bones and cartilage
 protection – bones and blood
 movement – bones
 storage – fat, calcium, phosphorus
 transport - blood

Structural Elements of Connective
Tissue

Ground substance
◦ Medium through which solutes diffuse
between blood capillaries and cells
◦ Components:
 Interstitial fluid
 Adhesive glycoproteins (“glue”)
 Proteoglycans
Connective Tissue Fibers

Collagen (white fibers)
◦ Strongest and most abundant type
◦ tough, flexible, and resist stretching
◦ tendons, ligaments, and deep layer of the skin are mostly
collagen

Elastic (yellow fibers)
◦ Thinner than collagen fibers
◦ Allows stretch and recoil

Reticular
◦ thin collagen fibers coated with glycoprotein
◦ form framework of such organs as spleen and lymph
nodes
Structural Elements of Connective
Tissue

Cells
◦ Immature, secretory cells = “blasts”
◦ Mature cells = “cytes”
 Fibroblasts – produce fibers and ground substances
 Chondroblasts and chondrocytes in cartilage
 Osteoblasts and osteocytes in bone
 Hematopoietic stem cells in bone marrow
 Adipocytes, leukocytes, mast cells, and
macrophages
Cell types
Extracellular matrix
Ground substance
Macrophage
Fibers
• Collagen fiber
• Elastic fiber
• Reticular fiber
Fibroblast
Lymphocyte
Fat cell
Mast cell
Neutrophil
Capillary
Connective Tissue Categories
Categorized by physical properties
 Circulating connective tissue
◦ Blood

Generalized (fibrous) connective tissue
◦ Loose: Areolar, Adipose and Reticular
◦ Dense: Regular, Irregular and Elastic

Structural connective tissue
◦ Cartilage: Hyaline, Elastic, Fibrocartilage
◦ Osseous (Bone) Tissue
Blood
Description: Red and white
blood cells in a fluid matrix
(plasma).
Plasma
Function: Transport of
respiratory gases, nutrients,
wastes, and other substances.
Location: Contained within
blood vessels.
Neutrophil
Red blood
cells
Lymphocyte
Photomicrograph: Smear of human blood (1860x); two
white blood cells (neutrophil in upper left and lymphocyte
in lower right) are seen surrounded by red blood cells.
Types of Generalized (Fibrous)
Connective Tissue

loose connective tissue
◦ much gel-like ground substance
between cells

dense connective tissue
◦ fibers fill spaces between cells
Tendons
Areolar (loose connective tissue)
Description: Gel-like matrix with all
three fiber types; cells: fibroblasts,
macrophages, mast cells, and some
white blood cells.
Elastic
fibers
Function: Wraps and cushions
organs; its macrophages phagocytize
bacteria; plays important role in
inflammation; holds and conveys
tissue fluid.
Collagen
fibers
Location: Widely distributed under
epithelia of body, e.g., forms lamina
propria of mucous membranes;
packages organs; surrounds
capillaries.
Fibroblast
nuclei
Epithelium
Lamina
propria
Photomicrograph: Areolar connective tissue, a
soft packaging tissue of the body (300x).
Adipose (loose connective tissue)
Description: Matrix as in areolar,
but very sparse; closely packed
adipocytes, or fat cells, have
nucleus pushed to the side by large
fat droplet.
Function: Provides reserve food
fuel; insulates against heat loss;
supports and protects organs.
Nucleus of
fat cell
Location: Under skin in the
hypodermis; around kidneys and
eyeballs; within abdomen; in breasts.
Vacuole
containing
fat droplet
Adipose
tissue
Mammary
glands
Photomicrograph: Adipose tissue from the
subcutaneous layer under the skin (350x).
Reticular (loose connective tissue)
Description: Network of reticular
fibers in a typical loose ground
substance; reticular cells lie on the
network.
Function: Fibers form a soft internal
skeleton (stroma) that supports other
cell types including white blood cells,
mast cells, and macrophages.
Location: Lymphoid organs (lymph
nodes, bone marrow, and spleen).
White blood
cell
(lymphocyte)
Reticular
fibers
Spleen
Photomicrograph: Dark-staining network of reticular
connective tissue fibers forming the internal skeleton
of the spleen (350x).
Dense Regular Connective tissue
Description: Primarily parallel
collagen fibers; a few elastic fibers;
major cell type is the fibroblast.
Collagen
fibers
Function: Attaches muscles to
bones or to muscles; attaches bones
to bones; withstands great tensile
stress when pulling force is applied
in one direction.
Location: Tendons, most
ligaments, aponeuroses.
Nuclei of
fibroblasts
Shoulder
joint
Ligament
Tendon
Photomicrograph: Dense regular connective
tissue from a tendon (500x).
Dense Irregular Connective Tissue
Description: Primarily
irregularly arranged collagen
fibers; some elastic fibers;
major cell type is the fibroblast.
Nuclei of
fibroblasts
Function: Able to withstand
tension exerted in many
directions; provides structural
strength.
Location: Fibrous capsules of
organs and of joints; dermis of
the skin; submucosa of
digestive tract.
Fibrous
joint
capsule
Collagen
fibers
Photomicrograph: Dense irregular
connective tissue from the dermis of the
skin (400x).
Elastic (dense connective tissue)
Description: Dense regular
connective tissue containing a high
proportion of elastic fibers.
Function: Allows recoil of tissue
following stretching; maintains
pulsatile flow of blood through
arteries; aids passive recoil of lungs
following inspiration.
Elastic fibers
Location: Walls of large arteries;
within certain ligaments associated
with the vertebral column; within the
walls of the bronchial tubes.
Aorta
Heart
Photomicrograph: Elastic connective tissue in
the wall of the aorta (250x).
Connective Tissue: Cartilage
cartilage lacks blood vessels (avascular)
 Cartilage Cells:

◦ Chondroblasts – immature cartilage cells; produce
extracellular material (matrix)
◦ Chondrocytes – mature cartilage cells; once trapped
in matrix, chondroblasts become chondrocytes
 Three
types of cartilage:
◦ Hyaline cartilage
◦ Elastic cartilage
◦ Fibrocartilage
Hyaline Cartilage
Description: Amorphous but firm
matrix; collagen fibers form an
imperceptible network; chondroblasts
produce the matrix and when mature
(chondrocytes) lie in lacunae.
Function: Supports and reinforces;
has resilient cushioning properties;
resists compressive stress.
Location: Forms most of the
embryonic skeleton; covers the ends
of long bones in joint cavities; forms
costal cartilages of the ribs; cartilages
of the nose, trachea, and larynx.
Chondrocyte
in lacuna
Matrix
Costal
cartilages
Photomicrograph: Hyaline cartilage from the
trachea (750x).
Elastic Cartilage
Description: Similar to hyaline
cartilage, but more elastic fibers
in matrix.
Function: Maintains the shape
of a structure while allowing
great flexibility.
Chondrocyte
in lacuna
Location: Supports the external
ear (pinna); epiglottis.
Matrix
Photomicrograph: Elastic cartilage from
the human ear pinna; forms the flexible
skeleton of the ear (800x).
Fibrocartilage
Description: Matrix similar to
but less firm than that in hyaline
cartilage; thick collagen fibers
predominate.
Function: Tensile strength
with the ability to absorb
compressive shock.
Location: Intervertebral discs;
pubic symphysis; discs of knee
joint.
Chondrocytes
in lacunae
Intervertebral
discs
Collagen
fiber
Photomicrograph: Fibrocartilage of an
intervertebral disc (125x). Special staining
produced the blue color seen.
Osseous (Bone) Tissue
Description: Hard, calcified
matrix containing many collagen
fibers; osteocytes lie in lacunae.
Very well vascularized.
Central
canal
Function: Bone supports and
protects (by enclosing);
provides levers for the muscles
to act on; stores calcium and
other minerals and fat; marrow
inside bones is the site for blood
cell formation (hematopoiesis).
Lacunae
Lamella
Location: Bones
Photomicrograph: Cross-sectional view
of bone (125x).
Excitable Tissues: Muscular &
Nervous

excitability – ability to respond to stimuli
◦ a characteristic of all living cells but developed to highest
degree in nervous and muscular tissues

membrane potential – electrical charge difference
(voltage) that occurs across the plasma
membranes is the basis for their excitation
◦ respond quickly to outside stimulus by means of changes
in membrane potential
◦ nerves – changes result in rapid transmission of signals
to other cells
◦ muscles – changes result in contraction, shortening of
the cell
Muscular Tissue Functions
muscular tissue is made up of elongated cells
that are specialized to contract in response
to stimulation
 primary job is to exert physical force on
other tissues and organs
 creates movements involved in body and
limb movement, digestion, waste elimination,
breathing, speech, and blood circulation
 important source of body heat
 three types of muscle: skeletal, cardiac, and
smooth

Muscle Tissue

Skeletal muscle
◦ Voluntary muscle
◦ Striated muscle
◦ Multinucleated

Cardiac muscle (myocardium)
◦ Involuntary muscle
◦ Striated; Intercalated disks
◦ Uninucleated

Smooth muscle (visceral muscle)
◦ Involuntary muscle
◦ Non-striated
◦ uninucleated
Skeletal muscle
Description: Long, cylindrical,
multinucleate cells; obvious
striations.
Striations
Function: Voluntary movement;
locomotion; manipulation of the
environment; facial expression;
voluntary control.
Nuclei
Location: In skeletal muscles
attached to bones or
occasionally to skin.
Part of
muscle
fiber (cell)
Photomicrograph: Skeletal muscle (approx. 460x).
Notice the obvious banding pattern and the
fact that these large cells are multinucleate.
Cardiac Muscle
Description: Branching,
striated, generally uninucleate
cells that interdigitate at
specialized junctions
(intercalated discs).
Striations
Intercalated
discs
Function: As it contracts, it
propels blood into the
circulation; involuntary control.
Location: The walls of the
heart.
Nucleus
Photomicrograph: Cardiac muscle (500X);
notice the striations, branching of cells, and
the intercalated discs.
Smooth muscle
Description: Spindle-shaped
cells with central nuclei; no
striations; cells arranged
closely to form sheets.
Function: Propels substances
or objects (foodstuffs, urine,
a baby) along internal passageways; involuntary control.
Smooth
muscle
cell
Location: Mostly in the walls
of hollow organs.
Nuclei
Photomicrograph: Sheet of smooth muscle (200x).
Nervous Tissue
Body’s communication system is made of
nervous tissue
 Brain
 Nerves
 Spinal cord
The Neuron
The main cell type of nervous tissue
 A neuron has 3 parts:

◦ Nerve cell body
◦ Dendrite
◦ Axon
Neuroglia

Neuroglia (glial cells) support and protect
the neurons neurons and nervous tissue.
Nervous tissue
Description: Neurons are
branching cells; cell processes
that may be quite long extend from
the nucleus-containing cell body;
also contributing to nervous tissue
are nonirritable supporting cells
(not illustrated).
Nuclei of
supporting
cells
Neuron processes Cell body
Axon
Dendrites
Cell body
of a neuron
Function: Transmit electrical
signals from sensory receptors
and to effectors (muscles and
glands) which control their activity.
Neuron
processes
Location: Brain, spinal
cord, and nerves.
Photomicrograph: Neurons (350x)
Membranes

Thin sheets of tissue that cover surfaces, line body cavities,
line hollow organs or anchor an organ

Epithelial Membranes
◦ Serous
◦ Mucous
◦ Cutaneous

Connective Membranes
◦
◦
◦
◦
◦
◦
◦
Synovial membranes
Meninges
Superficial (subcutaneous) fascia
Deep fascia
Fibrous pericardium
Periosteum
Perichondrium
Serous Membranes
Three types of serous membranes
 Pleurae
 Serous pericardium
 Peritoneum
Organization of the serous membrane
 Parietal layer
 Visceral layer
Mucous Membranes
Vary in structure and function
 Trap and remove foreign particles
 Protect deeper tissue
 Absorb food materials
Benign and Malignant Tumors
Abnormal growth of cells is called a tumor
or neoplasm.
 Benign
 Malignant
 Cancer
Benign Tumors
Do not invade other tissues or spread to other sites
 Papilloma – in epithelium (ex. Wart)
 Adenoma – in a gland
 Lipoma – adipose tissue
 Osteoma – in bone
 Myoma – in muscle tissue. (most commonly smooth
muscle)
 Angioma – in small blood vessels (ex.
Hemangioma=birthmark)
 Nevus – in skin (ex. Moles)
 Chondroma – in cartilage
Malignant Tumors
Classified according to tissues of origin
 Carcinoma – form in epithelium (ex. Skin, breast,
lungs, prostate, colon, stomach, uterus)
 Sarcoma – form in connective tissue (anywhere in
the body)
Classified according to cells of origin
 Neuroma – originate in nerves
 Glioma – originate in neuroglia (of brain and spinal
cord)
 Lymphoma – in lymphatic tissue
 Leukemia – in white blood cells
Symptoms of Cancer









Unusual bleeding or discharge
Persistent indigestion
Chronic hoarseness or cough
Changes in the color or size of moles
Sore that does not heal
Unusual lump
White patches in mouth or white spots on
tongue
Weight loss
Pain
Treatment of Cancer
Treatment methods may be combined
 Surgery
 Radiation
 Chemotherapy
 Immunotherapy
 Hormone receptor blockers
 Angiogenesis blockers
Tissues and Aging
Tissues lose elasticity as they age
 Skin
 Blood vessels
 Tendons and ligaments
 Bones
 Muscles
End of Presentation