Analyze the statements regarding the nodal tissue of the human heart:
(i) The sino-atrial node (SAN) is situated in the upper right corner of the right atrium. (ii) The atrio-ventricular node (AVN) is found in the lower left corner of the left atrium. (iii) The AV bundle continues from the AVN and emerges at the top of the inter-ventricular septum. (iv) Purkinje fibres are minute branches distributed throughout the atrial walls.
Explanation: Statement (ii) is incorrect because the AV node is situated in the lower left corner of the right atrium near the atrio-ventricular septum. Statement (iv) is incorrect because Purkinje fibres are distributed throughout the ventricular musculature. Statements (i) and (iii) are correct.
Question 62 of 100
📘 CLASS XI
Read these statements about cardiac autoexcitability:
(i) The heart is described as myogenic because its normal activities are intrinsically regulated by specialized muscle fibers. (ii) The sino-atrial node (SAN) generates the maximum number of action potentials, about 70–75 per minute. (iii) The AV bundle branch generates action potentials at a rate higher than the SAN. (iv) SAN activity is responsible for initiating and maintaining the rhythmic contractile activity of the heart.
Explanation: Statement (iii) is incorrect because the SAN has the highest rate of impulse generation and functions as the pacemaker. Statements (i), (ii), and (iv) are correct.
Question 63 of 100
📘 CLASS XI
Examine these statements regarding the Joint Diastole phase:
(i) The tricuspid and bicuspid valves are open, allowing blood to enter the ventricles. (ii) The semilunar valves are closed, preventing arterial blood from returning to the ventricles. (iii) Blood from the vena cava and pulmonary veins flows directly into the right and left ventricles respectively. (iv) The SA node is actively firing action potentials, maintaining high pressure in the ventricles.
Explanation: Statement (iv) is incorrect because during joint diastole all four chambers are relaxed, and ventricular pressure is low. Statements (i), (ii), and (iii) are correct.
Question 64 of 100
📘 CLASS XI
Study the statements regarding Atrial Systole events:
(i) Atrial systole is triggered by the action potential generated by the sino-atrial node. (ii) It results in a simultaneous contraction of both the right and left atria. (iii) It increases the volume of blood flowing into the ventricles by about 70 percent. (iv) During atrial systole, the atrio-ventricular valves are forced closed.
Explanation: Statement (iii) is incorrect because atrial systole contributes about 30% additional ventricular filling. Statement (iv) is incorrect because the atrio-ventricular valves remain open during atrial systole. Statements (i) and (ii) are correct.
Question 65 of 100
📘 CLASS XI
Consider these statements about Ventricular Systole:
(i) The action potential is transmitted through the entire ventricular musculature by the AVN and AV bundle. (ii) Contraction of ventricles increases ventricular pressure, causing immediate closure of the semilunar valves. (iii) Closure of atrio-ventricular (AV) valves prevents deoxygenated and oxygenated blood from leaking back into the atria. (iv) When ventricular pressure rises significantly, the semilunar valves are forced open.
Explanation: Statement (ii) is incorrect because increased ventricular pressure first closes the AV valves and later opens the semilunar valves. Statements (i), (iii), and (iv) are correct.
Question 66 of 100
📘 CLASS XI
Read the statements below regarding Stroke Volume and Cardiac Output:
(i) Stroke volume is the quantity of blood pumped out by each ventricle per cardiac cycle, which is about 70 mL. (ii) Cardiac output is calculated by multiplying the stroke volume by the heart rate. (iii) The average healthy individual has a resting cardiac output of approximately 5000 mL per minute. (iv) The human body lacks any physiological mechanism to alter the stroke volume.
Explanation: Statement (iv) is incorrect because stroke volume and heart rate are physiologically regulated according to the body's needs. Statements (i), (ii), and (iii) are correct.
Question 67 of 100
📘 CLASS XI
Read these statements regarding the physical heart sounds:
(i) The first heart sound is 'dub' and is linked with the closure of semilunar valves. (ii) The second heart sound is 'lub' and is linked with the closure of the AV valves. (iii) Heart sounds are of high clinical diagnostic significance. (iv) These sounds are easily heard using a stethoscope.
Explanation: Statements (i) and (ii) are incorrect because the first heart sound is 'lub' (closure of AV valves) and the second heart sound is 'dub' (closure of semilunar valves). Statements (iii) and (iv) are correct.
Question 68 of 100
📘 CLASS XI
Study these statements regarding standard ECG connection leads:
(i) A standard ECG requires connecting the patient with three electrical leads: one to each wrist and one to the left ankle. (ii) For standard monitoring, one lead is attached to the right wrist, one to the left wrist, and one to the right ankle. (iii) Chest leads are attached when a more detailed evaluation of heart function is needed. (iv) Any deviation from the standard ECG wave shape signals a possible clinical abnormality.
Explanation: Statement (ii) is incorrect because the standard ECG leads are attached to each wrist and the left ankle, not the right ankle. Statements (i), (iii), and (iv) are correct.
Question 69 of 100
📘 CLASS XI
Analyze the statements below regarding standard ECG waves:
(i) The P-wave corresponds to the electrical depolarization of the atria. (ii) The QRS complex represents the depolarization of the ventricles. (iii) Ventricular contraction begins shortly after Q and marks the beginning of systole. (iv) The T-wave represents the repolarization of the ventricles, and the end of the T-wave marks the beginning of diastole.
Explanation: Statement (iv) is incorrect because the end of the T-wave marks the end of ventricular systole, not the beginning of diastole. Statements (i), (ii), and (iii) are correct.
Question 70 of 100
📘 CLASS XI
Read these statements regarding the histology of blood vessels:
(i) Arteries and veins consist of three distinct tissue layers. (ii) Tunica intima is the middle layer consisting of smooth muscle and elastic fibres. (iii) Tunica media is the inner layer lined with squamous endothelium. (iv) Tunica externa is the outermost layer of fibrous connective tissue with collagen fibres.
Explanation: Statements (ii) and (iii) are incorrect because they are interchanged. Tunica intima is the inner endothelial lining, whereas tunica media is the middle layer composed of smooth muscle and elastic fibres. Statements (i) and (iv) are correct.
