Flashcards in Calcium Homeostasis Deck (26):
What are the roles of calcium?
bone and teeth rigidity
What can result due to hypocalcemia?
the nervous system becomes more excitable causing tetanic muscle contraction and cramps
rickets and osteomalacia
What can result with hypercalcemia?
moans - constipation, abd pain, nausea
stones - kidney stones, frequent peeing
groan - confusion, dementia, memory loss, depression
bones - bone aches, pains, fractures
also abnormal heart rhythms, and cardiac malfunction
What are the primary regulators of calcium balance?
PTH, Calcitonin and Vit D
Where is PTH manufactured?
chief cells of PT glands
What is the target organs of PTH?
bone and kidney
What is the action of PTH?
Why is a thyroid ectomy not fatal?
because there are small clusters of PTH producing cells outside the PT gland
How is PTH secretion controlled?
an EC calcium sensing receptor
High Ca prevents PTH secretion
How does high Ca prevent exocytosis of PTH granules?
activates PLC which inhibits AC
generates IP3 which decreases cAMP
What results from hyperparathyroidism?
bone resorption, intestinal Ca absorption and renal tubular reabsorption
related to excessive Vit D3
What can cause hyperparathyroidism?
adenomatous or hyperplastic parathyroid tissue
What causes hypoparathyroidism?
inadequate response of VitD-PTH axis to hypocalcaemic stimuli
What is the effect of calcitonin on bone?
decreased activity of osteoclasts and osteoblasts
What effect does calcitonin have on VitD?
increases production of inactive version
What is calcitonin released in response to?
rising circulating Ca
What is the target cell of calcitonin?
What is the effect of calcitonin on the osteoclast?
increases cAMP concentrations which inhibits osteoclast motility, changes their shape and inactivates them
What is the major effect of calcitonin?
rapid fall in Ca caused by inhibition of bone resorption
Where is VitD acquired from?
sun and diet
Why is VitD not a classic hormone?
because it is not produced or secreted by an endocrine gland
Where is VitD converted to its active form?
through the liver and then the kidney
What does VitD do in the bone?
activates both osteoblasts and osteoclasts increasing the rate of bone remodelling but with little net effect on bone present
What is the effect of VitD in the GI?
increases GI calcium and phosphate absorption and renal calcium reabsorption
What does active Vit D bind to?
a typical nuclear receptor