Cardiovascular and Nervous System

Blood pressure varies during sleep cycles and can fluctuate with body movements, REM sleep, and autonomic nervous system activity. While it generally decreases during sleep compared to wakefulness, it doesn't remain perfectly constant.

The cardiac cycle lasts approximately 0.8 seconds at a normal heart rate of 75 beats per minute (60 seconds ÷ 75 beats = 0.8 seconds). This duration includes systole (contraction) and diastole (relaxation) phases. At this rate, the heart completes approximately 72 cardiac cycles per minute.

A heart attack (myocardial infarction) occurs when blood flow to the heart muscle is blocked, usually by a blood clot in a coronary artery. This lack of blood supply causes heart muscle cells to die. It's not caused by bacteria, and the heart doesn't completely stop beating (that's cardiac arrest).

Chordae tendineae are fibrous cords connecting atrioventricular valve cusps to papillary muscles in the ventricles. They prevent valve inversion (prolapse) when ventricles contract, ensuring unidirectional blood flow. Without them, high ventricular pressure would force valves back into atria, causing regurgitation. They do not open valves or support the septum.

 The function of this valve is to prevent the back flow of blood into the right atrium.

Atrioventricular valves remain closed during isovolumetric contraction, ventricular ejection and isovolumetric relaxation.

Arteries have thicker walls than veins because the blood flows through the arteries at a much higher pressure. The tricuspid valve is located between the right atrium and the right ventricle.

The autonomic nervous system regulates involuntary visceral functions: heart rate (cardiac innervation), respiratory rate (respiratory centers), and blood pressure (vasomotor control). Memory and intelligence are cognitive functions regulated by the central nervous system (cerebral cortex, hippocampus), not the autonomic system.

The first heart sound (S1) is the "lubb" sound caused by the closure of the atrioventricular valves (mitral and tricuspid) at the beginning of systole. The second heart sound (S2) is the "dupp" sound caused by semilunar valve closure at the end of systole.

Correct statement. Average cardiac output is 5.3 liter per minute.

Cardiac output is defined as the volume of blood pumped by each ventricle per minute, calculated as the product of heart rate (beats per minute) and stroke volume (blood pumped per beat). Option B is nonsensical, C lacks the formula, and D describes stroke volume, not cardiac output.

The coronary sinus is a major coronary vein. It returns the majority of the left ventricular blood flow to the right atrium. The coronary sinus orifice of the right atrium is the aperture via which approximately 90% venous drainage of the heart is returned to the circulation by the coronary sinus.

The pericardium and parietal pleura are innervated by the phrenic nerve (C3-C5). This explains why pericarditis pain is typically retrosternal and may radiate to the shoulder (via C3-C5 dermatomal distribution). The phrenic nerve mediates the pain sensation from these structures.

The c-wave in the jugular venous pulse occurs due to bulging of the closed tricuspid valve into the right atrium during early ventricular systole (isovolumetric contraction). This creates a small rise in atrial pressure. It is distinct from the a-wave (atrial contraction) and v-wave (atrial filling against closed tricuspid valve).

Mitral regurgitation causes volume overload of the left ventricle and left atrium. This leads to pulmonary venous hypertension, which increases pulmonary blood volume. The increased residual volume occurs because of the elevated pulmonary venous pressure and subsequent fluid shifts. This is a manifestation of pulmonary congestion secondary to left-sided valvular insufficiency.