السبت، 22 نوفمبر 2014

Stratified Epithelial Tissue

Stratified Squamous epithelium - keratinized
§Formed of multiple layers of cells. The topmost layer is formed of squamous cells. The epithelium is covered with keratin (a non-living material).
§
§It’s found in areas that require protection:
      - Skin à Epidermis
§Function:
     1) Stratification à protection
     2) Keratin à prevent water loss

Stratified Squamous epithelium – Non-keratinized
§Formed of multiple layers of cells. The topmost layer is formed of squamous cells. The epithelium is not covered with keratin.
§
§It’s found in areas that require protection and water loss is not a problem:
      - Mouth, esophagus, anal canal
      - Vagina
§Function: protection, secretion.

Stratified Cuboidal and Columnar epithelium
qThese are rare in the body. They’re formed of several layers of cuboidal and columnar cells respectively.
§
qFound in:
      - Columnar: Conjunctiva
      - Cuboidal: Lining of large excretory ducts of salivary and sweat glands.
qFunctions: protection and secretion

Transitional epithelium (Urothelium):
vThe topmost cells of this stratified epithelium are dome-like (also called umbrella cells).
v
vFound in: Urinary bladder, ureters and renal calyces.
v
vThe umbrella cells are dome-shaped when the bladder is empty. Once it’s full, these cells will become flattened (hence the name transitional).
v
Functions: protection against the adverse effects of urine. Allow the bladder to change size


Pseudostratified columnar ciliated epithelium:
ØIn this epithelium, the cells have different heights. All cells rest on the basal lamina, but not all of them reach the surface. This makes the nuclei occupy different levels giving the epithelium a false stratified appearance.
Ø
ØFound in trachea, bronchi and nasal cavity.
Ø
ØFunctions: protection, secretion. Ciliary movement remove particles from the airway passages.
 

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