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Epithelium, cells,tissues & histology
1. Chapter 4
Tissues and Histology
• Tissues - collections of similar cells and the substances
surrounding them
• Tissue classification based on structure of cells, composition
of noncellular extracellular matrix, and cell function
• Major types of adult tissues
– Epithelial
– Connective
– Muscle
– Nervous
• Histology: Microscopic Study of Tissues
– Biopsy: removal of tissues for diagnostic purposes
– Autopsy: examination of organs of a dead body to
determine cause of death
2. Embryonic Tissue
• 3 major germ layers that form the embryonic disc (source of stem cells)
– Endoderm
• Inner layer
• Forms lining of digestive tract and derivatives
– Mesoderm
• Middle layer
• Forms tissues as such muscle, bone, blood vessels
– Ectoderm
• Outer layer
• Forms skin and neuroectoderm
3. I. Epithelial Tissue
• Cellularity - Consists almost
entirely of cells
• Covers body surfaces, lines
hollow organs, and forms glands
– Outside surface of the body
– Lining of digestive, respiratory
and urogenital systems
– Heart and blood vessels
– Linings of many body cavities
• Polarity - Has apical, basal, and
lateral surfaces
• Rests on a basement membrane
• Specialized cell contacts bind
adjacent cells together
• Avascular - no blood vessels
• Regenerative -Replaces lost cells
by cell division
4. Functions of Epithelia
• Protecting underlying structures; e.g.,
epithelium lining the mouth
• Acting as barriers; e.g., skin
• Permitting the passage of substances; e.g.,
cells lining air sacs in lungs and nephrons in
kidney
• Secreting substances; e.g., pancreatic cells
• Absorbing substances; e.g., lining of stomach
and small intestine
6. Classification of Epithelium
• Number of layers of cells
– Simple- one layer of cells. Each extends from
basement membrane to the free surface
– Stratified- more than one layer.
– Pseudostratified- tissue appears to be stratified,
but all cells contact basement membrane so it is in
fact simple
• Shape of cells
– Squamous- flat, scale-like
– Cuboidal- about equal in height and width
– Columnar- taller than wide
12. Stratified Epithelia
• Contain two or more layers of cells
• Regenerate from below
• Major role is protection
• Are named according to the shape of
cells at apical layer
13. Stratified Squamous
Epithelium
• Description
– Many layers of cells – squamous in shape
– Deeper layers of cells appear cuboidal or
columnar
– Thickest epithelial tissue – adapted for
protection
14. Stratified Squamous
Epithelium
• Specific types
– Keratinized – contain the protective protein
keratin
• Surface cells are dead and full of keratin
– Non-keratinized – forms moist lining of
body openings
15. Stratified Squamous
Epithelium
• Function – Protects underlying tissues
in areas subject to abrasion
• Location
– Keratinized – forms epidermis
– Non-keratinized – forms lining of
esophagus, mouth, and vagina
18. Epithelium: Glandular
• A gland is one or more cells that makes and secretes
an aqueous fluid
• Two types of glands formed by infolding of epithelium:
– Endocrine: no contact with exterior of body; ductless; produce
hormones (pituitary, thyroid, adrenals, pancreas)
– Exocrine: open to exterior of body via ducts (sweat, oil)
• Exocrine glands classified either by structure or by the
method of secretion
• Classified by structure
– Unicellular: goblet cells
– Multicellular: sweat, oil, pituitary, adrenal
19. Multicellular Exocrine Glands
• Classified on the basis of types of
ducts or mode of secretion
• Types of ducts
– Simple: ducts with few
branches
– Compound: ducts with many
branches
• If ducts end in tubules or
sac-like structures: acini.
Pancreas
• If ducts end in simple
sacs: alveoli. Lungs
21. Membrane Junctions: Tight Junction
• Integral proteins of adjacent
cells fuse together
• Completely encircle the cell
and form an adhesion belt.
• Form an impermeable
junction.
• Common near apical region
22. Lateral Surface Features –
Cell Junctions
• Desmosomes – two disc-like plaques
connected across intercellular space
– Plaques of adjoining cells are joined by
proteins called cadherins
– Proteins interdigitate into extracellular
space
– Intermediate filaments insert into plaques
from cytoplasmic side
23. Membrane Junctions: Desmosome
Linker proteins extend
from plaque like teeth of
a zipper.
Intermediate filaments
extend across width of
cell.
• Common in superficial layers of skin; skin
peels after a sunburn
• Reduces chance of tearing, twisting, stretching
Figure 3.5b
24. Membrane Junctions: Gap Junction
• Connexon proteins are trans-
membrane proteins.
• Present in electrically excitable
tissues (heart, smooth muscle)
25. Basal Feature: The Basal
Lamina
• Noncellular supporting sheet between the
epithelium and the connective tissue deep to it
• Consists of proteins secreted by the epithelial
cells
• Functions:
• Acts as a selective filter, determining which
molecules from capillaries enter the epithelium
• Acts as scaffolding along which regenerating
epithelial cells can migrate
• Basal lamina and reticular layers of the
underlying connective tissue deep to it form the
basement membrane
26. Epithelial Surface Features
• Apical surface features
– Microvilli – finger-like extensions of plasma
membrane
• Abundant in epithelia of small intestine and kidney
• Maximize surface area across which small
molecules enter or leave
– Cilia – whip-like, highly motile extensions of
apical surface membranes
• Movement of cilia – in coordinated waves
27. Connective Tissue
• Most diverse and abundant tissue
• Main classes
– Connective tissue proper
– Cartilage
– Bone tissue
– Blood
• Characteristics
– Mesenchyme as their common tissue of origin
(mesenchyme derived from mesoderm)
– Varying degrees of vascularity
– Nonliving extracellular matrix, consisting of ground
substance and fibers
– Cells are not as abundant nor as tightly packed together
as in epithelium
29. Functions of Connective Tissue
• Enclose organs as a capsule and separate
organs into layers. Areolar
• Connect tissues to one another. Tendons and
ligaments.
• Support and movement. Bones.
• Storage. Fat.
• Insulation. Fat.
• Transport. Blood.
• Protection. Bone, cells of the immune
system.
30. Structural Elements of Connective Tissue
• Ground substance – unstructured
material that fills the space between cells
• Fibers – collagen, elastic, or reticular
• Cells – fibroblasts, chondroblasts,
osteoblasts, hematopoietic stem cells,
and others
31. Connective Tissue Cells
• Fibroblasts - secrete the proteins needed for fiber
synthesis and components of the extracellular matrix
• Adipose or fat cells (adipocytes). Common in some
tissues (dermis of skin); rare in some (cartilage)
• Mast cells. Common beneath membranes; along small
blood vessels. Can release heparin, histamine, and
proteolytic enzymes in response to injury.
• Leukocytes (WBC’s). Respond to injury or infection
• Macrophages. Derived from monocytes (a WBC).
Phagocytic; provide protection
• Chondroblasts - form cartilage
• Osteoblasts - form bone
• Hematopoietic stem cells - form blood cells
• Undifferentiated mesenchyme (stem cells). Have
potential to differentiate into adult cell types.
32. Extracellular Matrix - ECM
• ECM has 3 major components
1. Protein fibers 2. Ground substance 3. Fluid
• Protein fibers
– Collagen fibers. Composed of the protein collagen.
Strong, flexible, inelastic; great tensile strength (i.e.
resist stretch). Perfect for tendons, ligaments
– Elastic fibers. Contain molecules of protein elastin that
resemble coiled springs. Returns to its original shape
after stretching or compression. Perfect for lungs,
large blood vessels
– Reticular fibers. Formed from fine collagenous fibers;
form branching networks (stroma). Fill spaces
between tissues and organs.
33. Ground Substance
• Interstitial (tissue) fluid within which are one or more of
the molecules listed below:
– Hyaluronic acid: a polysaccharide. Very slippery;
serves as a good lubricant for joints. Common in
most connective tissues.
– Proteoglycans: protein and polysaccharide complex.
Polysaccharides called glyocosaminoglycans
(chondroitin sulfate, keratin sulfate). Protein part
attaches to hyaluronic acid. Able to trap large
amounts of water.
– Adhesive molecules: hold proteoglycan aggregates
together. Chondronectin in cartilage, osteonectin in
bone, fibronectin in fibrous connective tissue.
• Functions as a molecular sieve through which nutrients
diffuse between blood capillaries and cells
34. Embryonic Connective Tissue
• Mesenchyme: source of all
adult connective tissue.
– Derived from mesoderm
– Delicate collagen fibers
embedded in semifluid matrix
• Mucus: found only in the
umbilical cord. Wharton’s
jelly.
40. Elastic Connective Tissue
• Bundles and sheets of collagenous and elastic fibers
oriented in multiple directions
• In walls of elastic arteries (aorta), lungs, vocal
ligaments
• Strong, yet elastic; allows for recoil of tissue after
being stretched
41. Connective Tissue: Cartilage
• Composed of chondrocytes (cells) located in matrix-
surrounded spaces called lacunae.
• Type of cartilage determined by components of the matrix.
• Firm consistency.
• Ground substance: Proteoglycans and hyaluronic acid
complexed together trap large amounts of water
(microscopic sponges). Allows tissue to spring back after
being compressed.
• Avascular and no nerve supply. Heals slowly.
• Perichondrium. Dense irregular connective tissue that
surrounds cartilage. Fibroblasts of perichondrium can
differentiate into chondroblasts (cartilage-forming cells)
• Types of cartilage
– Hyaline
– Fibrocartilage
– Elastic
47. Muscle Tissue
• Characteristics
– Cells are referred to as fibers
– Contracts or shortens with force when
stimulated
– Moves entire body and pumps blood
• Types
– Skeletal:attached to bones
– Cardiac: muscle of the heart.
– Smooth: muscle associated with tubular
structures and with the skin. Nonstriated and
involuntary.
52. Tissues and Aging
• Cells divide more slowly
• Collagen fibers become more irregular in structure, though
they may increase in number
– Tendons and ligaments become less flexible and more fragile
• Elastic fibers fragment, bind to calcium ions, and become
less elastic
– Arterial walls and elastic ligaments become less elastic
• Changes in collagen and elastin result in
– Atherosclerosis and reduced blood supply to tissues
– Wrinkling of the skin
– Increased tendency for bones to break
• Rate of blood cell synthesis declines in the elderly
• Injuries don’t heal as readily