Plasma Osmolarity

Question 0

Describe some of the effects of ADH

Answer 0

Vasoconstriction of glomerulus
Increased Na, Cl, K reabsorption in ascending loop
Increased water reabsorption in late DT
Increased water reabsorption and K+ secretion in cortical CD

Question 1

Describe the regulation of body fluid osmolarity in terms of responses to water deprivation and drinking

Answer 1

Water intake > water excretion = plasma osmolarity decreases
Water intake < water excretion = plasma osmolarity increases

Question 2

Describe the handling of water by the nephron

Answer 2

PCT - 67% 
Descending LoH - 10-15%
Ascending LoH - 0%
DCT - 0%
Collecting duct - 5-24%

Question 3

Distinguish the factors that regulate thirst and cause secretion of ADH

Answer 3

Sensed by hypothalamic osmoreceptors (OVLT)
Water deprivation:
Efferent pathway - ADH 
Effector - kidney 
Affect on - renal water excretion 
Release of ADH from posterior pituitary 
Thirst:
Efferent pathway - thirst
Effector - brain (drinking behaviour)
Affect on - water intake
Need ingestion of water

Question 4

Describe the role of ADH and the production of hypo and hyperosmotic urine

Answer 4

Aquaporin 3+4 always on basolateral membrane
Aquaporin 2 inserted into apical membrane
Decreased ADH = diuresis
Increased ADH = anti-diuresis

Question 5

Describe the syndrome of the inappropriate secretion of ADH (SIADH) and its potential consequence

Answer 5

Excessive release of ADH from posterior pituitary
Dilutional hyponatremia
Increase in total body fluid

Question 6

Describe the condition of diabetes insipidus and its treatment

Answer 6

Pituitary gland doesn’t produce enough ADH/acquired sensitivity –> diuresis
Treatment - ADH injection/nasal spray