Questions & explanations
1. Which of the following statements best explains why the cardiac output of an athlete is higher than that of an ordinary man?
- Athletes have a larger heart size and stronger heart muscles, leading to higher stroke volume and cardiac output.
- Athletes have a faster heart rate at rest, increasing cardiac output.
- Athletes have a lower blood volume, which reduces the workload on the heart.
- Athletes have a higher number of heart beats per minute during exercise, but lower stroke volume.
Answer: Athletes have a larger heart size and stronger heart muscles, leading to higher stroke volume and cardiac output.
Cardiac output is the product of stroke volume and heart rate. Athletes typically have a larger heart and stronger cardiac muscles, which allows for a greater stroke volume. Even at rest, their cardiac output can be higher due to this increased stroke volume, and during exercise, both stroke volume and heart rate contribute to a much higher cardiac output compared to an ordinary person.
2. The closure of the tricuspid and bicuspid valves during ventricular systole is caused by:
- Increased ventricular pressure leading to attempted backflow of blood into the atria.
- Contraction of the papillary muscles pulling the valves closed.
- Relaxation of the ventricles.
- Decreased atrial pressure.
Answer: Increased ventricular pressure leading to attempted backflow of blood into the atria.
As ventricles contract, pressure rises, causing blood to try to flow back into the atria, which pushes the AV valves (tricuspid and bicuspid) closed. Papillary muscles contract to prevent valve prolapse but do not close the valves. Ventricular relaxation would open the valves, and decreased atrial pressure is not the direct cause.
3. The action potential from the atria is conducted to the ventricles via:
- AVN and AV bundle
- SAN and Purkinje fibres
- Bundle of His and chordae tendineae
- Vagus nerve and sympathetic nerves
Answer: AVN and AV bundle
The atrioventricular node (AVN) and the atrioventricular bundle (bundle of His) conduct the impulse from atria to ventricles. SAN is the pacemaker, Purkinje fibres distribute impulse in ventricles, chordae tendineae are valve structures, and nerves modulate heart rate but do not conduct the action potential for contraction.
4. Which of the following is a primary function of haemoglobin?
- Transport of respiratory gases
- Blood clotting
- Immune response
- Production of antibodies
Answer: Transport of respiratory gases
Haemoglobin is the iron-containing protein in red blood cells that binds to oxygen and carbon dioxide, facilitating their transport between the lungs and tissues. Blood clotting involves platelets and clotting factors, immune response involves white blood cells, and antibody production is carried out by lymphocytes.
5. During ventricular systole, which of the following occurs?
- Atria undergo relaxation (atrial diastole) and blood is forced into the aorta and pulmonary artery.
- Atria contract simultaneously with ventricles.
- Ventricular pressure decreases, allowing blood to flow into ventricles.
- All heart chambers are in diastole.
Answer: Atria undergo relaxation (atrial diastole) and blood is forced into the aorta and pulmonary artery.
During ventricular systole, ventricles contract, increasing pressure, which forces blood into the aorta and pulmonary artery. At the same time, atria are in diastole (relaxation). Atria do not contract during ventricular systole; ventricular pressure increases, not decreases; and not all chambers are in diastole.
6. The instrument used to record the electrical activity of the heart is called:
- Electrocardiograph
- Electroencephalograph
- Electromyograph
- Sphygmomanometer
Answer: Electrocardiograph
An electrocardiograph (ECG) is the device that records the electrical activity of the heart, producing an electrocardiogram. The other options record different biological signals: electroencephalograph records brain activity, electromyograph records muscle activity, and sphygmomanometer measures blood pressure.
7. The action potential generated by the sinoatrial node (SAN) causes:
- Simultaneous contraction of both atria (atrial systole), increasing ventricular filling by about 30%.
- Contraction of the ventricles directly.
- Relaxation of the atria.
- Closure of the semilunar valves.
Answer: Simultaneous contraction of both atria (atrial systole), increasing ventricular filling by about 30%.
The SAN initiates atrial systole, which pushes additional blood into the ventricles, contributing about 30% of ventricular filling. Ventricular contraction is initiated later by the AVN and Purkinje fibres. Atrial relaxation occurs after systole, and semilunar valves close during ventricular diastole.
8. What is the average life span of a red blood cell (RBC) and where are they destroyed?
- 60 days; liver
- 120 days; spleen
- 90 days; bone marrow
- 150 days; kidneys
Answer: 120 days; spleen
Red blood cells have an average life span of about 120 days. They are primarily destroyed in the spleen, which is often called the 'graveyard of RBCs'. The liver and bone marrow are involved in other functions but not the primary site of RBC destruction; kidneys filter blood but do not destroy RBCs.
9. Which of the following statements correctly describes the two common types of blood grouping?
- ABO grouping and Rh grouping are based on the presence of antigens on white blood cells.
- ABO grouping is based on antigens on RBCs, while Rh grouping is based on the Rh factor on RBCs.
- Both ABO and Rh grouping are determined by antibodies in the plasma.
- Rh grouping is based on the presence of anti-A and anti-B antibodies.
Answer: ABO grouping is based on antigens on RBCs, while Rh grouping is based on the Rh factor on RBCs.
ABO grouping depends on the presence or absence of A and B antigens on red blood cells (RBCs), while Rh grouping depends on the presence or absence of the Rh factor (D antigen) on RBCs. The other options incorrectly attribute the basis to white blood cells, antibodies, or misrepresent Rh grouping.
10. Which of the following best describes the events of the cardiac cycle?
- They occur simultaneously and in a highly synchronised manner, repeated cyclically.
- They occur sequentially with no overlap.
- They occur randomly without any pattern.
- They occur only during exercise.
Answer: They occur simultaneously and in a highly synchronised manner, repeated cyclically.
The cardiac cycle involves coordinated contraction and relaxation of heart chambers. Atrial and ventricular events are synchronised and repeat cyclically. The other options are incorrect because the events are not purely sequential, not random, and occur continuously, not only during exercise.
11. The type of circulation in which blood flows through a closed system of vessels is called:
- Open circulation
- Closed circulation
- Single circulation
- Double circulation
Answer: Closed circulation
In closed circulation, blood is confined to vessels (arteries, veins, capillaries) and does not directly bathe the tissues. Open circulation involves blood flowing into sinuses. Single and double circulation refer to the number of circuits through the heart, not the containment of blood.
12. During the delivery of the first child, what is the possible consequence of exposure of maternal blood to Rh+ve fetal blood?
- A. The mother develops immediate hemolytic disease
- B. The mother starts producing anti-Rh antibodies
- C. The fetus develops erythroblastosis fetalis
- D. The mother becomes Rh positive
Answer: B. The mother starts producing anti-Rh antibodies
When an Rh-negative mother is exposed to Rh-positive fetal blood during delivery, her immune system may recognize the Rh antigen as foreign and begin producing anti-Rh antibodies. This sensitization does not usually affect the first child but can cause problems in subsequent pregnancies.