Epithelial Tissue

Epithelial tissue cell are arranged in

sheets and are densely packed

ET cell junctions

many cell junctions present

cells attach to

a basement membrane

Epithelial tissue vascularity

avascular but does have a nerve supple

Epithelial tissue mitosis

mitosis occurs frequently

Main functions of ET

protection

absorption

filtration

excretion

secretion

sensory reception

ET apical surface (free side)

exposed to surface or cavity

some have microvilli

ET basal surface (attached side)

inwards toward body

attached to basement membrane

adhesive sheet holding basal surface of epithelial cells to underlying cells

defines epithelial boundary

Cancerous epithelial cells

not contained like other cells

penetrate the boundary and invade underlying tissues, resulting in spread of cancer

First name of ET indicates

number of cell layers

simple, pseudostratified, stratified

simple

single layer

simple ET functions

diffusion, osmosis, filtration, secretion, absorption

Pseudostratified ET

single layer that looks like many layers

Pseudostratified ET functions

similar functions as simple ET

Often have cilia or goblet cells (mucus production)

Stratified ET

2+ layers

Stratified ET function

protection

Second name indicates

cell shape

squamous, cuboidal, columnar, transitional

squamous

flattened and scale-like

rapid passage

cuboidal

box-like cube

secretion and absorption

columnar

tall columns

protection, secretion, absorption

transitional

change shape from cuboidal to squamous and back

allows for stretch/distension

naming of stratified epithelia

named according to the shape in the apical layer

Squamous categories

simple, stratified

Cuboidal categories

simple, stratified

columnar categories

simple (nonciliated, ciliated), pseudo-stratified (ciliated, nonciliated), stratified

glandular ET categories

endocrine, exocrine

Gland

single cell or mass of epithelial cells adapted for secretion

endocrine Glandular epithelia

ductless

secretions (hormones) enter interstitial fluid and diffuse into blood

Exocrine glandular epithelia

have ducts

secretions enter ducts that empty onto surface of a covering/lining epithelium

unicellular exocrine glands

• mucous cells and goblet cells

• found in epithelial linings of intestinal and respiratory tracts

• all produce mucin = a sugar-protein that can dissolve in water to form mucus, which functions as a slimy protective, lubricating coating

Structure of multicellular exocrine glands

composed of duct and secretory unit

many cells that form a distinctive microscopic structure or a macroscopic organ

Structural classification of multicellular exocrine glands

simple tubular, simple branched tubular, simple coiled tubular, simple acinar, simple branched acinar, compound tubular, compound acinar, compound tubuloacinar

Functional classification in multicellular exocrine glands

merocrine

apocrine

holocrine

merocrine

fluid product released through exocytosis

ex: sweat, pancreas, salivary

apocrine

accumulate products within, but only apex ruptures

ex. mammary, ceruminous

holocrine

entire cell ruptures releasing secretions and cell fragments

eg: sebaceous