Antidiuretic hormone (Vasopressin)

Question 1

What stimulates vasopressin (ADH) release?
a) High plasma osmolarity or low blood pressure
b) Low plasma osmolarity and high BP
c) High sodium and high potassium
d) High glucose and low oxygen

Answer 1

a) High plasma osmolarity or low blood pressure

Explanation: ADH is released in response to high plasma osmolarity (dehydration) or decreased blood volume/pressure.

Question 2

Where does vasopressin act in the nephron?
a) Proximal tubule
b) Loop of Henle
c) Distal convoluted tubule
d) Collecting duct

Answer 2

d) Collecting duct

Explanation: Vasopressin acts on principal cells in the collecting duct, increasing water reabsorption by inserting aquaporin-2 channels.

Question 3

What is the mechanism of ADH action?
a) Activates aquaporin-1 on basolateral side
b) Binds V2 receptors → cAMP → AQP2 insertion on apical membrane
c) Binds to aldosterone receptors in the nucleus
d) Stimulates Na+/K+ ATPase directly

Answer 3

b) Binds V2 receptors → cAMP → AQP2 insertion on apical membrane

Explanation: ADH binds V2 receptors on basolateral membrane, triggering a cascade that inserts AQP2 channels on the apical membrane for water reabsorption.

Question 4

What effect does vasopressin have on urine?
a) Increases volume and decreases osmolarity
b) Decreases volume and increases osmolarity
c) Decreases volume and increases concentration
d) Increases volume and concentration

Answer 4

c) Decreases volume and increases concentration

Explanation: ADH promotes water reabsorption, concentrating urine and reducing volume.

Question 5

Which condition is characterized by insufficient vasopressin action?
a) Diabetes mellitus
b) Addison’s disease
c) Diabetes insipidus
d) Conn’s syndrome

Answer 5

c) Diabetes insipidus

Explanation: Diabetes insipidus involves ADH deficiency or resistance, leading to excessive water loss and dilute urine.