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An important aspect of calcium metabolism is plasma calcium homeostasis, the regulation of calcium ions in the blood plasma within narrow limits. [2] The level of the calcium in plasma is regulated by the hormones parathyroid hormone (PTH) and calcitonin.
Parathyroid hormone regulates serum calcium through its effects on bone, kidney, and the intestine: [5] In bone, PTH enhances the release of calcium from the large reservoir contained in the bones. [16] Bone resorption is the normal destruction of bone by osteoclasts, which are indirectly stimulated by PTH.
In a healthy physiology, extracellular calcium levels are maintained within a tight range through the actions of parathyroid hormone, vitamin D and the calcium sensing receptor. [1] Disorders in calcium metabolism can lead to hypocalcemia, decreased plasma levels of calcium or hypercalcemia, elevated plasma calcium levels.
Calcium homeostasis. The plasma ionized calcium (Ca 2+) concentration is very tightly controlled by a pair of homeostatic mechanisms. [61] The sensor for the first one is situated in the parathyroid glands, where the chief cells sense the Ca 2+ level by means of specialized calcium receptors in their membranes.
It acts to reduce blood calcium (Ca 2+), opposing the effects of parathyroid hormone (PTH). [7] Its importance in humans has not been as well established as its importance in other animals, as its function is usually not significant in the regulation of normal calcium homeostasis. [8] It belongs to the calcitonin-like protein family.
The US Institute of Medicine (IOM) established Recommended Dietary Allowances (RDAs) for calcium in 1997 and updated those values in 2011. [6] See table. The European Food Safety Authority (EFSA) uses the term Population Reference Intake (PRIs) instead of RDAs and sets slightly different numbers: ages 4–10 800 mg, ages 11–17 1150 mg, ages 18–24 1000 mg, and >25 years 950 mg. [10]
The parathyroid glands, of which there are 4–6, are found on the back of the thyroid glands, and secrete parathyroid hormone, [2] This causes an increase in blood calcium levels by targeting bone, the intestine, and the kidneys. The parathyroid hormone is the antagonist of calcitonin. Parathyroid hormone release is triggered by falling blood ...
The activity of this enzyme is stimulated by PTH. This is an important control point in Ca 2+ homeostasis. [25] Additional effects on the production of calcitriol include an increase by prolactin, a hormone which stimulates lactogenesis (the formation of milk in mammary glands), a process which requires large amounts of calcium. [29]