Download HCB Objectives 2

HCB Objectives 3
1.
Types of epithelia:
Simple: one layer of cells
Squamous: thin cells (inside of blood vessels (endothelium))
Cuboidal: thick cells with width longer than height (secretory ducts –
kidney tubules)
Columnar: thick cells with height longer than width (GI tract)
Pseudostratified: columnar cells with different height nuclei so they
appear to be stratified (respiratory tract)
Stratified: more than one layer of cells
Squamous: thin cells (epidermis)
Cuboidal: thick cells with width longer than height (large excretory ducts
– sweat glands)
Columnar: thick cells with height longer than width (large ducts of
salivary glands)
Transitional: cells modified for expansion and contraction with
characteristic dome during relaxation that flattens under stress (urinary
tract)
2.
Major functions of epithelia: protection, selective diffusion, absorption,
secretion, ion transport, sensory transduction, filtration, passive immunity
How they perform their function: high packing density, specialized junctions,
polarization, avascularity, renewal, and basement membrane
3.
Membrane specializations:
apical:
 microvilli (to increase surface area for absorption)
 cilia (to move surface fluids)
 stereocilia (extra-long microvilli to increase surface area)
lateral:
 occluding junctions (“tight junctions” to make seal layer, band is called
zonula occludens)
 adhering junctions (macula adherens includes both desomosomes and
hemisdesmosomes. Desmosomes link intermediate filaments to
neighboring cell membranes, hemidesmosomes link intermediate
filaments to the basement membrane. Band of junctions below zonula
occludens makes zonula adherens. Major function of occluding junctions
is also to provide stability and adhesion)
o Note: zona occludens, zona adherens, and desmosome form a
“junctional complex”
 communicating junctions (“gap junctions” to allow communication
between two cells
basal:
 basement membrane (to provide a border between epithelia and
connective tissue as well as to provide support for epithelia)
4.
Epithelial Cell Polarity: portion facing outside is structurally and functionally
different than portion facing inside
examples: respiratory tract (ciliated/nonciliated), GI tract (microvilli/no
microvilli), etc.
5.
Metaplasia: conversion of one cell type to another