Calcium Homeostasis: The Role of Bones and Hormones in Maintaining Blood Calcium Levels, Study notes of Anatomy

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BONE HOMEOSTASIS

Presented by; MERCIFUL GROUP

OBJECTIVES

 Describe the importance of calcium in the body.  Explain how blood calcium level is regulated.

BONE’S ROLE IN CALCIUM HOMEOSTASIS  The role of bones in calcium homeostasis is to help buffer the blood calcium ions level, releasing calcium ions into blood plasma, (using osteoclasts ) when the level decreases, and absorbing calcium ions using osteoblasts when the level rises.

CONT’D

 Calcium ion exchange is regulated by hormones, the most important of which is parathyroid hormone ( PTH ) secreted by parathyroid glands.  This hormone increases blood calcium levels.

CONT’D

 The gene for PTH within the nucleus of a parathyroid gland cell ( the control centre) detects the intracellular increase in cyclic AMP ( the input).  As a result, PTH synthesis speeds up and more PTH ( the output) is released into the blood.  The presence of higher levels of PTH increases the number and activity of osteoclasts( the effectors) , which step up the pace of bone reabsorption.

CONT’D

The resultant release of calcium ions from bone into blood returns blood calcium ions to normal. PTH also acts on the kidneys( effectors) to decrease loss of calcium ions in the urine, so more is retained in blood.  PTH stimulates the formation of Calcitriol(the active form of vitamin D), a hormone that promotes absorption of calcium from food in the GIT into the blood. Both of these actions help to elevate blood calcium levels. NB : Too low calcium ions make one be at a risk of getting respiratory arrest.