Calcium Metabolism Flashcards
What is normal serium calcium levels?
2.2-2.6mM
Where is most of the calcium stored?
Skeleton
- hydroxyapatite
- calcium carbonate
What are the functions of calcium?
Build + maintain teeth and bones Regulates heart rhythm Assists in blood clotting Maintain nerve + muscle function - NMJ transmission Used in intracellular pathways Important in normal kidney function
What happens in hypocalcaemia?
Hyper-excitability of NMJ
What are the symptoms of hypocalcaemia?
Pins + needles
Tetany
Paralysis
Convulsions
What are the symptoms of chronic hypercalcaemia?
Renal calculi Kidney damage Constipation Dehydration Tiredness Depression
What is the pneumonic for hypercalcaemia?
Stones - renal calculi
Moans - depression
Groans - abdominal pain
Where do the parathyroid glands lie?
2 on each lobe of the thyroid - posterior part
What cell types make up the parathryoid gland?
Chief cells
Oxyphil cells
What do chief cells produce?
PTH
What are the main hormones involved in calcium and phosphate regulation?
Parathyroid hormone (PTH)
Calcitriol
Calcitonin
How is calcium homeostasis controlled?
Dietary calcium consumed
Absorbed by digestive tract (calcitriol)
Blood calcium
Deposited by osteoblasts (weak calcitonin)
Stored in bone
Resorbed by osteoclasts (calcitriol + PTH)
Filtered by kidneys
Urine
Reabsorption by kidneys (calcitriol + PTH)
What regulates PTH synthesis?
Low serum calcium - up-regulates gene transcription
High serum calcium - down-regulates gene transcription
What are the effects of PTH?
Kidney
- decreases loss to urine
Gut
- activates vitamin D
- increases transcellular uptake from GI tract
Bone
- increase resorption
What are the actions of PTH on bone?
Stimulates osteolysis
- induces osteoblastic cells to synthesise and secrete cytokines
- cytokines stimulate differentiation and activity in osteoclasts
- PTH decreases osteoblast activity
- exposes surface to osteoclasts
- reabsorption of mineralised bone
