Control of Calcium Balance

Question 1

What are the functions of calcium in the body?

Answer 1

Signalling 
Blood clotting 
Apoptosis 
Skeletal strength 
Membrane excitability

Question 2

How does calcium affect membrane excitability?

Answer 2

Ca2+ decreases Na+ permeability

Question 3

What is the effect of hypocalcaemia on membrane excitability?

Answer 3

Increases neuronal Na+ permeability

Hyper excitation of neurons

Question 4

What can extreme cases of hypocalcaemia cause?

Answer 4

Tetany

Question 5

What can happen if tetany spreads to the larynx and respiratory muscles?

Answer 5

Asphyxiation

Suffocating

Question 6

What is the effect of hypercalcaemia on membrane excitability?

Answer 6

Decreases neuronal Na+ permeability
Reduces excitability
Depress neuromuscular activity

Question 7

What is the distribution of calcium in the body?

Answer 7

Bones 99%
Intracellular fluid - 0.9%
Extracellular fluid - 01.%

Question 8

Where is the vast majority of calcium found in our bodies?

Answer 8

In our bones

Question 9

What % of calcium is found in our cells?

Answer 9

0.9%

Question 10

What is calcium in our bones mostly in the form of?

Answer 10

Hydroxyapatite

Question 11

What does calcium require to lay it down in the bones?

Answer 11

Phosphate homeostasis

Question 12

What is the calcium level in the plasma?

Answer 12

2.2-2.6mM

Question 13

What does calcium have a high affinity for?

Answer 13

Proteins

Question 14

What % of calcium is bound to plasma proteins?

Answer 14

40%

Question 15

In what form is calcium physiologically active?

Answer 15

Unbound calcium is active

Question 16

How does Ca2+ binding change with pH?

Answer 16

Binding capacity increases under alkalotic conditions

Question 17

What happens to calcium binding in hyperventillation?

Answer 17

Plasma pH rises
Binding capacity increase
Casing plasma Ca2++ to fall and therefore precipitate hypocalcaemic tetany

Question 18

What happens to calcium binding in hypoventilation?

Answer 18

Acidosis occurs

Binding capacity reduces and free Ca2+ in plasma rises

Question 19

Where does all the calcium that enters our body come from?

Answer 19

Diet

Question 20

What happens if calcium levels are disrupted in the body?

Answer 20

The bone will release calcium at the expense of bone strength

Question 21

What are osteoblasts?

Answer 21

Bone building cells

Highly active cells which lay down collagen extracellular matrix which then calcify

Question 22

What do osteoblasts differentiate to form?

Answer 22

Osteocytes

Question 23

What do osteoclasts do?

Answer 23

Cells that breakdown bones

Cells that are responsible for mobilizing bone

Question 24

What 2 hormones control calcium homeostasis?

Answer 24

Parathyroid Hormone

Calcitriol

Question 25

Where is PTH produced?

Answer 25

Parathyroid glands

Question 26

Where is calcitriol produced?

Answer 26

Vitamin D by the liver and kidneys

Question 27

How many parathyroid glands are there?

Answer 27

4

Question 28

What is the most important hormone for controlling calcium?

Answer 28

PTH

Question 29

Where are the parathyroid glands found?

Answer 29

On the posterior surface of the thyroid gland

Question 30

When is PTH secreted?

Answer 30

In response to decreased calcium conc. in the plasma

Question 31

How do PTH increase free Ca conc.?

Answer 31

Stimulate oesteoclasts to release Ca2+ from bones Inhibit osteoblasts from laying down more bone Increase reabsorption of Ca2+ from kidneys Increases renal secretion of phosphate Stimulates the kidneys to synthesis calcitriol from vitamin D which promotes calcium absorption at the gut and kidneys Increase calcium absorption from the gut

Question 32

What is calcitriol?

Answer 32

Secondary hormone in terms of maintaining calcium levels

Question 33

What does calcitriol complement the action of?

Answer 33

the action of PTH to increase plasma Ca2+

Question 34

What type of hormone is calcitriol?

Answer 34

Steroid hormones

Question 35

How is calcitriol produced?

Answer 35

In 2 steps | From dietary vitamin D

Question 36

How is the formation of calcitriol stimulated?

Answer 36

By hormone prolactin in lactating women

Question 37

How is active vitamin D3 formed?

Answer 37

From cholesterol derivatives by the action of UV light on the skin Gained from the diet also

Question 38

How does the conversion to the active form of calcitriol come bout?

Answer 38

Via the release of PTH

Question 39

What is the most important action of calcitriol?

Answer 39

Increase absorption of Ca2+ from the gut. | - That’s its most important action

Question 40

What is the active transport system that moves Ca2+ from the intestinal lumen to the blood under the control of?

Answer 40

Calcitriol

Question 41

In a situation of low Ca2+ plasma what happens to PTH and calcitriol?

Answer 41

Increase in PTH leads to increase in calcitriol leads to increase in Ca2+ absorption

Question 42

What is the result of increased plasma Ca2+?

Answer 42

Inhibition of PTH causing a greater osteoblast deposition and less osteoclast resorption

Question 43

What are all the actions of calcitriol?

Answer 43

Binds to nucleur receptors in target tissue to increase absorption of Ca2+ from the gut Facilitate the renal absorption of Ca2+ Mobilisecalcium stores in bone by stimulating osteoclast activity

Question 44

What circulating molecule controls the proportion of dietary calcium absorbed from the gut?

Answer 44

1,25(OH)2D

Question 45

What is classed as vitamin D deficiency?

Answer 45

Circulating levels less than 20ng/ml

Question 46

What things add to the problem of lack of sunlight?

Answer 46

UVB sunscreen | clothing diet

Question 47

What is the effect of GH on bones?

Answer 47

Constant stimulus for bone formation

Question 48

What is the effect of plasma pH on hperventillation?

Answer 48

Increase in plasma pH

Question 49

What is the effect of hypoventillation on plasma pH?

Answer 49

Decrease in plasma pH

Question 50

What is 1,25 dihydroxycholecalciferol (1,25(OH)2D3) another name for?

Answer 50

Vitamin D3

Question 51

What is the effect of vitamin D3 deficiency?

Answer 51

intestinal malabsorption of Ca2+ , this decreases [Ca2+ ] plasma which increases PTH which then promotes phosphate deficiency – aggravates Ca2+ loss from bone.

Question 52

What is the hormone which acts to decrease Ca2+?

Answer 52

Calcitonin

Question 53

What type of hormone is calcitonin?

Answer 53

Peptide hormone

Question 54

Where is calcitonin released?

Answer 54

Thyroid gland

Question 55

What is calcitonin secretion stimulated by?

Answer 55

Increase Ca2+ plasma conc.

Question 56

What is the main actions of calcitonin?

Answer 56

Bind to osteoclasts to inhibit bone breakdown as well as increase renal excretion To decrease Ca2+

Question 57

Is there much evidence that calcitonin is important in humans?

Answer 57

No very little | Patients with no calcitonin have normal Ca2+ levels

Question 58

What is the direct effect of Vit D3?

Answer 58

To release Ca2+ from the bone

Question 59

What is the net effect of Vitamin D3 on calcium?

Answer 59

Increase plasma Ca2+ conc.

Question 60

What is calcitriol the active form of?

Answer 60

Vitamin D3

Question 61

What is the effect of cortisol on calcium?

Answer 61

Inhibits osteoblasts Increase renal excretion of Ca2+ Thus decreasing intestinal absorption of Ca2+ Decreases plasma Ca2+

Question 62

What is the effect of insulin on calcium?

Answer 62

Increases bone formation | Antagonises the action of cortisol

Question 63

What is the effect of oestrogen on calcium?

Answer 63

Promotes bone formation

Question 64

What is the effect of prolactin on calcium?

Answer 64

Promotes calcium absorption of the gut by stimulating the synthesis of calcitriol

Question 65

What happens in Vitamin D deficiency?

Answer 65

PTH has to work hard to maintain plasma Ca2+ In doing so continually breaks down bone Can lead to osteomalacia