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41 Cards in this Set

  • Front
  • Back
what factor of blood / plasma does the renal concentating mechanism directly control?
osmolarity
what is the difference between osmolarity and osmolality
osmolality is per kg
osmolarity is per litre
what is the site where solute and water are separated?
the ascending limb of the loop of Henle
what two mechanisms are responsible for generation of concentrated urine?
countercurrent exchange (the single effect)
urea recycling
how does the nephron secrete dilute urine?
must simply absorbe more salts than water
occurs in the loop of Henle
when no ADH is present
what is the problem with trying to excrete hyperosmotic urine
must try and remove water without removing salts
water movement occurs through osmosis - passive
how does the kidney manage to remove water without salt?
generates a hyperosmotic compartment in the medullary interstitium
which hormone is nessecary to also create hyperosmotic urine?
ADH
what is the driving force for countercurrent multiplication`
reabsorption of NaCl by thick ascending limb
from where is H20 reabsorbed in countercurrent multiplication?
from the descending limb
which parts of the loop equilibriate
descending limb equilibriates horizontally with the interstitium
ascending limb does not equilibriate
what happens to the tubular fluid through the loop of Henle
starts 290mOsm
in descending limb gets more concentrated
then gets diluted in ascending limb: to more dilute than it was previously
how does the gradient go in the medullary interstitium?
cortical area: around 290mOsm
at bottom: up to 1200mOsm depending on how much ADH there is
what are the affects of ADH
increases IMCD permeability to water and urea
what provides most of the concentration of the coritcal interstitium?
NaCl
what are the consituents of the medullary interstitium concentration at max?
50/50 urea/NaCl
what is the maximum osmolarity of urine?
1200mOsm/ whatever the medullary interstitium reaches
which parts of the collecting duct are permeable / not permeable to urea?
outer medullary and cortical part are not permeable
inner medullary parts are permeable
how does urea leave the collecting duct?
passive reabsorbtion through UT1 channels
how much does urea contribute to the medullary concentration?
50%
apart from NaCl an urea, what else contributes to osmolarity of urine?
non reabsorbed salts such as creatinine
why is it important to regulate body osmolarity?
water moves freely across cell membranes
if ECF osmolality decreases, water moves into cell, swell
if ECF osmolality increaes, water moves out of cell, shrink
what happens if ECF osmolality increases?
cells shrink
what happens if ECF osmolatlity decreases?
cells swell
which organ is especialy vulnerable to changes in osmolality?
brain
what stimulates ADH production?
1% increase in osmolality
5-10% decrease in blood volume
what stimulates thirst?
2-3% increase in osmolality and 10-15% decrease in blood volume
describe regulation of osmolality - when low osmolaltiy?
no ADH secretion, max dilution of urine = 100mOsm
describe regulation of osmolaltiy - when high osmolaltiy?
ADH released
small hypoosmotic amount of urine produced
as little as 0.5 litres, 1200mOsm
what is the threshold for ADH release?
280-290mOsm
increase in osmolarity by 1%
decrease in bp/volume by 5-10%
what is the purpose of the vasa recta?
deliver oxygen and nutrients to the neprhon
what is the risk of the vasa recta?
they could cause wash out of the medullary concentratoin gradient
how is wash out by the vasa recta prevented
countercurrent system
descending: water out, solutes absorbed (bad)
ascending: water in, solutes back out (good)
what is the effect of the vasa recta on the cells deep in the medullar#?
they have a low O2 conc and high PCO2
what happens to the osmolality of blood as it passes through the vasa recta?
at the end, it is more concentrated than it was before (not completely efficient)
what would increased blood flow do to the concentration gradient of the medullary intersitiutm?
decrease / wash out
where is ADH released from?
made in suproptic and paraventricular nuclei of hypothalamus
released from neurohypophysis (posterior lobe of pitutiatary)
what are the affects of ADH on the kidney?
increased AQP2, water reabsorbtion in colelcting duct and distal convoluted tubule
increased urea reabsorption in medullary collecting duct
what are the other affects of ADH apart from on the water / urea absorption rate?
decreases renin release
at high concentrations can cause splanchnic vasoconstriciton
what is the affect of ADH on extracellular fluid volume?
increases extracellular fluid volume
don't forget to revise calculations at end of this lecture!!!!
revise!