Session 11 - Calcium Metabolism

Question 1

What is the normal range for calcium?

Answer 1

2.2 - 2.5 mM/l

Question 2

What is calcium used for?

Answer 2

Nerve transmissions (release of synaptic vesicles)
Builds and maintains bone (prevents osteoporosis)
Regulates heart rhythm
Assists blood clotting (released by platelets and aids carboxylation of glutamine)
Muscle contraction (released from sarcoplasmic reticulum and binds with TnC)
Kidney function

Question 3

Give three hormones involved in control of calciu levels in serum

Answer 3

Parathyroid Hormone
Vitamin D (calcitriol)
Calcitonin

Question 4

What does PTH do?

Answer 4

raises serum calcium.N.B. parathyroid glands located on the posterior wall of the thyroid gland.

Question 5

What does vitamin D do?

Answer 5

produces calcitriol which raises serum calcium

Question 6

What does calcitonin do?

Answer 6

produced by the thyroid gland and lowers serum calcium, however, seems inactive in humans

Question 7

What are three places PTH and Calcitriol have an effect?

Answer 7

Bone, kidney, gut

Question 8

What effects does PTH have in bone?

Answer 8

Induces osteoblasts to synthesise and secrete cytokines on cells surface
Cytokines stimulate differentiation and activity of osteoclasts and protects them from apoptosis
PTH decreases osteoblast activity – bony surface now exposed to osteoclasts
– clasts secrete acid which breaks down bone
Ca2+ and Pi released into extracellular fluid

Question 9

What effect does PTH have in kidney?

Answer 9

Prevents kidney stones
PTH increases Ca2+ reabsorption and reduces its excretion
Pi removed from circulation

Question 10

What effect does PTH have in gut?

Answer 10

PTH stimulates conversion of vitamin D, in kidney, to its active form Calcitriolwhich increases uptake of Ca2+ from the gut

Question 11

What effect does calcitriol have on bone?

Answer 11

Induces osteoblasts to synthesise and secrete cytokines on cells surface
Cytokines stimulate differentiation and activity of osteoclasts and protects them from apoptosis
PTH decreases osteoblast activity – bony surface now exposed to osteoclasts
– clasts secrete acid which breaks down bone
Ca2+ and Pi released into extracellular fluid

Question 12

Wjat effect does calcitriol have on kidney?

Answer 12

Decreases urinary loss of Ca2+ by stimulating reabsorption

Question 13

What effect does calcitriol have on gut?

Answer 13

1. Active uptake of Ca2+ on brushborder of small intestine (greatest in the duodenum and jejunum)
2. Transcellular transport with CaBP carrier
3. Endocytosis and exocytosis of Ca2+ and CaBP comples

Question 14

How does PTH interact with vitamin D, and what does this enable?

Answer 14

PTH stimulates the conversion of vitamin D to its active form (calcitriol) by stimulating renal C-1 hydroxylase activity. Enables calcitriol to oversee the absorption of Ca2+ in the gut.

Question 15

Explain regulation of PTH and vitamin D

Answer 15

Changes in [Ca2+] alter PTH and vitamin D activity via negative feedback

Chief cells (parathyroid) has unique calcium protein receptors on the cell surface; calcium binds; reduced camp; reduced PTH release

Question 16

What is the significance of renal function on calcium metabolism

Answer 16

Prevents the occurrence of kidney stones mainly by the action of PTH

Kidneys are able reabsorb Ca2+ which has been filtered

Question 17

What are the causes of hypercalcaemia?

Answer 17

Malignancy: tumours produce PTHrP which activates osteoclasts but NOT renal C-1 hydroxylase

Question 18

What are the symptoms of hypercalcaemia?

Answer 18

Kidney stones
Constipation
Dehydration (increased urine output due to high ion concentration)
Kidney damage
Tiredness (neurologic)
Depression (neurologic)

Question 19

What are the causes of hypocalcaemia?

Answer 19

Hypoparathyroidism (uncommon)

Accidental surgical removal of parathyroid gland

Question 20

What are the symptoms of hypocalcaemi?

Answer 20

Rickets/osteomalacia – pliable bones
Hyper-excitability in the nervous system
Hyper-excitability in the neuromuscular junction – paraesthesia (burning and prickling sensation in the extremities)
Tetany – paralysis – convulsions