Cardiovascular and Nervous System

When changing from standing to lying down, gravity no longer pulls blood downward into the legs, so venous return to the heart increases immediately. Heart rate may transiently decrease due to increased baroreceptor firing, not increase. Cerebral blood flow is relatively stable in both positions due to autoregulation. Pulmonary blood flow distribution becomes more uniform in the supine position.

Mitral valve prolapse is characterized by myxomatous degeneration of the valve leaflets, which involves accumulation of glycosaminoglycans and disruption of collagen fibers. This makes the leaflets floppy and prolapsed. Hyalinization and fibrinoid necrosis are not typical findings in MVP.

Mitral valve prolapse is pathologically characterized by myxomatous degeneration, where the valve leaflets become floppy and redundant due to accumulation of glycosaminoglycans in the connective tissue. This causes the valve to billow backward into the left atrium during systole. Hyalinization is seen in aging valves, while fibrinoid necrosis occurs in vasculitis.

Tetralogy of Fallot (TOF) consists of four essential components: ventricular septal defect (VSD), right ventricular outflow tract obstruction (typically infundibular/subvalvular pulmonary stenosis), overriding aorta, and right ventricular hypertrophy. Valvular pulmonic stenosis is NOT part of the classic tetrad - the obstruction is infundibular (subvalvular) rather than at the valve itself. This distinction is important for surgical planning and prognosis.

ECG (Electrocardiogram) records the electrical activity of the heart from electrodes placed on the skin. It shows the cardiac cycle (P wave, QRS complex, T wave) and is essential for diagnosing arrhythmias, myocardial infarction, conduction defects, and electrolyte imbalances. EEG (Electroencephalogram) is for brain electrical activity. Kidney function tests (creatinine, BUN) and liver function tests assess those organs. ECG is exclusively cardiac.

In a healthy resting adult, the cardiac output of either ventricle is roughly 5 liters per minute, calculated as heart rate multiplied by stroke volume (e.g., 70 beats per minute times 70 milliliters per beat).

The P wave in an ECG represents the depolarization of atrial muscle tissue, which is the electrical event that precedes atrial contraction. Option A incorrectly states it represents contraction itself - the ECG records electrical activity, not mechanical contraction. The QRS complex represents ventricular depolarization.

The autonomic nervous system (ANS) controls involuntary functions including heart rate and force (cardiac regulation) and digestive gland secretions (gastrointestinal regulation). The CNS processes information but the ANS executes these specific involuntary controls. Spinal and cranial nerves are pathways but don't regulate these functions autonomously.

The contractions of cardiac muscle fibres are described as myogenic since they are produced spontaneously without requiring stimulation from nerve cells. The heart of elephant is myogenic. 

Calcium ions (Ca++) are essential for the blood clotting cascade. Factor IV in the coagulation pathway is actually calcium ions, which are required cofactors for multiple steps in the clotting process.

Correct option is (1). 

A healthy adult human heart rate is 72 beats per minute on average, with the normal resting range being 60-100 bpm. The 70-80 range is the most typical for healthy adults at rest. Rates below 60 suggest bradycardia, while rates above 100 at rest indicate tachycardia. Athletes often have lower resting rates (50-60) due to cardiovascular conditioning.

The normal systolic pressure is about 120 mm Hg. 

Depolarization and repolarization are extremely rapid processes during an action potential, typically occurring within milliseconds. Depolarization involves the rapid influx of sodium ions, while repolarization involves the rapid efflux of potassium ions to restore the resting potential.