regulation of osmolarity

Question 1

what is water regulation controlled by

Answer 1

ADH (vasopressin)

Question 2

where is ADH synthesised

Answer 2

in the supraoptic an dparaventricular nuclei of the hypothalamus in brain

Question 3

where is ADH released from

Answer 3

posterior pituitary

Question 4

what effects ADH secretion

Answer 4

primary control is plasma osmolarity

also ECF volume

Question 5

what happens to ADH secretion when plasma osmolarity increases

Answer 5

increase release of ADH

Question 6

what are changes in neuronal discharge mediated by

Answer 6

osmoreceptors

Question 7

osmoreceptors: increased osmolairy

Answer 7

H2O leaves cell
cell shrinks - stretch sensitive ion channel activated
inc neural dischare
inc ADH secretion

Question 8

osmoreceptors: decreased osmolarity

Answer 8

H2O enters cell
cell swells
decrease neural discharge
dec ADH secretion

Question 9

normal plasma osmolality

Answer 9

280-290mOsm/kg H2O

regulated very preciscely

Question 10

why ‘effecitive’ osmolarity

Answer 10

an increase in osmolarity that does not cause an increase in tonicity is ineffective in causing increase in ADH

solutes that can penetrate membranes move together with water and don’t produce any ‘osmotic drag’ or tonictiy

Question 11

what does amount of urine produced depend on

Answer 11

[ADH]

amount of solute to be excreted

Question 12

ingestion of hypertonic solutions (e.g. seawater)

Answer 12

increase solute load to be excreted –> inc urine flow –> dehydration as more water required to excrete solute load than was ingested with it

Question 13

what does ADH act on to control permeability collecting duct

Answer 13

H2O channels in luminal membrane (aquaporins)

Question 14

if ADH is present

Answer 14

water is able to leave collecting duct

this means cortical CD becomes equilibrated with that of cortical interstitium ie 300

Question 15

with maximal ADH

Answer 15

produce small volume of highly concentrated urine

• relatively less of filtered water than solute
• compensate for water deficit

Question 16

absence of ADH

Answer 16

collecting duct impermeable to water

large volume of dilute urine is excreted
-compensate for water excess

Question 17

role of urea

Answer 17

in presence of ADH, water moves out CF and greatly concentrates urea. CD is relatively permable to urea, esp at medullary tips

as urea approaches medullary tips it moves out down conc gradien into interstitium where it acts to reinforce the interstition gradient in the region of asc loops of henle

Question 18

urea recycling during maximum anti-diuresis

Answer 18

in anti-diuresis with high levels ADH, urea is retained in order to save water and reinforce medullary gradient at ascending limb LoH

ureaemia occurs

Question 19

what would happen iif urea wasnt reabsorbed

Answer 19

it would remain in tubule and exert osmotic effects to hold water in tubule and reduce potential for rehydration

Question 20

how does ECF volume effect ADH secretion

Answer 20

inc ECF volume –> less ADH

dec ECF volume –? more ADH

Question 21

where are low P receptors located

Answer 21

L and R atria

great veins

Question 22

where are high P receptors located

Answer 22

carotid and aortic arch baroreceptors

Question 23

relationship between ADH secertion and discharge of stretch P receptors

Answer 23

inverse relationship between rate of ADH secretion and rate of discharge of stretch receptor afferents in the low and high P areas of circulation

Question 24

other stimuli affecting ADH: more ADH

Answer 24

pain 
emotion 
stress
excercise
nicotine 
morphine

Question 25

other stimuli affecting ADH: less ADH

Answer 25

alcohol

Question 26

diabetes insipidu s

Answer 26

ADH deciciency