Page 27 - Headlines Histology2024_Neat

• t is highly specialized to resist a great degree of stretch and to withstand the
toxicity of urine.

• In relaxed state (empty bladder) it is consists of 4-5 layers of cells, the
basal layer is cuboidal in shape rests on thin basal lamina. The intermediate
layer consists of several layers of polyhedral or pear-shaped cells. The
surface cells are large cuboidal or dome-shaped with convex outer surface
and concave inner surface. Their nuclei are large, spherical with prominent
nucleoli, some cells are bi-nucleated.

• In stretched state (full bladder) it appears only as two or three cell layers
thickness. The intermediate and surface layers are extremely flattened. The
superficial cells have a thicker plasmalemma that acts as a barrier against
diffusion of fluid from the subepithelial tissue to the hypertonic urine.

MEMBRANE SPECIALIZATION OF EPITHELIA

• The basal, luminal and intercellular surfaces of epithelial cells have a
variety of specializations.

BASAL SURFACE

Basement membrane
• The epithelium is separated from the underlying connective tissue by a thin
membrane known as basement membrane. It consists of two layers; basal
lamina and reticular lamina.
• The basal lamina is synthesized by the adjacent epithelial cells and is
located in contact with the epithelial basal plasmalemma. It is composed of
type IV collagen embedded in an amorphous matrix of structural
glycoprotein called laminin.
• The reticular lamina is derived mainly from the underlying connective
tissue and is located deep to the basal lamina. It consists of fine reticular
fibers embedded in an amorphous ground substance.

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