Calcium Balance

Question 1

Why are plasma Ca2+ levels important?

Answer 1

• Bone formation
• Muscle contraction
• Insulin release
• Neurotransmission

Question 2

What is an osteoclast?

Answer 2

cells that degrade bone to initiate normal bone remodeling and mediate bone loss in pathologic conditions by increasing their resorptive activity

Question 3

What is an osteoblast?

Answer 3

cells that form bone tissue

Question 4

What is an osteocyte?

Answer 4

cells are highly specialised in nature and are responsible for the maintenance of the bony matrix.

Question 5

What are the steps of bone remodelling?

Answer 5

1. Osteoclasts resorb previously formed bone by secreting H+ and Ca2+ and PO42- are released back into blood
2. Osteoblasts acquire Ca2+ and PO42- from the blood to produce hydroxyapatite that is deposited into the matrix to form mineralised tissue
3. PTH 1,25-dihydroxyvitamin D stimulates RANKL (made by osteoblasts) bind to RANK on osteoclasts -> increase bone resorption
4. OBG (prod by osteoblasts) prevents RANKL from binding to RANK -> decrease bone resorption

Question 6

What are some hormones that favour bone resorption and decreased bone mass?

Answer 6

• PTH (parathyroid hormone)
• Cortisol
• Thyroid hormones

Question 7

What are some hormones that favour bone formation and increased bone mass

Answer 7

• HGH
• Insulin
• Androgens
• IGF-1

Question 8

Summary of Calcium reg.

Answer 8

Question 9

What is PTH secreted by? and what is it stimulated by?

Answer 9

• chief cells of the parathyroid glands
• Low Ca2+ levels stimulate the secretion of PTH and low levels suppress PTH secretion

Question 10

What are the actions of Parathyroid hormone?

Answer 10

• stim. 1,25 dihydroxyvitamin D formation
• directly increases resorption of bone by osteoclasts
• directly increases calcium reabsorption in kidneys

Question 11

What are the actions of 1,25 dihydroxyvitamin D

Answer 11

• stimulates intestinal reabsorption of Ca2+
• stimulates resorption of bone by osteoclasts

Question 12

What does Calcitonin do?

Answer 12

inhibits osteoclast activity in bones

Question 13

What is Osteoporosis?

Answer 13

• both bone matrix and minerals lost as a result of imbalance between bone resorption and bone formation
• results in decreased bone mass and strength so fragile bones

Question 14

What is Hypercalcaemia and what is it caused by?

Answer 14

= too much calcium
- increased bone resorption, increased Ca2+ absorption from the gut and decreased renal Ca2+ excretion
- caused by hyperparathyroidism -> increased PTH and 1,25 -dihydroxyvitamin D from kidney

Question 15

What are symptoms of hypercalcaemia?

Answer 15

• fatigue
• weakened muscles
• pain
• gastric effects

Question 16

What is hypocalcaemia and what is caused by?

Answer 16

= too little calcium
- decreased bone resorption, decreased Ca2+ from gut and increased Ca2+ excretion
- caused by loss of parathyroid gland function leading to decreased PTH levels and 1,25-dihydroxyvitamin D
- leads to increased excitability of nerves and muscles