Regulation of Osmolarity

Question 1

another name for ADH

Answer 1

vasopressin

Question 2

site of vasopressin synthesis

Answer 2

supraoptic and paraventricular nuclei of hypothalamus, secreted from posterior pituitary

Question 3

where is vasopressin stored

Answer 3

in the posterior pituitary

Question 4

what does ADH stand for

Answer 4

anti-diuretic hormone

Question 5

what receptors of the anterior hypothalamus mediate ADH secretion

Answer 5

osmoreceptors

Question 6

what stimuli trigger ADH release

Answer 6

high osmolarity of plasma and low BP detected by atrial receptors

Question 7

process of osmoreceptor reacting to osmolarity changes

Answer 7

high plasma osmolarity –> H2O out of cell –> cell shrinks –> stretch sensitive ion channel activated –> ADH secretion stimulated

Question 8

true/false ADH regulation of osmolarity is rapid and precise

Answer 8

true - it has a half life of only 10 minutes so must act fast. only 2.5% increase of osmolality will produce a 10x increase in ADH secretion

Question 9

ingestion of hypertonic solutions has what effect

Answer 9

increased solute to be excreted –> increased H2O excreted –> dehydration

Question 10

in what part of the nephron does ADH has its effect on water regulation

Answer 10

collecting duct

Question 11

what does ADH do to the collecting duct to increase water resorption

Answer 11

increases permeability of collecting duct cells to H2O

Question 12

mechanism of ADH on collecting duct cell

Answer 12

ADH binds to cell –> cAMP messenger –> cell inserts AQP2 water pores into duct side membrane –> water absorbed through pores by osmosis into blood

Question 13

H2O channels in membrane

Answer 13

aquaporins

Question 14

when maximum ADH is secreted what happens to the osmolality of the collecting duct

Answer 14

H2O is very permeable and so when passing through the medulalry interstitium the collecting duct becomes equilibrated it.

The collecting duct is very concentrated at the tip of the medulla

Question 15

where does water removed from collecting duct in medulla go

Answer 15

reabsorbed into vasa recta by it oncotic pressure

Question 16

oncotic pressure of medullary vasa recta is higher/lower than normal (300)

Answer 16

higher - it has lost water to the interstitial gradient

Question 17

when ADH is absent what happens to the concentration of excreted urine

Answer 17

it is very low and dilute, lots of water because the ADH hasn’t been there making the collecting duct permeable to H2O

Question 18

urea is permeable/impermeabe to collecting duct cell membranes

Answer 18

permeable

Question 19

where is urea most permeable along the collecting duct

Answer 19

at the medullary tips

Question 20

what is antidiuresis

Answer 20

a state of dehydration and trying to reabsorb water at kidneys?

Question 21

effect of ADH on urea permeability

Answer 21

increases it

Question 22

what is the effect of urea being reabsorbed into the interstitium

Answer 22

reinforces the interstitial gradient around ascending loop of henle to maintain osmotic force moving across water through the pores made via ADH

Question 23

effect of ECF volume on ADH secretion

Answer 23

high ECF volume reduces ADH levels

Question 24

low pressure receptors

Answer 24

monitor return of blood in left and right atria

Question 25

high pressure receptors

Answer 25

carotid and aortic arch baroreceptors

Question 26

what receptors will respond first to ECF volume decrease

Answer 26

atrial receptors (low pressure)

Question 27

atrial receptor response to low ECF volume

Answer 27

low ECF volume --> low atrial receptor activity --> reduced inhibition of ADH via vagus --> ADH release

Question 28

what cardiovascular trigger will create a carotid and aortic receptor response

Answer 28

change in mean blood pressure

Question 29

through which nerve do the atrial receptors inhibit ADH release

Answer 29

the vagus nerve

Question 30

if someone is stressed, exercising or in pain, will ADH secretion go up or down

Answer 30

up

Question 31

ADH is suppressed by what drink

Answer 31

alcohol

Question 32

3 key controls of ADH release

Answer 32

1. high plamsa osmolarity detected by hypothalamic osmoreceptors 2. low blood volume detected by atrial stretch receptors 3. decreased blood pressure detected by carotid and aortic baroreceptors

Question 33

what is diabetes insipidus

Answer 33

an ADH deficiency

Question 34

what is the urine like in diabetes insipidus

Answer 34

very dilute, no ADH doing water reabsorption

Question 35

why does someone with diabetes insipidus need to drink lots

Answer 35

because they are not reabsorbing H2O from urine so plasma osmolarity is low. this stimulates thirst

Question 36

name for diabetes insipidus where collecting duct is insensitive to ADH

Answer 36

peripheral DI

Question 37

name for diabetes insipidus where hypothalamic region is malfunctioning and ADH is not produced

Answer 37

central DI

Question 38

which type of diabetes insipidus is usually secondary to hypercalcaemia or hypokalaemia

Answer 38

peripheral (imbalance of these ions affects sensitivity to ADH)

Question 39

name of the collecting duct ADH receptors

Answer 39

V2