Session 4 - Changes in Plasma Volume + Control of BP

Question 1

How may the ECF be expanded?

Answer 1

• If Sodium excretion < intake
• water will be drawn out of the nephron
• blood volume will increase and hence so will BP

Question 2

How may the ECF be contracted?

Answer 2

• If sodium excretion > intake
• Less water will be drawn out of the nephron
• ECF volume drops
• as does blood volume and BP

Question 3

How can increases in sodium concentration in the ECF potentially not affect ECF osmolarity?

Answer 3

• If concentration of sodium in ECF increases then so will volume
• Higher ECF volume means higher cardiac output
• This will increase the amount delivered to the kidneys so more will be excreted

Question 4

Name some of the molecules that sodium is co-transported with in the PCT

Answer 4

• Glucose
• Hydrogen ions
• aa’s
• Phosphate
• Carboxylic acids

Question 5

How does the concentration gradient of the kidney as a whole allow water absorption along the descending limb of the loop of Henle?

Answer 5

There is a concentration gradient going towards the medulla of the kidneys.
As the descending limb travels down into the medulla this drives osmosis in the descending limb

Question 6

What and where is the target for loop diuretics?

Answer 6

The NaKCC2 channel in the ascending limb of the Loop of Henle.

Question 7

What and where do thiazide diuretics target?

Answer 7

The NCC transporter in the DCT

Question 8

What and where do Amiloride diuretics target?

Answer 8

The eNaC transporter in the later DCT

Question 9

What is the main function of the Collecting Duct?

Answer 9

Fine-tuning of the filtrate

Question 10

What is the uptake of water dependent on in the Collceting duct?

Answer 10

Levels of Anti-diuretic hormone present. The more there is the more water will be absorbed

Question 11

How does the sympathetic nervous system cause sodium reabsorption?

Answer 11

• causes vasoconstriction via alpha adrenorceptors
• this decreases the renal blood flow
• this lowers GFR and hence sodium excretion
• also stimulates renin release

Question 12

How does Atrial Natriuretic Peptide effect sodium reabsorption?

Answer 12

• promotes Sodium excretion
• released when atrial cells are stretched more
• increases excretion by causing Afferent arteriole vasodialtion
• increasing GFR and hence sodium excretion

Question 13

How is renin release stimulated?

Answer 13

Decreased perfusion pressure in kidney detected by Baroreceptors
This causes release of renin from granular cells of the Juxtaglomerular apparatus

Question 14

How does Vasoconstriction, caused by angiotensin II stimulate increased sodium reabsorption?

Answer 14

• Afferent and efferent arteriole are vasoconstricted

- GFR reduced and hence more sodium reabsorbed

Question 15

How does the break down of bradykinin cause increased sodium reabsorption?

Answer 15

• bradykinin is a vasodilator
• breaking it down means vessels are more vasoconstricted
• decreased GFR
• more sodium reabsorption

Question 16

Describe the auction of ADH in terms of Aquaporin channels?

Answer 16

• adds more Aquaporin channels to collecting duct

- increases amount of water reabsorbed