What is the function of myoglobin in cardiac muscle?
It binds and stores oxygen for aerobic metabolism.
It transports glucose into heart cells.
It generates electrical impulses for contraction.
It breaks down fatty acids into АТР.
The Correct Answer is A
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.
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Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is D
Explanation
A. It is caused only by infections: Heart failure has multiple causes, including chronic hypertension, coronary artery disease, myocardial infarction, valvular disorders, and cardiomyopathies. While infections such as myocarditis can contribute, they are not the sole cause.
B. It always results in a heart attack: Heart failure is a condition of impaired cardiac function, whereas a heart attack (myocardial infarction) is an acute event caused by coronary artery blockage. Heart failure may develop after a heart attack, but it does not always result from one.
C. It does not affect blood circulation: Heart failure directly impairs the heart’s ability to pump blood effectively, reducing cardiac output and often causing fluid buildup in the lungs and systemic circulation. Circulatory compromise is a hallmark of the condition.
D. It is a condition where the heart can't pump blood properly: Heart failure occurs when the myocardium cannot generate sufficient force to maintain adequate blood flow to meet the body’s metabolic demands. This can involve systolic dysfunction (impaired contraction), diastolic dysfunction (impaired filling), or a combination, leading to fluid retention, congestion, and reduced tissue perfusion.
Correct Answer is B
Explanation
A. A 40-year-old person would have an expected maximum HR of 160 bpm: Maximum heart rate is estimated using the formula 220 minus age. For a 40-year-old, the expected maximum HR would be approximately 180 bpm, not 160 bpm. This formula provides a general guideline for exercise and stress testing.
B. Resting HR decreases from infancy to young adulthood: Resting heart rate is higher in infants (typically 120–160 bpm) due to higher metabolic demands and smaller stroke volume. As the cardiovascular system matures and stroke volume increases, resting HR gradually decreases through childhood into young adulthood, stabilizing around 60–100 bpm in healthy adults.
C. Maximum HR is independent of age and remains around 220 bpm throughout life: Maximum heart rate declines with age due to physiological changes in the sinoatrial node and cardiac responsiveness to sympathetic stimulation. It is not constant at 220 bpm; instead, it decreases roughly 1 bpm per year after adolescence.
D. Newborns typically have a resting HR of around 75 bpm: Newborns normally have a resting HR between 120–160 bpm due to their high metabolic rate and limited stroke volume. A HR of 75 bpm in a newborn would be abnormally low and may indicate bradycardia or cardiac compromise.
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