Renal Concentrating Mechanism

Front 1

what factor of blood / plasma does the renal concentating mechanism directly control?

Back 1

osmolarity

Front 2

what is the difference between osmolarity and osmolality

Back 2

osmolality is per kg
osmolarity is per litre

Front 3

what is the site where solute and water are separated?

Back 3

the ascending limb of the loop of Henle

Front 4

what two mechanisms are responsible for generation of concentrated urine?

Back 4

countercurrent exchange (the single effect)
urea recycling

Front 5

how does the nephron secrete dilute urine?

Back 5

must simply absorbe more salts than water
occurs in the loop of Henle
when no ADH is present

Front 6

what is the problem with trying to excrete hyperosmotic urine

Back 6

must try and remove water without removing salts
water movement occurs through osmosis - passive

Front 7

how does the kidney manage to remove water without salt?

Back 7

generates a hyperosmotic compartment in the medullary interstitium

Front 8

which hormone is nessecary to also create hyperosmotic urine?

Back 8

ADH

Front 9

what is the driving force for countercurrent multiplication`

Back 9

reabsorption of NaCl by thick ascending limb

Front 10

from where is H20 reabsorbed in countercurrent multiplication?

Back 10

from the descending limb

Front 11

which parts of the loop equilibriate

Back 11

descending limb equilibriates horizontally with the interstitium
ascending limb does not equilibriate

Front 12

what happens to the tubular fluid through the loop of Henle

Back 12

starts 290mOsm
in descending limb gets more concentrated
then gets diluted in ascending limb: to more dilute than it was previously

Front 13

how does the gradient go in the medullary interstitium?

Back 13

cortical area: around 290mOsm
at bottom: up to 1200mOsm depending on how much ADH there is

Front 14

what are the affects of ADH

Back 14

increases IMCD permeability to water and urea

Front 15

what provides most of the concentration of the coritcal interstitium?

Back 15

NaCl

Front 16

what are the consituents of the medullary interstitium concentration at max?

Back 16

50/50 urea/NaCl

Front 17

what is the maximum osmolarity of urine?

Back 17

1200mOsm/ whatever the medullary interstitium reaches

Front 18

which parts of the collecting duct are permeable / not permeable to urea?

Back 18

outer medullary and cortical part are not permeable
inner medullary parts are permeable

Front 19

how does urea leave the collecting duct?

Back 19

passive reabsorbtion through UT1 channels

Front 20

how much does urea contribute to the medullary concentration?

Back 20

50%

Front 21

apart from NaCl an urea, what else contributes to osmolarity of urine?

Back 21

non reabsorbed salts such as creatinine

Front 22

why is it important to regulate body osmolarity?

Back 22

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

Front 23

what happens if ECF osmolality increases?

Back 23

cells shrink

Front 24

what happens if ECF osmolatlity decreases?

Back 24

cells swell

Front 25

which organ is especialy vulnerable to changes in osmolality?

Back 25

brain

Front 26

what stimulates ADH production?

Back 26

1% increase in osmolality
5-10% decrease in blood volume

Front 27

what stimulates thirst?

Back 27

2-3% increase in osmolality and 10-15% decrease in blood volume

Front 28

describe regulation of osmolality - when low osmolaltiy?

Back 28

no ADH secretion, max dilution of urine = 100mOsm

Front 29

describe regulation of osmolaltiy - when high osmolaltiy?

Back 29

ADH released
small hypoosmotic amount of urine produced
as little as 0.5 litres, 1200mOsm

Front 30

what is the threshold for ADH release?

Back 30

280-290mOsm
increase in osmolarity by 1%
decrease in bp/volume by 5-10%

Front 31

what is the purpose of the vasa recta?

Back 31

deliver oxygen and nutrients to the neprhon

Front 32

what is the risk of the vasa recta?

Back 32

they could cause wash out of the medullary concentratoin gradient

Front 33

how is wash out by the vasa recta prevented

Back 33

countercurrent system
descending: water out, solutes absorbed (bad)
ascending: water in, solutes back out (good)

Front 34

what is the effect of the vasa recta on the cells deep in the medullar#?

Back 34

they have a low O2 conc and high PCO2

Front 35

what happens to the osmolality of blood as it passes through the vasa recta?

Back 35

at the end, it is more concentrated than it was before (not completely efficient)

Front 36

what would increased blood flow do to the concentration gradient of the medullary intersitiutm?

Back 36

decrease / wash out

Front 37

where is ADH released from?

Back 37

made in suproptic and paraventricular nuclei of hypothalamus
released from neurohypophysis (posterior lobe of pitutiatary)

Front 38

what are the affects of ADH on the kidney?

Back 38

increased AQP2, water reabsorbtion in colelcting duct and distal convoluted tubule
increased urea reabsorption in medullary collecting duct

Front 39

what are the other affects of ADH apart from on the water / urea absorption rate?

Back 39

decreases renin release
at high concentrations can cause splanchnic vasoconstriciton

Front 40

what is the affect of ADH on extracellular fluid volume?

Back 40

increases extracellular fluid volume

Front 41

don't forget to revise calculations at end of this lecture!!!!

Back 41

revise!