401. In a normal heartbeat, which mechanical event most directly follows the electrical event represented by the P wave?
ⓐ. Closure of semilunar valves and beginning of ventricular relaxation
ⓑ. Ventricular contraction with blood ejection into the aorta
ⓒ. Atrial contraction that helps complete ventricular filling
ⓓ. Opening of the aortic valve with systemic outflow
Correct Answer: Atrial contraction that helps complete ventricular filling
Explanation: The P wave represents atrial depolarization, which is the electrical activation of the atria. Electrical activation is followed by mechanical response, so the atria contract shortly after the P wave appears. This atrial systole helps push the final amount of blood into the ventricles before ventricular contraction begins. The event is therefore part of the filling phase of the cardiac cycle rather than the major pumping phase.
402. A normal ECG shows the beginning of the QRS complex. Which event is most closely associated with the early mechanical consequence of this phase?
ⓐ. Atrial depolarization and passive ventricular filling
ⓑ. Beginning of ventricular systole with closure of atrioventricular valves
ⓒ. Ventricular relaxation with closure of semilunar valves
ⓓ. Opening of atrioventricular valves during joint diastole
Correct Answer: Beginning of ventricular systole with closure of atrioventricular valves
Explanation: The QRS complex mainly represents ventricular depolarization. This electrical activation is followed by ventricular contraction, or ventricular systole. As ventricular pressure rises, the atrioventricular valves close to prevent backflow into the atria, producing the first heart sound. It shows how electrical activity leads to a mechanical event and then to a sound. So the early consequence of QRS is the beginning of ventricular systole with atrioventricular valve closure.
403. Which statement best links the T wave with the cardiac cycle?
ⓐ. It represents atrial depolarization just before atrial systole
ⓑ. It represents ventricular depolarization just before blood enters the aorta
ⓒ. It represents ventricular repolarization, after which ventricular relaxation progresses and semilunar valves close
ⓓ. It represents closure of atrioventricular valves during ventricular systole
Correct Answer: It represents ventricular repolarization, after which ventricular relaxation progresses and semilunar valves close
Explanation: The T wave corresponds to ventricular repolarization, which is the electrical recovery of the ventricles. This recovery is associated with the later part of the pumping sequence and is followed by ventricular relaxation. As ventricular pressure falls after ejection, the semilunar valves close and the second heart sound is produced. It is more advanced than simply asking what the T wave means in isolation. So the best integrated description is ventricular repolarization followed by relaxation and semilunar valve closure.
404. Considering both ABO and Rh grouping together, which blood type is the best emergency red cell donor when the recipient’s blood group is unknown?
ⓐ. $AB^+$
ⓑ. $O^-$
ⓒ. $A^+$
ⓓ. $B^-$
Correct Answer: $O^-$
Explanation: In the ABO system, group O red blood cells lack A and B antigens, so they are least likely to react with ABO antibodies in the recipient. In the Rh system, Rh negative blood lacks the Rh antigen, reducing the risk of Rh incompatibility. When both systems are considered together, $O^-$ is treated as the safest emergency red cell donor type.
405. A patient with blood group $B^-$ urgently requires a transfusion. Which donor blood type among the following is the safest compatible choice under standard ABO and Rh rules?
ⓐ. $B^+$
ⓑ. $AB^-$
ⓒ. $O^-$
ⓓ. $O^+$
Correct Answer: $O^-$
Explanation: A recipient with blood group $B^-$ can receive red blood cells that do not present incompatible ABO or Rh antigens. Group $O^-$ lacks A and B antigens and is also Rh negative, so it avoids both major incompatibility problems in this case. By contrast, $B^+$ and $O^+$ introduce Rh antigen, and $AB^-$ introduces the A antigen, which is not suitable for a group B recipient. It therefore tests combined compatibility reasoning.
406. During vigorous exercise, a healthy person shows increased cardiac output, yet the basic sequence of conduction in the heart remains normal. Which statement best explains this?
ⓐ. Sympathetic and adrenal influences raise heart activity, but normal impulse spread still begins at the SA node
ⓑ. Parasympathetic stimulation increases heart rate, while the AV node replaces the SA node as pacemaker
ⓒ. Ventricular depolarization stops during exercise, but stroke volume rises enough to maintain output
ⓓ. The bundle of His directly secretes hormones that replace autonomic control during exertion
Correct Answer: Sympathetic and adrenal influences raise heart activity, but normal impulse spread still begins at the SA node
Explanation: Exercise increases the body’s demand for oxygen and nutrients, so cardiac output must rise. This happens because sympathetic stimulation and adrenal medullary hormones increase heart rate and usually the force of contraction. Even with this increased activity, the normal conduction pathway remains the same: the SA node still initiates the impulse and the rest of the conduction system follows in order. It shows that the heart can beat faster without changing its basic electrical sequence.
407. If oxygenated and deoxygenated blood were allowed to mix extensively in the human heart, which major advantage of double circulation would be reduced most directly?
ⓐ. The ability of the heart to beat without voluntary control
ⓑ. The delivery of highly oxygenated blood to body tissues
ⓒ. The formation of tissue fluid from plasma in capillaries
ⓓ. The presence of valves between atria and ventricles
Correct Answer: The delivery of highly oxygenated blood to body tissues
Explanation: One of the most important benefits of double circulation is that oxygenated and deoxygenated blood remain largely separate. Because of this separation, body tissues receive blood rich in oxygen, which supports efficient metabolism. If the two kinds of blood mixed extensively, the oxygen content of blood reaching systemic tissues would fall. This would weaken one of the central advantages of the human circulatory design. It shows why chamber separation and separate circuits matter functionally. So the most directly reduced advantage would be efficient oxygen-rich supply to tissues.
408. A person with narrowed coronary arteries develops chest pain during physical exertion, especially when the heart is beating faster and more forcefully. Which explanation best fits this situation?
ⓐ. Increased sympathetic drive lowers myocardial oxygen need, causing pain by over-relaxation
ⓑ. Exertion raises the heart’s oxygen demand, but narrowed coronary vessels may fail to supply enough blood, producing angina
ⓒ. The vagus nerve sharply increases coronary pressure, causing blood to bypass the myocardium
ⓓ. The heart stops pumping during exercise, so chest pain appears from loss of all circulation
Correct Answer: Exertion raises the heart’s oxygen demand, but narrowed coronary vessels may fail to supply enough blood, producing angina
Explanation: During physical exertion, sympathetic influence and hormonal support make the heart beat faster and more forcefully. This increases the oxygen requirement of the myocardium. If the coronary arteries are narrowed, they may not be able to provide enough blood to match that higher demand. The result can be temporary myocardial ischemia, which presents as angina pectoris. Therefore, the best explanation is increased demand with insufficient coronary supply.
409. Which sequence best traces one complete path of a drop of blood leaving the left ventricle, becoming deoxygenated in body tissues, getting reoxygenated, and returning to the left atrium?
ⓐ. Left ventricle $\rightarrow$ aorta $\rightarrow$ body tissues $\rightarrow$ vena cava $\rightarrow$ right atrium $\rightarrow$ right ventricle $\rightarrow$ pulmonary artery $\rightarrow$ lungs $\rightarrow$ pulmonary vein $\rightarrow$ left atrium
ⓑ. Left ventricle $\rightarrow$ pulmonary artery $\rightarrow$ lungs $\rightarrow$ pulmonary vein $\rightarrow$ body tissues $\rightarrow$ vena cava $\rightarrow$ right ventricle $\rightarrow$ right atrium $\rightarrow$ aorta $\rightarrow$ left atrium
ⓒ. Left ventricle $\rightarrow$ aorta $\rightarrow$ pulmonary vein $\rightarrow$ lungs $\rightarrow$ vena cava $\rightarrow$ right atrium $\rightarrow$ right ventricle $\rightarrow$ body tissues $\rightarrow$ pulmonary artery $\rightarrow$ left atrium
ⓓ. Left ventricle $\rightarrow$ aorta $\rightarrow$ body tissues $\rightarrow$ pulmonary artery $\rightarrow$ lungs $\rightarrow$ right atrium $\rightarrow$ vena cava $\rightarrow$ right ventricle $\rightarrow$ pulmonary vein $\rightarrow$ left atrium
Correct Answer: Left ventricle $\rightarrow$ aorta $\rightarrow$ body tissues $\rightarrow$ vena cava $\rightarrow$ right atrium $\rightarrow$ right ventricle $\rightarrow$ pulmonary artery $\rightarrow$ lungs $\rightarrow$ pulmonary vein $\rightarrow$ left atrium
Explanation: Oxygenated blood leaves the left ventricle through the aorta and reaches body tissues, where it gives up oxygen and becomes deoxygenated. It then returns through the venae cavae to the right atrium, passes into the right ventricle, and is sent to the lungs by the pulmonary artery. After gas exchange in the lungs, the blood becomes oxygenated again and returns through the pulmonary veins to the left atrium.
410. Which sequence correctly describes the relationship among plasma, tissue fluid, lymph, and blood return?
ⓐ. Plasma in capillaries $\rightarrow$ tissue fluid around cells $\rightarrow$ lymphatic vessels $\rightarrow$ lymph $\rightarrow$ return to bloodstream
ⓑ. Plasma in arteries $\rightarrow$ erythrocytes $\rightarrow$ lymph nodes $\rightarrow$ tissue fluid $\rightarrow$ serum
ⓒ. Serum in veins $\rightarrow$ lymph $\rightarrow$ plasma proteins $\rightarrow$ tissue fluid $\rightarrow$ blood clot
ⓓ. Plasma in ventricles $\rightarrow$ lymphocytes $\rightarrow$ tissue fluid $\rightarrow$ fibrin $\rightarrow$ bloodstream
Correct Answer: Plasma in capillaries $\rightarrow$ tissue fluid around cells $\rightarrow$ lymphatic vessels $\rightarrow$ lymph $\rightarrow$ return to bloodstream
Explanation: Plasma filters through capillary walls to form tissue fluid, which surrounds body cells and acts as the immediate medium of exchange. Not all of this fluid returns directly to the blood capillaries. Some of the excess enters lymphatic vessels, and once inside those vessels it is called lymph. The lymphatic system then returns this fluid toward the bloodstream. This sequence links several units of the chapter into one continuous fluid pathway. It shows how blood, tissue fluid, and lymph are functionally connected rather than isolated body fluids.
411. Human circulation is best described as both closed and double because:
ⓐ. blood mixes freely with body spaces and passes once through the heart in one full circuit
ⓑ. blood remains within vessels and passes through the heart twice in one complete circulation
ⓒ. blood flows only in arteries and never returns through veins
ⓓ. blood enters lymphatic vessels before reaching the lungs in every cycle
Correct Answer: blood remains within vessels and passes through the heart twice in one complete circulation
Explanation: Human circulation is called closed because blood normally stays inside blood vessels rather than bathing tissues directly in open spaces. It is called double because, in one complete round, blood passes through the heart twice: once in the pulmonary circuit and once in the systemic circuit. These two features together make human circulation more efficient and highly organized. Closed circulation emphasizes vessel confinement, while double circulation emphasizes the two-circuit pathway.
412. A patient with blood group $A^-$ receives blood of group $A^+$. Which statement best explains why this transfusion may still be unsuitable even though the ABO type matches?
ⓐ. The donor blood lacks antigen A, so the recipient’s anti-A antibodies will destroy it.
ⓑ. The donor blood contains Rh antigen, which may sensitize an Rh negative recipient.
ⓒ. The recipient’s plasma contains anti-B, which always attacks group A blood first.
ⓓ. The donor blood has no plasma proteins, so tissue fluid cannot be formed.
Correct Answer: The donor blood contains Rh antigen, which may sensitize an Rh negative recipient.
Explanation: ABO compatibility alone is not enough to ensure a safe transfusion. In this case, both donor and recipient are group A, so there is no ABO mismatch. However, the donor is Rh positive and the recipient is Rh negative. That means the donor erythrocytes carry the Rh antigen, which the recipient may recognize as foreign. This can lead to Rh sensitization and possible danger in later exposures. Therefore, the problem here is Rh incompatibility, not ABO incompatibility.
413. If plasma albumin falls markedly while lymphatic drainage is still functioning, which effect is most likely to increase?
ⓐ. Retention of water within blood due to stronger osmotic pull
ⓑ. Movement of blood cells out of arteries into lymphatic vessels
ⓒ. Accumulation of fluid in tissue spaces because plasma retains less water
ⓓ. Conversion of tissue fluid directly into serum around body cells
Correct Answer: Accumulation of fluid in tissue spaces because plasma retains less water
Explanation: Albumin is a major plasma protein that helps maintain osmotic balance by holding water within the blood. If albumin levels fall significantly, the blood loses part of its ability to retain fluid. As a result, more fluid tends to remain in or move into the tissue spaces, increasing tissue fluid accumulation. Even if lymphatic drainage is normal, the balance may still shift toward edema-like fluid buildup.
414. Which structural feature of the human heart most directly supports efficient separation of oxygenated and deoxygenated blood in double circulation?
ⓐ. Presence of chordae tendineae in the ventricles only
ⓑ. Double-walled pericardium around the heart
ⓒ. Complete partitioning into right and left sides with separate chambers
ⓓ. Opening of the venae cavae into the right atrium
Correct Answer: Complete partitioning into right and left sides with separate chambers
Explanation: Efficient double circulation depends on keeping oxygenated and deoxygenated blood largely separate. In humans, this is achieved mainly by the structural separation of the heart into right and left sides, each with its own atrium and ventricle. This chamber arrangement prevents extensive mixing and allows one side to handle pulmonary circulation while the other handles systemic circulation. Other features of the heart are also important, but they do not directly create this fundamental separation. So complete partitioning of the heart is the key feature.
415. In a healthy person, increased vagal stimulation is most likely to produce which effect while leaving the normal origin of the heartbeat unchanged?
ⓐ. Faster firing of the SA node and stronger ventricular contraction
ⓑ. Slower heart rate because the SA node is influenced, though it remains the normal pacemaker
ⓒ. Transfer of pacemaker control from the SA node to Purkinje fibres
ⓓ. Closure of semilunar valves before atrial depolarization begins
Correct Answer: Slower heart rate because the SA node is influenced, though it remains the normal pacemaker
Explanation: The vagus nerve carries the main parasympathetic influence to the heart and generally slows cardiac activity. In a healthy heart, this slowing effect acts on the normal pacemaker rather than replacing it. The SA node still remains the usual origin of the heartbeat, but its rate of impulse generation becomes lower. It is more advanced than asking only which division slows the heart. So the key idea is slower SA nodal pacing without a change in pacemaker identity.
416. Which sequence correctly links electrical activity, valve action, and heart sound during the start of ventricular systole?
ⓐ. P wave $\rightarrow$ semilunar valve closure $\rightarrow$ “dub”
ⓑ. QRS complex $\rightarrow$ atrioventricular valve closure $\rightarrow$ “lub”
ⓒ. T wave $\rightarrow$ atrioventricular valve opening $\rightarrow$ “lub”
ⓓ. P wave $\rightarrow$ semilunar valve opening $\rightarrow$ “dub”
Correct Answer: QRS complex $\rightarrow$ atrioventricular valve closure $\rightarrow$ “lub”
Explanation: The QRS complex represents ventricular depolarization, which is the electrical event that precedes ventricular contraction. As ventricular systole begins, pressure rises in the ventricles and the atrioventricular valves close. The closure of these valves produces the first heart sound, commonly written as “lub.”
417. Which sequence best explains how a coronary circulation problem can eventually contribute to heart failure?
ⓐ. Increased tissue fluid formation $\rightarrow$ more lymph $\rightarrow$ stronger ventricular pumping
ⓑ. Narrowed coronary arteries $\rightarrow$ reduced blood supply to myocardium $\rightarrow$ impaired cardiac performance
ⓒ. More vagal stimulation $\rightarrow$ faster heartbeat $\rightarrow$ widened coronary arteries
ⓓ. Increased ABO antibodies $\rightarrow$ reduced plasma proteins $\rightarrow$ weaker atrial contraction
Correct Answer: Narrowed coronary arteries $\rightarrow$ reduced blood supply to myocardium $\rightarrow$ impaired cardiac performance
Explanation: Coronary arteries supply blood to the heart muscle itself, so narrowing of these vessels reduces oxygen and nutrient delivery to the myocardium. If this becomes significant or persistent, the heart muscle may not function efficiently. Over time, impaired myocardial performance can reduce the heart’s pumping ability and contribute to heart failure.
418. Which statement best combines the ideas of ECG and cardiac output?
ⓐ. ECG gives the amount of blood pumped per minute, while cardiac output shows atrial depolarization
ⓑ. ECG and cardiac output are both direct measures of blood pressure in the aorta
ⓒ. ECG reflects electrical timing of the heartbeat, whereas cardiac output reflects how much blood the heart pumps per minute
ⓓ. ECG measures tissue fluid formation, whereas cardiac output measures lymph return
Correct Answer: ECG reflects electrical timing of the heartbeat, whereas cardiac output reflects how much blood the heart pumps per minute
Explanation: ECG and cardiac output are both important in studying heart function, but they describe different things. ECG is an electrical record that shows the timing and pattern of cardiac activation and recovery. Cardiac output is a volume-based measure that tells how much blood is pumped by each ventricle in one minute. One deals with electrical coordination, while the other deals with pumping effectiveness.
419. If the total blood volume of a person is approximately $5 , \text{L}$ and plasma makes up about $55%$ of it, what is the approximate plasma volume?
ⓐ. $2.75 , \text{L}$
ⓑ. $2.25 , \text{L}$
ⓒ. $3.50 , \text{L}$
ⓓ. $4.50 , \text{L}$
Correct Answer: $2.75 , \text{L}$
Explanation: Plasma forms about $55%$ of total blood volume in a normal adult. So if the total blood volume is $5, \text{L}$, the plasma volume is calculated as $5 \times \dfrac{55}{100} = 2.75, \text{L}$. Plasma is the liquid matrix of blood, so this value represents the fluid part rather than the formed elements. Thus, the correct approximate plasma volume is $2.75, \text{L}$.
420. Assume erythrocytes live for about $120$ days and are replaced at a steady rate. Approximately what fraction of the circulating erythrocyte population would be replaced in $30$ days?
ⓐ. $\dfrac{1}{10}$
ⓑ. $\dfrac{1}{5}$
ⓒ. $\dfrac{1}{4}$
ⓓ. $\dfrac{1}{2}$
Correct Answer: $\dfrac{1}{4}$
Explanation: If erythrocytes survive for about $120$ days and replacement is steady, then the fraction replaced in $30$ days is $\dfrac{30}{120} = \dfrac{1}{4}$. This means about $25%$ of the erythrocyte population would be renewed in that period. It also reinforces the idea that erythrocytes are continuously removed and replaced. Since the lifespan is limited, steady turnover is a necessary part of normal blood maintenance.
