Calcium Metabolism - Endocrine Control

Question 1

Name 3 types of bone cells.

Answer 1

Osteoblasts (move Ca2+ into bone), Osteoclasts (move Ca2+ out of bone), and osteocytes (mature bone cells that have lost the ability to synthesize collagen)

Question 2

Which of these add Ca2+ to bones and which degrade bone removing Ca2+?

Answer 2

Osteoblasts build bone by adding Ca2+ while osteoclasts degrade bone by removing Ca2+.

Question 3

What is the mechanism by which bone is cut by these cells?

Answer 3

Osteoclasts are released as monocytes into the bloodstream where they collect and fuse at the surface of bone matrix to form huge multinucleated osteoclasts which cling to the bone surface. They use collagenase, other enzymes, and acids to tunnel through mineralized bone forming cavities that are invaded by other cells. Eventually a capillary sprouts off a nearby blood vessel, grows into the tunnel and osteoblasts line its walls making new layers of bone.

Question 4

Name the 3 major hormones involved in Ca2+ homeostasis.

Answer 4

Parathyroid hormone (PTH), Calcitonin and Calcitriol

Question 5

Which of the 3 major hormones involved in Ca 2+ homeostasis are peptides?

Answer 5

PTH and Calcitonin

Question 6

Where are each of the 3 major hormones in Ca2+ homeostasis synthesized?

Answer 6

1) PTH synthesized by chief cells of parathyroid gland.
2) Calcitriol synthesized from Vitamin D in the liver, with minor modifications occurring in the kidney.
3) Calcitonin synthesized by parafollicular C cells of thyroid gland.

Question 7

What is the effect of each of these hormones upon circulating Ca2+ ion concentrations?

Answer 7

1) PTH - stimulates the production of calcitriol, increases the rate of bone dissolution by osteoclasts to yield more Ca2+ in the extracellular fluid and reduces renal clearance of Ca2+ while enhancing clearance of phosphate. Major function is to prevent hypocalcemia by increasing the circulation Ca2+ ion concentration.
2) Calcitriol - is responsible for translocation of Ca2+ across intestinal membrane against a concentration gradient.
3) Calcitonin - activates adenylate cyclase and decreases the activity and number of osteoclasts. Overall, is antagonistic to PTH.