Regulation of Water Balance

Question 1

What is the osmolality of plasma?

Answer 1

280-290 mosmol

Question 2

What does ADH do?

Answer 2

Increase H2O permeability , concentrating urine

Question 3

What is diuresis?

Answer 3

Increased production of urine

Question 4

without ADH how many litres of dilute urine can be produced?

Answer 4

20 L

Question 5

With ADH how much concentrated urine can be produced?

Answer 5

300mls

Question 6

What is ADH also known as?

Answer 6

Vasopressin

Question 7

How many peptides in ADH?

Answer 7

9 - nonapeptide

Question 8

Where is ADH synthesized?

Answer 8

supraoptic and paraventricular nuclei in the hypothalamus

Question 9

What is the half of ADH?

Answer 9

15 minutes - degraded in liver and kidney

Question 10

What is ADH a part of?

Answer 10

Large precursor molecule - 166 aa

Question 11

Where does ADH move to after synthesis?

Answer 11

to neurohypophysis (posterior pituitary)in axons on hypothalamohypophyseal tract

Question 12

What happens to ADH during movement?

Answer 12

progressively cleaved

Question 13

Where is ADH stored after synthesis?

Answer 13

with neurophysin in nerve terminals, released into blood when required

Question 14

What causes ADH release?

Answer 14

Primary stimulus is plasma osmolality

Question 15

What is plasma osmolality sensed by?

Answer 15

Osmoreceptors

Question 16

Where are osmoreceptors linked?

Answer 16

near supraoptic nuclei

Question 17

What is the threshold for activation of osmoreceptors?

Answer 17

280 mosmol

Question 18

What happens when osmoreceptors active?

Answer 18

small amount of tonic ADH release - causes big increase in plasma ADH

Question 19

What can the threshold for osmoreceptors be reset by?

Answer 19

hypovolaemia (low blood volume)

Question 20

How does Haemodynamics stimulate ADH release?

Answer 20

via baroreceptors (low pressure/volume)

Question 21

How does haemodynamics respond to ADH release?

Answer 21

less sensitive - exponential response, big changes affect

Question 22

How can plasma ADH levels be affected?

Answer 22

Through drugs that affect BP

Question 23

What sympton can cause ADH release?

Answer 23

nausea - instant and profound, plasma ADH increases 1000 fold

Question 24

What other factors/hormones affect ADH release?

Answer 24

Hypoglycaemia - modest
Hypoxia - carotid chemoreceptors
Angiotensin - osmotic receptors

Question 25

What do principal cells have on its basal membrane?

Answer 25

V2 receptors (vasopressin/adh)

Question 26

What is the mechanism of action of ADH?

Answer 26

ADH occupies receptor
activates g protein pathway
adenyl cyclase - cAMP - PKA - aquaporin 2 water channels - apical lumen membrane

Question 27

What does Aquaporin 2 do?

Answer 27

Causes water permeability to increase - urine concentrated

Question 28

What is the max urine osmolality?

Answer 28

1400 mosmol

Question 29

What does volume of urine excretion depend on?

Answer 29

Level of circulating ADH

Amount of solute to be excreted

Question 30

What is micturation?

Answer 30

urination

Question 31

Where is urine conveyed from?

Answer 31

renal pelvis to bladder via ureters

Question 32

How do ureters encourage urine flow?

Answer 32

peristalsis - by pacemaker cells in renal pelvis

Question 33

What happens when bladder fills?

Answer 33

rugae unfold - little pressure change, pressure rises with volume of urine

Question 34

What receptors in bladder activate pelvic nerve afferents?

Answer 34

Stretch

Question 35

What relaxes internal urethral sphincters?

Answer 35

Pelvic nerve efferents

Question 36

Why do babies have involuntary micturation reflex?

Answer 36

nerve pathways to higher centres underdeveloped

Question 37

What is micturation influenced by?

Answer 37

Degree of bladder distension

Question 38

How is voluntary control of micturation achieved?

Answer 38

integration with higher centres - pons via pudendal nerves

Question 39

What do pudendal nerves do?

Answer 39

Keep external urethral sphincter closed as tonically active