Major functions of epithelia:
- forming a protective barrier
- diffusion and absorption
- synthesis and secretion of glandular products
basement membrane
supports all epithelia, separates epithelia from underlying supporting tissues
basal surface
facing the basement membrane
Apical surface
faces outward
Do blood vessels cross epithelial basement membranes?
NO
Simple Squamous epithelia function
- diffusion
- synthesis and secretion
Endothelium
simple squamous epithelium of the lining of the heart, blood vessels, and lymphatic channels
mesothelium
simple squamous cells forming serous membranes lining internal body cavities
Where is simple squamous epithelia?
- loops of Henle in kidney
- alveoli in lungs
- peritoneum
- blood vessels
Simple Cuboidal Epithelium structure
- box like cubes
- one spherical, centrally placed nucleus
- may contain microvilli
Simple Cuboidal Epithelium Function
- protection
- conduits for gland ducts
- may be specialized for excretory, secretory, or absorptive functions
Where is Simple Cuboidal Epithelium?
- usually lines small ducts and tubules
- surface of ovary
- renal tubules and collecting ducts
- excretory ducts of salivary glands and pancreas
- thyroid
Simple Columnar Epithelium structure
-one layer of tall cells
-ovoid, elongated nucleus centrally or basally placed
may contain surface cilia or microvilli
-may contain goblet cells
Simple Columnar Epithelium Function
- protection of wet surfaces
- nutrient absorption
- secretion
Where is simple columnar epithelium?
- small intestine (microvilli)
- stomach
- female reproductive tract (cilia)
goblet cells
non-ciliated mucus-secreting cells, often found in small and large bowel. also found in respiratory tract
Pseudostratified
simple epithelium with all cells resting on basement membrane, but appears as if there is more than 1 layer of cells
How pseudostratified differs from true stratified epithelium?
- pseudostratified cells exhibit polarity (nuclei mainly confined to basal 2/3 of epithelium)
- cilia almost never present on stratified epithelium
Where is Pseudostratified epithelium found?
Airways of respiratory system
Cilia in pseudostratified epithelium
propel surface layer of mucus containing entrapped particles towards the pharynx
Stratified epithelium function
- protection
- poorly suited for absorption and secretion
