Regulation of calcium and phosphate

Question 1

What is the most abundant metal in the body?

Answer 1

Calcium

Question 2

What meets all requirements for calcium?

Answer 2

Diet

Question 3

What percentage of calcium is found in skeleton and teeth?

Answer 3

99%

Question 4

What form is calcium in in bone?

Answer 4

Calcium hydroxyapatite crystals

Question 5

Is extracellular calcium tightly regulated?

Answer 5

Yes

Question 6

What is the biologically active component of calcium?

Answer 6

‘Unbound’ ionised calcium

Question 7

What percentage of calcium is intracellular?

Answer 7

1%

Question 8

What percentage of calcium is extracellular?

Answer 8

0.1%

Question 9

What hormones increase serum calcium?

Answer 9

Parathyroid hormone
Vitamin D

Question 10

What hormones decrease serum calcium?

Answer 10

Calcitonin- can reduce calcium if injected, but generally in body has not overall effect

Question 11

What are the names of the two types of vitamin D?

Answer 11

Ergocalciferol-
Cholecalciferol-

Question 12

Where is Ergocalciferol derived from?

Answer 12

UV irradiation of plants

Question 13

Where is Cholecalciferol derived from?

Answer 13

UV irradiation of skin (animals and humans) and certain foods (oily fish, egg yolks)

Question 14

What is calcitriol?

Answer 14

The active form of vitamin D

Question 15

What is the major role of calcitriol?

Answer 15

↑ Ca2+ and
PO43- reabsorption from the GUT

Question 16

What cells secrete PTH?

Answer 16

Chief cells in parathyroid gland

Question 17

What is PTH secreted as?

Answer 17

large precursor (pre-pro-PTH) & cleaved to PTH

Question 18

What does the G-protein coupled calcium sensing receptor on chief cells do?

Answer 18

detects change in circulating calcium concentration

Question 19

What is the relationship between PTH secretion and serum calcium?

Answer 19

Inversely proportional

Question 20

Why does low extracellular calcium cause release of PTH?

Answer 20

Less calcium binds to receptors on parathyroid cells

Question 21

Does PTH increase or decrease bone re-absorption?

Answer 21

Increase

Question 22

How does PTH lead to bone resoprtion?

Answer 22

Binds to PTH receptor on osteoblasts, activating osteoclast activating factors (OAFs)

Question 23

How does cacitriol affect bone when serum calcium is low?

Answer 23

calcitriol works with PTH to increase calcium reabsorption from bone
osteoclasts > osteoblasts

Question 24

How does cacitriol affect bone when serum calcium is normal?

Answer 24

calcitriol promotes bone formation
osteoblasts > osteoclasts

Question 25

What is calcitonin?

Answer 25

A hormone

Question 26

Where is calcitonin secreted from?

Answer 26

parafollicular (C) cells of the thyroid gland

Question 27

What does calcitonin do?

Answer 27

Reduces serum calcium

Question 28

Does removal of the thyroid gland affect serum calcium?

Answer 28

No

Question 29

What are the effects of calcitonin?

Answer 29

1. Decreased osteoclast activity 2. Increased calcium excretion in kidneys 3. ↓ plasma Ca2+

Question 30

Describe the affects of hypercalcaemia on membrane excitability

Answer 30

Ca2+ blocks Na+ influx, so LESS membrane excitability

Question 31

Describe the affects of hypocalcaemia on membrane excitability

Answer 31

enables GREATER Na+ influx, so MORE membrane excitability

Question 32

What are the symptoms of hypocalcaemia?

Answer 32

1.Paraesthesia (hands, mouth, feet , lips) 2. Convulsions 3. Arrhythmias 4. Tetany Mnemonic - [CATs go numb]

Question 33

What is Chvostek’s sign?

Answer 33

Tap facial nerve just below zygomatic arch Positive response = twitching of facial muscles Indicates neuromuscular irritability due to hypocalcaemia

Question 34

What is Trousseau’s sign?

Answer 34

Inflation of BP cuff for several minutes induces carpopedal spasm = neuromuscular irritability due to hypocalcaemia

Question 35

What are the two causes of hypocalcaemia?

Answer 35

Low PTH levels = hypoparathyroidism Vitamin D deficiency

Question 36

What are the causes of hypoparathyroidism?

Answer 36

Surgical – neck surgery Auto-immune Magnesium deficiency Congenital (agenesis, rare)

Question 37

What are the causes of vitamin D deficiency?

Answer 37

1. Inadequate sun exposure 2. Malabsorption or dietary insufficiency leads to lack of ergocalciferol 3. Liver disease 4. Renal disease 5. Vit D receptor defects

Question 38

What are the consequences of vitamin D deficiency?

Answer 38

Lack of bone mineralisation = ‘soft’ bones In children – rickets (bowing of bones) In adults – osteomalacia (fractures, proximal myopathy)

Question 39

What are the symptoms of hypercalcaemia?

Answer 39

‘Stones, abdominal moans and psychic groans’ Reduced neuronal excitability – atonal muscles Stones – renal effects Nephrocalcinosis – kidney stones, renal colic Abdominal moans - GI effects Anorexia, nausea, dyspepsia, constipation, pancreatitis Psychic groans - CNS effects Fatigue, depression, impaired concentration, altered mentation, coma (usually >3mmol/L)

Question 40

What are the 3 causes of hypercalcaemia?

Answer 40

Primary hyperparathyroidism Malignancy Vitamin D excess (rare)

Question 41

What are the causes of Primary hyperparathyroidism

Answer 41

Too much PTH Usually due to a parathyroid gland adenoma No negative feedback - high PTH, but high calcium

Question 42

How does malignancy cause hypercalcaemia?

Answer 42

Bony metastases produce local factors to activate osteoclasts, increasing calcium reabsorption from bone