Calcium in biology

<a href="/facts/Calcium/hf252CC0">Calcium</a> ions (Ca2+) contribute to the <a href="/facts/Physiology/fh25y2pQ">physiology</a> and <a href="/facts/Biochemistry/fa2pWEBp">biochemistry</a> of organisms' <a href="/facts/Cell_(biology)/bLM9UQvy">cells</a>. They play an important role in <a href="/facts/Signal_transduction/1bs0Me6w">signal transduction</a> pathways, where they act as a <a href="/facts/Second_messenger/J0eEENxQ">second messenger</a>, in <a href="/facts/Neurotransmitter/LlpYFSU3">neurotransmitter</a> release from <a href="/facts/Neurons/G7CyTVdH">neurons</a>, in contraction of all <a href="/facts/Muscle/dmxrL8pH">muscle</a> cell types, and in <a href="/facts/Fertilization/g8u3UKzF">fertilization</a>. Many <a href="/facts/Enzyme/DSI1Fh7y">enzymes</a> require calcium ions as a <a href="/facts/Cofactor_(biochemistry)/AGo0PCUU">cofactor</a>, including several of the <a href="/facts/Coagulation_factor/vnfEevM0">coagulation factors</a>. Extracellular calcium is also important for maintaining the <a href="/facts/Potential_difference/EN2po6N2">potential difference</a> across <a href="/facts/Excitable_cell/DpNG14c7">excitable cell</a> <a href="/facts/Cell_membrane/vAXSD0DT">membranes</a>, as well as proper bone formation.
Plasma calcium levels in mammals are tightly regulated, with <a href="/facts/Bone/kwJaR6IQ">bone</a> acting as the major <a href="/facts/Mineral_storage/LkUFbNmv">mineral storage</a> site. Calcium <a href="/facts/Ion/3bePpDna">ions</a>, Ca2+, are released from bone into the bloodstream under controlled conditions. Calcium is transported through the bloodstream as dissolved ions or bound to proteins such as <a href="/facts/Serum_albumin/KW1YhuF3">serum albumin</a>. <a href="/facts/Parathyroid_hormone/Dh7Uld78">Parathyroid hormone</a> secreted by the <a href="/facts/Parathyroid_gland/HmyY4S4m">parathyroid gland</a> regulates the <a href="/facts/Bone_resorption/cMx23mGW">resorption</a> of Ca2+ from bone, <a href="/facts/Reabsorption/8S2Im6RU">reabsorption</a> in the kidney back into circulation, and increases in the activation of <a href="/facts/Vitamin_D3/ILqn7syS">vitamin D3</a> to <a href="/facts/Calcitriol/3SXesdFb">calcitriol</a>. Calcitriol, the active form of vitamin D3, promotes <a href="/facts/Small_intestines/1AQ8RJ4m">absorption</a> of calcium from the intestines and bones. <a href="/facts/Calcitonin/E0xGEcr5">Calcitonin</a> secreted from the <a href="/facts/Parafollicular_cell/y5lhNJQz">parafollicular cells</a> of the <a href="/facts/Thyroid_gland/bjovTJVu">thyroid gland</a> also affects calcium levels by opposing parathyroid hormone; however, its physiological significance in humans is dubious.
<a href="/facts/Intracellular/UEPUhSN8">Intracellular</a> calcium is stored in <a href="/facts/Organelle/vhDFnGbs">organelles</a> which repetitively release and then reaccumulate Ca2+ ions in response to specific cellular events: storage sites include <a href="/facts/Mitochondria/ErHqrdJ1">mitochondria</a> and the <a href="/facts/Endoplasmic_reticulum/DVbLA7GE">endoplasmic reticulum</a>.
Characteristic concentrations of calcium in model organisms are: in E. coli 3 <a href="/facts/Millimolar/P2WL5b9q">mM</a> (bound), 100 <a href="/facts/Nanomolar/P2WL5b9q">nM</a> (free), in budding yeast 2 mM (bound), in mammalian cell 10–100 nM (free) and in blood plasma 2 mM.

Calcium in biology open-in-new

Calcium in biology