consequences of solute recovery W1

Question 1

summary of what occurs in the proximal tubule?

Answer 1

sodium pulled through by basal pump which also dumps potassium into tubule lumen

glucose, amino acids, phosphate etc pulled through by sodium gradient

biphosphate recovered (with H+ cycling) by sodium gradient

chloride leaves passively

Question 2

what does solute movement in the proximal tubule aim to achieve?

Answer 2

lower the osmolarity of the tubule, so water flows passively from the tubule to counteract this (through aquaporins).

Question 3

what has and hasn’t the proximal tubule achieved in the larger picture?

Answer 3

recovery of sodium/chloride/phosphate/calcium etc and water

not controlled urine concentration
not controlled acid/base

Question 4

osmosis?

Answer 4

water will follow ions - will move from dilute area of ions to concentrated area of ions

Question 5

how do we use osmosis to concentrate urine?

Answer 5

must provide a destination that is more concentrated than urine to tempt water out the tubule

Question 6

how are ions but not water pulled from the tubule to the tissues? what does this result in?

Answer 6

sodium chloride co-transporter, then Na+/K+ ATPase and chloride channels.
no H2O entry because no aquaporins and tight junctions between cells.

this results in hypertonic basal side (as long as ions don’t get washed away…)

Question 7

loop of Henle anatomy?

Answer 7

descending thin limb
ascending thin limb
thick ascending limb

Question 8

features of descending thin limb cells?

Answer 8

permeable to water
‘impermeable’ to ions
‘impermeable’ to urea

Question 9

features of ascending thin limb cells?

Answer 9

impermeable to water
permeable to ions
permeable to urea

Question 10

function of thick ascending limb?

Answer 10

active recovery of ions (driven by Na+ pump)

Question 11

tubular contents concentration in loop of Henley?

Answer 11

descending limb - increasingly concentrated as water is drawn out
thin ascending limb - concentrated
thick ascending limb - more diluted as many ions have been recovered

Question 12

why are ions recovered in the ascending thin limb?

Answer 12

creates a hypertonic area to draw out water from the descending limb

Question 13

concentrations throughout the nephron and collecting duct?

Answer 13

in osmol/kg:
corpuscle - 0.29
pct - 0.29
descending limb - 1.4
thick ascending limb - 0.1
dct - 0.08
collecting duct - 1.4

Question 14

how do we stop the high osmolarity of the Henle’s loop area being washed away?

Answer 14

all loops of Henle in medulla causing increased osmolality here.

efferent arterioles continue around LoH, gets concentrated then unconcentrated so balances out (counter current exchange)

Question 15

osmolality in overall kidney structure?

Answer 15

cortex (renal corpuscles) - 0.29
medulla (LoH) - 1.4

Question 16

distal tubule recovery quanitites?

Answer 16

95% NaCl recovered
75% water recovered

Question 17

what occurs in the collecting duct?

Answer 17

water reabsorption driven by hypertonic zone (up to 24% of filtered water removed - cumulative = 99%)

Question 18

how do cells in the collecting duct regulate how permeable to water they are?

Answer 18

aquaporins can be in cell membrane (allowing water to cross) or stored in vacuoles (not allowing water to cross). movement of aquaporins is regulated by vasopressin.

Question 19

what can the collecting duct do other than water resorption? why?

Answer 19

leak urea! (back into blood?)
leaking concentrated urea adds to hypertonicity. this increases water recovery in serious cases of water loss, pays price of small amount of urea toxicity.

Question 20

general anatomical arrangement of kidneys?

Answer 20

normal zone (cortex) on outside
hypertonic zone (medulla on inside
urine collected on inside
several of these units with one central collective place (pelvis)

Question 21

why are kidneys particularly sensitive to ischaemia? (therefore first to detect dropped haematocrit?)

Answer 21

long runs of parallel arteries/arterioles and veins/venules mean there is counter-current exchange of oxygen, so that much gets shunted from artery to vein before the blood enters capillaries.

Question 22

what does low renal oxygen trigger?

Answer 22

erythropoietin release, leading to more red cells made in bone marrow

Question 23

3 things that regulate blood pressure in a glomerulus?

Answer 23

systemic blood pressure (sets maximum that could reach glomerulus)
constriction of afferent arterioles
constriction of efferent arterioles

Question 24

how does the kidney maintain constant flow rates across the glomerulus?

Answer 24

direct pressure sensing in the afferent arteriole (the myogenic mechanism)

monitoring the performance of the nephron (tubuloglomerular feedback)

Question 25

what is the safe window of arterial pressure for the kidneys to maintain constant flow rate?

Answer 25

10.7kPa to 24kPa

Question 26

how does the myogenic mechanism work?

Answer 26

stretch activated cation channels depolarise membrane and cause smooth muscle to contract: fast and protective against acute surges

Question 27

how does tubuglomerular feedback work?

Answer 27

urine about to leave nephron is sampled and information is fed back to afferent/efferent arteriole. local for each individual nephron.

Question 28

name of specialised zone in distal tubule where contact is made with the glomerulus? what cells do they contact?

Answer 28

macula densa
make contact with juxtaglomerular cells

Question 29

how does the macula densa work?

Answer 29

elevated glob bp
filtrate flows faster
less time for solute recovery
more NaCl remains in distal tubule
macula densa cells pump out more NaCl than usual
JGCs release adenosine
afferent arteriole constricts in response to adenosine
glom bp returns to normal