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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.
Calcitonin is a 32 amino acid peptide hormone secreted by parafollicular cells (also known as C cells) of the thyroid (or endostyle) in humans and other chordates [5] in the ultimopharyngeal body. [6] It acts to reduce blood calcium (Ca 2+), opposing the effects of parathyroid hormone (PTH). [7]
The plasma total calcium concentration is in the range of 2.2–2.6 mmol/L (9–10.5 mg/dL), and the normal ionized calcium is 1.3–1.5 mmol/L (4.5–5.6 mg/dL). [4] The amount of total calcium in the blood varies with the level of plasma albumin, the most abundant protein in plasma, and therefore the main carrier of protein-bound calcium in the blood.
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.
If the underlying cause of the hypocalcemia can be addressed, the hyperparathyroidism will resolve. In people with chronic kidney failure, treatment consists of dietary restriction of phosphorus; supplements containing an active form of vitamin D, such as calcitriol, doxercalciferol, paricalcitol; and phosphate binders, which are either calcium-based and non-calcium based.
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]
Hypoparathyroidism is a common cause of hypocalcemia. [9] Calcium is tightly regulated by the parathyroid hormone (PTH). In response to low calcium levels, PTH levels rise, and conversely, if there are high calcium levels then PTH secretion declines. [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 ...