Session 6 - Changes In Plasma Osmolarity + Diuretics

Question 1

What are change in plasma osmolarity detected by?

Answer 1

Hypothalamic Osmoreceptors

Question 2

Where are the receptors that detect plasma osmolarity changes located specifically?

Answer 2

Organum Vasculoum of the Laminae Terminalis (OVLT)

Question 3

What are the two efferent pathways which work to concentrate urine when stimulated by the Hypothalamic osmoreceptors?

Answer 3

ADH and thirst

Question 4

Which part of the nephron is the major site for water reabsorption and which aquaporin is situated here?

Answer 4

PCT

AQP1

Question 5

Describe AQP1

Answer 5

A channel allowing the movement of water in the kidneys. It spans both the apical and basolateral membranes, allowing the water to move straight from the tubule to the intersticium

Question 6

Which gradient drives water reabsorption in the descending loop of henle?

Answer 6

Corticopapillary Gradient

Question 7

How is water reabsorbed in the ascending loop of henle?

Answer 7

It isn’t

Question 8

Which Aquaporin channels are present in the collecting duct?
And what stimulates there expression?

Answer 8

AQP2 on apical surface and AQP3+4 on basolateral surface

ADH

Question 9

What is the purpose of the Vasa recta?

Answer 9

Maintain the corticopapillary gradient (not create)

Question 10

What is the specific action of ADH on collecting duct cells? (Relating to Aquaporin channels)

Answer 10

Causes the insertion of AQP2 channels into the apical membrane allowing for reabsorption of water in this region

Question 11

What is the specific action of ADH on collecting duct cells? (In terms of urea)

Answer 11

Increases permeability of cells to allow urea to be recycled and water reabsorption to be increased

Question 12

How does urea recycling allow increased water reabsorption?

Answer 12

• Urea reabsorbed in collecting duct cells, water follows
• Urea then moves down conc gradient into ascending limb lumen
• water cannot follow but osmolarity has now increased
• urea is then absorbed again and water follows (urea recycled with more water absorbed)

Question 13

What does SIADH stand for?

Answer 13

Syndrome of Innapropiate ADH secretion

Question 14

What are some of the symptoms of hyponatraemia?

Answer 14

• nausea and vomiting
• restlessness and irritability
• Headaches and confusion
• muscle weakness, lethargy and fatigue
• loss of appetite
• seizures and potential coma

Question 15

How do some diuretics cause Hypokalaemia?

Answer 15

• Decreasing ECF activates RAAS system
• Increased sodium reabsorption
• Increased potassium excretion
• Hypokalaemia

Question 16

How can carbonic anhydrase inhibitors cause a metabolic acidosis?

Answer 16

• Less HCO3- absorbed
• Less protons are buffered in blood
• pH falls
• metabolic acidosis

Question 17

Give an example of a loop diuretic?
Where do loop diuretics act?
And on what specific channel?

Answer 17

• Furosemide + Bumetanide
• Loop of Henle
• Na-K-2Cl channel

Question 18

Give an example of a Thiazide diuretic?
Where do these act?
And on what channel specifically?

Answer 18

• Bendroflumethiazide
• Early DCT
• Block Na-Cl transporter

Question 19

Give an example a Potassium sparing diuretics.

Where do these act?

Answer 19

• Amiloride

- Late DCT

Question 20

Give an example of an Aldosterone Antagonist.

Where does this act?

Answer 20

• Spironolactone

- Late DCT