TOPIC 9

Loops allow fluid to be edited by environment of kidney

Dips down into medulla (where peritubular capillaries/vasa recta are located)

Extension of the loop

The longer the papilla, the longer the loop

Arid species have the longest papilla (need to conserve as much as possible because little access to water)

Mesic species (land/terrestrial) have an "average" papilla (have regular access to water)

Aquatic species have the shortest papilla (don't need to conserve as much water because live in water)

Thick medulla allows increased urine osmolarity

Medulla osmotic gradient determines max urine osmolarity

Thicker medulla --> longer loops --> more concentrated urine --> more reabsorption of water

Descending

Water permeable (moves out of tubules because of hyperosmotic medulla)

Water moves out to concentrate fluid

Ascending

Thin: Na and Cl are transported actively out of tubule (movement of solutes out = lower osmolarity = hypoosmotic fluid)

Thick: NaKCl cotransporter 2 (NKCC2) absorbs NaCl. Gap junctions are leaky and allow Na+ to slip through

Stimulates aquaporin translocation into collecting duct of apical membranes

Helps us increase BP by increasing water reabsroption.

Comes from the blood stream

Increase plasma osmolarity, increase plasma vasopressin

Regulation

Diuresis: high urine flow rate (unable to retain water)

low urine osmolarity

stimulated by low plasma osmolarity

U/P < 1

Antidiuresis: low urine flow rate

high urine osmolarity

stimulated by high plasma osmolarity

U/P > 1