5) Calcium Homeostasis

Question 1

1) Importance of Calcium

Answer 1

stability of membrane potential

muscle contraction

acetylcholine release

blood coagulation

bone formation

Question 2

2) Observation on Hypocalcemic tetany

Answer 2

Trousseau’s sign

Question 3

3) Signs of Milk Fever/ Hypocalcemia

Answer 3

restlessness

nervousness

panting

trembling

ataxia

muscle tetany can lead to convulsions and death if not treated

condition appears at times of high calcium demand

Question 4

4) Hormonal control of plasma calcium levels

Answer 4

Parathyroid hormone (PTH)- increase in plasma Ca2+

Calcitonin- decreases plasma Ca2+

Question 5

5) Steps for bone remodelling

Answer 5

osteoclast recruitment and activation

resorption and osteoclast recruitment

osteoblastic bone formation

completed remodelling cycle

Question 6

6) Role of osteoclasts

Answer 6

breakdown bone material

Question 7

7) Role of osteoblasts

Answer 7

build up bone material

Question 8

8) Actions of parathyroid hormone

Answer 8

increase osteoclast activity

causes Ca2+ (and PO43-) mobilisation from bone

increases PO43- and decreases Ca2+ excretion in the kidney

increases formation of 1,25-(OH)2 D3 (activates 1a-hydroxylase activity in the kidney)

Question 9

9) Result of excess parathyroid

Answer 9

demineralisation of bone

hypocalcaemia

deposition of Ca2+ and PO4 in kidney and soft tissues (stones)

Question 10

10) Result of parathyroid deficiency

Answer 10

hypocalcaemia

muscle spasm (tetany)

death (asphyxiation)

Question 11

11) Role of Calcitonin

Answer 11

helps to protect skeleton

synthetic forms of calcitonin are used to treat skeletal problems

Question 12

12) Stimulation of parathyroid hormone secretion and what it is not controlled by

Answer 12

decreases in extracellular Ca2+ directly stimulate parathyroid hormone secretion

no pituitary control

Question 13

13) Detection of changes in parathyroid hormone and inhibition of parathyroid hormone release

Answer 13

changes sensed by G-protein coupled membrane receptor

high Ca2+ inhibits parathyroid hormone

Question 14

14) Flowchart displaying feedback control of parathyroid hormone

Answer 14

low concentration of Ca2+ in blood- release of parathyroid hormone- efflux of Ca2+ from bone and decreased loss of Ca2+ in urine- vitamin D- enhanced absorption of Ca2+ from intestine

Question 15

15) Actions of 1,25-(OH2) D3

Answer 15

increased Ca2+ uptake in gut

through increased synthesis of Ca2+ binding protein in cells of small intestine

increased Ca2+ reabsorption in kidney

mobilisation of Ca2+ and PO43- from bone (effect becomes obvious from vitamin D overdosage)

Question 16

16) Control of 1,25-(OH2) D3 production

Answer 16

decrease in Ca2+ in extracellular fluid

increase in parathyroid hormone secretion

increase in 1a hydroxylase activity

increase in formation of 1,25-(OH2) D3

decrease in formation of 24,25-(OH2) D3

Question 17

17) Production of calcitonin

Answer 17

parafollicular (cells in mammals between the follicles in the thyroid gland)

Question 18

18) Actions of calcitonin

Answer 18

inhibition of bone resorption (through reduction of osteoclast activity)

increased Ca2+ excretion in urine

Question 19

19) Flowchart displaying actions of calcitonin

Answer 19

increase in Ca2+ levels- increase in calcitonin secretion- increase in plasma calcitonin levels- decrease in osteoclast activity and increase in calcium excretion- decrease in calcium levels