Question

When blood calcium levels are low, parathyroid hormone (PTH) stimulates the release of calcium from bones.

a) Sodium reabsorption in the kidneys
b) The release of calcium from bones
c) Glycogen synthesis in the liver
d) Insulin secretion from the pancreas

Answer 1

Parathyroid hormone (PTH) increases blood calcium levels by stimulating osteoclasts to release calcium from bones, enhancing renal calcium reabsorption, and indirectly increasing intestinal calcium absorption via calcitriol production.

Step-by-step explanation:

When blood calcium levels are low, parathyroid hormone (PTH) orchestrates the increase in calcium levels. Primary actions of PTH include:

1. Stimulation of osteoclasts in the skeleton to release calcium from the bones into the bloodstream.
2. Enhancement of calcium reabsorption in the kidneys.
3. Increasing dietary calcium absorption in the intestines, indirectly through the production of calcitriol, the active form of vitamin D.

These mechanisms work in concert to elevate blood calcium levels and are regulated via a negative feedback loop where high calcium levels inhibit further PTH release.