Blood and Immunity — MCQs

Blood and Immunity Indian Medical PG Practice Questions and MCQs

Question 461: Females have a lower RBC count compared to males due to?

A. Low erythropoietin (Correct Answer)
B. High estrogen
C. Low stem cells
D. Menstrual blood loss

Explanation: ***Low erythropoietin (relative to males)*** - The primary reason females have lower RBC counts is due to **hormonal differences**, specifically the lack of androgenic stimulation of erythropoiesis that males experience. - **Testosterone in males** directly stimulates erythropoietin production and enhances erythropoiesis, leading to higher RBC counts (males: 4.5-5.5 million/µL vs females: 4.0-5.0 million/µL). - Females have relatively lower erythropoietic drive compared to males due to the absence of significant androgenic hormones, which can be conceptualized as relatively lower erythropoietic stimulus. - This difference exists across all age groups, including pre-menarchal and post-menopausal women, confirming it is **hormonal rather than blood loss-related**. *High estrogen* - Estrogen does not significantly suppress erythropoiesis to cause lower RBC counts. - Estrogen has various effects on the hematopoietic system but is not the primary cause of the gender difference in RBC count. *Low stem cells* - Hematopoietic stem cell numbers and functionality are comparable between males and females. - There is no evidence of lower stem cell counts in females accounting for RBC differences. *Menstrual blood loss* - While menstrual blood loss can contribute to **iron deficiency anemia** in some women, it does NOT explain the baseline physiological difference in RBC counts between genders. - Most healthy menstruating women maintain normal RBC counts despite regular menstruation. - The RBC count difference exists even in pre-menarchal girls and post-menopausal women, proving menstruation is not the primary cause.

Question 462: What is the primary physiological effect of increased 2,3-DPG on hemoglobin?

A. Increased affinity of hemoglobin to oxygen
B. Decreased affinity of hemoglobin to oxygen (Correct Answer)
C. Left shift of oxygen-hemoglobin dissociation curve
D. Right shift of oxygen-hemoglobin dissociation curve

Explanation: ***Decreased affinity of hemoglobin to oxygen*** - **2,3-Diphosphoglycerate (2,3-DPG)** binds to the beta subunits of deoxyhemoglobin, stabilizing the **deoxygenated state** and thus **reducing hemoglobin's affinity for oxygen**. - This is the **primary molecular mechanism** by which 2,3-DPG exerts its effect, facilitating **oxygen unloading** in peripheral tissues. - This decreased affinity manifests graphically as a **right shift** in the oxygen-hemoglobin dissociation curve. *Increased affinity of hemoglobin to oxygen* - This is incorrect because 2,3-DPG specifically works to **decrease hemoglobin's affinity** for oxygen, promoting oxygen release. - Increased affinity would mean oxygen is held more tightly, which is counterproductive for **oxygen delivery** to tissues. *Left shift of oxygen-hemoglobin dissociation curve* - A **left shift** indicates **increased affinity** of hemoglobin for oxygen, meaning oxygen is held more tightly. - Since 2,3-DPG decreases affinity, it causes a **right shift**, not a left shift. *Right shift of oxygen-hemoglobin dissociation curve* - While this is the **graphical representation** of 2,3-DPG's effect, it is a **consequence** of the primary molecular mechanism (decreased affinity). - A right shift signifies that for any given partial pressure of oxygen, hemoglobin is **less saturated** with oxygen, reflecting the decreased affinity caused by 2,3-DPG binding.

Question 463: Which isotope is used to measure RBC volume?

A. Cr 51 (Correct Answer)
B. H-3
C. D2O
D. I-135

Explanation: ***Cr 51*** - **Chromium-51** attaches irreversibly to the beta chain of hemoglobin, making it an ideal tracer for measuring **red blood cell volume** and survival. - After injection, the labeled red blood cells distribute throughout the circulation, and their dilution allows for the calculation of the total **RBC mass**. *H-3* - **Tritium (H-3)** is typically used as tritiated water to measure **total body water**, as it readily equilibrates throughout all fluid compartments. - It does not specifically bind to red blood cells for mass measurement. *D2O* - **D2O (heavy water)** is used to measure **total body water** content, similar to tritiated water. - It exchanges with water in the body and diffuses into all fluid compartments, rather than targeting red blood cells. *I-135* - While various **iodine isotopes** are used in medicine, such as **I-131** for thyroid imaging or therapy, **I-135** is not a commonly used isotope for measuring red blood cell volume. - Other tracers like **radio-iodinated human serum albumin** (e.g., I-125 HSA) can be used to measure plasma volume, not specifically RBC volume.

Question 464: In general pathophysiology, the most direct and fundamental mechanism by which death occurs typically involves which of the following?

A. Damage to the plasmalemma
B. Decreased oxygen-carrying capacity of blood
C. Poisoning of oxidative phosphorylation (Correct Answer)
D. Increased calcium transport into mitochondria

Explanation: ***Correct Option: Poisoning of oxidative phosphorylation*** - **ATP depletion** is the most fundamental and direct mechanism of cell death in pathophysiology - **Poisoning of oxidative phosphorylation** (e.g., cyanide, carbon monoxide at mitochondrial level) directly inhibits the electron transport chain, immediately stopping ATP production - Without ATP, cells cannot maintain: - **Ion gradients** (Na+/K+ ATPase failure) - **Membrane integrity** (leading to cell swelling and rupture) - **Cellular homeostasis** (all active transport mechanisms fail) - This represents the **final common pathway** of cell death - regardless of the initial insult (hypoxia, toxins, trauma), death ultimately occurs when ATP production fails - Death occurs within minutes when oxidative phosphorylation is poisoned, demonstrating its fundamental nature *Incorrect Option: Decreased oxygen-carrying capacity of blood* - While decreased oxygen-carrying capacity (severe anemia, carbon monoxide poisoning) causes **hypoxic injury**, it is one step removed from the fundamental mechanism - It causes death **by ultimately affecting oxidative phosphorylation**, making it less direct - The body has compensatory mechanisms (increased cardiac output, increased extraction) that can partially compensate for reduced oxygen-carrying capacity - This is an **upstream cause** rather than the most direct mechanism *Incorrect Option: Damage to the plasmalemma* - Plasmalemma (plasma membrane) damage is typically a **consequence** of ATP depletion, not the primary cause - When ATP fails, Na+/K+ ATPase stops working, causing cell swelling and membrane rupture - This represents a **downstream effect** of energy failure rather than the fundamental mechanism *Incorrect Option: Increased calcium transport into mitochondria* - Excessive mitochondrial calcium can trigger apoptosis and disrupt oxidative phosphorylation - However, this is a **specific mechanism** of injury in certain contexts (ischemia-reperfusion, excitotoxicity) - It is not as universally fundamental as the failure of oxidative phosphorylation itself - Calcium dysregulation is often secondary to ATP depletion and loss of calcium pump function

Question 465: Which cytokine activates eosinophils?

A. IL-1
B. IL-4
C. IL-5 (Correct Answer)
D. IL-6

Explanation: ***IL-5*** - **Interleukin-5 (IL-5)** is the primary cytokine responsible for activating **eosinophils**, stimulating their **production, maturation, and release** from the bone marrow. - It also enhances eosinophil survival and function at sites of inflammation, particularly in **allergic reactions** and **parasitic infections**. *IL-1* - **Interleukin-1 (IL-1)** is a **pro-inflammatory cytokine** primarily involved in fever, acute phase responses, and activating lymphocytes, but not directly in eosinophil activation. - It plays a role in general immune responses and inflammation by activating various cell types, including **macrophages and endothelial cells**. *IL-4* - **Interleukin-4 (IL-4)** is crucial for **Th2 differentiation** and isotype switching to IgE in B cells, promoting allergic responses. - While involved in allergic reactions, it primarily affects B cell and T cell function rather than direct activation of eosinophils, though it can support their development indirectly. *IL-6* - **Interleukin-6 (IL-6)** is a **pro-inflammatory cytokine** involved in acute phase reactions, hematopoiesis, and immune responses. - It is critical for B cell differentiation and T cell activation but does not directly activate eosinophils.

Question 466: Endothelial cells synthesize which of the following substances?

A. Fibrinogen
B. Factor-X
C. Factor-XII
D. Factor VIII (Correct Answer)

Explanation: ***Factor VIII (Correct Answer)*** * Endothelial cells synthesize and secrete **von Willebrand factor**, a carrier protein for **Factor VIII**; they also produce Factor VIII itself, playing a crucial role in hemostasis. * **Weibel-Palade bodies** within endothelial cells are storage sites for both von Willebrand factor and Factor VIII, which are released upon endothelial activation. *Incorrect: Fibrinogen* * **Fibrinogen** is primarily synthesized by the **liver** and is a key component of the coagulation cascade, forming the fibrin clot. * While endothelial cells play a role in regulating coagulation, they are not the primary site of **fibrinogen production**. *Incorrect: Factor-X* * **Factor X** (Stuart-Prower factor) is a coagulation factor that is **synthesized in the liver** and is vitamin K-dependent. * Endothelial cells do not synthesize Factor X; instead, they *regulate* its activation and activity through various mechanisms. *Incorrect: Factor-XII* * **Factor XII** (Hageman factor) is a protein of the contact activation pathway of coagulation, primarily **synthesized by the liver**. * Endothelial cells influence the activation of Factor XII on their surface but do not **produce** this coagulation factor themselves.

Question 467: Fever occurs due to which of the following mechanisms?

A. Endorphin
B. Enkephalin
C. Histamine
D. IL-1 (Correct Answer)

Explanation: ***IL1*** - Interleukin-1 (IL-1) is a **proinflammatory cytokine** that plays a key role in the immune response and is a primary mediator of fever [1]. - It stimulates the **hypothalamus** to increase body temperature set-point, thus inducing fever. *Enkephalin* - Enkephalins are **opioid peptides** involved in pain modulation, not in the fever response. - They primarily act in the **central nervous system** and do not directly influence thermoregulation. *Endorphin* - Endorphins, like enkephalins, are also **opioid peptides** related to pain relief and mood regulation, with no significant role in fever induction. - Their main function is to provide **analgesic** effects rather than influencing body temperature. *Histamine* - Histamine is predominantly involved in **allergic responses** and inflammation but is not a direct mediator of fever. - It causes **vasodilation** and increases vascular permeability, but does not raise the body temperature set-point like IL-1 does. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 110-111.

Question 468: The principal site for granulocytic hemopoiesis in the adult human is:

A. Red bone marrow (Correct Answer)
B. Spleen
C. Yellow bone marrow (primarily fat storage)
D. Liver

Explanation: ***Red bone marrow*** - In adult humans, **red bone marrow** is the primary site for all types of **hematopoiesis**, including granulocytic hemopoiesis. - It contains **hematopoietic stem cells** that differentiate into myeloid and lymphoid lineages, producing mature blood cells. *Liver* - The liver is a major site of **hematopoiesis during fetal development**, especially in the second trimester. - In adults, the liver only resumes hematopoietic function under conditions of **extramedullary hematopoiesis**, such as severe bone marrow failure. *Spleen* - The spleen is involved in **hematopoiesis** during fetal life and can also contribute to **extramedullary hematopoiesis** in adults when red bone marrow is compromised. - However, it is not the principal site for normal, ongoing granulocytic hemopoiesis in healthy adults. *Yellow bone marrow* - **Yellow bone marrow** primarily consists of **adipocytes (fat cells)** and has limited hematopoietic activity. - While it can convert to red bone marrow under extraordinary demand, it is not the principal site for granulocytic hemopoiesis.

Question 469: Which of the following agents is least likely to be found in plasma?

A. Fibrinogen
B. Prothrombin
C. Calcium ion
D. Thrombin (Correct Answer)

Explanation: ***Thrombin*** - **Thrombin** is an active enzyme that converts **fibrinogen to fibrin** during coagulation. Its presence in significant amounts in plasma would lead to widespread, uncontrolled clotting. - Due to its potent procoagulant activity, thrombin is typically present in circulation only transiently and in very low concentrations, being rapidly inactivated by **antithrombin** and other inhibitors. *Fibrinogen* - **Fibrinogen** is a large plasma protein that is a precursor to fibrin and is crucial for **blood clot formation**. - It is a normal and abundant component of plasma, synthesized by the liver, and is continuously present in significant concentrations. *Prothrombin* - **Prothrombin** (Factor II) is the inactive precursor of thrombin, synthesized by the liver with the help of **vitamin K**. - It circulates in the plasma in relatively high concentrations, ready to be activated into thrombin upon injury. *Calcium ion* - **Calcium ions (Ca2+)** are essential **cofactors** for many steps in the coagulation cascade. - They are continuously present in plasma and play vital roles in bone health, muscle contraction, and nerve function, in addition to coagulation.

Question 470: The factor responsible for the left shift of the HbO2 dissociation curve is

A. Increase in 2,3 DPG in RBC
B. Fall in temperature (Correct Answer)
C. Fall in pH
D. Increase level of CO2 in blood

Explanation: ***Fall in temperature*** - A **decrease in temperature** causes the hemoglobin to bind more tightly to oxygen, reducing its release into the tissues. - This increased affinity of hemoglobin for oxygen shifts the **HbO2 dissociation curve to the left**. *Increase in 2,3 DPG in RBC* - An **increase in 2,3-Bisphosphoglycerate (2,3-DPG)** in red blood cells decreases hemoglobin's affinity for oxygen. - This effect promotes oxygen release to tissues and causes a **right shift** of the HbO2 dissociation curve. *Fall in pH* - A **decrease in pH** (increased acidity), known as the **Bohr effect**, reduces hemoglobin's affinity for oxygen. - This facilitates oxygen unloading in tissues and results in a **right shift** of the HbO2 dissociation curve. *Increase level of CO2 in blood* - An **increase in CO2 levels** in the blood also contributes to the Bohr effect by lowering pH and forming carbaminohemoglobin. - This reduces hemoglobin's affinity for oxygen, promoting oxygen release and causing a **right shift** of the HbO2 dissociation curve.

Practice by Chapter

Composition and Functions of Blood

Practice Questions

Erythrocytes and Hemoglobin

Practice Questions

Leukocytes and Immune Function

Practice Questions

Platelets and Hemostasis

Practice Questions

Blood Groups and Transfusion

Practice Questions

Coagulation and Fibrinolysis

Practice Questions

Hematopoiesis

Practice Questions

Innate Immunity

Practice Questions

Adaptive Immunity

Practice Questions

Immunological Memory and Tolerance

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free