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All questions of Circulatory System (BIO) for MCAT Exam

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How can the circulatory system promote heat retention/conservation, such as on a cold day?
  • a)
    Decreasing tunica media contraction
  • b)
    Increasing capillary surface area
  • c)
    Vasodilation
  • d)
    Vasoconstriction
Correct answer is option 'D'. Can you explain this answer?

Harper White answered
Vasoconstriction is the process by which blood vessels narrow, reducing blood flow and increasing resistance to blood flow. It is the correct answer because it helps to promote heat retention and conservation in the circulatory system.

Explanation:

1. Cold Weather Response:
In cold weather, the body needs to conserve heat to maintain a stable internal temperature. When the external temperature drops, the body's thermoregulatory system activates several mechanisms to retain heat and prevent hypothermia.

2. Role of the Circulatory System:
The circulatory system plays a crucial role in regulating body temperature. It helps to distribute heat throughout the body and maintain a stable core temperature.

3. Vasoconstriction:
Vasoconstriction is one of the primary responses of the circulatory system to cold temperatures. It involves the contraction of smooth muscles in the walls of blood vessels, leading to a decrease in their diameter. This constriction reduces blood flow to the skin's surface and extremities, minimizing heat loss through the skin.

4. Reducing Heat Loss:
By constricting blood vessels, the circulatory system minimizes the amount of warm blood reaching the skin's surface and extremities. This reduces the surface area available for heat exchange with the environment, effectively reducing heat loss. As a result, more warm blood is directed towards vital organs and tissues to maintain their temperature.

5. Shunting Mechanism:
The circulatory system employs a shunting mechanism during vasoconstriction. It redirects blood flow away from the skin's surface and extremities towards the body's core. This further assists in heat conservation by ensuring that warm blood is circulated internally, keeping vital organs adequately perfused and preventing heat loss through the skin.

6. Physiological Response:
Vasoconstriction is mediated by the sympathetic nervous system. When the body is exposed to cold temperatures, the sympathetic nervous system releases norepinephrine, a neurotransmitter that triggers vasoconstriction. The smooth muscles in the blood vessel walls contract, narrowing the vessels and decreasing blood flow to the skin and extremities.

In conclusion, vasoconstriction is an important physiological response of the circulatory system to cold temperatures. It reduces blood flow to the skin's surface and extremities, minimizing heat loss and promoting heat retention in vital organs and tissues.

A given arteriole has a resistance of 2. What would the new resistance of this vessel be if its radius were to double?
  • a)
    1
  • b)
    1/16
  • c)
    1/8
  • d)
    4
Correct answer is option 'C'. Can you explain this answer?

Amelia Taylor answered
Given Information:
- Resistance of the arteriole = 2
- The radius of the arteriole doubles

To find:
- The new resistance of the arteriole after the radius doubles

Formula:
- Resistance (R) is inversely proportional to the fourth power of the radius (r) of the vessel.
- Mathematically, R ∝ 1/r^4

Solution:
1. Initial Resistance:
- According to the given information, the initial resistance of the arteriole is 2.

2. Relationship between Resistance and Radius:
- The resistance of a vessel is inversely proportional to the fourth power of its radius.
- When the radius of a vessel doubles, the resistance will change accordingly.

3. Doubling the Radius:
- Let's assume the initial radius of the arteriole is 'r'.
- When the radius doubles, the new radius becomes '2r'.

4. Relationship between Initial and New Resistance:
- According to the formula, the initial resistance is inversely proportional to the fourth power of the initial radius: R ∝ 1/r^4.
- The new resistance will be inversely proportional to the fourth power of the new radius: R' ∝ 1/(2r)^4.

5. Calculating the New Resistance:
- Substituting the new radius (2r) into the formula, we get: R' ∝ 1/(2r)^4 = 1/16r^4.
- The new resistance is 1/16 times the initial resistance.
- Therefore, the new resistance of the arteriole after the radius doubles is 1/16 of the initial resistance.

6. Answer:
- The new resistance of the arteriole after the radius doubles is 1/8 (which is equivalent to 1/16).

What layer of the heart would be most immediately susceptible to infections caused by bacteria circulating in the blood?
  • a)
    Epicardium
  • b)
    Myocardium
  • c)
    Pericardium
  • d)
    Endocardium
Correct answer is option 'D'. Can you explain this answer?

Eduskill Classes answered
The endocardium is the innermost layer of the heart wall, lining the chambers and valves of the heart. It consists of a thin layer of endothelial cells supported by connective tissue.
Infections caused by bacteria circulating in the blood, known as bacterial endocarditis, primarily affect the endocardium. This condition occurs when bacteria enter the bloodstream and adhere to damaged or abnormal heart valves or other areas of the endocardium. The bacteria can form colonies (vegetations) on these surfaces, leading to inflammation and potential damage to the endocardium.
The endocardium is susceptible to infections because it comes into direct contact with circulating blood. It is also more prone to damage and exposure to bacteria due to the turbulent flow of blood through the heart, especially around the valves.
On the other hand, the epicardium (outermost layer), myocardium (middle muscular layer), and pericardium (fibrous sac surrounding the heart) are not in direct contact with the circulating blood. While infections can occasionally affect these layers, they are less immediately susceptible to bacterial infections compared to the endocardium.

Which heart valves are NOT actively closed by the contraction of muscular structures?
  • a)
    Mitral valves
  • b)
    Semilunar valves
  • c)
    Atrioventricular valves
  • d)
    Tricuspid valves
Correct answer is option 'B'. Can you explain this answer?

Orion Classes answered
  • The papillary muscles contract during systole to prevent blood from flowing backwards within the heart.
  • Blood flows from high pressure to low pressure. The papillary muscles are only necessary in areas where this fact may propagate flow in a backwards direction.
  • The pressure generated by ventricular systole is substantial enough that it overcomes the pressure of the blood vessels they supply. This force opens the pulmonary and aortic valves, which then shut passively when the pressure of the ventricles is equal to or less than the pressure upstream.
  • The mitral and tricuspid valves are both atrioventricular valves.
  • Semilunar valves are not associated with the papillary muscles, and are not actively closed.

What vessels carry deoxygenated blood away from the heart?
  • a)
    Pulmonary artery only
  • b)
    Coronary arteries only
  • c)
    Neither coronary arteries or pulmonary artery
  • d)
    Both coronary arteries and pulmonary artery
Correct answer is option 'A'. Can you explain this answer?

Orion Classes answered
The pulmonary artery is the blood vessel that carries deoxygenated blood away from the heart. It is the only artery in the body that carries deoxygenated blood. The pulmonary artery originates from the right ventricle of the heart and divides into two branches, which lead to the left and right lungs.
The deoxygenated blood is pumped from the right ventricle into the pulmonary artery and is then transported to the lungs. In the lungs, the blood undergoes oxygenation through the process of gas exchange, where carbon dioxide is released, and oxygen is taken up by the red blood cells. After oxygenation, the blood returns to the heart through the pulmonary veins as oxygenated blood.
Coronary arteries, on the other hand, are responsible for supplying oxygenated blood to the heart muscle itself. They originate from the aorta, the main artery leaving the heart, and supply the heart with oxygen and nutrients.

In terms of being open or closed, what is the state of the mitral and tricuspid valves (left and right atrioventricular valves, respectively) at the end of the first heart sound?
  • a)
    Mitral is closed, tricuspid is open
  • b)
    Mitral is open, tricuspid is closed
  • c)
    Both are open
  • d)
    Both are closed
Correct answer is option 'D'. Can you explain this answer?

Freak Artworks answered
The first heart sound, also known as S1, is produced by the closure of the mitral and tricuspid valves. These valves close at the beginning of ventricular systole, which is the contraction phase of the ventricles.
During ventricular systole, the pressure in the ventricles increases as they contract, causing the blood to be forcefully ejected into the pulmonary artery and aorta. In order to prevent backflow of blood into the atria during this contraction, the mitral and tricuspid valves close tightly.
As the ventricles contract, the pressure within the ventricles rises above the pressure in the atria, causing the mitral and tricuspid valves to close simultaneously, generating the first heart sound.
Therefore, at the end of the first heart sound, both the mitral and tricuspid valves are closed (option D). This marks the beginning of ventricular systole and the ejection of blood into the circulation.

Which of the following is a protein involved in the transport of oxygen in the blood?
  • a)
    Fibrinogen
  • b)
    Albumin
  • c)
    Immunoglobulin
  • d)
    Hemoglobin
Correct answer is option 'D'. Can you explain this answer?

Orion Classes answered
Hemoglobin is the protein responsible for transporting oxygen in the blood. It binds to oxygen in the lungs and releases it to tissues throughout the body. Hemoglobin is primarily found in red blood cells.

What physical feature of large systemic arteries (resistance vessels) makes them relatively more responsive to changes in intracellular calcium concentrations?
  • a)
    Absent tunica intima
  • b)
    Thick tunica media
  • c)
    Absent tunica media
  • d)
    Thick tunica intima
Correct answer is option 'B'. Can you explain this answer?

Orion Classes answered
The tunica media is the middle layer of the arterial wall and is composed primarily of smooth muscle cells. The smooth muscle cells in the tunica media are responsible for regulating the diameter (vasoconstriction and vasodilation) of the arteries.
In large systemic arteries, such as the aorta and the major arterial branches, the tunica media is relatively thicker compared to smaller arteries and arterioles. This increased thickness provides a greater amount of smooth muscle tissue.
Smooth muscle contraction is regulated by intracellular calcium concentrations. When intracellular calcium levels increase, it triggers the contraction of smooth muscle cells, leading to vasoconstriction and narrowing of the arterial diameter. On the other hand, when intracellular calcium levels decrease, smooth muscle relaxation occurs, resulting in vasodilation and widening of the arterial diameter.
Due to the greater amount of smooth muscle tissue in the thick tunica media of large systemic arteries, these arteries are more responsive to changes in intracellular calcium concentrations. Even small changes in calcium levels can have a significant effect on smooth muscle contraction and arterial diameter.
Therefore, the relatively thick tunica media in large systemic arteries makes them more responsive to changes in intracellular calcium concentrations (option B).

At the instant following the second heart sound, which heart valves are open?
  • a)
    Both atrioventricular valves and semilunar valves
  • b)
    Semilunar valves only
  • c)
    Atrioventricular valves only
  • d)
    All valves are closed
Correct answer is option 'D'. Can you explain this answer?

Orion Classes answered
The second heart sound (S2) occurs when the semilunar valves (pulmonary valve and aortic valve) close at the end of ventricular systole. After the closure of the semilunar valves, all four heart valves (both atrioventricular valves and both semilunar valves) are closed. This marks the beginning of ventricular diastole, during which all valves remain closed momentarily before the next cardiac cycle begins.
During ventricular diastole, the atrioventricular valves (mitral valve and tricuspid valve) are closed to prevent the backflow of blood from the ventricles to the atria. Simultaneously, the semilunar valves are closed to prevent the backflow of blood from the aorta and pulmonary artery back into the ventricles.
Therefore, at the instant following the second heart sound, all heart valves are closed (option D). This brief period of closure allows the ventricles to relax and refill with blood before the next contraction.

An individual with blood type O- could potentially have which blood antibodies present in their plasma?
  • a)
    Both A and B antibodies
  • b)
    Neither A or B antibodies
  • c)
    B antibodies only
  • d)
    A antibodies only
Correct answer is option 'A'. Can you explain this answer?

Orion Classes answered
An individual with blood type O- could potentially have which blood antibodies present in their plasma?
A.Both A and B antibodies
B.Neither A or B antibodies
C.B antibodies only
D.A antibodies only

Which of the following does not play an active role in the production of red blood cells?
  • a)
    Thymus
  • b)
    Kidney
  • c)
    Bone marrow
  • d)
    Spleen
Correct answer is option 'A'. Can you explain this answer?

Orion Classes answered
  • The bone marrow is the major site of hematopoiesis in adults, and is the home of all precursor cells relating to both white and red blood cells.
  • The spleen is most important as a filter for blood, though it also plays a key role in red cell production during infancy and in situations of disease.
  • The kidney secretes erythropoietin in response to low oxygen levels. This hormone stimulates red blood cell production.
  • The thymus is important for immune cell (white cell) production and maturation, but does not play an active role in the production of red blood cells.

When whole blood is run through a centrifuge, why does plasma separate to the top of the tube, while red blood cells separate to the bottom?
  • a)
    The red cell fraction occupies a greater volume than the plasma fraction
  • b)
    The red cell fraction has a greater mass than the plasma fraction
  • c)
    The components of the red cell fraction are larger than the components of the plasma fraction
  • d)
    The red cell fraction has a greater density than the plasma fraction
Correct answer is option 'D'. Can you explain this answer?

Orion Classes answered
Blood is composed of nearly 50% water by volume. The plasma fraction typically occupies a much larger volume than the red cell fraction.
In whole blood, the components are suspended equally within the fluid. Centrifugation displaces the components by applying a rotational force to the suspension.
Centrifugation separates particles in a suspension on the basis of their density. Red blood cells (iron) is much more dense than other blood components.
The red cell fraction has a greater density than the plasma fraction.

What coagulation factor is common to both the intrinsic and extrinsic pathway?
  • a)
    VII (Proconvertin/ stable factor)
  • b)
    IX (Antihemophilic factor B/ Christmas factor)
  • c)
    X (Stuart-Prower factor)
  • d)
    VIII (Antihemophilic factor
Correct answer is option 'C'. Can you explain this answer?

Orion Classes answered
The coagulation cascade involves a series of enzymatic reactions that lead to the formation of a fibrin clot, which helps in the process of blood coagulation. There are two primary pathways involved: the intrinsic pathway and the extrinsic pathway.
The intrinsic pathway is initiated by factors present within the blood, while the extrinsic pathway is triggered by factors outside the blood. These pathways eventually converge to a common pathway, which leads to the final formation of a fibrin clot.
Factor X, also known as Stuart-Prower factor, is a coagulation factor that plays a crucial role in both the intrinsic and extrinsic pathways. It is activated in each pathway and acts as a common link between them. Once activated, Factor X converts prothrombin to thrombin, which in turn converts fibrinogen to fibrin, resulting in clot formation.

What is the principal component which activates and drives the extrinsic pathway of the coagulation cascade?
  • a)
    Intrinsic pathway activation
  • b)
    Plasmin
  • c)
    Upstream coagulation factors such as factors XII and X
  • d)
    Endothelial cell insult
Correct answer is option 'D'. Can you explain this answer?

Orion Classes answered
The extrinsic pathway of the coagulation cascade is primarily triggered by an endothelial cell insult or tissue factor (TF) exposure. Endothelial cells are the cells that line the blood vessels, and when they are damaged or injured, they release tissue factor (TF), also known as factor III. Tissue factor is a protein that plays a crucial role in initiating the extrinsic pathway.
When endothelial cells are insulted, tissue factor comes into contact with circulating factor VII, which then binds to tissue factor and becomes activated. The activated factor VII, together with tissue factor, forms a complex known as the extrinsic tenase complex. This complex subsequently activates factor X, which is a key step in the coagulation cascade.

What physiological condition would produce a relative increase in hematocrit?
  • a)
    High serum protein concentration
  • b)
    Dehydration
  • c)
    Hemolysis
  • d)
    Iron deficiency
Correct answer is option 'B'. Can you explain this answer?

Orion Classes answered
Hematocrit refers to the percentage of the total blood volume occupied by red blood cells. It is a measure of the concentration of red blood cells in the blood. A relative increase in hematocrit means there is a higher proportion of red blood cells compared to the total blood volume.
Dehydration is a condition characterized by inadequate fluid intake or excessive fluid loss, leading to a decrease in the overall blood volume. In this state, the concentration of red blood cells in the blood remains relatively constant, but the plasma volume decreases. As a result, the proportion of red blood cells in the blood increases, leading to a higher hematocrit value.

How would an increase in bicarbonate (HCO3−) relative to all other molecules in the blood affect the oxygen affinity of hemoglobin and why?
  • a)
    Increase oxygen affinity by directly binding with hemoglobin
  • b)
    Decrease oxygen affinity by binding with free protons
  • c)
    Decrease oxygen affinity by directly binding with hemoglobin
  • d)
    Increase oxygen affinity by binding with free protons
Correct answer is option 'D'. Can you explain this answer?

Orion Classes answered
An increase in bicarbonate (HCO3-) in the blood is typically associated with a decrease in blood pH (acidosis). In an acidic environment, the affinity of hemoglobin for oxygen decreases, causing a rightward shift of the oxygen-hemoglobin dissociation curve. This shift promotes the release of oxygen from hemoglobin, allowing it to be delivered to the tissues.
The increase in bicarbonate indirectly affects the oxygen affinity of hemoglobin by binding with free protons (H+). When bicarbonate combines with protons, it forms carbonic acid (H2CO3), which can then dissociate into carbon dioxide (CO2) and water (H2O). This reaction helps regulate blood pH and maintain acid-base balance.
The binding of free protons by bicarbonate leads to a decrease in the concentration of protons in the blood. This reduction in proton concentration helps to stabilize the deoxygenated form of hemoglobin (T-state), which has a higher affinity for oxygen. As a result, the oxygen affinity of hemoglobin increases, allowing it to bind more readily with oxygen in the lungs and release it to the tissues.
Therefore, the correct answer is D. An increase in bicarbonate relative to all other molecules in the blood would increase the oxygen affinity of hemoglobin by binding with free protons.

In terms of cell lineage, how are red blood cells, macrophages, and B cells each classified?
  • a)
    Red blood cells and macrophages are of myeloid lineage, B cells are of lymphoid lineage
  • b)
    Red blood cells are of myeloid lineage, macrophages and B cells are of lymphoid lineage
  • c)
    Macrophages and B cells are of myeloid lineage, red blood cells are of lymphoid lineage
  • d)
    B cells are of myeloid lineage, red blood cells and macrophages are of lymphoid lineage
Correct answer is option 'A'. Can you explain this answer?

Orion Classes answered
Cell lineage refers to the developmental pathway that cells undergo to reach their mature functional state. In terms of cell lineage, red blood cells and macrophages belong to the myeloid lineage, while B cells belong to the lymphoid lineage.
The myeloid lineage gives rise to various types of blood cells involved in innate immunity, including red blood cells (erythrocytes) and macrophages. Red blood cells are responsible for oxygen transport, while macrophages play a role in phagocytosis and immune defense.
The lymphoid lineage gives rise to cells involved in adaptive immunity, including B cells. B cells are responsible for producing antibodies and are crucial in humoral immune responses.

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