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Chapter 5
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Histology
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Introduction
• There are 50 trillion cells of 200 different cell types
• Four broad categories of tissues
– Epithelial tissue
– Connective tissue
– Nervous tissue
– Muscular tissue
• Organ—structure with discrete boundaries that is
composed of two or more tissue types
• Histology (microscopic anatomy)—the study of
tissues and how they are arranged into organs
5-2
The Study of Tissues
• Expected Learning Outcomes
– Name the four primary classes into which all adult
tissues are classified.
– Name the three embryonic germ layers and some
adult tissues derived from each.
– Visualize the three-dimensional shape of a structure
from a two-dimensional tissue section.
5-3
The Primary Tissue Classes
• Tissue—a group of similar cells and cell products
that arise from the same region of the embryo
and work together to perform a specific structural
or physiological role in an organ
• Four primary tissues differ from one another, as
follows:
– Types and functions of their cells
– Characteristics of the matrix (extracellular material)
– Relative amount of space occupied by cells versus
matrix
5-4
The Primary Tissue Classes
• Matrix (extracellular material) is composed of:
– Fibrous proteins
– Clear gel called ground substance, tissue fluid,
extracellular fluid (ECF), interstitial fluid, or tissue
gel
5-5
Embryonic Tissues
• Human development begins as single cell, the
fertilized egg
– Divides to produce scores of identical, smaller cells
– First tissues appear when these cells start to organize
themselves into layers; First two, and then three strata
5-6
Embryonic Tissues
• Three primary germ layers
– Ectoderm (outer)
• Gives rise to epidermis and nervous system
– Endoderm (inner)
• Gives rise to mucous membrane lining digestive and respiratory
tracts, digestive glands, among other things
– Mesoderm (middle) becomes gelatinous tissue called
mesenchyme
• Wispy collagen fibers and fibroblasts in gel matrix
• Gives rise to muscle, bone, blood
5-7
Interpreting Tissue Sections
• Preparation of histological specimens
– Fixative prevents decay (formalin)
– Histological sections: tissue is sliced into thin
sections one or two cells thick
– Stains: tissue is mounted on slides and artificially
colored with histological stain
• Stains bind to different cellular components
• Sectioning reduces three-dimensional structure
to two-dimensional slice
5-8
Interpreting Tissue Sections
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
• Sectioning a cell
with a centrally
located nucleus
• Some slices miss
the cell nucleus
• In some, the
nucleus is smaller
(a)
Figure 5.1a
5-9
Interpreting Tissue Sections
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
• Cross section of
blood vessel, gut, or
other tubular organ
• Longitudinal
section of a sweat
gland—notice what a
single slice could
look like
Figure 5.1b,c
(b)
(c)
5-10
Longitudinal, Cross, Oblique Sections
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Longitudinal sections
• Longitudinal section (l.s.)
– Tissue cut along long direction
of organ
Cross sections
• Cross section (c.s. or x.s.)
or transverse section (t.s.)
– Tissue cut perpendicular to
length of organ
• Oblique section
Oblique sections
– Tissue cut at angle between
cross and longitudinal sections
Figure 5.2
5-11
Interpreting Tissue Sections
• Smear—tissue is rubbed or spread across
the slide
– Spinal cord or blood
• Spread—cobwebby tissue is laid out on a
slide
– Areolar tissue
5-12
Epithelial Tissue
• Expected Learning Outcomes
– Describe the properties that distinguish
epithelium from other tissue classes.
– List and classify eight types of epithelium,
distinguish them from each other, and state
where each type can be found in the body.
– Explain how the structural differences between
epithelia relate to their functional differences.
– Visually recognize each epithelial type from
specimens or photographs.
5-13
Epithelial Tissue
• Consists of a flat sheet of closely adhering cells
• One or more cells thick
• Upper surface usually exposed to the
environment or an internal space in the body
• Covers body surface and lines body cavities
• Forms the external and internal linings of many
organs
5-14
Epithelial Tissue
• Constitutes most glands
• Extracellular material is so thin it is not visible
with a light microscope
• Epithelia allow no room for blood vessels
• Lie on a layer of loose connective tissue and
depend on its blood vessels for nourishment and
waste removal
5-15
Epithelial Tissue
• Basement membrane—layer between an
epithelium and the underlying connective tissue
– Collagen
– Laminin and fibronectin adhesive glycoproteins
– Heparin sulfate: large protein–carbohydrate complex
• Anchors the epithelium to the connective tissue
below it
• Basal surface—surface of an epithelial cell that
faces the basement membrane
• Apical surface—surface of an epithelial cell that
faces away from the basement membrane
5-16
Epithelial Tissue
• Stratified epithelium
• Simple epithelium
– Contains one layer of cells
– Named by shape of cells
– All cells touch the basement
membrane
– Contains more than one layer
– Named by shape of apical cells
– Some cells rest on top of others
and do not touch basement
membrane
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
(a)
Classes of
epithelium
Simple
(b)
Pseudostratified
columnar
Stratified
Cell
shapes
Squamous
Cuboidal
Figure 5.3
Columnar
5-17
Simple Epithelia
• Four types of simple epithelia
• Three named for their cell shapes
– Simple squamous (thin, scaly cells)
– Simple cuboidal (square or round cells)
– Simple columnar (tall, narrow cells)
5-18
Simple Epithelia
• Fourth type
– Pseudostratified columnar
•
•
•
•
Not all cells reach the free surface
Shorter cells are covered over by taller ones
Looks stratified
Every cell reaches the basement membrane
• Goblet cells—wineglass-shaped mucus-secreting
cells in simple columnar and pseudostratified
epithelia
5-19
Simple Epithelia
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Squamous epithelial cells
Nuclei of smooth muscle
Basement membrane
Figure 5.4a
(a)
(b)
a: © The McGraw-Hill Companies, Inc./Dennis Strete, photographer
• Simple squamous epithelium
•
•
•
•
Figure 5.4b,i
Single row of thin cells
Permits rapid diffusion or transport of substances
Secretes serous fluid
Alveoli, glomeruli, endothelium, and serosa
5-20
Simple Epithelia
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Lumen of kidney tubule
(a)
Cuboidal epithelial cells
Basement membrane
(b)
Figure 5.5a
a: © The McGraw-Hill Companies, Inc./Dennis Strete, photographer
• Simple cuboidal epithelium
Figure 5.5b,i
– Single layer of square or round cells
– Absorption and secretion, mucus production and movement
– Liver, thyroid, mammary and salivary glands, bronchioles, and
kidney tubules
5-21
Simple Epithelia
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Brush border
(microvilli)
(a)
Connective
tissue
Basement
membrane
Goblet
Nuclei cell
Columnar
cells
(b)
Figure 5.6a
• Simple columnar epithelium
a: © Lester V. Bergman
Figure 5.6b,i
– Single row of tall, narrow cells
– Oval nuclei in basal half of cell
– Brush border of microvilli, ciliated in some organs, may possess
goblet cells
– Absorption and secretion; secretion of mucus
– Lining of GI tract, uterus, kidney, and uterine tubes
5-22
Pseudostratified Epithelium
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cilia
(a)
Figure 5.7a
Basement membrane
Basal cells Goblet cell
(b)
a: © The McGraw-Hill Companies, Inc./Dennis Strete, photographer
• Pseudostratified epithelium
Figure 5.7b,i
– Looks multilayered; some not reaching free surface; all touch
basement membrane
– Nuclei at several layers
– With cilia and goblet cells
– Secretes and propels mucus
– Respiratory tract and portions of male urethra
5-23
Stratified Epithelia
• 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
– Stratified squamous
– Stratified cuboidal
– Stratified columnar (rare)
• Fourth type
– Transitional epithelium
5-24
Stratified Epithelia
• 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
• Two kinds of stratified squamous epithelia
– Keratinized—found on skin surface, abrasion
resistant
– Nonkeratinized—lacks surface layer of dead cells
5-25
Stratified Epithelia
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Dead squamous cells
Living epithelial cells
Dense irregular
connective tissue
Areolar tissue
(a)
Figure 5.8a
(b)
a: © The McGraw-Hill Companies, Inc./Joe DeGrandis, photographer
• Keratinized stratified squamous
Figure 5.8b,i
– Multiple cell layers with cells becoming flat and scaly toward
surface
– Epidermis; palms and soles heavily keratinized
– Resists abrasion; retards water loss through skin; resists
penetration by pathogenic organisms
5-26
Stratified Epithelia
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Living epithelial cells
(a)
Figure 5.9a
Connective tissue
(b)
a: © Ed Reschke
• Nonkeratinized stratified squamous
Figure 5.9b,i
– Same as keratinized epithelium without the surface layer of dead cells
– Tongue, oral mucosa, esophagus, and vagina
– Resists abrasion and penetration of pathogens
5-27
Stratified Epithelia
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cuboidal cells
Epithelium
Connective tissue
(b)
(a)
Figure 5.10a
a: © The McGraw-Hill Companies, Inc./Dennis Strete, photographer
• Stratified cuboidal epithelium
Figure 5.10b,i
– Two or more cell layers; surface cells square or round
– Secretes sweat; sperm production and ovarian hormone production
– Sweat gland ducts; ovarian follicles and seminiferous tubules
5-28
Stratified Epithelia
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Basement
membrane
(a)
Figure 5.11a
Connective
tissue
Binucleate
epithelial cell
(b)
a: Johnny R. Howze
Figure 5.11b,i
• Transitional epithelium
– Multilayered epithelium surface cells that change from round to
flat when stretched
– Allows for filling of urinary tract
– Ureter and bladder
5-29
Connective Tissue
• Expected Learning Outcomes
– Describe the properties that most connective tissues
have in common.
– Discuss the types of cells found in connective tissue.
– Explain what the matrix of a connective tissue is and
describe its components.
– Name and classify 10 types of connective tissue,
describe their cellular components and matrix, and
explain what distinguishes them from each other.
– Visually recognize each connective tissue type from
specimens or photographs.
5-30
Connective Tissue: Overview
• Connective tissue—a type of tissue in which cells
usually occupy less space than the extracellular
material
• Binds organs to each other, supports and protects
organs
• Most cells of connective tissue are not in direct
contact with each other
– Separated by extracellular material
• Highly vascular—richly supplied with blood vessels
• Most abundant, widely distributed, and histologically
variable of the primary tissues
5-31
Connective Tissue: Overview
•
•
•
•
•
•
•
•
Binding of organs—tendons and ligaments
Support—bones and cartilage
Physical protection—cranium, ribs, sternum
Immune protection—white blood cells attack foreign
invaders
Movement—bones provide lever system
Storage—fat, calcium, phosphorus
Heat production—metabolism of brown fat in infants
Transport—blood
5-32
Fibrous Connective Tissue
• Cells
– Fibroblasts produce fibers and ground substance
– Macrophages phagocytize foreign material and activate
immune system when they sense foreign matter (antigen)
• Arise from white blood cells called monocytes
– Leukocytes, or white blood cells
• Neutrophils wander about attacking bacteria
• Lymphocytes react against bacteria, toxins, and other foreign
material
– Plasma cells synthesize disease-fighting antibodies
• Arise from lymphocytes
– Mast cells are found alongside blood vessels
• Secrete heparin to inhibit clotting
• Secrete histamine to dilate blood vessels
– Adipocytes store triglycerides (fat molecules)
5-33
Fibrous Connective Tissue
• Fibers
– Collagenous fibers
•
•
•
•
Most abundant of the body’s proteins—25%
Tough, flexible, and resist stretching
Tendons, ligaments, and deep layer of the skin are mostly collagen
Less visible in matrix of cartilage and bone
– Reticular fibers
• Thin collagen fibers coated with glycoprotein
• Form framework of such organs as spleen and lymph nodes
– Elastic fibers
•
•
•
•
•
Thinner than collagenous fibers
Branch and rejoin each other
Made of protein called elastin
Allows stretch and recoil
Yellow fibers—fresh elastic fibers
5-34
Fibrous Connective Tissue
• Ground substance
– Usually a gelatinous to rubbery consistency resulting from
three classes of large molecules
– Glycosaminoglycans (GAG)
• Long polysaccharide composed of unusual disaccharides
called amino sugars and uronic acid
• Play important role of regulating water and electrolyte
balance in the tissues
• Chondroitin sulfate—most abundant GAG
– In blood vessels and bone
– Responsible for stiffness of cartilage
• Hyaluronic acid—viscous, slippery substance that
forms an effective lubricant in joints and constitutes
much of the vitreous body of the eyeball
5-35
Fibrous Connective Tissue
Cont.
– Proteoglycan
• Gigantic molecule shaped like a test-tube brush
• Forms thick colloids that create strong structural bond
between cells and extracellular macromolecules; holds
tissues together
– Adhesive glycoproteins—bind components of
tissues together
5-36
Types of Fibrous Connective Tissue
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• Loose connective tissue
– Much gel-like ground
substance between cells
– Types
Tendons
• Areolar
• Reticular
• Dense connective tissue
– Fibers fill spaces between cells
– Types vary in fiber orientation
• Dense regular connective
tissue
• Dense irregular connective
tissue
© The McGraw-Hill Companies, Inc./Rebecca Gray, photographer/Don Kincaid, dissections
Figure 5.13
5-37
Types of Fibrous Connective Tissue
• Loosely organized fibers, abundant blood vessels, and a lot
of seemingly empty space
• Possess all six cell types
• Fibers run in random directions
– Mostly collagenous, but elastic and reticular also present
• Found in tissue sections from almost every part of the body
– Surrounds blood vessels and nerves
• Nearly every epithelium rests on a layer of areolar tissue
– Blood vessels provide nutrition to epithelium and waste removal
– Ready supply of infection-fighting leukocytes that move about freely
in areolar tissue
5-38
Types of Fibrous Connective Tissue
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Ground
substance
(a)
Figure 5.14a
Elastic
fibers
Collagenous
fibers
Fibroblasts
(b)
a: © The McGraw-Hill Companies, Inc./Dennis Strete, photographer
• Areolar tissue
Figure 5.14b,i
– Loosely organized fibers, abundant blood vessels, and a lot of
seemingly empty space
– Underlies all epithelia, in serous membranes, between muscles,
passageways for nerves and blood vessels
5-39
Types of Fibrous Connective Tissue
Leukocytes
Reticular
fibers
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(a)
Figure 5.15a
(b)
a: The McGraw-Hill Companies, Inc./Al Telser, photographer
• Reticular tissue
Figure 5.15b,i
– Mesh of reticular fibers and fibroblasts
– Forms supportive stroma (framework) for lymphatic organs
– Found in lymph nodes, spleen, thymus, and bone marrow
5-40
Types of Fibrous Connective Tissue
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Collagen fibers
(a)
Figure 5.16a
Ground substance
Fibroblast nuclei
(b)
a: © The McGraw-Hill Companies, Inc./Dennis Strete, photographer
• Dense regular connective tissue
Figure 5.16b,i
– Densely packed, parallel collagen fibers
– Compressed fibroblast nuclei
– Elastic tissue/fibers, wavy sheets
• Tendons attach muscles to bones and ligaments hold bones
together
5-41
Types of Fibrous Connective Tissue
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Bundles of
Gland
collagen fibers ducts
(a)
Figure 5.17a
Fibroblast Ground
nuclei
substance
(b)
a: © The McGraw-Hill Companies, Inc./Dennis Strete, photographer
• Dense irregular connective tissue
Figure 5.17b,i
– Densely packed, randomly arranged, collagen fibers and few
visible cells
– Withstands unpredictable stresses
– Deeper layer of skin; capsules around organs
5-42
Adipose Tissue
• Adipose tissue (fat)—tissue in which adipocytes are the
dominant cell type
• Space between adipocytes is occupied by areolar tissue,
reticular tissue, and blood capillaries
• Fat is the body’s primary energy reservoir
– The quantity of stored triglyceride and the number of
adipocytes are quite stable in a person
– Fat is recycled continuously to prevent stagnation
– New triglycerides are constantly synthesized and stored
– Old triglycerides are hydrolyzed and released into circulation
5-43
Adipose Tissue
• Provides thermal insulation
• Anchors and cushions organs such as eyeballs,
kidneys
• Contributes to body contours—female breast and
hips
– On average, women have more fat than men
– Too little fat can reduce female fertility
• Most adult fat is called white fat
• Brown fat—in fetuses, infants, children—a heatgenerating tissue
5-44
Adipose Tissue
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Blood
vessel
(a)
Figure 5.18a
Adipocyte
nucleus
Lipid in
adipocyte
(b)
a: © The McGraw-Hill Companies, Inc./Dennis Strete, photographer
Figure 5.18b,i
• Empty-looking cells with thin margins; nucleus pressed against
cell membrane
• Energy storage, insulation, cushioning
– Subcutaneous fat and organ packing
– Brown fat (hibernating animals) produces heat
5-45
Cartilage
• Supportive connective tissue with flexible, rubbery
matrix
• Gives shape to ear, tip of nose, and larynx
• Chondroblasts produce matrix and surround
themselves until they become trapped in little cavities
(lacunae)
• Chondrocytes—cartilage cells in lacunae
• Perichondrium—sheath of dense irregular connective
tissue that surrounds elastic and most hyaline cartilage
(not articular cartilage)
– Contains a reserve population of chondroblasts that
contribute to cartilage growth throughout life
5-46
Cartilage
• No blood vessels
– Diffusion brings nutrients and removes wastes
– Heals slowly
• Matrix rich in chondroitin sulfate and contains
collagen fibers
• Types of cartilage vary with fiber types
– Hyaline cartilage, fibrocartilage, and elastic cartilage
5-47
Cartilage
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Matrix
(a)
Figure 5.19a
Cell
nest Perichondrium
Lacunae
Chondrocytes
(b)
a: © Ed Reschke
• Hyaline cartilage
Figure 5.19b,i
– Clear, glassy microscopic appearance because of unusual
fineness of the collagen fibers
– Usually covered by perichondrium
• Articular cartilage, costal cartilage, trachea, larynx, fetal skeleton
• Eases joint movement, holds airway open, moves vocal cords
5-48
during speech
Cartilage
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Perichondrium
(a)
Elastic
fibers
Lacunae
Chondrocytes
(b)
Figure 5.20a
a: © Ed Reschke
• Elastic cartilage
Figure 5.20b,i
– Cartilage containing elastic fibers
• Covered with perichondrium
• Provides flexible, elastic support
– External ear and epiglottis
5-49
Cartilage
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Collagen
fibers
(a)
Figure 5.21a
Chondrocytes
(b)
a: Dr. Alvin Telser
• Fibrocartilage
Figure 5.21b,i
– Cartilage containing large, coarse bundles of collagen fibers
• Never has perichondrium
• Resists compression and absorbs shock
– Pubic symphysis, menisci, and intervertebral discs
5-50
Bone
• The term bone has two meanings:
– An organ of the body: femur, mandible; composed of multiple
tissue types
– Bone tissue (osseous tissue) makes up most of the mass of
bone
• Two forms of osseous tissue
– Spongy bone: spongy in appearance
• Delicate struts of bone: trabeculae
• Covered by compact bone
• Found in heads of long bones and in middle of flat bones such as
the sternum
– Compact bone: denser, calcified tissue with no visible spaces
• More complex arrangement
• Cells and matrix surround vertically oriented blood vessels in long
bones
5-51
Bone
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Concentric
Central
lamellae
Lacunae Canaliculi of osteon canal Osteon
(a)
(b)
Figure 5.22a
a: © The McGraw-Hill Companies, Inc./Dennis Strete, photographer
Figure 5.22b,i
• Compact bone is arranged in cylinders that surround
central (haversian or osteonic) canals that run
longitudinally through shafts of long bones
– Blood vessels and nerves travel through central canal
• Bone matrix deposited in concentric lamella
– Onionlike layers around each central canal
5-52
Bone
• Osteon—central canal and its surrounding lamellae
• Osteocytes—mature bone cells that occupy the
lacunae
• Canaliculi—delicate canals that radiate from each
lacuna to its neighbors, and allow osteocytes to
contact each other
• Periosteum—tough fibrous connective tissue
covering of the bone as a whole
5-53
Blood
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• Fluid connective tissue
Platelets
Neutrophils
Lymphocyte
Erythrocytes
Monocyte
• Transports cells and dissolved
matter from place to place
• Plasma—blood’s liquid ground
substance
• Formed elements—cells and
cell fragments
– Erythrocytes—red blood
cells: transport O2 and CO2
– Leukocytes—white blood
cells: defense against
infection and other diseases
– Platelets—cell fragments
involved in clotting and other
mechanisms
(b)
Figure 5.23b,i
5-54
Nervous and Muscular Tissues—
Excitable Tissues
• Expected Learning Outcomes
– Explain what distinguishes excitable tissues from
other tissues.
– Name the cell types that compose nervous tissue.
– Identify the major parts of a nerve cell.
– Visually recognize nervous tissue from specimens or
photographs.
– Name the three kinds of muscular tissue and describe
the differences between them.
– Visually identify any type of muscular tissue from
specimens or photographs.
5-55
Nervous and Muscular Tissues—
Excitable Tissues
• Excitability—a characteristic of all living cells
– 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
5-56
Nervous Tissue
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Nuclei of glial cells
Axon
Neurosoma
Dendrites
• Nervous tissue—specialized
for communication by electrical
and chemical signals
• Consists of neurons (nerve
cells)
– Detect stimuli
– Respond quickly
– Transmit coded information
rapidly to other cells
(b)
• Neuroglia (glial)
– Protect and assist neurons
– ―Housekeepers‖ of nervous
system
Figure 5.24b,i
5-57
Nervous Tissue
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
• Neuron parts
Nuclei of glial cells
Axon
Neurosoma
Dendrites
– Neurosoma (cell body)
• Houses nucleus and other
organelles
• Cell’s center of genetic
control and protein synthesis
– Dendrites
• Multiple short, branched
processes
• Receive signals from other
cells
• Transmit messages to
neurosoma
– Axon (nerve fiber)
• Sends outgoing signals to
other cells
• Can be more than a meter
long
(b)
Figure 5.24b,i
5-58
Muscular Tissue
• Muscular tissue—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
5-59
Muscular Tissue
• Skeletal muscle
– Long, threadlike cells called muscle fibers
• Most attach to bone
• Exceptions: in tongue, upper esophagus, facial muscles, some
sphincter muscles (ringlike or cufflike muscles that open and close
body passages)
• Contains multiple nuclei adjacent to plasma membrane
• Striations—alternating dark and light bands
• Voluntary—conscious control over skeletal muscles
Nuclei
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
(a)
Striations
Muscle fiber
(b)
Figure 5.25a
a: © Ed Reschke
Figure 5.25b,i
5-60
Muscular Tissue
• Cardiac muscle
– Limited to the heart
• Myocytes or cardiocytes are shorter, branched, and notched at
ends
• Contain one centrally located nucleus surrounded by lightstaining glycogen
• Intercalated discs join cardiocytes end to end
– Provide electrical and mechanical connection
• Striated and involuntary (not under conscious control)
Intercalated discs
Striations
Glycogen
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
(a)
(b)
Figure 5.26a
© Ed Reschke
Figure 5.26b,i
5-61
Muscular Tissue
Nuclei
Muscle cells
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
(a)
(b)
Figure 5.27a
a: © The McGraw-Hill Companies, Inc./Dennis Strete, photographer
• Smooth muscle
Figure 5.27b,i
– Lacks striations and is involuntary
• Relatively short, fusiform cells (thick in middle, tapered at ends)
• One centrally located nucleus
• Visceral muscle—forms layers of digestive, respiratory, and
urinary tract: propels contents through an organ, regulates
diameter of blood vessels
5-62
Cell Junctions, Glands,
and Membranes
• Expected Learning Outcomes
– Describe the junctions that hold cells and tissues
together.
– Describe or define different types of glands.
– Describe the typical anatomy of a gland.
– Name and compare different modes of glandular
secretion.
– Describe the way tissues are organized to form
the body’s membranes.
– Name and describe the major types of
membranes in the body.
5-63
Cell Junctions
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Intercellular space
Plasma membrane
Cell-adhesion proteins
(a) Tight junction
Intercellular space
Cell-adhesion
proteins
Plaque
Intermediate
filaments of
cytoskeleton
(b) Desmosome
Proteins
Connexon
Pore
(c) Gap junction
Basement membrane
(d) Hemidesmosome
Figure 5.28,
• Cell junctions—connections between one cell and another
• All cells (except blood and metastatic cancer cells) are anchored to
each other or their matrix by intercellular junctions
• Resist stress and communicate with each other
5-64
Tight Junctions
• Tight junction—a region in which adjacent cells are bound
together by fusion of the outer phospholipid layer of their
plasma membranes
– In epithelia, forms a zone that completely encircles each cell
near its apical pole
– Seals off intercellular space
– Makes it impossible for substance to pass between cells
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Intercellular space
Plasma membrane
Cell-adhesion proteins
(a) Tight junction
Intercellular space
Cell-adhesion
proteins
Plaque
Intermediate
filaments of
cytoskeleton
(b) Desmosome
Proteins
Connexon
Figure 5.28
Pore
(c) Gap junction
Basement membrane
(d) Hemidesmosome
5-65
Desmosomes
• Desmosomes—patch that holds cells together (like a clothing snap)
• Serves to keep cells from pulling apart—resists mechanical stress
• Hooklike J-shaped proteins arise from cytoskeleton
– Approach cell surface
– Penetrate into thick protein plaques linked to transmembrane proteins
• Hemidesmosomes—anchor the basal cells of epithelium to the
underlying basement membrane
– Epithelium cannot easily peel away from underlying tissues
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Intercellular space
Plasma membrane
Cell-adhesion proteins
(a) Tight junction
Intercellular space
Cell-adhesion
proteins
Plaque
Intermediate
filaments of
cytoskeleton
(b) Desmosome
Proteins
Figure 5.28
Connexon
Pore
(c) Gap junction
Basement membrane
(d) Hemidesmosome
5-66
Gap Junctions
• Gap (communicating) junction—formed by a ringlike
connexon
– Consists of six transmembrane proteins arranged like
segments of an orange
– Surrounding water-filled pores
– Ions, glucose, amino acids, and other solutes pass from one
cell to the next
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Intercellular space
Plasma membrane
Cell-adhesion proteins
(a) Tight junction
Intercellular space
Cell-adhesion
proteins
Plaque
Intermediate
filaments of
cytoskeleton
(b) Desmosome
Proteins
Figure 5.28
Connexon
Pore
(c) Gap junction
Basement membrane
(d) Hemidesmosome
5-67
Glands
• Gland—cell or organ that secretes substances
for use elsewhere in the body or releases them
for elimination from the body
– Composed of epithelial tissue in a connective tissue
framework and capsule
– May produce product synthesized by the gland
(digestive enzymes) or products removed from
tissues and modified by the gland (urine)
• Secretion—product useful to the body
• Excretion—waste product
5-68
Endocrine and Exocrine Glands
• 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
5-69
Endocrine and Exocrine Glands
• Some organs have both endocrine and exocrine
functions
– Liver, gonads, pancreas
• Unicellular glands—found in epithelium that is
predominantly nonsecretory
– Can be endocrine or exocrine
– Mucus-secreting goblet or endocrine cells of stomach
and small intestine
5-70
Exocrine Gland Structure
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
• Capsule—connective
covering of most glands
– Septa or trabeculae:
extensions of capsule that
divide the interior of the gland
into compartments (lobes)
– Further divided into smaller
lobules
Lobules
Secretory
acini
Lobes
Duct
Parenchyma
Secretory
vesicles
Stroma:
Capsule
Septum
(a)
Duct
Acinus
(b)
Figure 5.30
5-71
Exocrine Gland Structure
• Stroma—connective tissue framework of the
gland
– Supports and organizes glandular tissue
• Parenchyma—cells that perform the tasks of
synthesis and secretion
– Typically cuboidal or simple columnar epithelium
5-72
Exocrine Gland Structure
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Simple coiled tubular
Compound acinar
Compound tubuloacinar
Example: Sweat gland
Example: Pancreas
Key
Duct
Secretory portion
Example: Mammary gland
Figure 5.31
• Simple—unbranched duct
• Compound—branched duct
• Shape of gland
– Tubular: duct and secretory portion have uniform diameter
– Acinar: secretory cells form dilated sac (acinus or alveolus)
– Tubuloacinar: both tubular and acinar portions
5-73
Types of Secretions
• Serous glands
– Produce thin, watery secretions
• Perspiration, milk, tears, digestive juices
• Mucous glands
– Produce glycoprotein, mucin, which absorbs water to
form a sticky secretion called mucus
– Goblet cells: unicellular mucous glands
• Mixed glands
– Contain both cell types and produce a mixture of the two
types of secretions
• Cytogenic glands
– Release whole cells, sperm and egg cells
5-74
Modes of Secretion
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• Merocrine glands (eccrine
glands) have vesicles that
release their secretion by
exocytosis
– Tear glands, pancreas, gastric
glands, and others
Exocytosis
Nucleus
Secretory
vesicle
• Apocrine glands—primarily
merocrine mode of secretion
– Axillary sweat glands, mammary
glands
(a) Merocrine gland
Figure 5.32a
5-75
Modes of Secretion
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 5.32b
(b) Holocrine gland
• Holocrine glands—cells accumulate a product and then
the entire cell disintegrates
– Secretion of a mixture of cell fragments and synthesized substance
– Oil glands of scalp, glands of eyelids
5-76
Membranes
• Membranes line body cavities and cover
their viscera
• Cutaneous membrane (the skin)—largest
membrane in the body
– Stratified squamous epithelium (epidermis)
resting on a layer of connective tissue (dermis)
– Relatively dry layer serves protective function
5-77
Membranes
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Mucous coat
Cilia
Epithelium
Mucin in
goblet cell
Ciliated cells of
pseudostratified
epithelium
Basement
membrane
Mucous
membrane
(mucosa)
Blood vessel
Lamina
propria
Collagen fibers
Fibroblast
Elastic fibers
(a)
Figure
5.33a
Muscularis
mucosae
• Mucous membrane (mucosa) lines passages that
open to the external environment
5-78
Membranes
Cont.
– Digestive, respiratory, urinary, and reproductive tracts
– Epithelium, absorptive, ciliated, and other types of
cells
– Lamina propria—areolar connective tissue
– Muscularis mucosae—smooth muscle layer
• Absorptive, secretory, and protective functions
• Goblet cells produce mucus
5-79
Membranes
• Serous membrane (serosa)—internal
membrane
– Simple squamous epithelium resting on a layer of
areolar tissue
– Produces serous fluid that arises from blood
– Covers organs and lines walls of body cavities
• Endothelium lines blood vessels and heart
• Mesothelium lines body cavities (pericardium, peritoneum,
and pleura)
• Synovial membrane—lines joint cavities
– Connective tissue layer only, secretes synovial fluid
5-80
Tissue Growth, Development,
Repair, and Degeneration
• Expected Learning Outcomes
– Name and describe the modes of tissue growth.
– Define adult and embryonic stem cells and their
varied degrees of developmental plasticity.
– Name and describe the ways that a tissue can
change from one type to another.
– Name and describe the modes and causes of tissue
shrinkage and death.
– Name and describe the ways the body repairs
damaged tissues.
5-81
Tissue Growth
• Tissue growth—increasing the number of cells or
the existing cells grow larger
• Hyperplasia—tissue growth through cell
multiplication
• Hypertrophy—enlargement of preexisting cells
– Muscle growth through exercise
– Accumulation of body fat
• Neoplasia—development of a tumor (neoplasm)
– Benign or malignant
– Composed of abnormal, nonfunctional tissue
5-82
Tissue Development
• Tissues can change types within certain limits
• Differentiation
– Unspecialized tissues of embryo become specialized
mature types
• Mesenchyme to muscle
• Metaplasia
– Changing from one type of mature tissue to another
• Simple cuboidal tissue of vagina before puberty changes to
stratified squamous after puberty
• Pseudostratified columnar epithelium of bronchi of smokers
to stratified squamous epithelium
5-83
Stem Cells
• Stem cells—undifferentiated cells that are not yet
performing any specialized function
– Have potential to differentiate into one or more types of
mature functional cells
• Developmental plasticity—diversity of mature cell
types to which stem cells can give rise
5-84
Stem Cells
• Embryonic stem cells
– Totipotent: have potential to develop into any type of fully
differentiated human cell
• Source—cells of very early embryo
– Pluripotent: can develop into any type of cell in the
embryo
• Source—cells of inner cell mass of embryo
• Adult stem cells—undifferentiated cells in tissues
of adults
– Multipotent: bone marrow producing several blood cell
types
– Unipotent: most limited plasticity; only epidermal cells
produced
5-85
Tissue Repair
• Damaged tissues can be repaired in two ways:
– Regeneration: replacement of dead or damaged cells
by the same type of cell as before
• Restores normal function
• Skin injuries and liver regenerate
– Fibrosis: replacement of damaged cells with scar
tissue
• Holds organs together
• Does not restore normal function
– Severe cuts and burns, healing of muscle injuries, scarring
of lungs in tuberculosis
5-86
Tissue Repair
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• Healing of a cut in the skin:
– Severed blood vessels bleed into
cut
– Mast cells and damaged cells
release histamine
– Dilates blood vessels
– Increases blood flow to area
– Makes capillaries more permeable
1 Bleeding into the wound
Figure 5.34 (1)
• Blood plasma seeps into the
wound carrying:
– Antibodies
– Clotting proteins
– Blood cells
5-87
Tissue Repair
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• Blood clot forms in the
tissue
– Loosely knitting edges of cut
together
– Inhibits spread of pathogens
from injury site to healthy tissue
Scab
Blood clot
Macrophages
• Forms scab that temporarily
seals wound and blocks
infection
• Macrophages phagocytize
and digest tissue debris
Fibroblasts
Leukocytes
2 Scab formation and
macrophage activity
Figure 5.34 (2)
5-88
Tissue Repair
• New capillaries sprout
from nearby vessels and
grow into wound
• Deeper portions become
infiltrated by capillaries and
fibroblasts
– Transform into soft mass
called granulation tissue
– Macrophages remove the
blood clot
– Fibroblasts deposit new
collagen
– Begins 3–4 days after injury
and lasts up to 2 weeks
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Scab
Macrophages
Fibroblasts
Blood
capillary
Granulation
tissue
3 Formation of granulation tissue
(fibroblastic phase of repair)
Figure 5.34 (3)
5-89
Tissue Repair
• Surface epithelial cells around
wound multiply and migrate
into wound area beneath scab
• Epithelium regenerates
• Connective tissue undergoes
fibrosis
• Scar tissue may or may not
Epidermal
show through epithelium
regrowth
Scar tissue
• Remodeling (maturation)
(fibrosis)
phase begins several weeks
after injury and may last up to 2
years
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4 Epithelial regeneration and connective
tissue fibrosis (remodeling phase of repair)
Figure 5.34 (4)
5-90
Tissue Degeneration and Death
• Atrophy—shrinkage of a tissue through a loss in cell
size or number
– Senile atrophy through normal aging
– Disuse atrophy from lack of use (astronauts)
• Necrosis—premature, pathological death of tissue due to
trauma, toxins, or infections
– Infarction—sudden death of tissue when blood supply is cut off
– Gangrene—tissue necrosis due to insufficient blood supply
– Decubitus ulcer—bed sore or pressure sore
• Pressure reduces blood flow to an area
• Form of dry gangrene
– Gas gangrene—anaerobic bacterial infection
5-91
Tissue Degeneration and Death
• Apoptosis—programmed cell death
– Normal death of cells that have completed their function and
best serve the body by dying and getting out of the way
• Phagocytized by macrophages and other cells
• Billions of cells die by apoptosis
• Every cell has a built-in ―suicide program‖
– Extracellular suicide signal binds receptor protein in the
plasma membrane called Fas
– Fas activates enzymes: endonuclease chops up DNA and
protease destroys proteins
5-92
Tissue Engineering
• Tissue engineering—artificial production of
tissues and organs in the lab for implantation in
the human body
– Framework of collagen or biodegradable polyester
fibers
– Seeded with human cells
– Grown in ―bioreactor‖ (inside of mouse)
• Supplies nutrients and oxygen to growing tissue
5-93
Tissue Engineering
• Skin grafts already available
– Research in progress on heart valves, coronary
arteries, bone, liver, tendons
– Human outer ear grown on back of mouse and recent
replacement of urinary bladder wall sections
Figure 5.35
5-94
The Stem-Cell Controversy
• Possible treatment for diseases caused by loss of
functional cell types by embryonic stem cells
– Cardiac muscle cells, injured spinal cord, insulinsecreting cells
• Skin and bone marrow stem cells have been used
in therapy for years
• Adult stem cells have limited developmental
potential
– Difficult to harvest and culture
5-95