Test: Cardiac Cycle (NCERT) - NEET MCQ

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.

NCERT Topic: Heart sounds

NCERT Line: "During each cardiac cycle two prominent sounds are produced which can be easily heard through a stethoscope. The first heart sound (lub) is associated with the closure of the tricuspid and bicuspid valves whereas the second heart sound (dub) is associated with the closure of the semilunar valves."

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.

NCERT Topic: Ventricular systole

NCERT Line: "Oxygenated blood is pumped into the aorta which is carried to all the body tissues and the deoxygenated blood from there is collected by the veins and returned to the right atrium."

Ventricles are in relaxed phase during arterial systole. In arterial systole, simultaneous contraction of the auricles takes place and as a result, blood passes into the ventricles which are in relaxing phase.

NCERT Topic: Cardiac cycle

NCERT Line: "The atria undergoes relaxation (diastole), coinciding with the ventricular systole."

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.

The correct fill-ups for the respective blank numbers are as follows:
1. bicuspid valve
2. tricuspid valve
3. oxygenated
4. four
5. calcium
Explanation:
(i) Left auriculoventricular aperture is guarded by the bicuspid valve while the right auriculoventricular aperture is guarded by the tricuspid valve. This means that the correct fill-ups for the blanks in statement (i) are (1) bicuspid valve and (2) tricuspid valve.
(ii) In man, the left auricle receives oxygenated blood by four pulmonary veins. Therefore, the correct fill-ups for the blanks in statement (ii) are (3) oxygenated and (4) four.
(iii) Calcium ions play a significant role in clotting. Thus, the correct fill-up for the blank in statement (iii) is (5) calcium.
Therefore, option B: (1) bicuspid valve, (2) tricuspid valve, (5) calcium is the correct answer.

NCERT Topic: Heart valves and circulation

NCERT Line: "the opening between the right atrium and the right ventricle is guarded by a valve formed of three muscular flaps or cusps, the tricuspid valve, whereas a bicuspid or mitral valve guards the opening between the left atrium and the left ventricle."

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.

Correct option is A.
A-V node functions as a secondary pacemaker because when the wave of contraction originating from the sinoatrial node reaches the atrioventricular node (AV node – pace setter), the latter is stimulated and excitatory impulses are rapidly transmitted from it to all parts of the ventricles to contract simultaneously. The ventricles force blood through long system of arteries and hence must exert great pressure on the blood.

NCERT Topic: Coordinating electrical activity

NCERT Line: "Coordinating electrical activity in the atria with electrical activity in the ventricles by connecting them via the bundle of His"

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.

NCERT Topic: Cardiac cycle

NCERT Line: "During each cardiac cycle two prominent sounds are produced which can be easily heard through a stethoscope."

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.

NCERT Topic: Cardiac cycle and cardiac output

NCERT Line: Not Found

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.

NCERT Topic: Circulatory pathway

NCERT Line: "However, each of these septa are provided with an opening through which the two chambers of the same side are connected. The opening between the right atrium and the right ventricle is guarded by a valve formed of three muscular flaps or cusps, the tricuspid 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.

NCERT Topic: Cardiac cycle events

NCERT Line: "The sequential event in the heart which is cyclically repeated is called the cardiac cycle and it consists of systole and diastole of both the atria and ventricles."

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.

NCERT Topic: Right atrium

NCERT Line: "The deoxygenated blood from there is collected by the veins and returned to the right atrium."

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.

NCERT Topic: Cardiac cycle

NCERT Line: "Cardiac muscles do not undergo co-ordinated rhythmic movements"

Correct option: B
The P-wave represents the electrical excitation (or depolarisation) of the atria, which leads to the contraction of both the atria.
The contraction starts shortly after Q and marks the beginning of the systole.
QRS complex represents the depolarisation of ventricles. 
The T-wave represents the return of the ventricles from excited to normal state (repolarisation).