kidney function 2

Question 1

what is the definition for clearance ?

Answer 1

the volume of plasma that is cleared of a substance in a given time

Question 2

how is renal clearance calculated ?

Answer 2

(conc in urine x volume of urine/min ) divided by conc of plasma

Question 3

why is the clearance of inulin used to measure GFR ?

Answer 3

• it is freely filtered
• not reabsorbed
• not secreted
• not metabolised
• easily measured

Question 4

why isnt inulin used clinically to measure GFR ?

what is used instead ?

Answer 4

has to be adminstered via IV

use creatinine instead but isnt exact

Question 5

what does para-aminohippuric acid show ?

Answer 5

renal plasma flow

Question 6

how is renal blood flow calculated ?

Answer 6

renal plasma flow divided by plasma % in blood

Question 7

what is osmolality ?

what is it measured in ?

Answer 7

a measure of water conc. higher the solution osmolality = the lower the water conc
mosm/kg

Question 8

what is osmolarity ?

what is it measured in ?

Answer 8

a measure of water conc. the higher the solution osmolarity the lower the water conc

Question 9

what word is used to describe physiological fluids ?

Answer 9

osmolality + osmolarity can be used interchangeably

osmolality is preferred because it is independent of temp

Question 10

what are the 3 types of urine that the kidney can make ?

Answer 10

• dilute
• iso-osmotic
• concentrared

Question 11

what is the main osmotically active solute in plasma ?

Answer 11

sodium

Question 12

what is the average sodium plasma conc ?

Answer 12

135-145 mmol/l

Question 13

how can you calculate the amount of sodium filtered ?

Answer 13

plasma Na conc x GFR

Question 14

how can you calculate the amount of sodium filtered ?

Answer 14

plasma Na conc x GFR

Question 15

how is sodium reabsorbed in the loop of Henle

Answer 15

• none absorbed in descending limb

- passive in thin ascending limb

Question 16

plasma is electroneutral how is this maintained ?

Answer 16

by the Na + Cl conc

Question 17

where is the main site of Na reabsorption

how much is reabsorbed here ?

Answer 17

proximal tubule

65%

Question 18

how is Na absorbed in proximal tubule ?

Answer 18

• Na/K ATPase pump : actively pumps Na into interstitial fluid
• Na/H exchanger (NHE3) : drives Na out of lumen into cell
• Na nutrient symporter : Na moves into cell via conc gradient

Question 19

how is Na absorbed in the thick ascending limb ?

what % of Na is absorbed here ?

Answer 19

25 %

• Na/K ATPase pump : Na into interstitial fluid
• Na/K/2Cl cotransporter : Na pumped into cell

Question 20

how is Na absorbed in distal tubule ?

how much is reabsorbed ?

Answer 20

2-5%

• Na/K ATPase pump
• Na/Cl cotransporter

Question 21

how is Na reabsorbed in collecting duct ?

what % is reabsorbed ?

Answer 21

5%

• Na/K ATPase pump
• ENa channel : pumps Na in via its conc gradient

Question 22

what are the 2 cell types in ion transport ?

Answer 22

• principal cells ( Na transport )

- intercalated cells ( H transport)

Question 23

what does water reabsorption depend on ?

Answer 23

• osmosis
• sodium reabsorption
• tubule permeability

Question 24

how is filtrate volume reduced but osmolality kept the same ?

Answer 24

coupling of water reabsorption to sodium reabsorption in proximal tubule

Question 25

how can urine that is more concentrated than plasma be produced ?

Answer 25

• separate Na + water reabsorption

- have renal medulla interstitial fluid with high osmolality = water reabsorption

Question 26

where does water separation from sodium occur ?

Answer 26

loop of Henle

Question 27

how is water separated from Na ?

Answer 27

• have counter current flow in loop
• leads to different absorptions of salt to water
• only salts absorbed in ascending limb + only water absorbed in descending limb

Question 28

how does the loop of Henle make a renal medulla interstitial fluid with high osmolality ?

Answer 28

• sodium gradient of increasing osmolality
• countercurrent multiplier
• vasa recta

Question 29

what does it mean when the loop of Henle is referred to as a counter-current multiplier ?

Answer 29

it increases the osmotic gradient between the tubular filtrate + the medullary interstitial fluid

Question 30

what is a benefit of the vasa recta ?

Answer 30

supplies blood without washing away the gradient loop of Henle created

Question 31

what 2 components contribute to the renal medulla interstitial fluid ?

Answer 31

• urea

- sodium

Question 32

what are the stop of urea handling in the kidney ?

Answer 32

• freely filtered in renal corpuscle
• passively reabsorbed in proximal tubule
• secreted via urea transporters in loop of Henle
• reabsorbed via urea transporters in collecting duct

Question 33

what is urea recycling ?

Answer 33

refers to the secretion + reabsorption of urea

Question 34

how is urea reabsorption controlled ?

Answer 34

hormonally

Question 35

what are the functions of the loop of Henle ?

Answer 35

• separate sodium + water
• reabsorb more sodium than water
• create a gradient of increasing osmolality inn the medullary interstitial fluid

Question 36

what is water reabsorption at the collecting duct dependent on ?

Answer 36

anti-diuretic hormone (ADH)

Question 37

describe the action of ADH on collecting duct :

Answer 37

• ADH released from pituatry gland
• bind to v2 receptor on collecting duct
• this cause AQP2 to move towards edge of collecting duct (by using cAMP)
• AQP2 opens + allows water in

Question 38

what effect does ADH have on urine ?

Answer 38

makes it more concentrated

Question 39

what does concentrated urine depend on ?

Answer 39

• high osmolality of renal medulla interstitiual fluid

- permability of collecting duct