Calcium Homeostasis

Question 1

What are some of the roles of calcium in the body? (5)

Answer 1

Signalling
Blood clotting
Apoptosis 
Skeletal strength
Membrane excitability

Question 2

How does hypocalcaemia affect neurones?

Answer 2

Increases neuronal sodium permeability
Leads to hyperexcitability of neurones
Can cause tetany

Question 3

How does hypercalcaemia affect neurones?

Answer 3

Decreases neuronal permeability
Reduces excitibility
Depresses neuromusclar activity
Can cause arhythmias

Question 4

What are the calcium stores in the body? (3)

Answer 4

Bones (99%)
ICF - mitochondria and SR (0.9%)
ECF (0.1%)

Question 5

What is the normal range of calcium in plasma?

Answer 5

2.2-2.6Mm

Question 6

What is physiologically active calcium in the plasma?

Answer 6

Calcium ions that are free ionised and not bound to plasma proteins

Question 7

What percentage of calcium in the plasma is bound to protein?

Answer 7

40%

Question 8

What proteins may calcium be bound to in the blood?

Answer 8

Albumin

Globulin

Question 9

What pH conditions increase calcium binding?

Answer 9

Alkalotic (can precipitate hypocalcaemic tetany)

Question 10

Where is Ca2+ excreted in the body?

Answer 10

Faeces

Kidneys

Question 11

How do osteoclasts mobilize bone?

Answer 11

Secrete H+ ions to dissolve calcium salts and proteolytic enzymes to digest the extracellular matrix

Question 12

What are the two key enzymes that increase calcium in the plasma?

Answer 12

PTH

Calcitriol (active form of Vit D3)

Question 13

How is calcitriol produced?

Answer 13

Produced from Vit D in the liver and kidneys

Question 14

How many parathyroid glands do humans usually have?

Answer 14

4

Question 15

How does PTH increase plasma calcium? (5)

Answer 15

Stimulate osetoclasts 
Inhibit osteoblasts 
Increase resorption of Ca2+ from kidneys 
Increasing renal excretion of phosphate 
Stimulates kidney to produce calcitriol

Question 16

What hormone stimulates formation of calcitriol in lactating women?

Answer 16

Prolactin

Question 17

What dietary sources are there for vitamin D?

Answer 17

Mackeral and tuna
Fish liver oils
Egg yolk
Fortified milk

Question 18

What is 1,25(OH)2D3 also known as?

Answer 18

Calcitriol

Question 19

How does PTH influence calcitriol formation?

Answer 19

Stimulates production of it in the kidneys

Question 20

How does calcitriol increase plasma Ca2+?

Answer 20

Increase active transport of calcium from the gut
Facilitating renal absorption of calcium
Stimulates osteoclasts

Question 21

What is classed as vitamin D deficiency?

Answer 21

Circulating levels fall below 20ng/ml

Question 22

Which populations are most at risk of calcium and phosphate deficiency?

Answer 22

Elderly

Asian

Question 23

Why are Asian populations are at risk of calcium deficiency?

Answer 23

Diet involving chapatti flour contains phytate which binds dietary calcium
Dietary deficiency of calcium
Pigmented skin less able to make vitamin D in response to UV light

Question 24

What is the key hormone that decreases plasma Ca2+?

Answer 24

Calcitonin

Question 25

Where is calcitonin produced?

Answer 25

Thyroid

Question 26

What can calcitonin be used to treat?

Answer 26

Paget’s disease

Question 27

How does prolactin influence calcium homeostasis?

Answer 27

Stimulates synthesis of calcitriol

Question 28

How does growth hormone influence calcium homeostasis?

Answer 28

Constant stimulus for bone growth

Question 29

How does insulin influence calcium homeostasis?

Answer 29

Increases bone formation, antagonises cortisol

Question 30

How does oestrogen influence calcium homeostasis?

Answer 30

Promotes bone formation via oestrogen receptors on osteoblasts

Question 31

How does cortisol influence calcium homeostasis?

Answer 31

Stimulates osteoblasts
Increase renal excretion of Ca2+ and phosphate
Reduces intestinal Ca2+ absorption