In: Anatomy and Physiology
Proper blood calcium levels are required for muscle contraction, nerve function, and other critical activities in the body. How does the body maintain homeostasis in response to decreased blood calcium levels? Discuss the main gland, hormone, and target of the hormone.
- Calcium homeostasis is maintained in the body by two hormones
namely calcitonin and parathormone.
- Parathormone is a peptide hormone produced by chief cells of
parathyroid gland in response to low serum calcium ions
concentration.
- Parathormone stimulates osteoclast cells in the bones that
increase the resorption of bones and increase the serum calcium
ions level. As bones are the storehouse of calcium ions, resorption
of bones increases the serum calcium ions level.
- Parathormone increases the reabsorption of calcium from the distal tubules and collecting ducts of nephrons in the kidneys thus increasing the calcium ions level in the blood and reducing the excretion of calcium ions into the urine.
- Parathormone also causes the conversion of 25-hydroxy vitamin D into 1, 25- dihydroxy vitamin D which is also known as calcitriol. Calcitriol stimulates the absorption of calcium ions from small intestine into the blood.
- Thus, the hormone parathormone which is secreted by the chief cells of parathyroid gland in response to decreased blood calcium levels, by its action of bones, kidneys and small intestine increases the blood calcium levels.
- Calcitonin has its effect opposite to that of parathormone and thus it inhibits the activities of osteoclasts in the bones as well as inhibits the reabsorption of calcium ions from the nephrons of the kidneys thus lowering the serum calcium ions level.