Exam - Urine Formation

Question 1

how does the kidney regulate water balance

Answer 1

dilutes or concentrated urine in accordance with hydration state

Question 2

how does water movement occur

Answer 2

by osmosis through p ores

Question 3

what does the dilution/concentration of urine depend on

Answer 3

the osmolarity of interstitial and tubular fluids in the kidney

Question 4

what increases osmolarity from the medulla to the pelvis in kidneys

Answer 4

handling of ions, urea and water - allows urine to be secreted at a higher osmolarity than plasma

Question 5

what are the 3 components

Answer 5

hypertonic medullary interstitium
dilution of the tubule fluid in the thick ascending limb and distal convoluted tubule
variability in water permaibilty of collecting duct in response to vasopressin

Question 6

what does hypertonic medullary intersitium allow

Answer 6

concentrated urine

Question 7

what does the dilution of the tubule fluid in the thick ascending limb and the distal convoluted tubule allow for

Answer 7

diluted urine

Question 8

what is the counter-current multiplier

Answer 8

the loop of Henle has 2 parallel limbs that run in opposite directions

Question 9

what are the 2 limbs in the loop of henle

Answer 9

descending (cortex –> medulla)
ascending (medulla –> cortex)

Question 10

what do epithelial cells in the ascending limb of the loops of henle do

Answer 10

actively pump Na+ accompanied by secondary transport of K+ and Cl-

Question 11

what is the ion ratio in the ascending limb

Answer 11

1 Na+
1 K+
2 Cl-

Question 12

characteristic of the epithelial cells in the ascending limb

Answer 12

apical membrane is impermeable to water

Question 13

characteristic of epithelial cells in the descending l limb

Answer 13

no active pumps, highly permeable to water

Question 14

where does tubular fluid pass through distal tubule/collecting duct

Answer 14

from cortex to medulla = increase in interstitial osmolarity

Question 15

when will water be allowed to exit the duct through epithelial cells

Answer 15

only if ADH is present

Question 16

what does ADH stimulate

Answer 16

formation of aquaproins on the apical membrane of epithelial cells

Question 17

what happens when ADH decreases

Answer 17

number of aquaporins decreases and water is not reabsorbed

Question 18

where is ADH produced

Answer 18

hypothalamus

Question 19

where is ADH stored

Answer 19

posterior pituitaru

Question 20

what sense plasma osmotic pressure

Answer 20

hypothalamic osmoreceptors

Question 21

what does an increase in osmolarity do

Answer 21

increase stimulus for ADH release

Question 22

what does an increase in ADH release do

Answer 22

acts via cAMP/protein kinase to insert aquaporins in distal tubules and collecting ducts

Question 23

what do hypothalamic osmoreceptors send

Answer 23

excitatory signals to thirst centres in the hypothalamus

Question 24

what does urea participate in

Answer 24

maintaining the high interstitial osmolarity in the medulla

Question 25

what does urea account for

Answer 25

approx 40% of the osmolarity of the medullary interistitum

Question 26

how does urea recirculate

Answer 26

collecting duct epithelium is moderately permeable to urea –> moves into intersituium–> re-enters ascending limb of loop of henle

Question 27

what does the recirculation of urea help ensure

Answer 27

that the required amount of urea is excreted even if urine volume is low

Question 28

what do the capillaries of the vasa recta make

Answer 28

hairpin bends similar to the loop of Henle

Question 29

what does the osmolarity in the capillaries follow

Answer 29

the medulla gradient

Question 30

what is the result of the vasa recta

Answer 30

ions and urea responsible for the gradient along the loop of Henle remain in the interstitial fluid - if mot, no osmotic gradient would occur

Question 31

what percentage of body mass is water

Answer 31

60-70%

Question 32

where is half the water present

Answer 32

in cells

Question 33

where is the rest of water present

Answer 33

interstitial fluid
blood plasma
lymphs

Question 34

where is movement of water easy

Answer 34

between compartment

Question 35

what is water movement driven by

Answer 35

hydrostatic pressure
osmotic presseure