Which of following explains the increased intrinsic contractility of the myocardium during exercise.
Decreased parasympathetic stimulation Increased lactate
Decreased catecholamines Increased parasympathetic stimulation
Increased sympathetic stimulation
The correct answer and explanation is:
The correct answer is: Increased sympathetic stimulation.
During exercise, the body undergoes numerous physiological changes to meet the increased demands of physical activity. One of the critical adaptations is an increase in the intrinsic contractility of the myocardium (heart muscle). This increase is primarily due to increased sympathetic stimulation, which plays a pivotal role in regulating heart function.
The sympathetic nervous system releases catecholamines, such as norepinephrine and epinephrine, which bind to beta-1 adrenergic receptors in the heart. This activation results in several effects that enhance cardiac performance. First, it increases the heart rate (chronotropy) and the force of contraction (inotropy), thereby improving the heart’s ability to pump blood and deliver oxygen to muscles during exercise.
Additionally, the increase in sympathetic stimulation leads to enhanced calcium influx into the myocardial cells. This increases the amount of calcium available for muscle contraction, which boosts the contractile force of the heart muscle. This mechanism is known as positive inotropy. It is essential for meeting the increased demand for oxygenated blood during physical exertion.
On the other hand, decreased parasympathetic stimulation contributes to this effect, as parasympathetic activity, which is mediated by acetylcholine, normally works to slow the heart rate and decrease contractility. During exercise, parasympathetic activity is reduced to allow the sympathetic system to take control and prepare the body for increased physical activity.
Although factors such as increased lactate or decreased catecholamines may influence the body’s response to exercise, they do not directly contribute to the increased intrinsic contractility of the heart in the same way as sympathetic stimulation. In summary, increased sympathetic stimulation is the primary factor that explains the increased intrinsic contractility of the myocardium during exercise.