What structures hold up the AV valves and are anchored to the ventricular wall by the papillary muscles?

Correct Answer: A

Rationale: The correct answer is A: Chordae tendineae. These fibrous cords hold up the AV valves (mitral and tricuspid valves) and are anchored to the ventricular wall by the papillary muscles. The papillary muscles contract to prevent the AV valves from prolapsing into the atria during ventricular contraction. Choice B (Papillary muscles) is incorrect as they assist in the function but are not the structures that hold up the AV valves. Choices C (Semilunar valves) and D (Aortic valve) are incorrect as they are not directly involved in supporting the AV valves or anchored by the papillary muscles.

Correct Answer: A

Rationale: The correct answer is A: Excitability. Excitability refers to the ability of cardiac cells to respond to a stimulus by initiating a cardiac impulse. This process is essential for the heart to function properly. Contractility (B) is the ability of cardiac muscle to shorten forcibly when stimulated. Rhythmicity (C) refers to the heart's ability to generate a regular rhythm of contractions. Conductivity (D) is the ability of cardiac cells to transmit electrical impulses. Excitability is the most fitting term in this context as it specifically describes the response of cardiac cells to a stimulus.

Correct Answer: B

Rationale: The correct answer is B (Approximately 70 mL of blood per beat). The average human stroke volume is around 70 mL. This volume represents the amount of blood ejected by the left ventricle in each contraction. It is important to note that stroke volume can vary depending on factors such as age, fitness level, and cardiac health. Choices A, C, and D are incorrect because they do not align with the typical range of stroke volume in a healthy adult. Option A (60 mL) is slightly below the average, while options C (80 mL) and D (90 mL) are above the typical range. Therefore, the best approximation for stroke volume in the heart is around 70 mL per beat.

Correct Answer: A

Rationale: The correct answer is A: Baroreceptors. Baroreceptors are pressure-sensitive structures that detect changes in blood pressure in the aortic and carotid bodies. They help regulate blood pressure by sending signals to the brain to adjust heart rate and blood vessel dilation. Chemoreceptors (B) detect changes in chemical composition, not pressure. Nociceptors (C) detect pain stimuli. Mechanoreceptors (D) detect mechanical stimuli, not specifically pressure changes. Therefore, the correct answer is A as baroreceptors specifically respond to changes in blood pressure.

Correct Answer: A

Rationale: The correct answer is A: Acetylcholine. Acetylcholine is released by the parasympathetic nervous system and acts on the heart to decrease heart rate. It binds to muscarinic receptors in the heart, leading to a decrease in heart rate through inhibition of the SA node. Norepinephrine (B) is released by the sympathetic nervous system and increases heart rate. Dopamine (C) and Serotonin (D) are not directly involved in regulating heart rate through the parasympathetic pathway.