consequences of solute recovery W1 Flashcards
summary of what occurs in the proximal tubule?
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
what does solute movement in the proximal tubule aim to achieve?
lower the osmolarity of the tubule, so water flows passively from the tubule to counteract this (through aquaporins).
what has and hasn’t the proximal tubule achieved in the larger picture?
recovery of sodium/chloride/phosphate/calcium etc and water
not controlled urine concentration
not controlled acid/base
osmosis?
water will follow ions - will move from dilute area of ions to concentrated area of ions
how do we use osmosis to concentrate urine?
must provide a destination that is more concentrated than urine to tempt water out the tubule
how are ions but not water pulled from the tubule to the tissues? what does this result in?
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…)
loop of Henle anatomy?
descending thin limb
ascending thin limb
thick ascending limb
features of descending thin limb cells?
permeable to water
‘impermeable’ to ions
‘impermeable’ to urea
features of ascending thin limb cells?
impermeable to water
permeable to ions
permeable to urea
function of thick ascending limb?
active recovery of ions (driven by Na+ pump)
tubular contents concentration in loop of Henley?
descending limb - increasingly concentrated as water is drawn out
thin ascending limb - concentrated
thick ascending limb - more diluted as many ions have been recovered
why are ions recovered in the ascending thin limb?
creates a hypertonic area to draw out water from the descending limb
concentrations throughout the nephron and collecting duct?
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
how do we stop the high osmolarity of the Henle’s loop area being washed away?
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)
osmolality in overall kidney structure?
cortex (renal corpuscles) - 0.29
medulla (LoH) - 1.4
distal tubule recovery quanitites?
95% NaCl recovered
75% water recovered
what occurs in the collecting duct?
water reabsorption driven by hypertonic zone (up to 24% of filtered water removed - cumulative = 99%)
how do cells in the collecting duct regulate how permeable to water they are?
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.
what can the collecting duct do other than water resorption? why?
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.
general anatomical arrangement of kidneys?
normal zone (cortex) on outside
hypertonic zone (medulla on inside
urine collected on inside
several of these units with one central collective place (pelvis)
why are kidneys particularly sensitive to ischaemia? (therefore first to detect dropped haematocrit?)
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.
what does low renal oxygen trigger?
erythropoietin release, leading to more red cells made in bone marrow
3 things that regulate blood pressure in a glomerulus?
systemic blood pressure (sets maximum that could reach glomerulus)
constriction of afferent arterioles
constriction of efferent arterioles
how does the kidney maintain constant flow rates across the glomerulus?
direct pressure sensing in the afferent arteriole (the myogenic mechanism)
monitoring the performance of the nephron (tubuloglomerular feedback)
what is the safe window of arterial pressure for the kidneys to maintain constant flow rate?
10.7kPa to 24kPa
how does the myogenic mechanism work?
stretch activated cation channels depolarise membrane and cause smooth muscle to contract: fast and protective against acute surges
how does tubuglomerular feedback work?
urine about to leave nephron is sampled and information is fed back to afferent/efferent arteriole. local for each individual nephron.
name of specialised zone in distal tubule where contact is made with the glomerulus? what cells do they contact?
macula densa
make contact with juxtaglomerular cells
how does the macula densa work?
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
