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Information about Calcium Homeostasis

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Calcium
Calcium metabolism or calcium homeostasis is the mechanism by which the body maintains adequate calcium levels. Derangements of this mechanism lead to hypercalcemia or hypocalcemia, which both can have important consequences for health.

Calcium location and quantity

Calcium is the most abundant mineral in the human body. The average adult body contains in total approximately 1 kg, 99% in the skeleton in the form of calcium phosphate salts. The extracellular fluid (ECF) contains approximately 22.5 mmol, of which about 9 mmol is in the serum. Approximately 500 mmol of calcium is exchanged between bone and the ECF over a period of twenty-four hours.[1]

Normal ranges

The serum level of calcium is closely regulated with a normal total calcium of 2.2-2.6 mmol/L (9-10.5 mg/dL) and a normal ionized calcium of 1.1-1.4 mmol/L (4.5-5.6 mg/dL). The amount of total calcium varies with the level of serum albumin, a protein to which calcium is bound. The biologic effect of calcium is determined by the amount of ionized calcium, rather than the total calcium. Ionized calcium does not vary with the albumin level, and therefore it is useful to measure the ionized calcium level when the serum albumin is not within normal ranges, or when a calcium disorder is suspected despite a normal total calcium level.

Corrected calcium level

One can derive a corrected calcium level when the albumin is abnormal. This is to correct for the change in total calcium due to the change in albumin-bound calcium, and gives an estimate of what the calcium level would be if the albumin were within normal ranges.

Corrected calcium (mg/dL) = measured total Ca (mg/dL) + 0.8 (4.0 - serum albumin [g/dL]), where 4.0 represents the average albumin level.


When there is hypoalbuminemia (a lower than normal albumin), the corrected calcium level is higher than the total calcium.

Effector organs

Sources

About 25 mmol of calcium enters the body in a normal diet. It can be lower if the diet is low in milk or other calcium-containing substances. Of this, about 40% (10 mmol) is absorbed in gut, and 5 mmol leaves the body in feces, netting 5 mmol of calcium a day. Vitamin D is an important co-factor in the intestinal absorption of calcium, as it increases the number of calcium binding proteins, involved in calcium absorption through the apical membrane of enterocytes in small intestine.

Excretion

The kidney excretes 250 mmol a day in pro-urine, and resorbs 245 mmol, leading to a net loss in the urine of 5 mmol/l. In addition to this, the kidney processes Vitamin D into calcitriol, the active form that is most effective in assisting intestinal absorption. Both processes are stimulated by parathyroid hormone.

The role of bone

Although calcium flow to and from the bone is neutral, about 5 mmol is turned over a day. Bone serves as an important storage point for calcium, as it contains 99% of the total body calcium. Calcium is released from bone by parathyroid hormone. Calcitonin stimulates incorporation of calcium in bone, although this process is largely independent of calcitonin.

Low calcium intake may also be a risk factor in the development of osteoporosis. In one meta-analyses, the authors found that only two out of the 52 studies that they reviewed showed that calcium intake did not promote better bone balance.[2] With a better bone balance, the risk of osteoporosis is lowered.

Regulatory organs

Primarily calcium is regulated by the actions of Vitamin D, parathyroid hormone and calcitonin. The only real regulatory organ is the parathyroid gland. The parathyroid glands are located behind the thyroid, and produce parathyroid hormone in response to low calcium levels.

The parafollicular cells of the thyroid produce calcitonin in response to high calcium levels, but its significance is much smaller than that of PTH.

Pathology

Hypocalcemia and hypercalcemia are both serious medical disorders.

Renal osteodystrophy is a consequence of chronic renal failure related to the calcium metabolism.

Osteoporosis and osteomalacia have been linked to calcium metabolism disorders.

Research into cancer prevention

The role that calcium might have in reducing the rates of colorectal cancer has been the subject of many studies. However, given its modest efficacy, there is no current medical recommendation to use calcium for cancer reduction. Several epidemiological studies suggest that people with high calcium intake have a reduced risk of colorectal cancer. These observations have been confirmed by experimental studies in volunteers and in rodents. One large scale clinical trial shows that 1.2 g calcium each day reduces, modestly, intestinal polyps recurrence in volunteers.[3] Data from the four published trials are available.[4] Some forty carcinogenesis studies in rats or mice, reported in the Chemoprev.Database, also support that calcium could prevent intestinal cancer.[5]

References

1. ^ Marshall, W. J. 1995. Clinical Chemistry, 3rd ed. Mosby, London.
2. ^ Heaney, R. P., et al. Calcium, dairy products and osteoporosis. J Am Coll Nutr. 2000 Apr;19(2 Suppl):83S-99S.
3. ^ Baron J, Beach M, Mandel J, van Stolk R, Haile R, Sandler R, Rothstein R, Summers R, Snover D, Beck G, Bond J, Greenberg E (1999). "Calcium supplements for the prevention of colorectal adenomas. Calcium Polyp Prevention Study Group". N Engl J Med 340 (2): 101-7. PMID 9887161. 
4. ^ [1]
5. ^ [2]

External links

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Endocrinology
Calcium (IPA: /ˈkalsiəm/) is the chemical element in the periodic table that has the symbol Ca and atomic number 20. It has an atomic mass of 40.078.
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MeSH D006934 Hypercalcaemia (or Hypercalcemia) is an elevated calcium level in the blood. (Normal range: 9-10.5 mg/dL or 2.2-2.6 mmol/L). It can be an asymptomatic laboratory finding, but because an elevated calcium level is often indicative of other diseases, a
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Hypocalcemia
Classification & external resources

Calcium
ICD-10 E 83.5
ICD-9 275.41

DiseasesDB 6412

eMedicine emerg/271  
MeSH D006996

In medicine, hypocalcemia
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Blood plasma is the liquid component of blood, in which the blood cells are suspended. It makes up about 55% of total blood volume. Blood plasma is prepared simply by spinning a tube of fresh blood in a centrifuge until the blood cells fall to the bottom of the tube.
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Serum albumin, often referred to simply as albumin, is the most abundant plasma protein in humans and other mammals. Albumin is essential for maintaining the osmotic pressure needed for proper distribution of body fluids between intravascular compartments and body tissues.
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Ionization is the physical process of converting an atom or molecule into an ion by changing the difference between the number of protons and electrons. This process works slightly differently depending on whether an ion with a positive or a negative electric charge is being
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The mole (symbol: mol) is the SI base unit that measures an amount of substance. One mole contains Avogadro's number (approximately 6.0221023) entities.

A mole is much like "a dozen" in that both are absolute numbers (having no units) and can describe any type of
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Milk is an opaque white liquid produced by the mammary glands of female mammals (including monotremes). Mammary glands are highly specialized sweat glands. The female ability to produce milk is one of the defining characteristics of mammals.
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GUT may refer to:
  • Grand unification theory, one of several unified field theories in physics
  • Gastrointestinal tract, a system of digestive organs
  • Gut, a scientific journal of gastroenterology, part of the British Medical Journal group

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Vitamin D is a group of fat-soluble prohormones, the two major forms of which are vitamin D2 (or ergocalciferol) and vitamin D3 (or cholecalciferol).[1] The term vitamin D also refers to metabolites and other analogues of these substances.
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This article or section may be confusing or unclear for some readers.
Please [improve the article] or discuss this issue on the talk page. This article has been tagged since December 2006.
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The apical membrane of a polarized cell is the part of the plasma membrane that forms its lumenal surface, distinct from the basolateral membrane. This is particularly evident in epithelial cells, but also describes other polarized cells, such as neurons.
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Enterocyte is a type of epithelial cell of the innermost layer of the small and large intestine tissue. These cells can help break up molecules and transport them into the tissues.
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In biology the small intestine is the part of the gastrointestinal tract (gut) between the stomach and the large intestine and includes the duodenum, jejunum, and ileum. It is where the vast majority of digestion takes place.
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The kidneys are organs that filter wastes (such as urea) from the blood and excrete them, along with water, as urine. The medical field that studies the kidneys and diseases of the kidney is called nephrology[1].
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Calcitriol (INN) (IPA: [kælsɪˈtraɪɒl, kælˈsɪtrɪɒl]) or 1,25-dihydroxycholecalciferol (abbreviated 1,25-(OH)2D3
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Parathyroid hormone (PTH), or parathormone, is secreted by the parathyroid glands as a polypeptide containing 84 amino acids. It acts to increase the concentration of calcium in the blood, whereas calcitonin (a hormone produced by the parafollicular cells (C cells) of the
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Bones are rigid organs that form part of the endoskeleton of vertebrates. They function to move, support, and protect the various organs of the body, produce red and white blood cells and store minerals.
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Parathyroid hormone (PTH), or parathormone, is secreted by the parathyroid glands as a polypeptide containing 84 amino acids. It acts to increase the concentration of calcium in the blood, whereas calcitonin (a hormone produced by the parafollicular cells (C cells) of the
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Calcitonin is a 32 amino acid polypeptide hormone that is produced in humans primarily by the parafollicular (also known as C) cells of the thyroid, and in many other animals in the ultimobranchial body.
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The parathyroid glands are small endocrine glands in the neck, usually located behind the thyroid gland, which produce parathyroid hormone. In rare cases the parathyroid glands are located within the thyroid glands.
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For other uses, see Thyroid cartilage.


The thyroid is one of the largest endocrine glands in the body. This gland is found in the neck just below the laryngeal prominence.
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Parafollicular cells (also called C cells) are cells in the thyroid which produce and secrete calcitonin.

Embryologically, they are derived from the ultimobranchial body, which itself is a derivative of the fourth pharyngeal pouch.
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PTH can refer to:
  • Parathyroid hormone
  • Plated through hole, used in electronics to connect layers with plated through hole vias
  • Polskie Towarzystwo Historyczne
  • Protest the Hero, a Canadian post-hardcore metal band from Whitby, Ontario

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Hypocalcemia
Classification & external resources

Calcium
ICD-10 E 83.5
ICD-9 275.41

DiseasesDB 6412

eMedicine emerg/271  
MeSH D006996

In medicine, hypocalcemia
..... Click the link for more information.
MeSH D006934 Hypercalcaemia (or Hypercalcemia) is an elevated calcium level in the blood. (Normal range: 9-10.5 mg/dL or 2.2-2.6 mmol/L). It can be an asymptomatic laboratory finding, but because an elevated calcium level is often indicative of other diseases, a
..... Click the link for more information.
Renal osteodystrophy is a bone pathology, characterized by defective mineralization, that results from renal disease. renal - refers to kidney, osteo - refers to bone, and dystrophy - means degenerative disorder (like dystrophy in muscular dystrophy).
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MeSH D007676 Chronic kidney disease (CKD), also know as chronic renal disease, is a progressive loss of renal function over a period of months or years through five stages.
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Osteoporosis
Classification & external resources

ICD-10 M 80. -M 82.
ICD-9 733.0

DiseasesDB 9385

eMedicine med/1693   ped/1683
MeSH D010024 Osteoporosis is a disease of bone leading to an increased risk of fracture.
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Osteomalacia
Classification & external resources

ICD-10 M 83.
ICD-9 268.2

DiseasesDB 9351

eMedicine ped/2014   radio/610
MeSH D010018 Osteomalacia is a softening of the bones, resulting from defective bone mineralization.
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