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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.
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]
Disorders of calcium metabolism occur when the body has too little or too much calcium. The serum level of calcium is closely regulated within a fairly limited range in the human body. In a healthy physiology, extracellular calcium levels are maintained within a tight range through the actions of parathyroid hormone , vitamin D and the calcium ...
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.
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.
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]
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 calcium-sensing receptor (CaSR) is a Class C G-protein coupled receptor which senses extracellular levels of calcium ions. It is primarily expressed in the parathyroid gland, the renal tubules of the kidney and the brain. [5] [6] In the parathyroid gland, it controls calcium homeostasis by regulating the release of parathyroid hormone (PTH ...