Calcium regulation Flashcards
1
Q
Roles of calcium in body
A
- Muscle contraction
- neuronal activity
- exocytosis
- coagulation of blood
- cell communication
- bone and teeth structural integrity
2
Q
Where is calcium stored?
A
- 99% is in bone; hydroxyapatite crystals
- calcium, phosphate and water
- Intracellular calcium; bound to proteins or in mitochondria/ER
- ECF; in solution
- Blood calcium 3 forms
3
Q
3 Forms of blood calcium
A
- bound to albumins 40%
- complexed to anions 10%
- free ionised Ca2+ 50%
4
Q
Regulation of calcium levels
A
- continual movement between the ECF, bone, GI tract and the kidneys
- calcium is excreted at the kidneys; distal tubules
- calcium is absorbed by the GI tract; dietary calcium
5
Q
Calcium excretion and reabsorption
A
- free calcium filtered at the glomerulus NOT protein bound
- 70% of reabsorption occurs in proximal CT secondary to osmosis
- remaining 30% in DCT and collecting duct transcellularly via calcium channels
- DCT and CD absorption regulated by PTH parathyroid hormone
6
Q
Types of calcium store in bones
A
- 2x types of Ca store; readily-exchangeable and slowly exchangeable
- slowly = 99%; called stable pool
7
Q
Readily-exchangeable calcium stores
A
- rapid exchange in soluble portion of bone
- crystals and soluble calcium
- located in canaliculi between osteoblasts and osteocytes
- can mobilise calcium to blood quickly
8
Q
Slow-exchange calcium stores
A
- bone remodelling
-growing animals transfer more calcium into stable store than adults
9
Q
Bone stores when low blood calcium
A
- rapid; Ca2+ is transported from bone fluid to plama by PTH stimulated pumps in osteocytes
- slow; PTH increases osteoclast activity, but Ca2+ transported by PTH independent process
10
Q
Phosphate
A
- absorbed from intestines, stored in bone pools, excreted by kidneys
- inorganic phosphate acts as a buffer in blood
- important for; cell membranes, DNA synthesis, ATP
11
Q
Phosphate regulation
A
- regulated in kidney
- renal tubules (mainly PCT) reabsorb 80-90% of phosphate
- PTH decreases renal reabsorption of phosphates
- PTH decreases Na/P transporters
