Mineral Homeostasis

Question 1

List organs involved in calcium regulation

Answer 1

• Skin
• Kidneys
• Gut
• Liver

Question 2

Describe parathyroid hormone (main regulating hormone) in Calcium ion regulation

Answer 2

Action -> increase blood calcium

• increase Calcium release from bone
• Increase conversion of Vitamin D to Calcitriol
• Calcium ion conservation and phosphate dumping in kidney

Release:

• Increased by low blood calcium
• Decreased by calcitriol (negative feedback)
• Decreased by high calcium ion
• Not released in low phosphate

Question 3

Describe calcitriol = 1,25-(OH)2D = Vitamin D hormone in calcium ion regulation

Answer 3

Synthesis path of calcitriol:

• UV from skin - 7 dehydrocholesterol -> Vitamin D
• Activation in Liver - Vitamin D -> 25 OH Vitamin D
• Activation in Kidneys - 25OH Vitamin D -> calcitriol (this step is heavily regulated)

synthesis of Vitamin D to calcitriol (in kidneys) increased by:

• PTH (during low calcium ion)
• Low PO4 (directly)
• Growth
• Pregnancy

Action:

• Increase absorption of calcium and phosphate from digestion
• Increase calcium release from bone: direct function of calcitriol but overall function of calcitriol on bones is decrease in resorption since blood calcium levels are higher

Question 4

Describe fibroblast growth factor (FGF23) in calcium ion regulation

Answer 4

Stimulated by:

• Calcitriol (negative feedback)
• PTH
• High phosphate

Action:

• Increase phosphate wasting
• Decrease calcitriol production
• Increase calcitriol degradation

Question 5

Describe calcitonin in calcium ion regulation

Answer 5

• Minor role - non-essential
• Inhibits osteoclast activity
• Released in high calcium and gut hormones

Question 6

Skin’s function in bone resorption

Answer 6

Converts 7 dehydrocholesterol to vitamin D

Question 7

Liver’s function in bone resorption

Answer 7

Converts vitamin D to 25(OH) Vitamin D

Question 8

Bones’ function in bone resorption

Answer 8

Resorption -> increase blood Calcium and phosphate

• PTH
• Calcitriol

Formation -> Decrease blood calcium and phosphate

• high blood calcium and phosphate
• Calcitonin

Question 9

Kidney’s function in bone resorption

Answer 9

PTH

• Calcium reabsorption is increased
• Phosphate reabsorption decreased
• Increase calcitriol production

Low phosphate cause phosphate reabsorption (directly affected)

Question 10

Gut’s function in bone resorption

Answer 10

Calcitriol

• Increase calcium absorption
• Increase phosphate absorption

Question 11

Describe the short and long term consequences of hypocalcaemia

Answer 11

Low blood calcium.
Causes: low PTH (e.g. accidental removal of parathyroid glands)

Short term:
- Increased sodium permeability of cells -> partial depolarization: muscle spasms, seizures, pins and needles

Long term: rickets and osteomalacia

Question 12

Describe short and long term consequneces of hypercalcaemia (high blood calcium)

Answer 12

Causes: high PTH (e.g. overactive parathyroid glands)

Short-term: decreased sodium permeability of cells -> hyperpolarization:
- Neurological dysfunction 
- Cardiac arrythmias
- constipation
Increased urine flow in short term. 

Long term: kidney calcification and stones