Term | Definition |
Tissues | Groups of cells similar in structure that perform common or related function |
Histology | – Study of tissues |
4 Main Tissues | • Epithelial tissue
– Covers
• Connective tissue
– Supports
• Muscle tissue
– Produces movement
• Nerve tissue
– Controls |
Studying Human Tissue: Microscopy | • Tissue is fixed
– Preserved
• Cut
– Sliced thin enough to transmit light or
l t
electrons
• Stained
– Enhances contrast |
Epithelial Tissue (Epithelium) | • Form boundaries
• Two main types (by location)
– Covering and lining epithelia
• On external and internal surfaces
Gl d l ith li
– Glandular epithelia
• Secretory tissue in glands |
Epithelial Tissue Functions | • Protection
• Absorption
• Filtration
• Excretion
• Secretion
• Sensory reception |
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:
Specialized Contacts | • Covering and lining epithelial tissues fit
closely together
– Form continuous sheets
• Specialized contacts bind adjacent cells
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– Lateral contacts
• Tight junctions
• Desmosomes |
Characteristics of Epithelial Tissue:
Connective Tissue Support | • All are supported by connective tissue
• Reticular lamina
Deep to basal lamina
Network of collagen fibers
• Basement membrane
B L + R L
Reinforces epithelial sheet
Resists stretching and tearing
Defines epithelial boundary |
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 can replace lost cells
by cell division |
Classification of Epithelia | • All epithelial tissues have two names
–# of layers
• Simple epithelia = 1 layer
• Stratified epithelia = 2 or more layers
– Shape
• Squamous
• Cuboidal
• Columnar
• In stratified epithelia, epithelia classified by
cell shape in apical layer |
Cells of Epithelial Tissues | • Squamous cells
– Flattened and scalelike
– Nucleus flattened
• Cuboidal cells
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– Boxlike
– Nucleus round
• Columnar cells
– Tall; column shaped
– Nucleus elongated |
Classification of Epithelia:
Simple Epithelia | • Absorption
• Secretion
• Filtration
• Very thin |
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 |
Simple Squamous Epithelium | • 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 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 |
Simple Columnar Epithelium | • Single layer of tall, closely packed cells
• Absorption
• Secretion
• Note description, function, location on next
slide |
Pseudostratified Columnar Epitheliem | • Cells vary in height
– Cell nuclei at different levels
– Appears stratified, but is not
– Secretion
Ab ti
– Absorption
– Note description, function, location on next
slide |
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 |
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 |
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 columnar |