Session 11

Question 1

Why are calcium homeostasis and phosphate homeostasis intimately linked?

Answer 1

• They are principal components of hydroxyapatite crystals

- Regulated by the same hormones

Question 2

Which hormone primarily regulates calcium and phosphate homeostasis?

Answer 2

Parathyroid hormone (PTH)

Question 3

Apart from PTH, which other hormones are involved in the regulation of calcium and phosphate homeostasis?

Answer 3

Calcitrol and calcitonin

Question 4

What do PTH, calcitrol and calcitonin act on?

Answer 4

Bone, kidneys and GI tract

Question 5

Where is most of the body’s calcium found?

Answer 5

Within the bone

Question 6

What is the major dietary source of calcium?

Answer 6

Diary products

Question 7

What is the main organ involved in calcium homeostasis?

Answer 7

Intestine

Question 8

What is the second major organ governing calcium homeostasis?

Answer 8

Bone

Question 9

How does calcium exist in plasma?

Answer 9

• Free ionised species
• Bound to anionic sites on serum protein (esp albumin)
• Complexed with low molecular weight organic anions

Question 10

What is the total concentration of all the different forms of calcium?

Answer 10

2.2 - 2.7 mol/L

Question 11

Which form of calcium is the most important with regards to regulating the secretion of PTH?

Answer 11

Ionised form of calcium

Question 12

What happens if plasma calcium levels alter?

Answer 12

Hypocalcaemia

Hypercalcaemia

Question 13

What is hypocalcaemia?

Answer 13

Calcium levels are too low

Question 14

What happens in hypocalcaemia?

Answer 14

Hyperexcitability in the nervous system including NMJ, leading to parasthesia, then tetany, paralysis and even convulsions

Question 15

What is hypercalcaemia?

Answer 15

This is when calcium levels are too high

Question 16

What happens in hypercalcaemia?

Answer 16

Results in formation of kidney stones (renal calculi), constipation, dehydration, kidney damage, tiredness and depression

Question 17

What hormones are important in the regulation of serum calcium?

Answer 17

Parathyroid hormone and active form vitamin D

Question 18

What is another name for the active form of vitamin D?

Answer 18

Calcitrol

Question 19

What is the function of PTH and calcitrol?

Answer 19

They both raise serum calcium concentrations

Question 20

What controls the short term regulation of serum calcium?

Answer 20

Parathyroid hormone

Question 21

What hormone is responsible for the long term regulation of serum calcium?

Answer 21

Calcitrol

Question 22

What are the two main forms of vitamin D?

Answer 22

VItamin D2

VItamin D3

Question 23

What is another name for vitamin D2?

Answer 23

Ergocalciferol

Question 24

What is another name for vitamin D3?

Answer 24

Cholecalciferol

Question 25

How is vitamin D obtained?

Answer 25

Sun exposure, food and supplements

Question 26

What might lead to hypercalcaemia?

Answer 26

PTHrP produced by tumours

Question 27

What is PTHrP?

Answer 27

Parathyroid hormone related peptide

Question 28

What does the measurement of PTHrP show?

Answer 28

Determining the cause of an otherwise unexplained hypercalcaemia

Question 29

What is PTHrP?

Answer 29

Peptide

Question 30

In patients is PTHrP most commonly produced?

Answer 30

Breast, prostrate cancer and occasionally people with myeloma

Question 31

What is the action of PTHrP?

Answer 31

Shares many actions with PTH. Lead to increase calcium release from bone, reduced renal calcium excretion and reduced renal phosphate reabsorption. However PTHrP does not increase calcitrol concentration, unlike PTH

Question 32

What does calcitonin do in most animals?

Answer 32

Lowers serum calcium levels