L31 Regulation of Haemoglobin and Calcium

Question 1

Which 166 AA glycoprotein is secreted mainly in the kidney and takes effect in the bone marrow?

Answer 1

Erythropoietin (EPO)

Question 2

From where is EPO secreted?

Answer 2

Mostly in the kidneys (80%) but also in the liver.

Mesangial cells and tubule cells secrete EPO

Question 3

What is the stimulus for erythropoiesis?

Answer 3

Hypoxia

Question 4

Describe the mechanism that accompanies erythropoiesis

Answer 4

1. Hypoxia stimulate mesangial/tubular cells to secrete EPO into the plasma
2. EPO stimulates stem cells in the bone marrow to differentiate into proerythroblasts
3. Proerythroblasts develop into erythrocytes

Question 5

What is a downside to synthetic EPO?

Answer 5

Expensive

Question 6

Why is it important to maintain calcium?

Answer 6

Calcium levels affect functioning of excitable cells

Question 7

What are the two forms of calcium in plasma?

Answer 7

Ionised (free) and bound

Question 8

Physiologically, which is the most important form of plasma calcium?

Answer 8

Ionised (free) calcium

Question 9

Total plasma calcium usually amounts to around 2.5mM. How much of this is ionised calcium?

Answer 9

1.25mM

In the blood are equal parts ionised and bound calcium

(1.25mM + 1.25mM = 2.5mM)

Question 10

True or false: Calcium reabsorption in the PCT parallels Na and H2O

Answer 10

True

Majority is passively reabsorbed

Possibly also uses Ca-ATPase transporter and Ca/Na antiport (3 Na for 1 Ca)

Question 11

True or false: 20-25% of filtered calcium is passively reabsorbed in the distal tubule and collecting duct

Answer 11

False

20-25% of filtered calcium is passively reabsorbed in the loop of Henle

5-10% is actively reabsorbed in the distal tubule and collecting duct

Question 12

Which agents regulate calcium reabsorption in the nephron?

Answer 12

PTH and Vitamin D

Question 13

Which 84 AA peptide hormone regulates calcium reabsorption in the nephron?

Answer 13

Parathyroid hormone

Synthesised in principal cells of parathyroid gland

Question 14

True or false: PTH is released in response to decreased plasma calcium levels

Answer 14

True

Question 15

What is the main function of PTH? How does it achieve this goal?

Answer 15

To increase plasma Ca

↑ liberation from bone

↑ reabsorption in nephron

↑ intestinal absorption

Question 16

How does PTH liberate calcium from bone?

Answer 16

Directly increases the number and activity of osteoclasts = ↑ bone resorption = ↑ plasma Ca

Question 17

How does PTH increase intestinal absorption of calcium?

Answer 17

PTH converts circulating form of vit D into calcitriol (active form). Calcitriol acts directly on intestine to increase calcium absorption.

This an indirect way by which PTH increases plasma calcium

Question 18

What is the endogenous antagonist to PTH?

Answer 18

Calcitonin

Question 19

Where is calcitonin produced?

Answer 19

Parafollicular cells of the thyroid gland

Question 20

What is calcitonin release triggered by?

Answer 20

↑ plasma Ca2+

Question 21

What effect does calcitonin have on bone resorption?

Answer 21

Opposes it - promotes laying down of bone