Calcium Hameostasis

Question 1

What is normal range for calcium?

Answer 1

2.2-2.6 mmol/L

Question 2

What are the roles of calcium in the body?

Answer 2

• Signalling
• Blood clotting
• Apoptosis
• Skeletal strength
• Membrane Excitability

Question 3

What proportion of calcium is distributed in bone?

Answer 3

99%

Question 4

What proportion of calcium is found in ICF?

Answer 4

0.9%

Question 5

What proportion of total body calcium is found in extracellular fluid?

Answer 5

0.1%

Question 6

What are the main forms which calcium exists in in blood?

Answer 6

• Bound to protein
• Ionised/Free
• Bound to anions

Question 7

What proportion of calcium is bound to protein in blood?

Answer 7

40% - 80% albumin, 20% to globulin

Question 8

What can alter the protein binding of calcium in blood?

Answer 8

pH

Question 9

What does acidosis do to free calcium?

Answer 9

Increases free calcium as H+ displaces calcium

Question 10

What does alkalosis do to free calcium levels in the blood?

Answer 10

Decreased plasma calcium due to increased binding sites on protein

Question 11

What is the function of osteoblasts?

Answer 11

Bone building cells - lay down collagen ECM

Question 12

What is the function of osteoclasts?

Answer 12

Bone mobilisation - secrete H+ to dissovle calcium salts and ezymes to digest ECM

Question 13

What is the function of parathyroid hormone?

Answer 13

1. Stimulates osteoclasts - release Ca2+ and phosphate in bone
2. Inhibit osteoblasts
3. Increase Ca2+ reabsorption at the kidneys - decreased excretion
4. Increasing renal excretion of phosphate - elevates free Ca2+ by preventing it from being deposited back in bone
5. Stimulates calcitriol synthesis by the kidneys from vitamin D3 - promotes calcium absorption at the gut and kidney

Question 14

What is PTH released in response to?

Answer 14

Decreased free Ca2+

Question 15

What senses fluctations in calcium levels?

Answer 15

Calcium sensing receptors - on parathyroid chief cells

Question 16

Draw how calcitriol is produced

Answer 16

Question 17

What are dietary sources of vitamin D?

Answer 17

• Fortified milk
• Egg
• Fish oil

Question 18

What is the action of calcitriol?

Answer 18

• Increases absorption of Ca2+ from the gut - In low [Ca2+] situation, increase in PTH, which increases Calcitriol, which increases intestinal absorption
• Facilitates renal reabsorption of Ca2+
• Mobilises calcium stores in bone by stimulating osteoclast activity

Question 19

What is calcitonin?

Answer 19

Peptide hormone produced by thyroid gland

Question 20

What is the main function of calcitonin?

Answer 20

Its main actions are to bind to osteoclasts and inhibit bone resorption as well as ­ renal excretion so preventing a further ­ in Ca2+ .

Question 21

How does cortisol affect calcium balance?

Answer 21

• Inhibits osteoblasts
• Increases renal excretion of Ca2+ and phosphate
• Reduces intestinal absorption of Ca2+ -> increased­ PTH -> increases bone resorption.

These factors together can, over time, produce osteoporosis.

Question 22

How does insulin influence calcium balance?

Answer 22

• Increases bone formation
• Antagonisis the action of cortisol

Question 23

What influence does oestrogen have on calcium balance?

Answer 23

Promotes bone formation via oestrogen receptors on osteoblasts

Question 24

How does prolactin influence calcium balance?

Answer 24

Promotes absoprtion from the gut by stimulating calcitriol synthesis

Question 25

How does growth hormone influence calcium balance?

Answer 25

Constant stimulus for bone formation