Blood and Immunity — MCQs

Blood and Immunity Indian Medical PG Practice Questions and MCQs

Question 401: CO poisoning causes which type of hypoxia?

A. Anemic hypoxia (Correct Answer)
B. Hypoxic hypoxia
C. Stagnant hypoxia
D. Histotoxic hypoxia

Explanation: ***Anemic hypoxia*** - **Carbon monoxide (CO)** binds to **hemoglobin** with an affinity much higher than oxygen, forming **carboxyhemoglobin**. - This effectively reduces the **oxygen-carrying capacity of the blood**, mimicking a severe anemia, despite normal arterial PO2. *Hypoxic hypoxia* - Occurs when there is **insufficient oxygen delivery to the blood** due to low arterial PO2, as seen in high altitudes or respiratory diseases. - In CO poisoning, **arterial PO2 is typically normal**, distinguishing it from hypoxic hypoxia. *Stagnant hypoxia* - Results from **inadequate blood flow** to tissues, leading to reduced oxygen delivery, as observed in heart failure or shock. - CO poisoning primarily affects oxygen transport by hemoglobin, not the **rate of blood flow**. *Histotoxic hypoxia* - Characterized by the **inability of tissues to utilize oxygen** effectively, even when oxygen delivery is adequate, as seen in cyanide poisoning inhibiting cytochrome oxidase. - In CO poisoning, tissues can utilize oxygen; the problem is the **reduced availability of oxygen** from hemoglobin.

Question 402: The graph below shows oxygen dissociation curves. What does the curve marked as 'A' indicate?

A. Myoglobin (Correct Answer)
B. Methemoglobin
C. Carboxyhemoglobinemia
D. Fetal hemoglobin

Explanation: ***Myoglobin*** - Curve A shows a **hyperbolic oxygen dissociation curve** which is characteristic of myoglobin, indicating high oxygen affinity even at low partial pressures. - Myoglobin has only one heme group, allowing it to bind a single oxygen molecule with high affinity to **store oxygen in muscles**. *Methemoglobin* - Methemoglobin has a **ferric (Fe3+) iron** in its heme group, which cannot bind oxygen, thus reducing the overall oxygen-carrying capacity. - It would typically cause a **left shift** of the remaining functional hemoglobin's dissociation curve due to increased oxygen affinity, but this isn't directly represented as curve A's primary characteristic. *Carboxyhemoglobinemia* - **Carbon monoxide (CO)** binds to hemoglobin with a much higher affinity than oxygen, forming carboxyhemoglobin. - This binding leads to a **left shift** in the oxygen dissociation curve of the remaining functional hemoglobin and a decreased oxygen-carrying capacity, but curve A represents a species with inherently higher oxygen affinity. *Fetal hemoglobin* - Fetal hemoglobin (HbF) has a **higher affinity for oxygen** than adult hemoglobin (HbA), which is represented by a **left-shifted sigmoidal curve** compared to adult hemoglobin. - While it has higher affinity, its curve is still **sigmoidal**, unlike the hyperbolic curve of myoglobin (A).

Question 403: What is the primary stimulus for erythropoietin production?

A. Increased temperature
B. Decreased blood pressure
C. Decreased plasma proteins
D. Tissue hypoxia (Correct Answer)

Explanation: ***Tissue hypoxia*** - Erythropoietin (EPO) production is primarily stimulated by sensing **low oxygen levels** in the kidneys. - This response is crucial for maintaining adequate oxygen delivery to tissues by increasing **red blood cell mass**. *Increased temperature* - An increase in body temperature is a stimulus for processes like **sweating** and **vasodilation**, to regulate body temperature. - It does not directly affect erythropoietin production or red blood cell synthesis. *Decreased blood pressure* - A decrease in blood pressure primarily stimulates the **renin-angiotensin-aldosterone system** and the release of **ADH** to regulate blood volume and pressure. - It does not directly cause an increase in erythropoietin release as its primary function is not related to oxygen sensing. *Decreased plasma proteins* - A decrease in plasma proteins primarily affects **oncotic pressure** and can lead to edema. - It is not a direct stimulus for erythropoietin production.

Question 404: What is needed for prothrombin to thrombin conversion?

A. Magnesium
B. Sodium
C. Calcium (Correct Answer)
D. Potassium

Explanation: ***Calcium*** - **Calcium ions (Ca2+)** are absolutely essential cofactors for the conversion of **prothrombin to thrombin** in the coagulation cascade. - They are required for the formation and function of the **prothrombinase complex** (Factor Xa + Factor Va + Ca2+ + phospholipid surface). - Calcium binds to **γ-carboxyglutamic acid (Gla) residues** on prothrombin and Factor Xa, enabling them to anchor to phospholipid surfaces where the conversion occurs. - This is why **EDTA and citrate** (calcium chelators) are used as anticoagulants in blood collection tubes. *Magnesium* - **Magnesium** is an important cofactor for numerous enzymatic reactions (e.g., ATP-dependent enzymes, DNA/RNA polymerases). - However, it is **not directly involved** in the prothrombin to thrombin conversion step of the coagulation cascade. - Its primary roles are in DNA synthesis, muscle function, and nerve transmission. *Sodium* - **Sodium** is vital for maintaining fluid balance, osmotic pressure, nerve impulses, and muscle contractions. - It does **not play a direct role** as a cofactor in the prothrombinase complex or prothrombin to thrombin conversion. *Potassium* - **Potassium** is essential for maintaining cell membrane potential, nerve impulses, cardiac function, and muscle contraction. - It is **not a cofactor** for the enzymatic reactions involved in the coagulation cascade.

Question 405: A pregnant woman is able to transfer oxygen to her fetus because fetal hemoglobin has a greater affinity for oxygen than does adult hemoglobin. Why is the affinity of fetal hemoglobin for oxygen higher?

A. There is less 2,3-BPG in the fetal circulation as compared to maternal circulation
B. Fetal hemoglobin binds 2,3-BPG with fewer ionic bonds than the adult form. (Correct Answer)
C. The tense form of hemoglobin is more prevalent in the circulation of the fetus
D. The oxygen-binding curve of fetal hemoglobin is shifted to the right.

Explanation: ***Fetal hemoglobin binds 2,3-BPG with fewer ionic bonds than the adult form.*** * **Fetal hemoglobin (HbF)**, composed of two alpha and two gamma subunits, interacts less effectively with **2,3-bisphosphoglycerate (2,3-BPG)** due to a difference in its gamma subunits compared to the beta subunits of **adult hemoglobin (HbA)**. * The reduced binding of 2,3-BPG to HbF stabilizes its **R (relaxed) state**, which has a higher oxygen affinity, facilitating oxygen transfer from the mother to the fetus. *There is less 2,3-BPG in the fetal circulation as compared to maternal circulation* * While 2,3-BPG plays a crucial role in regulating oxygen affinity, the primary reason for **fetal hemoglobin's higher oxygen affinity** is its inherent structural difference that leads to weaker binding of 2,3-BPG, not necessarily the concentration of 2,3-BPG in the fetal circulation. * The **concentration of 2,3-BPG is typically similar or even slightly higher in fetal blood** to enhance oxygen unloading at the tissues, but its effect on HbF is diminished. *The tense form of hemoglobin is more prevalent in the circulation of the fetus* * The **tense form (T-state)** of hemoglobin has a **lower affinity for oxygen**, and its prevalence would lead to reduced oxygen binding, which is contrary to the physiological need of the fetus to extract oxygen from the maternal blood. * **Fetal hemoglobin's higher oxygen affinity** means it spends more time in the **relaxed form (R-state)**, which is responsible for tighter oxygen binding. *The oxygen-binding curve of fetal hemoglobin is shifted to the right.* * An **oxygen-binding curve shifted to the right** indicates a **decreased affinity for oxygen** and would facilitate oxygen unloading, not oxygen loading. * For fetal hemoglobin to effectively extract oxygen from maternal blood, its **oxygen-binding curve must be shifted to the left**, signifying a higher oxygen affinity.

Question 406: Decreased O2 carrying capacity and Normal PO2 is a feature of

A. Anemic hypoxia (Correct Answer)
B. Hypoxic hypoxia
C. Histotoxic hypoxia
D. Stagnant hypoxia

Explanation: ***Anemic hypoxia*** - This condition is characterized by a **reduced number of circulating red blood cells** or a **low hemoglobin concentration**, leading to a decreased capacity to transport oxygen to tissues. - While the overall oxygen-carrying capacity is diminished, the **partial pressure of oxygen (PO2)** in the arterial blood remains normal because the lungs are still efficiently oxygenating the existing hemoglobin. *Hypoxic hypoxia* - This type of hypoxia involves a **decreased partial pressure of oxygen (PO2)** in the arterial blood, often due to conditions affecting lung function or environmental factors (e.g., high altitude). - While there is a reduced amount of oxygen available for transport, the **oxygen-carrying capacity** of the blood itself is not inherently impaired. *Histotoxic hypoxia* - In histotoxic hypoxia, the **cellular machinery responsible for oxygen utilization is impaired**, typically due to toxins like cyanide. - Both the **PO2** and the **oxygen-carrying capacity** of the blood are usually normal, but the tissues cannot effectively use the delivered oxygen. *Stagnant hypoxia* - Also known as **ischemic hypoxia**, this occurs when there is inadequate blood flow to the tissues, leading to insufficient oxygen delivery despite normal **PO2** and **oxygen-carrying capacity**. - This is often seen in conditions like **heart failure** or **localized arterial obstruction**.

Question 407: Oxygen dependent killing is done through

A. Superoxide dismutase
B. Glutathione peroxidase
C. Catalase
D. NADPH oxidase (Correct Answer)

Explanation: ***NADPH oxidase*** - **NADPH oxidase** is the enzyme responsible for the **respiratory burst**, producing **superoxide radicals (O2-)** which are crucial for oxygen-dependent killing by phagocytes. - This enzyme converts **molecular oxygen** into highly reactive **superoxide** by reducing NADP+ using NADPH. *Superoxide dismutase* - **Superoxide dismutase (SOD)** neutralizes **superoxide radicals** by converting them into hydrogen peroxide, acting as an antioxidant defense mechanism, rather than a killing mechanism. - While it deals with reactive oxygen species, its role is to protect the cell from oxidative damage, not to generate products for microbial killing. *Glutathione peroxidase* - **Glutathione peroxidase** is an antioxidant enzyme that reduces **hydrogen peroxide** and organic hydroperoxides to water using **reduced glutathione**, thus protecting cells from oxidative stress. - It does not directly produce reactive oxygen species for microbial killing but rather detoxifies them. *Catalase* - **Catalase** converts **hydrogen peroxide** into water and oxygen, functioning to protect cells from the damaging effects of hydrogen peroxide. - Like superoxide dismutase and glutathione peroxidase, its primary role is protective against reactive oxygen species, not in generating them for pathogen eradication.

Question 408: Which of the following cells will increase in case of parasite infection?

A. A: Lymphocyte
B. D: Basophil
C. C: Eosinophil (Correct Answer)
D. B: Neutrophil

Explanation: ***Eosinophil*** - **Eosinophils** play a crucial role in the immune response against **parasitic infections**, particularly helminths. - They release cytotoxic granules containing **major basic protein**, **eosinophil cationic protein**, and other mediators that damage the parasites. *Lymphocyte* - **Lymphocytes** are primarily involved in adaptive immunity and are crucial for fighting viral infections and certain bacterial infections, but their increase is not a primary marker for parasitic infections. - While T-helper cells (a type of lymphocyte) can activate eosinophils, a direct increase in total lymphocytes is not the hallmark of parasitic infections. *Basophil* - **Basophils** are involved in allergic reactions and chronic inflammation, releasing histamine and other mediators. - While they can be activated during some parasitic infections, their increase is not as prominent or specific as that of eosinophils. *Neutrophil* - **Neutrophils** are the most abundant white blood cells and are the primary responders to acute bacterial infections and inflammation. - They are less effective against parasitic infections, which often require specialized immune responses.

Question 409: Which of the following is not involved in local hemostasis?

A. Fibrinogen
B. Collagen
C. Calcium
D. Vitamin K (Correct Answer)

Explanation: ***Vitamin K*** - **Vitamin K** is crucial for the synthesis of **clotting factors (II, VII, IX, X, protein C, protein S)** in the liver, which are part of the **coagulation cascade** (secondary hemostasis). - Its role is systemic, affecting the production of factors involved in blood coagulation throughout the body, rather than directly participating in the *local* events at the site of injury. *Fibrinogen* - **Fibrinogen** is a soluble protein that is converted to **insoluble fibrin** by thrombin, forming the meshwork of the **blood clot** at the site of injury. - This conversion is a critical local event in strengthening the primary platelet plug during hemostasis. *Collagen* - Exposed **collagen** in the damaged vessel wall directly activates **platelets** (leading to their adhesion and aggregation) and also initiates the **intrinsic pathway** of the coagulation cascade. - It provides the initial signal and a crucial binding site for platelets, essential for forming the primary hemostatic plug. *Calcium* - **Calcium ions (Ca2+)** are essential cofactors for several steps in the **coagulation cascade**, including the activation of various clotting factors (e.g., factors X, IX, VIII, V, and prothrombin). - Its presence is required for the proper functioning of enzyme complexes that form on platelet surfaces, facilitating the generation of thrombin and fibrin at the local injury site.

Question 410: All true about interaction of SpO2 reading and methemoglobinemia, except:

A. Increase in MetHb produces an overestimation when true SpO2 <85%
B. Does not get affected in Methemoglobinaemia (Correct Answer)
C. MetHb absorbs red and infrared wavelength of light in a 1:1 ratio corresponding
D. Increase in MetHb produces an underestimation when true SpO2 >85%

Explanation: ***Correct: Does not get affected in Methemoglobinemia*** - This statement is **FALSE**, making it the correct answer for this EXCEPT question - **Methemoglobinemia significantly affects SpO2 readings** due to MetHb's optical properties - Pulse oximeters cannot distinguish methemoglobin from oxyhemoglobin and deoxyhemoglobin, leading to **inaccurate measurements** - As MetHb levels rise, the SpO2 reading tends to **plateau around 85%** regardless of true oxygen saturation *Incorrect: Increase in MetHb produces an overestimation when true SpO2 <85%* - This statement is TRUE - When **actual SpO2 is below 85%** and MetHb is elevated, the pulse oximeter reads **higher than the true value** (overestimation) - This occurs because MetHb absorption characteristics cause the reading to gravitate toward 85% *Incorrect: MetHb absorbs red and infrared wavelength of light in a 1:1 ratio* - This statement is TRUE - **Methemoglobin** has similar extinction coefficients at both **660 nm (red)** and **940 nm (infrared)** wavelengths - This 1:1 absorption ratio corresponds to an SpO2 reading of approximately **85%** on conventional pulse oximeters - This is why SpO2 readings plateau at 85% in methemoglobinemia regardless of true saturation *Incorrect: Increase in MetHb produces an underestimation when true SpO2 >85%* - This statement is TRUE - When **actual SpO2 is above 85%** and MetHb is elevated, the pulse oximeter reads **lower than the true value** (underestimation) - The reading is pulled down toward the 85% plateau created by MetHb's absorption characteristics

Practice by Chapter

Composition and Functions of Blood

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Erythrocytes and Hemoglobin

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Leukocytes and Immune Function

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Platelets and Hemostasis

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Blood Groups and Transfusion

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Coagulation and Fibrinolysis

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Hematopoiesis

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Innate Immunity

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Adaptive Immunity

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Immunological Memory and Tolerance

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