MCAT Biology Review

Chapter 7: The Cardiovascular System

Practice Questions

1. Which of the following is a FALSE statement regarding erythrocytes?

1. Erythrocytes contain hemoglobin.

2. Erythrocytes are anaerobic.

3. The nuclei of erythrocytes are located in the middle of the biconcave disc.

4. Erythrocytes are phagocytized in the spleen and liver after a certain period of time.

2. Which of the following is the correct sequence of a cardiac impulse?

1. SA node → AV node → Purkinje fibers → bundle of His → ventricles

2. AV node → bundle of His → Purkinje fibers → ventricles → atria

3. SA node → atria → AV node → bundle of His → Purkinje fibers → ventricles

4. SA node → AV node → atria → bundle of His → Purkinje fibers → ventricles

3. Hemoglobin’s affinity for O₂:

1. increases in exercising muscle tissue.

2. decreases as blood P_aCO₂ decreases.

3. decreases as blood pH decreases.

4. is higher in maternal blood than in fetal blood.

4. Which of the following correctly traces the circulatory pathway?

1. Superior vena cava → right atrium → right ventricle → pulmonary artery → lungs → pulmonary veins → left atrium → left ventricle → aorta

2. Superior vena cava → left atrium → left ventricle → pulmonary artery → lungs → pulmonary veins → right atrium → right ventricle → aorta

3. Aorta → right atrium → right ventricle → pulmonary artery → lungs → pulmonary veins → left atrium → left ventricle → superior vena cava

4. Superior vena cava → right atrium → right ventricle → pulmonary veins → lungs → pulmonary artery → left atrium → left ventricle → aorta

5. At the venous end of a capillary bed, the osmotic pressure:

1. is greater than the hydrostatic pressure.

2. results in a net outflow of fluid.

3. is significantly higher than the osmotic pressure at the arterial end.

4. causes proteins to enter the interstitium.

6. A patient’s chart reveals that he has a cardiac output of 7500 mL per minute and a stroke volume of 50 mL. What is his pulse, in beats per minute?

1. 50

2. 100

3. 150

4. 400

7. An unconscious patient is rushed into the emergency room and needs an immediate blood transfusion. Because there is no time to check her medical history or determine her blood type, which type of blood should she receive?

1. A^–

2. AB⁺

3. O⁺

4. O^–

8. Which of the following is true regarding arteries and veins?

1. Arteries are thin-walled, muscular, and elastic, whereas veins are thick-walled and inelastic.

2. Arteries always conduct oxygenated blood, whereas veins always carry deoxygenated blood.

3. The blood pressure in the aorta is always higher than the pressure in the superior vena cava.

4. Arteries facilitate blood transport by using skeletal muscle contractions, whereas veins make use of the pumping of the heart to push blood.

9. At any given time, there is more blood in the venous system than the arterial system. Which of the following features of veins allows for this?

1. Relative lack of smooth muscle in the wall

2. Presence of valves

3. Proximity of veins to lymphatic vessels

4. Thin endothelial lining

10.Which of the following is involved in the body’s primary blood-buffering mechanism?

1. Fluid intake

2. Absorption of nutrients in the gastrointestinal system

3. Carbon dioxide produced from metabolism

4. Hormones released by the kidney

11.Due to kidney disease, a person is losing albumin into the urine. What effect is this likely to have within the capillaries?

1. Increased blood pressure

2. Increased hydrostatic pressure

3. Decreased oncotic pressure

4. Decreased hydrostatic pressure

12.The tricuspid valve prevents backflow of blood from the:

1. left ventricle into the left atrium.

2. aorta into the left ventricle.

3. pulmonary artery into the right ventricle.

4. right ventricle into the right atrium.

13.The world record for the longest-held breath is 22 minutes and 0 seconds. If a sample were taken from this individual during the last minute of breath-holding, which of the following might be observed?

1. Increased hemoglobin affinity for oxygen

2. Decreased P_aCO₂

3. Increased hematocrit

4. Decreased pH

14.A person has a heart attack that primarily affects the wall between the two ventricles. Which portion of the electrical conduction system is most likely affected?

1. AV node

2. SA node

3. Bundle of His

4. Left ventricular muscle

15.Which vascular structure creates the most resistance to blood flow?

1. Aorta

2. Arterioles

3. Capillaries

4. Veins

PRACTICE QUESTIONS

Answers and Explanations

1. CErythrocytes, or red blood cells, are produced in the red bone marrow and circulate in the blood for about 120 days, after which they are phagocytized in the spleen and the liver, eliminating choice (D). Red blood cells have a disk-like shape and lose their membranous organelles (like mitochondria and nuclei) during maturation. This makes choice (C) the correct answer. Erythrocytes are filled with hemoglobin; their lack of mitochondria makes their metabolism solely anaerobic, eliminating choices (A) and (B).

2. CAn ordinary cardiac contraction originates in, and is regulated by, the sinoatrial (SA) node. The impulse travels through both atria, stimulating them to contract simultaneously. The impulse then arrives at the atrioventricular (AV) node, which momentarily slows conduction, allowing for completion of atrial contraction and ventricular filling. The impulse is then carried by the bundle of His and its branches through the Purkinje fibers in the walls of both ventricles, generating a strong contraction.

3. CAccording to the Bohr effect, decreasing the pH in the blood decreases hemoglobin’s affinity for O₂. This makes choice (C) the correct answer. The affinity is generally lowered in exercising muscle to facilitate unloading of oxygen to tissues, eliminating choice (A). A decrease in the P_aCO₂ would cause a decrease in [H⁺] or increased pH—which increases hemoglobin’s affinity for O₂, eliminating choice (B). Finally, choice (D) is incorrect because hemoglobin’s affinity for O₂ is higher in fetal blood than in adult blood.

4. ABlood drains from the superior and inferior venae cavae into the right atrium. It passes through the tricuspid valve and into the right ventricle, and then through the pulmonary valve into the pulmonary artery, which leads to the lungs. Oxygenated blood returns to the left atrium via the pulmonary veins. It flows through the mitral valve into the left ventricle. From the left ventricle, it is pumped through the aortic valve into the aorta for distribution throughout the body.

5. AThe exchange of fluid is greatly influenced by the relative balance between the hydrostatic and osmotic pressures of blood and tissues. The osmotic (oncotic) pressure remains relatively constant; however, the hydrostatic pressure at the arterial end is greater than the hydrostatic pressure at the venous end. As a result, fluid moves out of the capillaries at the arterial end and back in at the venous end. Fluid is reabsorbed at the venous end because the osmotic pressure exceeds the hydrostatic pressure. Proteins should not cross the capillary wall under normal circumstances.

6. C

The first step in solving this problem is to define cardiac output: cardiac output = heart rate × stroke volume. We can therefore divide the cardiac output by the stroke volume to determine heart rate:

7. DWithout knowing a patient’s blood type, the only type of transfusion that we can safely give is O^–. People with O^– blood are considered universal donors because their blood cells contain no surface antigens. Therefore, O^– blood can be given to anyone without causing potentially life-threatening consequences from ABO incompatibility.

8. CThe only answer choice that correctly describes arteries and veins is choice (C); the pressure in the aorta is usually about 120 or 80 mmHg, depending on whether the heart is in systole or diastole, whereas the pressure in the superior vena cava is near zero. Choice (A) is incorrect because arteries are thick-walled and veins are thin-walled. Choice (B) is also incorrect; this relationship is reversed in pulmonary and umbilical circulation. Choice (D) is reversed as well; arteries make use of the pumping of the heart and the “snapping back” of their elastic walls to transport blood, whereas venous blood is “pumped” by skeletal muscle contractions.

9. AThe relative lack of smooth muscle in venous walls allows stretching to store most of the blood in the body. Valves in the veins allow for one-way flow of blood toward the heart, not stretching. Both arteries and veins are close to lymphatic vessels, which has no bearing on their relative difference in volume. Both arteries and veins have a thin endothelial lining.

10.CCarbon dioxide is a byproduct of metabolism in cells that later combines with water to form bicarbonate in a reaction catalyzed by carbonic anhydrase. This system is blood plasma’s most important buffer system. Food and fluid absorption are not significant sources of buffering, eliminating choices (A) and (B). While the kidney can be involved in acid–base balance, it is through its filtration, secretion, and reabsorption mechanisms, not hormones, eliminating choice (D).

11.CIn circulation, plasma proteins play an important role in generating osmotic (oncotic) pressure. This allows water that is displaced at the arterial end of a capillary bed by hydrostatic pressure to be reabsorbed at the venule end. Loss of these plasma proteins would cause a decrease in the plasma osmotic (oncotic) pressure.

12.DThe atrioventricular valves are located between the atria and the ventricles on both sides of the heart. Their role is to prevent backflow of blood into the atria. The valve on the right side of the heart has three cusps and is called the tricuspid valve. It prevents backflow of blood from the right ventricle into the right atrium.

13.DHolding one’s breath for a prolonged period would result in a drop of oxygenation and an increase in P_aCO₂. The increased carbon dioxide would associate with water to form carbonic acid, which would dissociate into a proton and bicarbonate anion. Further, the low oxygen saturation would eventually lead to anaerobic metabolism in some tissues, causing an increase in lactic acid. These would all lead to a decreased pH.

14.CThe cardiac conduction system starts at the SA node, which is located near the top of the right atrium, and continues down to the AV node, which is located between the two AV valves. The bundle of His is located within the wall between the ventricles, and is likely to be affected if the wall between the ventricles has been damaged by a heart attack. This may affect the left ventricle, but the left ventricle is not part of the cardiac conduction system.

15.BThe greatest amount of resistance is provided by the arterioles, which also results in the greatest drop in blood pressure. Arterioles are highly muscular and have the ability to contract and dilate in order to affect blood pressure.