bio 2: kidneys 2

what are aqueous solutions made of

water (solvent) and solutes

what is osmolarity

total concentration of solutes

osmosis

diffusion of H2O across membranes from low to high osmolarity

where does water diffuse out of the tubule

wherever the interstitial fluid is at a higher osmolarity than the filtrate

At the ____ ____, water chases useful solutes that are being reabsorbed

proximal tubule

what are the descending limb and collecting duct surrounded by as they move down the medulla

increasing osmolarity of interstitial fluid

why does osmolarity of the medullary interstitial fluid increase

• at the outer medulla, Na+ and Cl- are actively transported into interstitial fluid

• at the inner medulla, urea passively diffuses into interstitial fluid

At the ascending limb of the loop of henle, transporters actively transport Na+ and Cl- out of the filtrate and into the interstitial fluid which…

1. increases the osmolarity of the interstitial fluid at the outer medulla

2. reduces the osmolarity of the filtrate

what diffuses out of the lower collecting duct and how does this happen

urea in the ultra-concentrated filtrate diffuses out via urea channels

what happens to urea after it diffuses out of the lower collecting duct

it re-enters the filtrate

what does urea do to osmolarity as it moves through the interstitial fluid

increases the osmolarity of the inner medulla interstitial fluid

what happens to useful solutes at the proximal tubule

they are actively transported from filtrate to interstitial fluid then passively diffuse to peritubular capillaries

what happens as solutes from the proximal tubule are being transported

increase osmolarity of spaces they move in; drives diffusion of water out of filtrate to peritubular capillaries

for water reabsorption at the proximal tubule: volume of filtrate ______, osmolarity _____

decreases, stays the same

what happens to water at the descending limb and why

it diffuses out of the filtrate via aquaporins bc of the higher osmolarity of the medullary interstitial fluid

what happens to water after it diffuses out of the filtrate at the descending limb

water diffuses from interstitial fluid into vasa recta capillaries

for water reabsorption at the descending limb: volume of filtrate _____ which causes its osmolarity to _____

decreases; increase

what is transported at the thick segment of the ascending limb

Na+ and Cl- are actively transported into interstitial fluid

does water diffuse at the ascending limb? why or why not

no bc there are no aquaporins, its impermeable to water

at the ascending limb: the volume of the filtrate ______, and its osmolarity _____

stays the same, decreases

why does the volume at the distal tubule stay the same

its impermeable to water

at the distal tubule, volume of filtrate _____, osmolarity _____

stays the same, increases slightly

why does water diffuse out of the collecting duct via aquaporins

bc of the higher osmolarity of the medullary interstitial fluid

for water reabsorption at the collecting duct: volume of the filtrate _____, osmolarity _____

decreases, increases

homeostasis of blood Na+, K+, and water occurs at the kidney and is regulated by…

aldosterone and ADH

what plays an important role in regulating blood pressure

aldosterone and ADH

what is aldosterone secreted in response to

low blood Na+ or low blood pressure

where does aldosterone bind intracellular receptors

late distal tubule and entire collecting duct

net effect of aldosterone

increase aldosterone → increase basal Na+/K+ pumps, increase Na+ and water reabsorption → increase blood Na+ and volume → increase blood pressure

when aldosterone is released, Na+ diffuses from filtrate into epithelial cells via what type of diffusion

facilitated

what happens to K+ bc of aldosterone

its secreted from blood to the filtrate

where is K+ secreted to in the filtrate after being stimulated by aldosterone

K+ is secreted to the distal tubule and then peed out

increase K+ secretion → ____ K+ blood levels

decreases

what is ADH secreted in response to

low blood pressure

ADH binds to extracellular receptors of the _____

collecting duct

what does the binding of ADH to the collecting duct do

increases the number of aquaporins at the apical membrane

what does increased aquaporins at the collecting duct do

increases water permeability of the collecting duct

net effect of ADH

increased ADH → increase apical aquaporins → increase water reabsorption → increase blood volume → increase blood pressure

ADH binds to the ADH receptor, which then begins an intracellular signaling cascade that cases the fusion of…

aquaporin containing vesicles to the apical membrane