Calcium Homeostasis

Question 1

What are the roles of calcium?

Answer 1

bone and teeth rigidity
muscle contraction
membrane stability
NT release
secretory process
DNA/RNA synthesis
blood clotting
enzyme regulation

Question 2

What can result due to hypocalcemia?

Answer 2

the nervous system becomes more excitable causing tetanic muscle contraction and cramps
osteoporosis
rickets and osteomalacia

Question 3

What can result with hypercalcemia?

Answer 3

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

Question 4

What are the primary regulators of calcium balance?

Answer 4

PTH, Calcitonin and Vit D

Question 5

Where is PTH manufactured?

Answer 5

chief cells of PT glands

Question 6

What is the target organs of PTH?

Answer 6

bone and kidney

Question 7

What is the action of PTH?

Answer 7

hypercalcaemia

Question 8

Why is a thyroid ectomy not fatal?

Answer 8

because there are small clusters of PTH producing cells outside the PT gland

Question 9

How is PTH secretion controlled?

Answer 9

an EC calcium sensing receptor

High Ca prevents PTH secretion

Question 10

How does high Ca prevent exocytosis of PTH granules?

Answer 10

activates PLC which inhibits AC

generates IP3 which decreases cAMP

Question 11

What results from hyperparathyroidism?

Answer 11

bone resorption, intestinal Ca absorption and renal tubular reabsorption
related to excessive Vit D3

Question 12

What can cause hyperparathyroidism?

Answer 12

adenomatous or hyperplastic parathyroid tissue

Question 13

What causes hypoparathyroidism?

Answer 13

inadequate response of VitD-PTH axis to hypocalcaemic stimuli

Question 14

What is the effect of calcitonin on bone?

Answer 14

decreased activity of osteoclasts and osteoblasts

Question 15

What effect does calcitonin have on VitD?

Answer 15

increases production of inactive version

Question 16

What is calcitonin released in response to?

Answer 16

rising circulating Ca

Question 17

What is the target cell of calcitonin?

Answer 17

the osteoclast

Question 18

What is the effect of calcitonin on the osteoclast?

Answer 18

increases cAMP concentrations which inhibits osteoclast motility, changes their shape and inactivates them

Question 19

What is the major effect of calcitonin?

Answer 19

rapid fall in Ca caused by inhibition of bone resorption

Question 20

Where is VitD acquired from?

Answer 20

sun and diet

Question 21

Why is VitD not a classic hormone?

Answer 21

because it is not produced or secreted by an endocrine gland

Question 22

Where is VitD converted to its active form?

Answer 22

through the liver and then the kidney

Question 23

What does VitD do in the bone?

Answer 23

activates both osteoblasts and osteoclasts increasing the rate of bone remodelling but with little net effect on bone present

Question 24

What is the effect of VitD in the GI?

Answer 24

increases GI calcium and phosphate absorption and renal calcium reabsorption

Question 25

What does active Vit D bind to?

Answer 25

a typical nuclear receptor

Question 26

What does it travel in the blood bound to and why?

Answer 26

it is lipid soluble so travels bound to hydroxylated a-globulin