Calcium Metabolism - Endocrine Control - Dr. Block

Question 1

Name three types of bone cells.

Answer 1

osteoblasts, osteoclasts, and osteocytes

Question 2

Which type of bone cells add calcium to bones, and which degrade bone removing calcium?

Answer 2

Osteoblasts - adds calcium to bones

Osteoclasts - remove calcium from bones

Question 3

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

Answer 3

Osteoclasts, from stem cells in the bone marrow, collect and sue at the surface of the bone matrix . Tbey use collagenase and other enzymes to tunnel through mineralized bone, forming cavities that is invaded by other cells.

Question 4

Name the three major hormones involved in calcium homeostasis?

Answer 4

• parthyroid hormone (PTH)
• calcitriol
• calcitonin

Question 5

Which of the hormones involved in calcium homeostasis are peptides?

Answer 5

Parathyroid hormone (PTH) and Calcitonin

Question 6

Where are the hormones involved in calcium homeostasis synthesized?

Answer 6

• parathyroid hormone (PTH) - chief cells of parathyroid gland
• calcitriol - Liver from Vitamin D.
• calcitonin - parafollicular C cells of the thyroid gland.

Question 7

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

Answer 7

PTH increases circulating calcium ion concentrations (by stimulating the production of calcitriol to increase intestinal absorption of calcium, increases rate of bone dissolution by osteoclasts to yield more extracellulcar calcium , and prevents precipitation of the calcium by reducing renal clearance of calcium while enhancing clearance of phosphate)

Calcitriol - increases the effects of calcium and phosphate across the intestinal mucosa. (think: because it’s not a peptide hormone, it can’t actually increase actual [Ca2+])

Calcitonin- reduces circulating calcium ion [induced by hypercalcemia]