Calcium Homeostasis

Question 1

How much calcium is bound to plasma proteins in blood?

Answer 1

~50% (Albumin most notably)

Question 2

How much calcium is ionised and what does it mean for it to be ionised?

Answer 2

Just under half

Ionised=Active Form

Question 3

How much calcium is complexed in the blood?

Answer 3

Very small amount

Question 4

What are the 3 main ways that calcium is distributed in the blood?

Answer 4

1) Ionised: Metabolically active and used for cell function
2) Bound to PP: Non-metabolically active
3) Complexed e.g. Citrate/Phosphate

Question 5

What does alkalosis do to ionised cacium

Answer 5

Increases pH and negative charge on albumin, so more calcium will bind to albumin and less is ionised

Question 6

Where in the intestine is calcium reabsorbed?

Answer 6

Actively: Duodenum and Jejunum
Passively: Ileum and Colon

Question 7

Where does majority of Ca2+ reabsorption occur in kidney? And where does active occur?

Answer 7

Majority: PCT
Active: DCT (Site of PTH acting)

Question 8

Where can Calcium come from to enter the blood?

Answer 8

1) Absorbed from the intestine
2) Resorbed from he bone
3) Reabsorbed at the kidney

Question 9

What causes release of PTH?

Answer 9

Low serum Ca2+ levels are detected by receptors in the Parathyroid

Question 10

What Cells release calcitonin, what triggers it and what is its action?

Answer 10

C-Cells, High Ca2+ levels and reduces bone resorption so Ca2+ lowered (PTH antagonist)

Question 11

What is the action of PTH?

Answer 11

1) Causes bone resorption: ^ Ca2+ and PO43-
2) Acts on kidneys causing increased Ca2+ reabsorption and decreased PO43- reabsorption
4) Stimulates 1-hydroxylase which causes increased formation of 1,25 -2vitD seeing an increase in Ca2+ absorption and phosphate absorption from kidney