After the AV node, the electrical impulse is then transmitted into the _________, and into the _________.

Correct Answer: C

Rationale: The correct answer is C: Bundle of His, Purkinje fibers. After the AV node, the electrical impulse is transmitted to the Bundle of His, which then branches into the Purkinje fibers to spread the impulse throughout the ventricles. This sequence ensures coordinated and efficient contraction of the heart muscle. Choices A, B, and D are incorrect because they do not follow the physiological pathway of the electrical conduction system of the heart. The Purkinje fibers are responsible for transmitting the impulse to the ventricles, not the atria or vice versa as suggested in the other choices.

Correct Answer: A

Rationale: The correct answer is A: Frank-Starling's Law. This law states that within physiologic limits, the greater the myocardial fiber stretch, the more forceful the ventricular contraction, leading to increased stroke volume. This is because increased fiber stretch results in optimal overlap of actin and myosin filaments in the sarcomeres, enhancing contractile force. Summary: B: Automaticity refers to the ability of cardiac cells to spontaneously generate electrical impulses. C: Contractility is the intrinsic ability of cardiac muscle to generate force. D: Excitability refers to the ability of cardiac cells to respond to electrical stimuli.

Correct Answer: D

Rationale: The correct answer is D: Epinephrine. Epinephrine acts as a central vasoconstrictor by constricting blood vessels in vital organs to redirect blood flow to muscles during fight-or-flight response. It also acts as a peripheral vasodilator by dilating blood vessels in skeletal muscles to increase oxygen delivery. Parasympathetic nervous system (A) mainly promotes relaxation, sympathetic nervous system (B) typically causes vasoconstriction, and dopamine (C) has limited vasoactive effects.

Correct Answer: C

Rationale: The correct answer is C, the left ventricle. The left ventricle receives oxygenated blood from the lungs through the left atrium and pumps it to the rest of the body via the aorta. This chamber has thicker muscular walls compared to the right ventricle to generate enough force to propel blood throughout the body. The left atrium receives oxygenated blood from the lungs but does not pump blood out to the body. The right atrium receives deoxygenated blood from the body and sends it to the right ventricle, which then pumps it to the lungs for oxygenation. Therefore, choices A, B, and D are incorrect as they do not accurately describe the function of the heart chamber that receives oxygenated blood from the lungs and pumps it to the rest of the body.

Correct Answer: A

Rationale: The correct answer is A: Diastole. Diastole refers to the relaxation phase of the heart, allowing the chambers to fill with blood. During diastole, the ventricles are relaxed, and blood flows into them from the atria. Systole, choice B, is the contraction phase where the heart pumps blood out. Refractoriness, choice C, refers to the period when the heart cannot respond to a new stimulus. Automaticity, choice D, is the ability of the heart to generate its own electrical impulses. So, diastole is the correct term for the relaxation phase of the heart where chambers fill with blood, making it the correct answer.