ANATOMY

Detailed explanation-1: -Cardiac sarcoplasmic reticulum (SR) Ca(2+) ATPase (SERCA2a) plays a central role in myocardial contractility. SERCA2a actively transports Ca(2+) into the SR and regulates cytosolic Ca(2+) concentration, SR Ca(2+) load, and the rate of contraction and relaxation of the heart.

Detailed explanation-2: -The calcium that enters the heart cell through the calcium ion channel activates the ryanodine receptor to release enough calcium from the sarcoplasmic reticulum to initiate heart muscle contraction. This is done by binding to another structure, named troponin, inside the heart muscle cell.

Detailed explanation-3: -Calcium homeostasis is maintained by actions of hormones that regulate calcium transport in the gut, kidneys, and bone. The 3 primary hormones are parathyroid hormone (PTH) 1, 25-dihydroxyvitamin D-3 (Vitamin D3), and calcitonin.

Detailed explanation-4: -Ca2+ ions play an important role in muscle contraction by creating interactions between the proteins, myosin and actin. The Ca2+ ions bind to the C component of the actin filament, which exposes the binding site for the myosin head to bind to in order to stimulate a muscle contraction.