Body Fluids and Circulation Test - 4

Diastolic right atrium has less pressure and post caval has high pressure, thus blood moves from post caval to right atrium. 

During ventricular systole, the contraction of ventricular muscles causes the closure of bicuspid and tricuspid valves (AV valves), producing a low pitched 'lubb' sound. At the end of ventricular systole, semilunar valves close, producing the second heart sound, the 'dup'. Pulsation of the radial artery is due to rhythmic contraction and relaxation in the aorta. Initiation of the heart beat occurs in the SA node.

Due to contraction of the ventricles (ventricular systole), the pressure inside the ventricles rises, that force open the semilunar valves of aorta and pulmonary artery so that the blood enters into these vessels. Oxygenated blood is pumped into the aorta from the left ventricle while deoxygenated blood is pumped into the pulmonary artery from the right ventricle.

Chordae tendineae are cords that prevent the valve from collapsing back into the right atrium during powerful right ventricular contraction. When the right ventricle contracts forcing blood into the pulmonary artery, the tricuspid valve closes the aperture to the right atrium thereby preventing any backflow of blood. Thus, if chordae tendineare of tricuspid valve becomes partially non-functional, then the flow of blood into the pulmonary artery will be reduced.

Normal blood pressure is 120/80 mm Hg. Blood pressure of 190/110 mm Hg is regarded as high blood pressure. It leads to heart diseases and also affects vital organs like brain and kidney.

During a cardiac cycle, each ventricle pumps out approximately 70 mL of blood which is called stroke volume. The stroke volume multiplied by the number of heart beats per minute (heart rate) gives the cardiac output. Therefore, Cardiac output = Stroke × heart rate =70×72=5040 mL per minute i.e., 5 litres per minute.

Pulse is the rhythmic contraction and relaxation in the aorta and its main aeteries. It is a regular jerk of an artery. It is same as the heart rate because an artery pulses every time the heart beats.

In figure (2), blood is entering into the right auricle through superior and inferior vena cava and blood is entering into left auricle through pulmonary vein. Figure (1) shows movement of blood from the auricles into the ventricles. Figure (2) shows movement of blood from the right ventricle into the pulmonary artery and from the left ventricle into aorta.

Red blood cell (blood) will first meet SAN in the right atrium. Then from the right atrium it passes into right ventricle through atrio ventricular valve. From the right ventricle it enters into pulmonary artery through semilunar valve.

i. S-A node has a unique property of self-excitation, which enables it to act as the "pacemaker" of the heart.

ii. The two auricles are separated from each other by a partition, the interauricular septum. The septum has an oval, thin area called the fossa ovalis. It marks the position of an opening the foramen ovale, between the two auricles in the foetus.

iii. The right auricle opens into the right ventricle through a wide passage, the right auriculoventricular or A-V aperture. This aperture is guarded by a one-way valve called tricuspid valve.

iv. In a normal adult person, the average systolic/ diastolic pressure are 120*80 mm Hg.

So, the correct answer is 'i-T, ii-F, iii-F, iv-F'.

Duration of joint diastole is 0.4 sec, that of auricular systole is 0.1 sec and that of ventricular systole is 0.3 sec.

Superior vena cava and inferior vena cava are the large veins. Superior vena cava brings deoxygenated blood from upper part of the body while inferior vena cava brings blood from lower part of the body into the right atrium of the heart.

The SA node possesses a unique property of self-excitation, which enables it to act as the pacemaker of heart. It spontaneously generates a wave of contraction which spreads over both the auricles more or less simultaneously along the muscle fibres that fan out from the pacemaker. The pacemaker establishes the basic rhythm at which the heart beats. Thus, if the pacemaker becomes nonfunction, then the cardiac muscles do not undergo co-ordinated rhythmic movements.