In this article we will discuss about Calcium (Ca++). After reading this article you will learn about: 1. Need of Calcium 2. Roles of Calcium 3. Metabolism.

Need of Calcium:

Calcium is vital for animal life. In verte­brates, this divalent ion is present at vari­ous sites, including body fluids, ER and endoskeleton. The mineral plays an essential role in many physiological events like muscle contraction, blood coagulation, nerve impulse propagation, hormone transduction etc.

In mammals, about 99% of Ca++ the body is in crystalline form within the skel­eton and teeth. The remaining 1% present intra cellularly within soft tissue and in ex­tracellular fluid. Ca++ metabolism is chiefly regulated by calcitonin (CT), parathyroid hormone (PTH) and vitamin D3.

Important Roles of Calcium:

1. Main structural component of bones and teeth.

2. Controls the membrane potentials in neu­rons.

3. Necessary for contraction of muscle.

4. Unique role in membrane potentials of pacemaker cells.

5. Acts as second messenger in hormone action.

6. Role in exocytosis of secretory products from cells.

7. Acts as one of the component of inter­cellular matrices.

Calcium Metabolism (CT):

CT is secreted continuously under normal condition. Regarding calcium metabolism, CT secretion is directly co-related with plasma calcium level. Elevated blood Ca++ level stimulates linear “rises in CT secretion, while fall in plasma Ca++ decreases its se­cretion. During Ca++ metabolism, CT chiefly reacts on—

1. Action on bones:

CT has two effects on bone, but in this case both effects de­crease plasma Ca++ levels.

First on a short term basis CT decreases Ca++ movement from the bone fluid into the plasma.

Second on a long-term basis CT decreases bone resorption by inhibiting the activities of osteoclasts, like, ruffling and microvilli on their membrane, activi­ties of lysosomal hydrolases, alkaline phosphatase and pyrophosphatase in bones collagen metabolism and urinary hydroxy-proline.

2. On kidney:

CT decreases reabsorption Ca++ from the tubular filtrate by ascend­ing limb and distal convoluted tubule. Thus, it enhances renal clearances of Ca++.

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