Which heart chamber ejects blood into the lungs via the pulmonary artery?

Correct Answer: C

Rationale: The correct answer is C, the right ventricle. The right ventricle is responsible for pumping deoxygenated blood to the lungs via the pulmonary artery for oxygenation. This process occurs during the pulmonary circulation phase of the cardiac cycle. The right atrium receives deoxygenated blood from the body and pumps it into the right ventricle. The right ventricle then contracts to push the blood through the pulmonary valve and into the pulmonary artery. The left atrium receives oxygenated blood from the lungs, which is then pumped into the left ventricle for distribution to the rest of the body. Therefore, choices A, B, and D are incorrect as they do not directly involve the ejection of blood into the lungs via the pulmonary artery.

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: B

Rationale: The correct answer is B (Approximately 4 to 8 L per minute) because the average cardiac output in a healthy adult at rest is around 5 L per minute. This range of 4 to 8 L per minute encompasses the typical cardiac output values. Choice A (Approximately 4 to 6 L per minute) is too narrow and excludes the upper range, while Choice C (Approximately 5 to 8 L per minute) is slightly broader but still within the acceptable range. Choice D (Approximately 3 to 7 L per minute) is too low and does not cover the full spectrum of average cardiac output values.

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.