Regulation of Water Balance Flashcards
What is the osmolality of plasma?
280-290 mosmol
What does ADH do?
Increase H2O permeability , concentrating urine
What is diuresis?
Increased production of urine
without ADH how many litres of dilute urine can be produced?
20 L
With ADH how much concentrated urine can be produced?
300mls
What is ADH also known as?
Vasopressin
How many peptides in ADH?
9 - nonapeptide
Where is ADH synthesized?
supraoptic and paraventricular nuclei in the hypothalamus
What is the half of ADH?
15 minutes - degraded in liver and kidney
What is ADH a part of?
Large precursor molecule - 166 aa
Where does ADH move to after synthesis?
to neurohypophysis (posterior pituitary)in axons on hypothalamohypophyseal tract
What happens to ADH during movement?
progressively cleaved
Where is ADH stored after synthesis?
with neurophysin in nerve terminals, released into blood when required
What causes ADH release?
Primary stimulus is plasma osmolality
What is plasma osmolality sensed by?
Osmoreceptors
Where are osmoreceptors linked?
near supraoptic nuclei
What is the threshold for activation of osmoreceptors?
280 mosmol
What happens when osmoreceptors active?
small amount of tonic ADH release - causes big increase in plasma ADH
What can the threshold for osmoreceptors be reset by?
hypovolaemia (low blood volume)
How does Haemodynamics stimulate ADH release?
via baroreceptors (low pressure/volume)
How does haemodynamics respond to ADH release?
less sensitive - exponential response, big changes affect
How can plasma ADH levels be affected?
Through drugs that affect BP
What sympton can cause ADH release?
nausea - instant and profound, plasma ADH increases 1000 fold
What other factors/hormones affect ADH release?
Hypoglycaemia - modest
Hypoxia - carotid chemoreceptors
Angiotensin - osmotic receptors
What do principal cells have on its basal membrane?
V2 receptors (vasopressin/adh)
What is the mechanism of action of ADH?
ADH occupies receptor
activates g protein pathway
adenyl cyclase - cAMP - PKA - aquaporin 2 water channels - apical lumen membrane
What does Aquaporin 2 do?
Causes water permeability to increase - urine concentrated
What is the max urine osmolality?
1400 mosmol
What does volume of urine excretion depend on?
Level of circulating ADH
Amount of solute to be excreted
What is micturation?
urination
Where is urine conveyed from?
renal pelvis to bladder via ureters
How do ureters encourage urine flow?
peristalsis - by pacemaker cells in renal pelvis
What happens when bladder fills?
rugae unfold - little pressure change, pressure rises with volume of urine
What receptors in bladder activate pelvic nerve afferents?
Stretch
What relaxes internal urethral sphincters?
Pelvic nerve efferents
Why do babies have involuntary micturation reflex?
nerve pathways to higher centres underdeveloped
What is micturation influenced by?
Degree of bladder distension
How is voluntary control of micturation achieved?
integration with higher centres - pons via pudendal nerves
What do pudendal nerves do?
Keep external urethral sphincter closed as tonically active
