What is the term that describes the inability of cardiac cells to respond to a new stimulus while they are still in contraction from a previous stimulus?

Correct Answer: A

Rationale: The correct answer is A: Refractoriness. Refractoriness refers to the period during which cardiac cells are unable to respond to a new stimulus while still contracting from a previous stimulus. This is essential for preventing premature re-stimulation and ensuring proper cardiac function. B: Excitability refers to the ability of cardiac cells to respond to a stimulus, which is the opposite of what is described in the question. C: Contractility is the ability of cardiac cells to contract in response to an electrical stimulus, not related to the inability to respond to a new stimulus during contraction. D: Automaticity is the ability of cardiac cells to spontaneously generate electrical impulses, unrelated to the inability to respond to a new stimulus during contraction.

Correct Answer: A

Rationale: The correct answer is A: Sympathetic nervous system. The sympathetic nervous system releases norepinephrine, which acts as a central vasodilator by dilating blood vessels in the heart and skeletal muscles. It also acts as a peripheral vasoconstrictor by constricting blood vessels in other areas to redirect blood flow to vital organs during fight-or-flight responses. B: Parasympathetic nervous system is incorrect as it primarily promotes rest and digestion, not vasodilation or vasoconstriction. C: Norepinephrine is incorrect as it acts as a peripheral vasoconstrictor, not a central vasodilator. D: Acetylcholine is incorrect as it primarily functions in the parasympathetic nervous system and is not associated with central vasodilation or peripheral vasoconstriction.

Correct Answer: A

Rationale: Step 1: Heart failure is characterized by the heart's inability to effectively pump blood, leading to fluid buildup and swelling. Step 2: Cardiomyopathy is a disease of the heart muscle, which may contribute to heart failure but is not the direct cause of fluid buildup. Step 3: Angina is chest pain due to reduced blood flow to the heart, not directly related to fluid buildup. Step 4: Myocarditis is inflammation of the heart muscle, which can lead to heart failure but is not the primary cause of fluid accumulation. Summary: Heart failure is the correct answer as it directly relates to the inability of the heart to pump blood effectively, leading to fluid accumulation. Cardiomyopathy, angina, and myocarditis are related to heart health but do not directly cause fluid buildup in the body.

Correct Answer: A

Rationale: The correct answer is A: Cardiac output. Cardiac output is the total amount of blood pumped by the heart in a minute. It is calculated by multiplying the heart rate (beats per minute) by the stroke volume (amount of blood pumped per beat). This measurement gives an indication of how effectively the heart is functioning in delivering oxygenated blood to the body. B: Stroke volume is the amount of blood pumped by the heart in each beat, not the total amount in a minute. C: End-diastolic volume is the amount of blood in the ventricles before contraction, not the total amount pumped in a minute. D: Ejection fraction is the percentage of blood pumped out of the ventricles with each contraction, not the total amount in a minute.

Correct Answer: A

Rationale: The correct answer is A: Cardiac arrest. Cardiac arrest is a life-threatening emergency where the heart stops beating suddenly. This leads to the cessation of blood flow to vital organs, causing loss of consciousness and death if not treated immediately with CPR and defibrillation. Myocardial infarction (B) is a heart attack where blood flow to the heart muscle is blocked, leading to tissue damage. Heart failure (C) is a chronic condition where the heart is unable to pump blood effectively. Atrial fibrillation (D) is an irregular heartbeat that can increase the risk of stroke but is not the same as cardiac arrest.