Which term refers to the ability of the heart to initiate impulses repetitively and spontaneously?

Correct Answer: C

Rationale: The correct answer is C: Automaticity. Automaticity refers to the ability of the heart to generate electrical impulses spontaneously, without external stimulation. This allows the heart to initiate its own contractions independently of external influences. Contractility (A) refers to the ability of the heart muscle to contract in response to an electrical stimulus. Excitability (B) refers to the ability of cardiac cells to respond to an electrical stimulus. Rhythmicity (D) refers to the regularity of the heart's electrical impulses. Thus, C is the correct answer as it specifically addresses the heart's ability to generate impulses spontaneously.

Correct Answer: A

Rationale: The correct answer is A: Norepinephrine. Norepinephrine is released by the sympathetic nervous system (SNS) to increase heart rate and the force of contraction. This neurotransmitter acts on beta-1 adrenergic receptors in the heart, leading to these effects. Epinephrine (choice B) is also released by the SNS and acts similarly to norepinephrine but is not as specific for the heart's beta-1 receptors. Dopamine (choice C) primarily acts as a precursor to norepinephrine and epinephrine and does not directly increase heart rate or force of contraction. Acetylcholine (choice D) is released by the parasympathetic nervous system and decreases heart rate and the force of contraction.

Correct Answer: A

Rationale: The correct answer is A: Cardiac Index. Cardiac Index is a more accurate indicator of tissue perfusion as it takes into account the individual's body surface area, providing a more standardized measure. It is calculated by dividing the cardiac output by body surface area. This normalization allows for a more precise assessment of tissue perfusion compared to just cardiac output alone. The normal range of Cardiac Index is 2.4-4 L/min/m^2. Summary: - Choice B (Stroke volume) is incorrect because it is the volume of blood pumped out by the heart with each heartbeat, not accounting for body surface area. - Choice C (Ejection fraction) is incorrect because it is the percentage of blood ejected from the heart's left ventricle with each heartbeat, not adjusted for body surface area. - Choice D (Cardiac output) is incorrect because it doesn't consider the individual's body surface area, making it less accurate in assessing tissue perfusion.

Correct Answer: A

Rationale: The correct answer is A: Aortic valve. The aortic valve is located between the left ventricle and the aorta, preventing the backflow of blood into the left ventricle during diastole. This is essential for maintaining proper blood flow direction and preventing regurgitation. The other choices, B: Mitral valve, C: Tricuspid valve, and D: Pulmonary valve, are all located in different areas of the heart and serve different functions. The mitral valve is between the left atrium and ventricle, the tricuspid valve is between the right atrium and ventricle, and the pulmonary valve is between the right ventricle and pulmonary artery. None of these valves are responsible for preventing backflow into the left ventricle from the aorta.

Correct Answer: A

Rationale: The correct answer is A: Heart failure. This condition occurs when the heart is unable to pump enough blood to meet the body's needs. It can result from various factors such as high blood pressure, heart muscle damage, or heart valve disorders. In contrast, B (Myocardial infarction) refers to a heart attack caused by a blockage in the coronary arteries, C (Cardiomyopathy) is a disease of the heart muscle, and D (Pericarditis) is inflammation of the pericardium surrounding the heart. These conditions may affect the heart's function but do not specifically indicate the inability to pump sufficient blood like heart failure does.