Renal Physiology

Question 1

Trace the flow of filtrate through the nephron

Answer 1

1. Glomerulus/Bowman’s capsule
2. Proximal tubule
3. Descending Loop of Henle
4. Ascending Loop of Henle
5. Distal convoluted tubule
6. Collecting duct

Question 2

What are the two major components that the kidney regulates?

Answer 2

Sodium

Water

Question 3

What is the function of the glomerulus? What components stay in the blood, and what passes into the urine?

Answer 3

Most drugs can pass into the glomerulus, which can then be excreted into the urine.

Normally, larger products like protein and protein-bound drugs stay in the blood (in via the afferent arteriole and out via the efferent arteriole). When damaged, albumin can pass into the urine and is an indicator of renal disease

Question 4

What is the function of the proximal tubule?

Answer 4

Remember this location is closest to Bowman’s Capsule, where filtrate comes into the kidney. This is where the majority of the Na, Cl, Ca and water that were filtered out of the blood are reabsorbed.

Also regulates pH through the exchange of H and H2CO3 ions

Question 5

Bonus: what drug works in the proximal tubule?

Answer 5

SGLT2 Inhibitors, which inhibits the reabsorption of glucose

Question 6

What is the function of the descending Loop of Henle?

Answer 6

Water is reabsorbed into the blood, but Na and Cl are not –> concentrates the filtrate

Question 7

What is the function of the ascending Loop of Henle?

Answer 7

Na (25%) and Cl, and also Ca (25%) are absorbed but water is not

If antidiuretic hormone (vasopressin) is present, water will be re-absorbed into the blood

Question 8

Bonus: what diuretic works in the ascending Loop of Henle?

Answer 8

Loop diuretics, which inhibit the Na/K pump in the ascending Loop of Henle.

• Less Na reabsorption into the blood
• More concentrated Na in filtrate
• Water follows the Na and leaves the blood
• As a consequence, loops also inhibit the reabsorption of Ca back into the blood –> long term use can decrease bone density

Question 9

What is the function of the distal convoluted tubule?

Answer 9

Regulation of K, Na (5% reabsorbed), Ca and H+ ion (pH)

Question 10

Bonus: what diuretic works in the distal convoluted tubule?

Answer 10

1. Thiazide type diuretics, which inhibit the Na/Cl pump in the distal convoluted tubule. They increase Ca reabsorption at the Ca pump here, and long term use has a protective effect on bones.

Remember, only ~5% of Na is absorbed here, which explains why thiazides are weaker diuretics than loops.

2. Aldosterone antagonists also work here

Question 11

What is the function of the collecting duct?

Answer 11

A network of tubules and ducts connecting the nephrons of the kidney to one of the ureters.

Involved in water and electrolyte balance

• influenced by levels of antidiuretic hormone and aldosterone

Question 12

What is the function of aldosterone on renal physiology?

Answer 12

Works in the distal convoluted tubule and the collecting duct:

• Increases Na and water reabsorption
• Decreases K reabsorption

Question 13

Bonus: what is the mechanism of action of aldosterone antagonists?

Answer 13

They work in the distal convoluted tubule and the collecting duct to block the actions of aldosterone:

• Increase the excretion of Na and water into the urine
• Cause the retention of K (hyperkalemia is a common side effect)