Which of the following statements about heart rate (HR) is correct?

Correct answer: Left coronary

The left coronary artery arises from the left side of the ascending aorta, just above the aortic valve, and quickly branches to supply the heart muscle. Its two main branches are the anterior interventricular artery (also called the left anterior descending artery), which runs along the interventricular groove supplying the anterior walls of both ventricles, and the circumflex artery, which curves around the left side of the heart to supply the lateral and posterior walls of the left ventricle and left atrium. This anatomical arrangement ensures that oxygen-rich blood from the aorta is delivered efficiently to the majority of the left heart myocardium.

A. It binds and stores oxygen for aerobic metabolism: Myoglobin is an oxygen-binding protein located within the cytoplasm of cardiac and skeletal muscle cells. It serves as an intracellular oxygen reservoir, facilitating rapid oxygen delivery to mitochondria during periods of high metabolic demand. This supports sustained aerobic metabolism and continuous ATP production necessary for cardiac contraction.

B. It transports glucose into heart cells: Glucose transport into cardiomyocytes is mediated by glucose transporters (GLUT1 and GLUT4), not by myoglobin. Myoglobin’s role is specifically related to oxygen handling, not nutrient transport.

C. It generates electrical impulses for contraction: Electrical impulses in the heart are generated by pacemaker cells in the sinoatrial node and conducted through the cardiac conduction system. Myoglobin has no role in depolarization or action potential propagation.

D. It breaks down fatty acids into ATP: Fatty acid oxidation occurs in mitochondria through beta-oxidation, producing ATP. Myoglobin does not catalyze this process; its primary function is oxygen storage and delivery to support mitochondrial metabolism.