• Hormonal control of Ca2 homeostasis W4

Question 1

Parathyroid Hormone

Answer 1

• Key player in Ca2+ homeostasis
• Peptide hormone (84 amino acids) - classified as a protein

Question 2

Parathyroid Hormone secretion

Answer 2

From the parathyroid glands and secretion increases when plasma [ca2+] falls

This hormone acts to increase plasma [ca2+]

Decreased Ca equals increased PTH

Question 3

What is ca2+ monitored by

Answer 3

Directly monitored by the parathyroid cels via Ca-sensing receptors in a neg feedback loop

Question 4

What does Parathyroid Hormone acts on

Answer 4

Bone, kidneys and GIT(indirectly)

Main action on bones

Question 5

Negative feedback loop of calcium monitoring

Answer 5

Secret PTH= increased plasma Ca= decrease PTH secretion

Question 6

Where is the thyroid/parathyroid glands and how many?

Answer 6

At the back of the neck and there are four parathyroid glands within the thyroid tissue

Question 7

Effect of PTH on bone

Answer 7

PTH leads to a release of Ca from the bone to increase plasma Ca levels

Question 8

Two phases of the effect of PTH on the bone

Answer 8

Fast and slow exchange

Question 9

What occurs during fast exchange

Answer 9

Rapid release/uptake of calcium between the bone and the extra cellular fluid from the bones labile pool – surface

• Keeps levels stable
• Minutes
• Controlled by PTH
• Short-term regulation

Question 10

PTH receptors are…

Answer 10

GPCR coupled to Gs

Question 11

What happens during slow exchange?

Answer 11

Calcium is released from deep in the bone by breaking the bone

• Days to weeks
• Involve osteoclasts
• Long-term regulation

Question 12

Effect of PTH on the kidneys

Answer 12

PTH has a direct effect on kidney epithelial cells and promotes calcium retention as well as phosphate excretion

Causes an activation of vitamin D

Question 13

Calcitonin

Answer 13

Is the antagonistic hormone to PTH

Is secreted by C cells of the thyroid gland

Secretion is increased when there is an increase in plasma Ca

It is a polypeptide of 32 amino acids

Receptors are also GPCR that increase CAMP

Question 14

Calcitonin aims to decrease levels of extracellular/plasma calcium by:

Answer 14

Decreasing calcium of movement from the canaliculi fluid into the plasma

Inhibiting osteoclast activity

Inhibiting absorption of calcium and phosphate in the kidney

Question 15

Vitamin D

Answer 15

Is a pre-hormone that following metabolism to active hormones increases calcium absorption in the GIT

It is a steroid like hormone (hydrophobic)

Is synthesised in the skin in response to sunlight and also absorbed from diet

Question 16

Vit D in the liver and kidney

Answer 16

Initially inactive and activated in the liver and kidney

One OH group added in the liver and stored until required

Second OH group added in kidney - caused by PTH