Page 733 - Atlas of Histology with Functional Correlations

Glomerular filtrate flows from distal convoluted tubules to collecting tubules

and ducts
During excessive water loss or dehydration, ADH is released from the
pituitary gland
ADH causes epithelium of collecting duct to become highly permeable to
water

Water-permeable cells contain transmembrane pore protein aquaporins that
function as channels for water passage
Aquaporin regulated by the ADH that binds to receptors and activates

aquaporins
Water that is retained in interstitium is collected by peritubular capillaries
and vasa recta
In the absence of ADH, increased water is retained in collecting ducts and
urine is diluted

URETER

Lined with transitional epithelium and consists of mucosa, muscularis, and
adventitia
Upper part lined with inner longitudinal and middle circular smooth muscle
layers

Third longitudinal smooth muscle layer added in the lower third of the ureter
Connective tissue adventitia surrounds the ureter

Bladder

Thick muscular wall with three indistinct layers of smooth muscle
Serosa lines superior surface and adventitia covers the inferior surface
Transitional epithelium in empty bladder exhibits about six layers of cells
When stretched, transitional epithelium appears stratified squamous

Changes in epithelium caused by thicker plasma membrane of superficial
cells and folded plaques
In relaxed bladder, plaques confined to vesicles

Plaques act like hinges and allow apical cells to expand during stretching;
cells become squamous
Thicker plasma membrane and transitional epithelium provide osmotic
barrier to urine

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