calcium

(noun)

A chemical element, atomic number 20, that is an alkaline earth metal and occurs naturally as carbonate in limestone and as silicate in many rocks.

Related Terms

Examples of calcium in the following topics:

  • Bone and Calcium Homeostasis

    • Calcium metabolism or calcium homeostasis is the mechanism by which the body maintains adequate calcium levels.
    • Calcium metabolism or calcium homeostasis is the mechanism by which the body maintains adequate calcium levels.
    • Bone serves as an important storage point for calcium, as it contains 99% of the total body calcium.
    • Removal of calcium from the bone is also inhibited.
    • This results in the removal of calcium from the bone to correct blood calcium levels.

  • Parathyroid Hormone

    • Parathyroid hormone maintains the body's calcium levels by increasing absorption of calcium from the bones, kidneys, and GI tract.
    • When blood calcium levels drop below a certain point, calcium-sensing receptors in the parathyroid gland are activated, and the parathyroid glands release parathyroid hormone (PTH) into the blood.
    • Parathyroid hormone acts to increase blood calcium levels, while calcitonin acts to decrease blood calcium levels.
    • Parathyroid hormone acts on the bone to increase blood calcium levels by stimulating osteoclasts to break down bone, releasing calcium into the bloodstream.
    • It acts on the kidneys to increase blood calcium levels by promoting calcium reabsorption in the nephrons.

  • Hormonal Control of Blood Calcium Levels

    • PTH is released in response to low blood calcium levels.
    • In the intestines, PTH increases dietary calcium absorption and in the kidneys, PTH stimulates re-absorption of the calcium.
    • PTH release is inhibited by rising blood calcium levels.
    • Calcitonin decreases blood calcium levels by inhibiting osteoclasts, stimulating osteoblasts, and stimulating calcium excretion by the kidneys.
    • It increases blood calcium levels by stimulating the resorption of bones, increasing calcium resorption in the kidneys, and indirectly increasing calcium absorption in the intestines.

  • Regulatory Proteins

    • The inward flow of calcium from the L-type calcium channels activates ryanodine receptors to release calcium ions from the sarcoplasmic reticulum.
    • This mechanism is called calcium-induced calcium release (CICR).
    • It is not understood whether the physical opening of the L-type calcium channels or the presence of calcium causes the ryanodine receptors to open.
    • Calcium remains in the sarcoplasmic reticulum until released by a stimulus.
    • Cross-bridge cling continues until the calcium ions and ATP are no longer available.

  • Mechanism and Contraction Events of Cardiac Muscle Fibers

    • Cardiac muscle fibers undergo coordinated contraction via calcium-induced calcium release, conducted through the intercalated discs.
    • In cardiac muscle, ECC is dependent on a phenomenon called calcium-induced calcium release (CICR), which involves the influx of calcium ions into the cell triggering further release of ions into the cytoplasm.
    • The mechanism for CIRC is that receptors within the cardiomyocyte will bind to calcium ions when calcium ion channels open during depolarization, and will release more calcium ions into the cell.
    • As the action potential travels between sarcomeres, it activates the calcium channels in the T-tubules, resulting in an influx of calcium ions into the cardiomyocyte.
    • Calcium in the cytoplasm then binds to cardiac troponin-C, which moves the troponin complex away from the actin binding site.

  • Parathyroid Glands

    • Calcium is important for metabolization to occur.
    • Blood cannot clot without sufficient calcium.
    • More specifically, PTH increases blood calcium concentrations when calcium ion levels fall below normal.
    • The parathyroid glands produce parathyroid hormone (PTH) which increases blood calcium concentrations when calcium ion levels fall below normal.
    • Describe how the parathyroid glands regulate calcium levels in the blood

  • Overview of the Parathyroid Glands

    • Parathyroid glands control the amount of calcium in the blood and within the bones.
    • When blood calcium levels drop below a certain point, calcium-sensing receptors in the parathyroid gland are activated to release parathyroid hormone (PTH) into the blood.
    • PTH modulates calcium and phosphate homeostasis, as well as bone physiology.
    • PTH has effects antagonistic to those of calcitonin by increasing blood calcium levels by stimulating osteoclasts to break down bone and release calcium.
    • PTH also increases gastrointestinal calcium absorption by activating vitamin D, and promotes calcium conservation by re-absorption in the kidneys.

  • Calcium and Phosphate Balance Regulation

    • Calcium is a very important electrolyte.
    • In the typical Australian diet, there is about 1200 mg/d of calcium.
    • There is also a constant loss of calcium via the kidneys even if there is none in the diet.
    • Calcium in plasma exists in three forms: ionized, nonionized and protein bound.
    • This increases ionized calcium levels by increasing bone re-absorption, decreasing renal excretion and acting on the kidney to increase the rate of formation of active Vitamin D, thereby increasing gut absorption of calcium.

  • Short-Term Chemical Control

    • When stimulated a signal transduction cascade leads to increased intracellular calcium from the sarcoplasmic reticulum through IP3 mediated calcium release, as well as enhanced calcium entry across the sarcolemma through calcium channels.
    • The rise in intracellular calcium complexes with calmodulin, which in turn activates myosin light chain kinase.
    • Once elevated, the intracellular calcium concentration is returned to its basal level through a variety of protein pumps and calcium exchangers located on the plasma membrane and sarcoplasmic reticulum.
    • This reduction in calcium removes the stimulus necessary for contraction allowing for a return to baseline.
    • Dephosphorylation by myosin light-chain phosphatase and induction of calcium symportersand antiporters that pump calcium ions out of the intracellular compartment both contribute to smooth muscle cell relaxation and therefore vasodilation.

  • Effect of a Common Ion on Solubility

    • In areas where water sources are high in chalk or limestone, drinking water contains excess calcium carbonate CaCO3.
    • In the water treatment process, sodium carbonate salt is added to precipitate the calcium carbonate.
    • The very pure and finely divided precipitate of calcium carbonate that is generated is used in the manufacture of toothpaste.
    • What is the solubility at 25°C of calcium fluoride (CaF2): (a) in pure water; (b) in 0.10 M calcium chloride (CaCl2); and (c) in 0.10 M sodium fluoride (NaF)?
    • (b) Here the calcium ion concentration is the sum of the concentrations of calcium ions from the 0.10 M calcium chloride and from the calcium fluoride whose solubility we are seeking: