Download Tissue Lecture - U of D Jesuit

CHAPTER 4
TISSUES
Tissue: The Living Fabric
• Individual body cells specialized
– Each type performs specific functions that
maintain homeostasis
• Tissues
– Groups of cells similar in structure that
perform common or related function
• Histology
– Study of tissues
Types of Primary Tissues
• Epithelial tissue
– Covers
• Connective tissue
– Supports
• Muscle tissue
– Produces movement
• Nerve tissue
– Controls
Figure 4.1 Overview of four basic tissue types: epithelial, connective, muscle, and nervous tissues.
Nervous tissue: Internal communication
• Brain
• Spinal cord
• 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
• Lining of digestive tract organs and other hollow
organs
• Skin surface (epidermis)
Connective tissue: Supports, protects, binds
other tissues together
• Bones
• Tendons
• Fat and other soft padding tissue
Studying Human Tissue: Microscopy
• Tissue is fixed
– Preserved
• Cut
– Sliced thin enough to transmit light or
electrons
• Stained
– Enhances contrast
Epithelial Tissue (Epithelium)
• Form boundaries
• Two main types (by location)
– Covering and lining epithelia
• On external and internal surfaces
– Glandular epithelia
• Secretory tissue in glands
Epithelial Tissue Functions
• Protection: internal from external
environment
• Absorption: digestive system/skin
• Filtration: capillaries
• Excretion: skin
• Secretion: skin/digestion
• Sensory reception: external & internal
Five Characteristics of Epithelial Tissues
•
•
•
•
•
Polarity
Specialized contacts
Supported by connective tissues
Avascular, but innervated
Can regenerate
Characteristics of Epithelial Tissue: Polarity
• Cells have polarity
– Apical surface (upper free) exposed to
exterior or cavity
– Basal surface (lower, attached)
• Both surfaces differ in structure and
function
Apical Surface of Epithelial Tissues
• May be smooth & slick
• Most have microvilli (e.g., brush border of
intestinal lining)
– Increase surface area
• Some have cilia (e.g., lining of trachea)
Basal Surface of Epithelial Tissues
• Noncellular basal lamina
– Glycoprotein and collagen fibers lies adjacent
to basal surface
– Adhesive sheet
– Selective filter
– Scaffolding for cell migration in wound repair
Characteristics of Epithelial Tissue:
Connective Tissue Support
• Reticular lamina
– Deep to basal lamina
– Network of collagen fibers
• Basement membrane
– Basal lamina + reticular lamina
– Reinforces epithelial sheet
– Resists stretching and tearing
– Defines epithelial boundary
Characteristics of Epithelial Tissue:
Specialized Contacts
• Covering and lining epithelial tissues fit
closely together
– Form continuous sheets
• Specialized contacts bind adjacent cells
– Lateral contacts
• Tight junctions
• Desmosomes
• Gap junctions
Characteristics of Epithelial Tissue:
Avascular but Innervated
• No blood vessels in epithelial tissue
– Must be nourished by diffusion from
underlying connective tissues
• Is supplied by nerve fibers
Characteristics of Epithelial Tissue:
Regeneration
• High regenerative capacity
• Stimulated by loss of apical-basal polarity
and lateral contacts
– Some exposed to friction
– Some exposed to hostile substances
• If adequate nutrients are present, can
replace lost cells by cell division
Classification of Epithelia
• All epithelial tissues have two names
– One indicates number of cell layers
• Simple epithelia = single layer of cells
• Stratified epithelia = two or more layers of cells
– Shape can change in different layers
– One indicates shape of cells
• Squamous
• Cuboidal
• Columnar
• In stratified epithelia, epithelia classified by
cell shape in apical layer
Figure 4.2a Classification of epithelia.
Apical surface
Basal surface
Simple
Apical surface
Basal surface
Stratified
Classification based on number of cell layers.
Cells of Epithelial Tissues
• Squamous cells
– Flattened and scalelike
– Nucleus flattened (ovoid)
• Cuboidal cells
Squamous
Cuboidal
– Boxlike
– Nucleus round
• Columnar cells
– Tall; column shaped
– Nucleus elongated (ovoid)
Columnar
Classification of Epithelia:
Simple Epithelia
• Very thin
• Functions:
– Absorption
– Secretion
– Filtration
Simple Squamous Epithelium
• Cells flattened laterally
• Cytoplasm sparse
• Function where rapid diffusion is priority
– i.e., kidney, lungs
• Note description, function, location on next
slide
– Endothelium: lining of lymphatic vessels,
blood vessels, and heart
– Mesothelium: epithelium of serous
membranes in the ventral body cavity
Figure 4.3a Epithelial tissues.
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
Nuclei of
squamous
epithelial
cells
Function: Allows materials to pass
by diffusion and filtration in sites
where protection is not important;
secretes lubricating substances in
serosae.
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 (140x).
Simple Cuboidal Epithelia
•
•
•
•
Single layer of cells
Secretion
Absorption
Forms walls of smallest ducts of glands
and many kidney tubules
• Note description, function, location on next
slide
Figure 4.3b Epithelial tissues.
Simple cuboidal epithelium
Description: Single layer of
cubelike cells with large, spherical
central nuclei.
Simple
cuboidal
epithelial
cells
Nucleus
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
•
•
•
•
Single layer of tall, closely packed cells
Absorption
Secretion
Note description, function, location on next
slide
Figure 4.3c Epithelial tissues.
Simple columnar epithelium
Description: Single layer of tall
cells with round to oval nuclei;
some cells bear cilia; layer may
contain mucus-secreting
unicellular glands (goblet cells).
Microvilli
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 rectum), gallbladder,
and excretory ducts of some
glands; ciliated variety lines small
bronchi, uterine tubes, and some
regions of the uterus.
Mucus of
goblet cell
Basement
membrane
Photomicrograph: Simple columnar
epithelium of the small intestine mucosa (660x).
Pseudostratified Columnar Epithelium
• Cells vary in height
– Cell nuclei at different levels, so appears
stratified, but is not
– Secretion
– Absorption
– Note description, function, location on next
slide
Figure 4.3d Epithelial tissues.
Pseudostratified columnar epithelium
Description: Single layer of cells
of differing heights, some not
reaching the free surface; nuclei
seen at different levels; may
contain mucus-secreting cells
and bear cilia.
Cilia
Pseudostratified
epithelial
layer
Function: Secrete substances,
particularly mucus; propulsion of
mucus by ciliary action.
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 (800x).
Basement
membrane
Stratified Epithelial Tissues
• Two or more cell layers
• Regenerate from below
– Basal cells divide, cells migrate to surface
• More durable than simple epithelia
• Protection is major role
• Always named for the type at apical
surface
Stratified Squamous Epithelium
• Most widespread of stratified epithelia
• Free surface squamous; deeper layers
cuboidal or columnar
• Located for wear and tear
• Those farthest from basal layer (and
therefore nutrients) less viable
• Note description, function, location on next
slide
Figure 4.3e Epithelial tissues.
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.
Location: Nonkeratinized type
forms the moist linings of the
esophagus, mouth, and vagina;
keratinized variety forms the
epidermis of the skin, a dry
membrane.
Nuclei
Basement
membrane
Connective
tissue
Photomicrograph: Stratified squamous
epithelium lining the esophagus (285x).
Stratified Cuboidal Epithelium
• Quite rare
• Found in some sweat and mammary
glands
• Typically two cell layers thick
Stratified Columnar Epithelium
• 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
• Only apical layer is columnar
Transitional Epithelium
•
•
•
•
•
Forms lining of hollow urinary organs
Basal layer cells are cuboidal or columnar
Ability to change shape with stretch
Apical cells vary in appearance
Note description, function, location on next
slide
Figure 4.3f Epithelial tissues.
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,
permits stored urine to distend
urinary organ.
Location: Lines the ureters,
bladder, and part of the urethra.
Photomicrograph: Transitional epithelium
lining the bladder, relaxed state (360x); note the
bulbous, or rounded, appearance of the cells at
the surface; these cells flatten and elongate
when the bladder fills with urine.
Basement
membrane
Connective
tissue
Glandular Epithelia
• Gland
– One or more cells that makes and secretes an
aqueous fluid called a secretion
• Classified by
– Site of product release: endocrine or exocrine
– Relative number of cells forming the gland
• Unicellular (e.g., goblet cells) or multicellular
Endocrine Glands
• Ductless glands
– Secretions not released into a duct
• Secrete (by exocytosis) hormones that
travel through lymph or blood to their
specific target organs
• Target organs respond in some
characteristic way
Exocrine Glands
• Secretions released onto body surfaces
(skin) or into body cavities
• More numerous than endocrine glands
• Secrete products into ducts
• Examples include mucous, sweat, oil, and
salivary glands
Unicellular Exocrine Glands
• The only important unicellular glands are
mucous cells and goblet cells
• Found in epithelial linings of intestinal and
respiratory tracts
• All produce mucin
– Dissolves in water to form mucus
• Slimy protective, lubricating coating
Figure 4.4 Goblet cell (unicellular exocrine gland).
Microvilli
Secretory
vesicles
containing
mucin
Golgi
apparatus
Rough ER
Nucleus
Multicellular Exocrine Glands
• Multicellular exocrine glands are
composed of a duct and a secretory unit
• Usually surrounded by supportive
connective tissue
– Supplies blood and nerve fibers
– Extends into and divides gland into lobes
Classification of Multicellular Glands
• By structure and type of secretion
– Structure
• Simple glands (unbranched duct) or compound
glands (branched duct)
– Type of secretion
• Merocrine: most abundant – secrete products by
exocytosis as produced
• Holocrine: accumulate products within then
rupture
• Apocrine: accumulates products within but only
apex ruptures – controversy if exist in humans
Connective Tissue
• Most abundant and widely distributed of
primary tissues
• Four main classes
– Connective tissue proper
– Cartilage
– Bone
– Blood
Major Functions of Connective Tissue
•
•
•
•
•
Binding and support
Protecting
Insulating
Storing reserve fuel
Transporting substances (blood)
Characteristics of Connective Tissue
• Have varying degrees of vascularity
• Have extracellular matrix
– Connective tissue not composed mainly of
cells
– Largely nonliving extracellular matrix
separates cells
• Can bear weight
• Withstand tension
• Endure abuse
Structural Elements of Connective Tissue
• Three elements
– Ground substance
– Fibers
– Cells
• Composition and arrangement varies in
different connective tissues
Ground Substance
• Unstructured material that fills space between
cells
– Substance through which solutes diffuse between
blood capillaries and cells
• Components
– Interstitial fluid
– Cell adhesion proteins ("glue" for attachment)
– Proteoglycans
• Protein core + large polysaccharides
• Trap water in varying amounts, affecting viscosity of ground
substance
Connective Tissue Fibers
• Three types of fibers provide support
– Collagen
• Strongest and most abundant type
• Tough; provides high tensile strength
– Elastic fibers
• Networks of long, thin, elastin fibers that allow for
stretch and recoil
– Reticular
• Short, fine, highly branched collagenous fibers
(different chemistry and form than collagen fibers)
• Branch, forming networks that offer more "give"
Cells
• "Blasts" cells
– Immature form; mitotically active; secrete ground
substance and fibers
– Fibroblasts in connective tissue proper
– Chondroblasts in cartilage
– Osteoblasts in bone
– Hematopoietic stem cells in bone marrow
• "Cyte" cells
– Mature form; maintain matrix
– Chondrocytes in cartilage
– Osteocytes in bone
Other Cell Types in Connective Tissues
• Fat cells
– Store nutrients
• White blood cells
– Neutrophils, eosinophils, lymphocytes
– Tissue response to injury/ infection
• Mast cells
– Initiate local inflammatory response against foreign
microorganisms they detect
• Macrophages
– Phagocytic cells that "eat" dead cells,
microorganisms; function in immune system
Types of Connective Tissues: Connective
Tissue Proper
• All connective tissues except bone, cartilage and
blood
• Two subclasses
– Loose connective tissues
• Areolar
• Adipose
• Reticular
– Dense connective tissues (also called fibrous
connective tissues)
• Dense regular
• Dense irregular
• Elastic
Areolar Connective Tissue
• Support and bind other tissues
– Universal packing material between other tissues
•
•
•
•
•
•
•
•
Most widely distributed
Provide reservoir of water and salts
Defend against infection
Store nutrients as fat
Fibroblasts
Loose arrangement of fibers
Ground substance
When inflamed, soaks up fluid  edema
Figure 4.8a Connective tissues.
Connective tissue proper: loose connective tissue, areolar
Description: Gel-like matrix with
all three fiber types; cells:
fibroblasts, macrophages, mast
cells, and some white blood cells.
Function: Wraps and cushions
organs; its macrophages
phagocytize bacteria; plays
important role in inflammation;
holds and conveys tissue fluid.
Location: Widely distributed
under epithelia of body, e.g., forms
lamina propria of mucous
membranes; packages organs;
surrounds capillaries.
Elastic
fibers
Ground
substance
Fibroblast
nuclei
Collagen
fibers
Epithelium
Lamina
propria
Photomicrograph: Areolar connective
tissue, a soft packaging tissue of the body (340x).
Adipose Tissue
• White fat
– Similar to areolar but greater nutrient storage
– Cell is adipocyte
• Stores nutrients
– Not much matrix
– Richly vascularized
– Shock absorption, insulation, energy storage
• Brown fat
– Use lipid fuels to heat bloodstream, not to
produce ATP
Figure 4.8b Connective tissues.
Connective tissue proper: loose connective tissue, adipose
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
adipose
(fat) cell
Location: Under skin in
subcutaneous tissue; around
kidneys and eyeballs; within
abdomen; in breasts.
Adipose
tissue
Fat droplet
Photomicrograph: Adipose tissue from
the subcutaneous layer under the skin (350x).
Mammary
glands
Reticular Connective Tissue
• Resembles areolar but fibers are reticular
fibers
• Fibroblasts called reticular cells
• Supports free blood cells in lymph nodes,
the spleen, and bone marrow
Figure 4.8c Connective tissues.
Connective tissue proper: loose connective tissue, reticular
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.
White blood
cell
(lymphocyte)
Location: Lymphoid organs
(lymph nodes, bone marrow, and
spleen).
Spleen
Reticular
fibers
Photomicrograph: Dark-staining network
of reticular connective tissue fibers forming
the internal skeleton of the spleen (350x).
Dense Regular Connective Tissue
• Closely packed bundles of collagen fibers
running parallel to direction of pull
– White structures with great resistance to
pulling
– Fibers slightly wavy so stretch a little
• Fibroblasts manufacture fibers and ground
substance
• Few cells
• Poorly vascularized
Figure 4.8d Connective tissues.
Connective tissue proper: dense connective tissue, dense regular
Description: Primarily parallel
collagen fibers; a few elastic fibers;
major cell type is the fibroblast.
Function: Attaches muscles to
bones or to muscles; attaches
bones to bones; withstands great
tensile stress when pulling force is
applied in one direction.
Collagen
fibers
Location: Tendons, most
ligaments, aponeuroses.
Nuclei of
fibroblasts
Shoulder
joint
Ligament
Tendon
Photomicrograph: Dense regular connective
tissue from a tendon (430x).
Dense Irregular Connective Tissue
• Same elements but bundles of collagen
thicker and irregularly arranged
• Resists tension from many directions
– Dermis
– Fibrous joint capsules
– Fibrous coverings of some organs
Figure 4.8e Connective tissues.
Connective tissue proper: dense connective tissue, dense irregular
Description: Primarily irregularly
arranged collagen fibers; some
elastic fibers; fibroblast is the
major cell type.
Nuclei of
fibroblasts
Function: Withstands tension
exerted in many directions;
provides structural strength.
Location: Fibrous capsules of
organs and of joints; dermis of the
skin; submucosa of digestive tract.
Collagen
fibers
Shoulder
joint
Fibrous
joint
capsule
Photomicrograph: Dense irregular connective
tissue from the fibrous capsule of a joint (430x).
Elastic Connective Tissue
• Some ligaments very elastic
– Those connecting adjacent vertebrae
• Contained in walls of larger arteries
Figure 4.8f Connective tissues.
Connective tissue proper: dense connective tissue, elastic
Description: Dense regular
connective tissue containing a
high proportion of elastic fibers.
Function: Allows tissue to recoil
after stretching; maintains pulsatile
flow of blood through arteries; aids
passive recoil of lungs following
inspiration.
Location: Walls of large arteries;
within certain ligaments associated
with the vertebral column; within
the walls of the bronchial tubes.
Elastic
fibers
Aorta
Heart
Photomicrograph: Elastic connective tissue
in the wall of the aorta (250x).
Cartilage
•
•
•
•
Chondroblasts and chondrocytes
Tough yet flexible
Lacks nerve fibers
Up to 80% water - can rebound after
compression
• Avascular
– Receives nutrients from membrane surrounding it
• Perichondrium
• Three types of cartilage:
– Hyaline cartilage
– Elastic cartilage
– Fibrocartilage
Figure 4.8g Connective tissues.
Cartilage: hyaline
Description: Firm matrix; collagen
fibers form an imperceptible
network; chondroblasts produce
the matrix and when mature
(chondrocytes) lie in lacunae.
Function: Supports and reinforces;
serves as resilient cushion; resists
compressive stress.
Chondrocyte
in lacuna
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.
Costal
cartilages
Matrix
Photomicrograph: Hyaline cartilage from
a costal cartilage of a rib (470x).
Figure 4.8h Connective tissues.
Cartilage: elastic
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
Matrix
Location: Supports the external
ear (pinna); epiglottis.
Photomicrograph: Elastic cartilage from
the human ear pinna; forms the flexible
skeleton of the ear (800x).
Figure 4.8i Connective tissues.
Cartilage: fibrocartilage
Description: Matrix similar to but
less firm than that in hyaline
cartilage; thick collagen fibers
predominate.
Function: Tensile strength allows
it 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.
Bone
•
•
•
•
•
•
•
•
•
Also called osseous tissue
Supports and protects body structures
Stores fat and synthesizes blood cells in cavities
More collagen than cartilage
Has inorganic calcium salts
Osteoblasts produce matrix
Osteocytes maintain the matrix
Osteons – structural units
Richly vascularized
Figure 4.8j Connective tissues.
Others: bone (osseous tissue)
Description: Hard, calcified
matrix containing many collagen
fibers; osteocytes lie in lacunae.
Very well vascularized.
Function: 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).
Central
canal
Lacunae
Lamella
Location: Bones
Photomicrograph: Cross-sectional view
of bone (125x).
Blood
• Most atypical connective tissue – is a fluid
• Red blood cells (RBCs) most common cell
type
• Also contains white blood cells (WBCs)
and platelets
• Fibers are soluble proteins that precipitate
during blood clotting
• Functions in transport
Figure 4.8k Connective tissues.
Connective tissue: blood
Description: Red and white blood
cells in a fluid matrix (plasma).
Red blood
cells
(erythrocytes)
Function: Transport respiratory
gases, nutrients, wastes, and other
substances.
White blood
cells:
• Lymphocyte
• Neutrophil
Location: Contained within blood
vessels.
Plasma
Photomicrograph: Smear of human blood
(1670x); shows two white blood cells
surrounded by red blood cells.
Muscle Tissue
• Highly vascularized
• Responsible for most types of movement
• Three types
– Skeletal muscle tissue
• Found in skeletal muscle
• Voluntary
– Cardiac muscle tissue
• Found in walls of heart
• Involuntary
– Smooth muscle tissue
• Mainly in walls of hollow organs other than heart
• Involuntary
Figure 4.9a Muscle tissues.
Skeletal muscle
Description: Long, cylindrical,
multinucleate cells; obvious
striations.
Part of
muscle
fiber (cell)
Function: Voluntary movement;
locomotion; manipulation of the
environment; facial expression;
voluntary control.
Nuclei
Location: In skeletal muscles
attached to bones or occasionally
to skin.
Striations
Photomicrograph: Skeletal muscle
(approx. 440x). Notice the obvious banding
pattern and the fact that these large cells are
multinucleate.
Figure 4.9b Muscle tissues.
Cardiac muscle
Description: Branching, striated,
generally uninucleate cells that
interdigitate at specialized
junctions (intercalated discs).
Intercalated
discs
Function: As it contracts, it
propels blood into the circulation;
involuntary control.
Striations
Location: The walls of the heart.
Nucleus
Photomicrograph: Cardiac muscle (900x);
notice the striations, branching of cells, and
the intercalated discs.
Figure 4.9c Muscle tissues.
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.
Nuclei
Location: Mostly in the walls of
hollow organs.
Smooth
muscle
cell
Photomicrograph: Sheet of smooth
muscle (720x).
Nervous Tissue
• Main component of nervous system
– Brain, spinal cord, nerves
– Regulates and controls body functions
• Neurons
– Specialized nerve cells that generate and conduct
nerve impulses
• Neuroglia
– Supporting cells that support, insulate, and protect
neurons
Figure 4.10 Nervous tissues.
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 nonexcitable supporting cells.
Nuclei of
supporting
cells
Neuron processes Cell body
Axon Dendrites
Cell body
of a neuron
Function: Neurons transmit
electrical signals from sensory
receptors and to effectors (muscles
and glands) which control their
activity; supporting cells support
and protect neurons.
Neuron
processes
Location: Brain, spinal
cord, and nerves.
Photomicrograph: Neurons (350x).
Covering and Lining Membranes
• Composed of at least two primary tissue
types
– An epithelium bound to underlying connective
tissue proper
– Are simple organs
• Three types
– Cutaneous membranes
– Mucous membranes
– Serous membranes
Cutaneous Membranes
• Skin
• Keratinized stratified squamous epithelium
(epidermis) attached to a thick layer of
connective tissue (dermis)
The cutaneous membrane
• Dry membrane
(the skin) covers the body
surface.
Mucous Membranes
• Mucosa indicates location not cell composition
• All called mucosae
– Line body cavities open to the exterior (e.g.,
Digestive, respiratory, urogenital tracts)
• Moist membranes bathed by secretions (or
urine)
• Epithelial sheet lies over layer of connective
tissue called lamina propria
• May secrete mucus
Figure 4.11b Classes of membranes.
Mucous membranes
Mucous membranes line body
cavities that are open to the
exterior.
Mucosa of
nasal cavity
Mucosa of
mouth
Esophagus
lining
Mucosa of
lung bronchi
Serous Membranes
• Serosae—found in closed ventral body cavity
• Simple squamous epithelium (mesothelium)
resting on thin areolar connective tissue
• Parietal serosae line internal body cavity walls
• Visceral serosae cover internal organs
• Serous fluid between layers
• Moist membranes
• Pleurae, pericardium, peritoneum
Figure 4.11c Classes of membranes.
Serous membranes
Serous membranes line body cavities that are
closed to the exterior.
Parietal
pleura
Visceral
pleura
Visceral
Parietal
pericardium pericardium
Parietal
peritoneum
Visceral
peritoneum
Tissue Repair
• Necessary when barriers are penetrated
• Cells must divide and migrate
• Occurs in two major ways
– Regeneration
• Same kind of tissue replaces destroyed tissue
• Original function restored
– Fibrosis
• Connective tissue replaces destroyed tissue
• Original function lost
Steps in Tissue Repair: Step 1
• Inflammation sets stage
– Release of inflammatory chemicals
– Dilation of blood vessels
– Increase in vessel permeability
– Clotting occurs
Figure 4.12. Tissue repair of a nonextensive skin wound: regeneration and fibrosis.
Slide 1
Scab
Epidermis
Vein
Blood clot in
incised wound
Inflammatory
chemicals
Migrating white
blood cell
Artery
1 Inflammation sets the stage:
• Severed blood vessels bleed.
• Inflammatory chemicals are released.
• Local blood vessels become more permeable, allowing white blood cells,
fluid, clotting proteins, and other plasma proteins to seep into the injured area.
• Clotting occurs; surface dries and forms a scab.
Steps in Tissue Repair: Step 2
• Organization restores blood supply
– The blood clot is replaced with granulation
tissue
– Epithelium begins to regenerate
– Fibroblasts produce collagen fibers to bridge
the gap
– Debris is phagocytized
Figure 4.12. Tissue repair of a nonextensive skin wound: regeneration and fibrosis.
Slide 2
Regenerating
epithelium
Area of
granulation
tissue
ingrowth
Fibroblast
Macrophage
Budding capillary
2 Organization restores the blood supply:
• The clot is replaced by granulation tissue, which restores the vascular
supply.
• Fibroblasts produce collagen fibers that
bridge the gap.
• Macrophages phagocytize dead and dying cells and other debris.
• Surface epithelial cells multiply and migrate over the granulation tissue.
Steps in Tissue Repair: Step 3
• Regeneration and fibrosis
– The scab detaches
– Fibrous tissue matures; epithelium thickens
and begins to resemble adjacent tissue
– Results in a fully regenerated epithelium with
underlying scar tissue
Figure 4.12. Tissue repair of a nonextensive skin wound: regeneration and fibrosis.
Regenerated
epithelium
Fibrosed area
3 Regeneration and fibrosis effect permanent repair:
• The fibrosed area matures and contracts; the epithelium thickens.
• A fully regenerated epithelium with an underlying area of scar tissue
results.
Slide 3
Regenerative Capacity in Different Tissues
• Regenerate extremely well
– Epithelial tissues, bone, areolar connective tissue,
dense irregular connective tissue, blood-forming
tissue
• Moderate regenerating capacity
– Smooth muscle and dense regular connective tissue
• Virtually no functional regenerative capacity
– Cardiac muscle and nervous tissue of brain and
spinal cord
– New research shows cell division does occur
• Efforts underway to coax them to regenerate better