tubular function 2

Question 1

define osmolarity

Answer 1

measure of the osmotic pressure exerted by a solution across a perfect semi-permeable membrane

Question 2

calculating osmolarity

Answer 2

depends on the number of particles not the nature of the particles
all the conc of different solutes added together - each ion counted separately

Question 3

define the minimum and maximum urine osmolarity in humans

Answer 3

50-1200mosmol/l

change massively - depends on how much of the solutes you’re excreting

Question 4

water reabsorption in descending loop

Answer 4

passive
followed by Na and K
because osmolarity of interstitial fluid is high

Question 5

ascending limb reabsorption

Answer 5

chloride is actively reabsorbed
Na passively reabsorbed - because actively pumped out on the other side
bicarb is reabsorbed
impermeable to water - no aquaporins, TJ

Question 6

tubular fluid at end of loop of henle

Answer 6

85% water and 90% na has been reabsorbed

fluid leaving is hypoosmolar

Question 7

loop diuretics

Answer 7

block the Na/K/2Cl transporter into the cell

Na is not reabsorbed despite the conc grad made by the Na/K ATPase

Question 8

What happens to water when there is high salt in the cell

Answer 8

Water enters the cell

Question 9

What happens to water when there is low salt in the cell

Answer 9

Water leaves the cell

Question 10

Regulation of salt and water

Answer 10

They are interrelated

If you increase the salt you also have to increase the water

Question 11

What determin3s the ability to produce concentrated urine

Answer 11

The ratio of medulla:cortex
Higher = more conc urine - larger length of nephron
Also depends on how active the system is

Question 12

permeability of the collecting duct

Answer 12

ascending us impermeable to water

descending limb - permeable to water

Question 13

how can you concentrate urine above normal plasma osmolarity

Answer 13

produce hyperosmolar interstitial fluid

Question 14

explain the mechanisms that lead to the development of the countercurrent multiplier

Answer 14

ascending tubule pump out Na - increase osmolarity of the interstitial fluid
gradient of 200
descending tube recognises this and water moves out of tubule by osmosis - increasing osmolarity of teh descending limb
tubule fluid moves round and the system repeats
less able to create such a high osmolarity at top because there is already a lower osmolarity in the tubule
this forms the osmolarity gradient throughout the medulla

Question 15

effect of urea on the osmolarity gradient

Answer 15

bottom of collecting duct is permeable to urea
it enters the interstitial fluid down conc grad
increase the osmolarity to max
bottom of loop also permeable to urea so it enters here

Question 16

significance of counter current mechanism

Answer 16

allows you to create highly concentrated urine

Question 17

position of urea transporters

Answer 17

UT-A1 - collecting duct
UT-A2 - DCT
UT-A3 - collecting duct
UT-B1 - blood vessel

Question 18

UT-A1/3 KO

Answer 18

reduced urea in medulla - cant leave the CD
cant conc urine
increased intake by 20%
cant reduce water output either

Question 19

UT-A2 KO

Answer 19

very mild phenotype

visible on low protein diet

Question 20

UT-B KO

Answer 20

don’t cycle urea into bv
increased urine production
reduced urine conc ability
weight loss

Question 21

urea transporter mutations in humans

Answer 21

UT-A2 point mutations observed - get rid of more fluid

loss of function in UT-B - reduction in conc ability

Question 22

why doesn’t the blood flow eliminate the gradient

Answer 22

blood flow is another counter-current
vasa recta
permeable to water and solutes
water out, solute in of descending - more concentrated
reverse in ascending limb
oxygen and nutrients are delivered w/o loss of gradient

Question 23

synthesis of vasopressin

Answer 23

in hypothalamus and packaged into granules

secreted form neurohypophesis

Question 24

where dies vasopressin act

Answer 24

bind to the specific receptors - V2 on basolateral mem of principle cells in cd

Question 25

action of vasopressin

Answer 25

insertion of water channels (aquaporins) into mem
increase permeability
mainly aquaporin 2 in luminal membrane
stimulate urea transport form inner medullary collecting duct to ascending limb by increasing UT-A1/3 in cortical collecting duct

Question 26

trigger of ADH

Answer 26

osmoreceptors in hypothalamus =- if >300mOs

marked fall in bp/vol - shock - monitored by baroreceptors/stretch receptor

Question 27

inhibitor of ADH

Answer 27

ethanol

lead to dehydration as urine vol increases

Question 28

series of actions if plasma os is low

Answer 28

hypothalamic osmoreceptors detects it
reduced adh
reduced permeability
increase urine flow rate

Question 29

series of actions if plasma os is high

Answer 29

detected 
ADH released
permeability increase
less urine 
thirst

Question 30

Components of ECF

Answer 30

Transcellular
Interstitial fluid
Plasma
Lymph

Question 31

Chemicals in ECF

Answer 31

High plasma na

Low k

Question 32

Chemicals in intracellular fluid

Answer 32

High k
Low na
high hpo4 2- This balances the low cl-

Question 33

what determines the volume of the ECF

Answer 33

the number of mosmoles in ECF - it causes movement of water in

Question 34

high ECF and bp

Answer 34

increase ECF
increase GFR 
increase ANP and BNP 
reduce ADH 
reduce symp activity - reduce renin - increase Na excretion

Question 35

low ecf and bp

Answer 35

reduce GFR
increase symp activity - increase renin 
recue ANP and BNP 
increase ADH 
increase Na reabsorption