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Medullary conc. gradient in the LOH (Loop of Henle (Ascending limb (Apical…
Medullary conc. gradient in the LOH
Urine output varies in volume and in osmolarity (concentration-ish), solute/litre mOsM
LOH sets up osmotic gradient
ISF in renal medulla gets increasingly hyperosmotic
ISF v.high ion concentration
Loop of Henle
Juxtamedullary nephrons drop down into the renal medulla and then return to the cortext.
Ascending limb
Apical (next to tubule lumen) and basolateral (next to capillary) side
No aquaporins - impermeable to water
so water doesnt follow the ions so no movement of water
Specific cotransporter on apical, pulls Cl- into limb cell. Brings Na+ with it
Descending limb
Permeable to water but not permeable to Na+
Descending limb lacks ion pumps but v. permeable to water
Ascending limb not permeable to water
Active transport of ions out of the ascending limb leads to osmotic transport of water out of descending limb
How concentrated loops gets at base affects osmolarity of urine
Countercurrent multiplication
Vasa recta
CC multiplication cannot maintain osmotic gradient alone. Would be washed out by blood supply
Vasa recta supplies oxygen and nutrients to medulla
Run parallel to limbs of LOH, blood flows in opposite direction
First takes up ions released from ascending limb, then water from descending limb
Urea recycling
Responsible for about 50% of osmotic gradient
Filtered out and about 50% is reabsorbed. As water & co reabsorbed is concentrated in filtrate
Medullary collecting duct, descending vasa recta and LOH have specific protein carriers to allow movement of urea DOWN conc.grad. ->recycles in medulla
Regulated reabsorption of water
Cannot be actively pumped, must be moved by osmosis
4-9% water is reabsorbed in DCT & collecting duct
ADH = Antidiuretic hormone.
nonapeptide hormone released from posterior pituitary
ADH inserts water pores into the apical membrane of collecting duct
So more permeable to water so more water reabsorbed
Ability to concentrate depends on relative length of LOH AND number of juxta medullary neurons.