Ca2+ homeostasis

Question 1

What hormone regulates Ca2+

Answer 1

Parathyroid hormone from parathyroid gland

Question 2

What is the function of Ca2+

Answer 2

Structural integrity of skeleton and tooth enamel
Neurotransmitter release.
Blood coagulation

Question 3

What is hypocalcaemic tetany?

Answer 3

Extracellular Ca2+ falls below normal, nervous system becomes progressively more excitable due to increased permeability of Na+ - this causes tetanic contraction

Question 4

What are the 3 ways in which calcium exists?

Answer 4

Ionised (free Ca2+), anion complex (CaCO3), bound to albumin or globulins

Question 5

What happens to calcium absorbed into the gut through the diet?

Answer 5

80% excreted in the faeces. 35% absorbed by the extracellular fluid, 15% secreted back into the gut from the extracellular fluid

Question 6

What happens to ca2+ absorbed into the extracellular fluid?

Answer 6

Some secreted back into gut, the rest is excreted in the urine

Question 7

What is the rapidly exchangeable pool?

Answer 7

Ca2+ on the surface of the skeleton, they are always being exchanged

Question 8

What occurs to Ca2+ in the rapidly exchangeable pool?

Answer 8

Bone formation - from pool to bone.

Bone resorption - from bone to pool

Question 9

What are the 3 major target organs of Ca2+?

Answer 9

Intestine
Kidney
Bone

Question 10

How is calcium absorbed from the intestine passively?

Answer 10

Across layer of epithelium, down the concentration gradient, between cells = paracellular pathway. This occurs in the ileum

Question 11

What is the transcellular pathway of absorption in the intestine?

Answer 11

Calcium ions taken up into the cell by diffusion and bind to calcium binding proteins to maintain concentration gradient, at the other end calcium gets released and is pumped out of the cell against the concentration gradient using ATP. This occurs in the duodenum and jejunum

Question 12

How is Ca2+ reabsorbed in the proximal tube in the kidneys?

Answer 12

Transcellular pathway

Question 13

How is Ca2+ reabsorbed int he loop of Henle in the kidneys?

Answer 13

Paracellular pathway

Question 14

How is Ca2+ absorbed in the distal tubule of the kidneys?

Answer 14

Transcellular pathway

Question 15

Why is the transcellualr pathway in the distal tubular important?

Answer 15

Ca2+ uptake can be regulated by parathyroid hormone

Question 16

What is bone remodelling?

Answer 16

The constant formation and resorption of bone

Question 17

In which area of bone does bone remodelling occur?

Answer 17

Trabecular bone

Question 18

What are the areas of bone?

Answer 18

Trabecular and compact

Question 19

Why does calcium exchange occur on the trabecular bone?

Answer 19

Greater SA as it is spongy

Question 20

What is the function of osteoblasts?

Answer 20

Bone forming cells that secrete organic bone matrix (osteoid) on which mineralisation occurs

Question 21

What is the function of osteocytes?

Answer 21

Mature bone cells enclosed in bone matrix. They are connected to other cells via cannaliculi to allow for nutrient and ion exchange

Question 22

What is the function of osteoclasts?

Answer 22

Large multinucleate cells that resorb bone

Question 23

From what cell type are osteoclasts derived?

Answer 23

Monocytes

Question 24

What 3 hormones function in Ca2+ homeostasis?

Answer 24

Parathyroid hormone (PTH)
1,25 DHCC
Calcitonin

Question 25

Where is PTH synthesised and secreted?

Answer 25

Parathyroid gland (behind thyroid gland)

Question 26

What cells int he parathyroid Galen are the site of PTH synthesis?

Answer 26

Chief cells

Question 27

How does pTH become active?

Answer 27

It is first formed as a pre-prohormone which is cleaves to form PTH

Question 28

What is the main effect of PTH on Ca2+ concentration?

Answer 28

Increases plasma Ca2+

Question 29

When is PTH stimulated for release?

Answer 29

low levels of Ca2+ in blood

Question 30

What is the mechanism of action of PTH on bone?

Answer 30

Increases the number of osteoclasts and increases osteoclast activity to increase bone resorption. Decreases bone formation by decreasing collagen synthesis by osteoblasts

Question 31

What is the mechanism of action of PTH on the kidneys?

Answer 31

Acts to increase Ca2+ resorption in the distal tubule by increasing ca2+ uptake into cells. Stimulates 1-alpha-hydroxylase which catalyses the formation of 1,25DHCC

Question 32

What is the mechanism of action of PTH on the intestine?

Answer 32

indirect action by stimulating 1,25DHCC

Question 33

How is 1,25DHCC formed?

Answer 33

From vitamin D to the liver where is is converted to 25 HCC, to kidney where PTH stimulates 1-alpha-hydroxylase which converted 25HCC to 1,25DHCC

Question 34

What is the mechanism of action of 1,25 DHCC?

Answer 34

Main affect on the intestine to increase Ca2+ absorption from the intestine by increasing number of calcium binding proteins.

Question 35

What is the mechanism of action of 1,25 DHCC on the kidney?

Answer 35

Increases tubular reabrotpion of CA2+ = minor affect

Question 36

What is the mechanism of action fo 1,25 DHCC on bone?

Answer 36

Promotes the actions of PTH = bone resorption

Question 37

PTH promotes the synthesis of 1,25DHCC and 1,25 DHCC promotes the effects of PTH. How is this controlled?

Answer 37

1,25 DHCC inhibits the production of PTH

Question 38

What is the effect of calcitonin?

Answer 38

Decrease plasma Ca2+ levels

Question 39

Where is calcitonin synthesised and secreted?

Answer 39

Parafollicular cells of the thyroid gland

Question 40

What is the main target cell of calcitonin?

Answer 40

Osteoclasts

Question 41

What is the affect of calcitonin on bone?

Answer 41

Inhibit osteoclast motility and cell shape to inactivate them so bone respotion can't occur

Question 42

What is the effect of calcitonin on kidneys?

Answer 42

Decrease tubular reabsorption oF CA2+ but this is a weak affect

Question 43

Why does excess calcitonin not produce hypocalcaemia?

Answer 43

PTH and 1,25 DHCC dominate

Question 44

What is osteoporosis?

Answer 44

Reduced bone mass and density

Question 45

What causes osteoporosis?

Answer 45

Uncoupling of the equilibrium of bone formation dn resorption

Question 46

In osteoporosis does bone formation exceed bone resorption?

Answer 46

No, other way around

Question 47

Is bone present in osteoporosis biochemically normal?

Answer 47

Yes

Question 48

What causes rickets?

Answer 48

Inadequate mineralisation of bone matrix

Question 49

What causes hypercalcaemia?

Answer 49

Excess PTH or 1,25DHCC