Blood and Immunity Practice Questions

Q: Fetal erythropoietin production is inhibited by?

Estrogen. **Explanation:** The primary stimulus for erythropoietin (EPO) production, both in the fetus and the adult, is **hypoxia**. However, various hormones modulate this response. **1. Why Estrogen is the Correct Answer:** Estrogen has an **inhibitory effect** on erythropoiesis. It acts by suppressing the production of erythropoietin in the liver (the primary site in the fetus) and kidneys. Additionally, estrogen can directly inhibit the proliferation of erythroid stem cells in the bone marrow. This hormonal difference is a key reason why adult females typically have lower hemoglobin levels and red cell counts compared to males. **2. Analysis of Incorrect Options:** * **Testosterone (A):** Testosterone **stimulates** EPO production and enhances the response of the bone marrow to EPO. This is why males have higher hematocrit levels post-puberty. * **Cortisol (C):** Glucocorticoids generally have a permissive or stimulatory effect on erythropoiesis; they do not inhibit fetal EPO production. * **Hypoxia (D):** Hypoxia is the **chief physiological stimulant** for EPO production. Low oxygen tension triggers Hypoxia-Inducible Factor (HIF-1α), which upregulates the EPO gene. **3. High-Yield Clinical Pearls for NEET-PG:** * **Site of EPO Production:** In the **fetus**, EPO is primarily produced in the **liver** (perisinusoidal cells). In **adults**, approximately 85-90% is produced in the **kidneys** (peritubular interstitial cells/fibroblasts) and 10-15% in the liver. * **Switching:** The transition from hepatic to renal EPO production occurs around the time of birth. * **Polycythemia:** Neonates often have high hemoglobin levels (Physiological Polycythemia) due to the relatively hypoxic intrauterine environment stimulating high EPO levels.

Q: Platelet aggregation is caused by all of the following, except?

Prostacyclin (PGI2). ### Explanation The correct answer is **Prostacyclin (PGI2)**. **1. Why Prostacyclin (PGI2) is the correct answer:** Hemostasis is a balance between pro-aggregatory and anti-aggregatory factors. **Prostacyclin (PGI2)** is synthesized by healthy vascular endothelial cells. It acts as a potent **inhibitor of platelet aggregation** and a vasodilator. It functions by increasing intracellular **cAMP** levels within platelets, which stabilizes them and prevents activation. This ensures that blood clots do not form on healthy vessel walls. **2. Analysis of Incorrect Options (Pro-aggregatory factors):** * **Thromboxane A2 (TXA2):** Produced by activated platelets via the COX-1 pathway. It is a powerful vasoconstrictor and a primary mediator of platelet aggregation (it decreases cAMP). * **Serotonin (5-HT):** Released from the dense granules of activated platelets. It acts as a local vasoconstrictor and recruits more platelets to the site of injury. * **Thrombin:** Perhaps the most potent activator of platelets. It acts through Protease-Activated Receptors (PAR) to trigger a shape change and the release of granule contents, leading to rapid aggregation. **3. NEET-PG High-Yield Clinical Pearls:** * **The cAMP Rule:** Factors that **increase cAMP** (like PGI2) inhibit platelets; factors that **decrease cAMP** (like TXA2) promote aggregation. * **Aspirin Mechanism:** Low-dose aspirin irreversibly inhibits COX-1, shifting the balance in favor of PGI2 (from endothelium) over TXA2 (from platelets), leading to its anti-thrombotic effect. * **ADP:** Another major aggregator released from dense granules; it is the target of drugs like **Clopidogrel** (P2Y12 receptor blockers). * **GP IIb/IIIa:** This receptor is the "final common pathway" for platelet aggregation, as it binds fibrinogen to link platelets together.

Q: Which is the most mature normoblast?

Oxyphilic normoblast. **Explanation:** The process of erythropoiesis involves the maturation of a hematopoietic stem cell into a mature erythrocyte. As a normoblast matures, it undergoes specific morphological changes: the cell size decreases, the nucleus condenses (pyknosis) and is eventually extruded, and the cytoplasm shifts from basophilic (high RNA) to eosinophilic (high hemoglobin). **Why Oxyphilic Normoblast is correct:** The **Oxyphilic normoblast** (also known as the Late Normoblast or Orthochromatic Normoblast) is the final stage of the nucleated red cell series. At this stage, the cytoplasm has attained its full complement of hemoglobin, giving it a pinkish/acidophilic (oxyphilic) appearance. The nucleus is small, dense, and pyknotic, prepared for extrusion to become a reticulocyte. **Analysis of Incorrect Options:** * **B. Pronormoblast:** This is the **earliest** recognizable erythrocyte precursor. It is a large cell with a large nucleus and visible nucleoli. * **D. Basophilic Normoblast:** The second stage. It is characterized by intense cytoplasmic basophilia due to a high concentration of ribosomes for protein synthesis. * **C. Polychromatic Normoblast:** The intermediate stage where hemoglobin starts appearing. The "muddy" or greyish color is due to the mixture of pink hemoglobin and blue RNA. **NEET-PG High-Yield Pearls:** 1. **Nucleus Extrusion:** Occurs at the transition from the Oxyphilic normoblast to the Reticulocyte. 2. **First Hemoglobin Appearance:** Hemoglobin synthesis begins in the **Basophilic normoblast**, but it first becomes visible light-microscopically in the **Polychromatic normoblast**. 3. **Last stage of Mitosis:** The Polychromatic normoblast is the last stage capable of cell division. 4. **Reticulocyte:** The immediate precursor to the mature RBC; it contains residual RNA (ribosomes) which can be stained with supra-vital stains like New Methylene Blue.

Q: What is the lifespan of neutrophils?

6 hours. **Explanation:** The lifespan of neutrophils is highly variable depending on their location, but for the purpose of medical examinations like NEET-PG, it is categorized into two phases: their time in the **circulating blood** and their time in the **tissues**. 1. **Why Option A is Correct:** In the peripheral blood, neutrophils have a very short half-life, typically circulating for only **6 to 10 hours**. After this brief period, they migrate into the tissues (diapedesis) or are removed by the spleen and liver. While they may survive for 2–5 days once they enter the tissues, the standard physiological answer for "lifespan" in a general context refers to their intravascular transit time. 2. **Why Other Options are Incorrect:** * **Option B (1 day):** While some newer studies suggest neutrophils might live longer under non-inflammatory conditions, "1 day" is not the classic textbook value used for standardized exams. * **Option C (7 days):** This is closer to the lifespan of **platelets** (8–12 days) or the maturation time in the bone marrow, but far exceeds the circulating life of a neutrophil. * **Option D (120 days):** This is the classic lifespan of **Red Blood Cells (RBCs)**. **High-Yield NEET-PG Pearls:** * **Granulopoiesis:** It takes about 14 days for a neutrophil to mature in the bone marrow before release. * **First Responders:** Neutrophils are the first cells to arrive at the site of acute inflammation. * **Left Shift:** An increase in immature neutrophils (band cells) in the blood indicates an active infection or "shift to the left." * **Death:** Neutrophils die via apoptosis and form the primary component of **pus**.

Q: Albumin is an important factor in maintaining osmotic pressure. Which of the following best describes albumin's characteristics relevant to this function?

Low molecular weight and high blood concentration. **Explanation:** The primary determinant of **Colloid Osmotic Pressure (Oncotic Pressure)** in the plasma is the number of particles present per unit volume, rather than the size of the particles. This is governed by **Van’t Hoff’s Law**. **Why Option A is Correct:** Albumin accounts for approximately **75–80% of the total plasma oncotic pressure** (approx. 25–28 mmHg). This dominance is due to two factors: 1. **High Concentration:** It is the most abundant plasma protein (3.5–5.0 g/dL). 2. **Low Molecular Weight:** Among the major plasma proteins (Albumin ≈ 69 kDa vs. Globulins ≈ 90–150 kDa vs. Fibrinogen ≈ 340 kDa), albumin is the smallest. Because it is small, a given mass of albumin contains a **higher number of individual molecules** compared to an equal mass of larger proteins, thereby exerting greater osmotic pull. **Analysis of Incorrect Options:** * **B & C:** Low blood concentration would result in decreased oncotic pressure, leading to edema (as seen in nephrotic syndrome or liver failure). * **D:** While albumin has a "high" weight compared to electrolytes, in the context of plasma proteins, it is considered the **lowest** molecular weight fraction. If it had a high molecular weight, there would be fewer molecules per gram, reducing its osmotic efficiency. **NEET-PG High-Yield Pearls:** * **Donnan Effect:** Albumin is negatively charged at physiological pH. It attracts cations (like $Na^+$), which further increases the osmotic pressure by ~50% more than the protein alone would account for. * **Synthesis:** Exclusively in the **liver**. * **Clinical Correlation:** Hypoalbuminemia leads to a drop in oncotic pressure, causing fluid to move from the intravascular to the interstitial space (**Edema/Ascites**). * **Half-life:** Approximately **20 days**.

Q: Which of the following is true regarding Thromboxane A2?

All of the above. **Explanation:** Thromboxane A2 (TXA2) is a potent eicosanoid derived from arachidonic acid that plays a central role in primary hemostasis [1]. 1. **Site of Synthesis (Option A):** TXA2 is synthesized primarily within **platelets**. Unlike endothelial cells which produce Prostacyclin (PGI2), platelets contain the enzyme **Thromboxane Synthase**, which converts endoperoxides into TXA2. 2. **Biochemical Pathway (Option B):** The synthesis follows the cyclooxygenase (COX) pathway. Arachidonic acid is first converted into the cyclic endoperoxides **PGG2 and PGH2** by the COX-1 enzyme [2]. These intermediates are then specifically converted into TXA2 by thromboxane synthase. 3. **Biological Action (Option C):** TXA2 is highly **prothrombotic**. It acts via G-protein coupled receptors (TP receptors) to cause: * **Platelet Aggregation:** It is a potent stimulator of platelet degranulation and recruitment [1]. * **Vasoconstriction:** It narrows blood vessels to reduce blood flow at the site of injury. Since all three statements are physiologically accurate, **Option D** is the correct answer. **High-Yield NEET-PG Pearls:** * **Aspirin Mechanism:** Low-dose Aspirin irreversibly inhibits **COX-1**, preventing the formation of TXA2 [2]. Since platelets are anucleated and cannot synthesize new enzymes, the effect lasts for the lifetime of the platelet (7–10 days). * **The "Prostacyclin-Thromboxane Balance":** PGI2 (from endothelium) inhibits aggregation and causes vasodilation, while TXA2 (from platelets) promotes aggregation and causes vasoconstriction. * **Half-life:** TXA2 is very unstable and spontaneously hydrolyzes to the inactive metabolite **TXB2** within about 30 seconds [3].

Q: Which of the following is an inhibitor of platelet aggregation?

PGI2. ### Explanation The balance between platelet aggregation and inhibition is crucial for maintaining vascular homeostasis. The correct answer is **PGI2 (Prostacyclin)**. **1. Why PGI2 is correct:** Prostacyclin (PGI2) is synthesized by vascular **endothelial cells**. It acts as a potent **vasodilator** and a strong **inhibitor of platelet aggregation**. It functions by increasing intracellular cyclic AMP (cAMP) levels within platelets, which stabilizes them and prevents the release of clotting factors. In a healthy vessel, PGI2 ensures that the blood remains fluid and does not clot against the vessel wall. **2. Why the other options are incorrect:** * **TXA2 (Thromboxane A2):** Produced by platelets via the COX-1 pathway, TXA2 is a potent **platelet aggregator** and vasoconstrictor. It is the functional antagonist to PGI2. * **PGG2 (Prostaglandin G2):** This is a transient intermediate in the arachidonic acid cascade. It is a precursor to both TXA2 and PGI2 but does not function as an inhibitor of aggregation itself; rather, it is converted into active prostanoids. **3. NEET-PG High-Yield Pearls:** * **The "PGI2 vs. TXA2" Balance:** Hemostasis depends on the ratio of these two. Aspirin (low dose) irreversibly inhibits COX-1 in platelets, reducing TXA2 levels. Since platelets lack a nucleus, they cannot regenerate COX-1, leading to an anti-thrombotic effect. * **Source Distinction:** Remember: **E**ndothelium produces **E**nhanced flow (PGI2), while **P**latelets produce **P**lug formation (TXA2). * **cAMP vs. Calcium:** Increased cAMP (by PGI2) inhibits aggregation, whereas increased cytosolic Calcium (triggered by TXA2) promotes aggregation.

Q: The universal blood recipient group is:

AB +Ve. **Explanation:** The concept of blood compatibility is determined by the presence or absence of specific antigens on the surface of Red Blood Cells (RBCs) and corresponding antibodies in the plasma. **Why AB +Ve is the Universal Recipient:** A person with **AB +Ve** blood has **A, B, and Rh (D) antigens** on their RBCs. Consequently, their plasma contains **no antibodies** against A, B, or Rh antigens. Because they lack these antibodies, they can receive blood from any group (A, B, AB, or O, whether Rh positive or negative) without triggering a life-threatening transfusion reaction (hemolysis). **Analysis of Incorrect Options:** * **O -Ve:** This is the **Universal Donor**. These RBCs lack A, B, and Rh antigens, meaning they can be given to patients of any blood type. However, O -Ve individuals have anti-A and anti-B antibodies in their plasma, so they can only receive O -Ve blood. * **O +Ve:** This is the most common blood type. While it can be donated to any Rh+ recipient, O +Ve individuals have anti-A and anti-B antibodies, limiting what they can receive. * **AB -Ve:** While these individuals lack anti-A and anti-B antibodies, they do not have the Rh antigen. If they receive Rh+ blood, they may develop anti-D antibodies, leading to transfusion reactions in the future. **High-Yield Clinical Pearls for NEET-PG:** * **Landsteiner’s Law:** States that if an antigen is present on RBCs, the corresponding antibody must be absent from the plasma (and vice versa). * **Emergency Transfusion:** In an unknown emergency, **O -Ve** packed RBCs are used. * **Plasma vs. Whole Blood:** While AB +Ve is the universal recipient for *cells*, **AB is the universal donor for *plasma*** because it contains no antibodies. * **Bombay Blood Group:** Lacks the H-antigen; these individuals can only receive blood from another Bombay group individual.

Question 1

Fetal erythropoietin production is inhibited by?

Accepted Answer

Estrogen

Answer

Testosterone

Answer

Cortisol

Answer

Hypoxia

Question 2

Platelet aggregation is caused by all of the following, except?

Accepted Answer

Prostacyclin (PGI2)

Answer

Thromboxane A2

Answer

Serotonin

Answer

Thrombin

Question 3

Which is the most mature normoblast?

Accepted Answer

Oxyphilic normoblast

Answer

Pronormoblast

Answer

Polychromatic normoblast

Answer

Basophilic normoblast

Question 4

What is the main reason for the lower hemoglobin level in females compared to males?

Accepted Answer

Low testosterone levels in females

Answer

Shorter erythrocyte half-life time

Answer

Decreased responsiveness of bone marrow stem cells to erythropoietin

Answer

Smaller number of bone marrow stem cells

Question 5

What is the lifespan of neutrophils?

Accepted Answer

6 hours

Answer

1 day

Answer

7 days

Answer

120 days

Question 6

Hematocrit increases in venous blood due to which of the following?

Accepted Answer

Increased chloride

Answer

Increased sodium

Answer

Increased potassium

Answer

Increased calcium

Question 7

Albumin is an important factor in maintaining osmotic pressure. Which of the following best describes albumin's characteristics relevant to this function?

Accepted Answer

Low molecular weight and high blood concentration

Answer

Low molecular weight and low blood concentration

Answer

High molecular weight and low blood concentration

Answer

High molecular weight and high blood concentration

Question 8

Which of the following is true regarding Thromboxane A2?

Accepted Answer

All of the above

Answer

Formed by platelets

Answer

Formed from PGG2/PGH2

Answer

Prothrombotic

Question 9

Which of the following is an inhibitor of platelet aggregation?

Accepted Answer

PGI2

Answer

TXA2

Answer

PGG2

Answer

All of the above

Question 10

The universal blood recipient group is:

Accepted Answer

AB +Ve

Answer

O -Ve

Answer

O +Ve

Answer

AB -Ve

Blood and Immunity — MCQs

Blood and Immunity — MCQs

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