IAS20 Flashcards
developmental origin of epithelial tissue
originate from all 3 germ layers
ectoderm -> layer of membrane exposed to ext. env. e.g. skin epidermis
mesoderm: lining of cavities that do not open to ext. env. e.g. kidney tubules, vessel endothelium, mesothelium covering lung, abdomen, heart
endoderm: body cavity & hollow passageway: e.g. respiratory & GI tracts
function of epithelial tissues
PAESS
protection (work w/ connective tissue to act as phy barrier, stratified protect against injuries, abrasion, infection)
absorption & excretion (simple, facilitate efficient material transportation
secretion (exocrine & endocrine)
sensation (specialized sensory receptors, convey signals to nervous system e.g. retina & olfactory)
6 characteristics of epithelial tissue
exhibit functional & morpho. polarity (prominent diff. in diff. side of cells)
contains cytokeratin (inter. filament) for providing strength to resist stretching
cells close together w/ little or no IC matrix, indi. cells joined by junctional complex
sit on basement membrane
avascular -> continuous layer, obtain nutrients & remove waste from connective tissue blood vessels
epithelium connection w/ connective tissue, basement membrane
epithelial supported by connective underlying, separated by basement membrane (acellular)
stained by periodic acid-schiff, blue
basal lamina: secreted by epithelium, type IV collagen
reticular lamina: secreted by fibroblasts in connective tissue, type III collagen
basement membrane function
attachment to connective tissue
act as scaffold to guide cell migration in tissue repair
classification of epithelia
shape of apical cell: squamous (flattened), cuboidal (equal dimensions, round nucleus), columnar (tall)
no. of layers: simple / pseudostratified (1), stratified (>1), transitional (varies)
general functions of epithelial types in cell layer & shape
simple: diffusion, secretion, absorption (filtration)
stratified: protection against abrasion
squamous: diffusion (filtration)
cuboidal: secretion & absorption
columnar: highly active secretion & absorption
simple squamous epithelium
very thin, flattened
facilitate exch. of materials, absorption & secretions (maximise rate of diffusion)
e.g. tissues or cells using diffusion for molec. movement, pulmonary alveoli, lining heart, blood & lymph vessels; appendix, peritoneal & pleural cavity
simple cuboidal epithelium
contain more cytoplasm, for secretion, excretion & absorption
participate in active transport e.g. gland duct, kidney tubule
simple columnar epithelium
elongated nuclei located near base of cell
fluid transport, secretion & absorption (larger cell -> higher level of secretion & absorption than cuboidal)
e.g. intestinal lining, gallbladder
simple ciliated columnar epithelium
contain motile cilia e.g. fallopian tube
stratified squamous epithelium, non-keratinised
apical layers are living cells w/ nuclei
basal membrane generally cuboidal
for protection against desication & abrasion
e.g. uterus surface
stratified squamous epithelium (keratinised)
cell on surface subject to mech. stress when exposed to high abrasion lvl
superficial layers contain rich amts of keratin but dead
surface protection & prevent desiccation / mech. stress / abrasion
e.g. skin
stratified cuboidal epithelium (note: no structure)
for protection, secretion & limited absorption
e.g. lining of larger excretory duct of exocrine glands (salivary, sweat)
stratified columnar epithelium
basal layer cells short & irregular shaped
for protection & secretion
e.g. larynx, larger ducts of exocrine glands (mammary gland)