Ca²⁺ Homeostasis

Definition

Ca²⁺ homeostasis is the dynamic equilibrium of Ca²⁺ ion concentration in the body or in the cell (“cellular Ca²⁺ homeostasis”).

Characteristics

Even if 99 % of the Ca²⁺ ions of the body are trapped in the bones and could be considered as stable, Ca²⁺ homeostasis refers to the control of the free Ca²⁺ ion concentrations at the extracellular (“[Ca²⁺]_ex”) and the intracellular (“[Ca²⁺]_i”) levels.

Control of [Ca²⁺]_ex is important because Ca²⁺ ions stabilize numerous ionic channels like the voltage-gated ones: thus a decrease of [Ca²⁺]_ex could induce spontaneous contraction of muscles, implying that [Ca²⁺]_ex must be tightly controlled in the blood. This is mainly done by parathyroid hormone that controls the uptake of Ca²⁺ ions by the gusts, the release by the bones, and the reabsorption by the kidneys.

Cellular Ca²⁺ Homeostasis

At the cellular level, [Ca²⁺]_i is an equilibrium between the Ca²⁺ ion concentration of the different compartments, mainly the cytosol ([Ca²⁺]_cyt),...