Blood and Immunity Practice Questions

Q: What is the primary determinant of colloidal osmotic pressure of plasma?

Albumin. **Explanation:** The **Colloidal Osmotic Pressure (COP)**, also known as **Oncotic Pressure**, is the osmotic pressure exerted by plasma proteins that serves to hold water within the vascular compartment, opposing hydrostatic pressure. **Why Albumin is the Correct Answer:** Albumin is the primary determinant of COP (contributing approximately **75-80%** of the total oncotic pressure) due to two main reasons: 1. **High Concentration:** It is the most abundant plasma protein (3.5–5.0 g/dL). 2. **Low Molecular Weight:** Osmotic pressure depends on the *number* of particles per unit volume rather than the mass. Being the smallest major plasma protein (~69 kDa), albumin has more molecules per gram than larger proteins like globulins. 3. **Gibbs-Donnan Effect:** Albumin is negatively charged and attracts cations (mainly Na+), further increasing the osmotic gradient. **Analysis of Incorrect Options:** * **B. Fibrinogen:** Although it has the highest molecular weight among common plasma proteins, its concentration is very low (200–400 mg/dL), making its contribution to COP negligible. * **C. Globulin:** Globulins have a higher molecular weight than albumin. While they contribute to COP, their lower molar concentration makes them less significant than albumin. * **D. Prothrombin:** This is a clotting factor present in trace amounts; it does not significantly influence plasma osmolarity. **High-Yield Clinical Pearls for NEET-PG:** * **Starling’s Forces:** A decrease in plasma albumin (hypoalbuminemia) leads to a drop in COP, resulting in the movement of fluid into the interstitial space, causing **edema** (e.g., in Nephrotic Syndrome or Liver Cirrhosis). * **Normal COP Value:** Approximately **25–28 mmHg**. * **Albumin:Globulin (A/G) Ratio:** Normally **1.2 to 1.5:1**. A reversal of this ratio is often seen in chronic liver disease or multiple myeloma.

Q: 2,3-DPG levels are decreased in which of the following conditions?

Acidosis. **Explanation:** The level of **2,3-Bisphosphoglycerate (2,3-DPG)** in red blood cells is a critical regulator of hemoglobin's affinity for oxygen. 2,3-DPG binds to the beta chains of deoxyhemoglobin, stabilizing the "T" (Tense) state and shifting the oxygen-dissociation curve to the **right**, facilitating oxygen unloading to tissues. **Why Acidosis is the Correct Answer:** The synthesis of 2,3-DPG is catalyzed by the enzyme **phosphoglycerate mutase**. This enzyme is highly sensitive to pH; it is **inhibited by a decrease in pH (acidosis)**. Therefore, in states of acidosis, the glycolytic pathway in RBCs is slowed, leading to decreased production of 2,3-DPG. This serves as a compensatory mechanism: while acidosis itself shifts the curve to the right (Bohr effect), the resulting decrease in 2,3-DPG shifts it back to the left, helping maintain equilibrium. **Analysis of Incorrect Options:** * **Anemia:** In anemia, there is a functional hypoxia. The body compensates by **increasing** 2,3-DPG levels to enhance oxygen delivery to tissues. * **High Altitude:** Low partial pressure of oxygen triggers an **increase** in 2,3-DPG to facilitate better peripheral unloading of oxygen. * **Exercise:** Strenuous exercise leads to increased metabolism and temporary hypoxia, which stimulates an **increase** in 2,3-DPG levels. **NEET-PG High-Yield Pearls:** * **Stored Blood:** 2,3-DPG levels **decrease** in stored blood (bank blood). Transfusing large amounts of old blood can impair oxygen delivery to tissues due to a leftward shift of the curve. * **Fetal Hemoglobin (HbF):** HbF has a **lower affinity** for 2,3-DPG because its gamma chains lack the specific binding sites found in beta chains. This results in HbF having a higher affinity for oxygen than adult hemoglobin (HbA). * **Mnemonic:** Factors that shift the curve to the **Right** (increase 2,3-DPG): **CADET**, face Right! (**C**O2, **A**cid, **D**PG, **E**xercise, **T**emperature).

Q: What is the half-life of monocytes in circulation?

1-3 days. ### Explanation **Correct Answer: D. 1-3 days** **Underlying Medical Concept:** Monocytes are the largest cells of the normal blood and are produced in the bone marrow. Once released into the peripheral circulation, they remain there for a relatively short duration compared to their total lifespan. In humans, the average half-life of a circulating monocyte is approximately **24 to 72 hours (1–3 days)**. After this period, they migrate through the capillary walls into the extravascular tissues, where they differentiate into specific **tissue macrophages** (e.g., Kupffer cells in the liver, alveolar macrophages in the lungs). Once they become macrophages, their lifespan increases significantly to months or even years. **Analysis of Incorrect Options:** * **A & B (6–12 hours):** This timeframe is more characteristic of **Neutrophils**. Neutrophils have a very short half-life in circulation (averaging 6–10 hours) before they enter tissues or are cleared. * **C (24 hours):** While 24 hours is within the range, "1–3 days" is the standard textbook definition (e.g., Guyton and Hall) and more accurately reflects the physiological variability of monocyte transit time. **High-Yield Facts for NEET-PG:** * **Monocyte-Macrophage System:** Formerly known as the Reticuloendothelial System (RES). * **Size:** Monocytes are the largest leukocytes in a peripheral smear (12–20 μm) and possess a characteristic kidney or horseshoe-shaped nucleus. * **Function:** They are professional phagocytes and act as **Antigen Presenting Cells (APCs)** by presenting fragments of antigens to T-lymphocytes via MHC II molecules. * **Ratio:** In a normal differential count, monocytes constitute about 2–8% of total WBCs.

Q: What is the typical volume of blood per kilogram of body weight in a child?

60-70 ml. **Explanation:** The total blood volume (TBV) in humans varies significantly based on age, body composition, and physiological state. The correct answer is **60-70 ml/kg**, which represents the standard physiological range for an older child or adolescent. **1. Why Option A is Correct:** As a child grows, their body composition changes. While neonates have a very high proportion of water and blood relative to their weight, this ratio decreases as they mature. In children and adolescents, the blood volume stabilizes to approximately **70 ml/kg** (ranging between 60-80 ml/kg depending on the specific age and lean body mass), which is slightly higher than the adult average of 65-70 ml/kg. **2. Why Other Options are Incorrect:** * **Option B (100-150 ml):** This is excessively high for a child. However, a **preterm neonate** can have a blood volume of approximately **90-100 ml/kg**. * **Options C & D (150-250 ml):** These values are physiologically impossible under normal conditions. Such high volumes would lead to circulatory overload and heart failure. **High-Yield Clinical Pearls for NEET-PG:** * **Age-wise TBV Distribution:** * **Preterm Neonate:** ~90-100 ml/kg * **Term Neonate:** ~80-90 ml/kg * **Infant:** ~75-80 ml/kg * **Child:** ~70-75 ml/kg * **Adult Male:** ~70 ml/kg * **Adult Female:** ~65 ml/kg (lower due to higher body fat percentage). * **Clinical Application:** Calculating TBV is critical in pediatrics for managing fluid resuscitation, estimating allowable blood loss during surgery, and determining dosages for blood component therapy (e.g., 10 ml/kg of packed RBCs typically raises hemoglobin by 2-3 g/dL).

Q: In an adult man, what is the approximate total amount of hemoglobin in the circulating blood in grams?

900. To determine the total amount of hemoglobin (Hb) in the circulating blood, we must apply the standard physiological values for an average adult male (approx. 70 kg). ### **The Calculation** 1. **Total Blood Volume:** The average blood volume in an adult male is approximately **5 liters** (or 70 ml/kg). 2. **Hemoglobin Concentration:** The normal average Hb concentration is **14–16 g/dL** (deciliter = 100 ml). 3. **The Formula:** Total Hb = (Hb concentration per 100 ml) × (Total blood volume in ml / 100). * Calculation: $15\text{ g/dL} \times 50\text{ dL} = \mathbf{750\text{--}900\text{ grams}}$. Among the given options, **900 grams** (Option C) is the most accurate representation of the upper limit for a healthy adult male. ### **Analysis of Incorrect Options** * **A (350g) & B (500g):** These values are too low. 350g would imply a blood volume of only 2.3L or severe anemia. * **D (1000g):** This value is slightly higher than the physiological average, typically seen only in cases of polycythemia or in very large individuals with high muscle mass. ### **High-Yield NEET-PG Pearls** * **Iron Content:** Each gram of Hb contains **3.34 mg of iron**. Therefore, the total body iron stored in Hb is approximately 2.5–3 grams. * **Oxygen Carrying Capacity:** 1 gram of Hb carries **1.34 ml of oxygen** (Hufner's constant). * **Life Span:** The average lifespan of an RBC is **120 days**, after which Hb is broken down into heme and globin in the Reticuloendothelial system (Spleen). * **Fetal Hb (HbF):** Has a higher affinity for oxygen than adult Hb (HbA) due to poor binding with 2,3-BPG.

Q: Von Willebrand's factor is synthesized in which one of the following?

Vascular endothelium. **Explanation:** **Von Willebrand Factor (vWF)** is a large multimeric glycoprotein essential for primary hemostasis. It acts as a molecular bridge between the subendothelial collagen and platelets (via the GpIb receptor) and serves as a carrier protein for Factor VIII. **Why Vascular Endothelium is Correct:** vWF is primarily synthesized in two locations: 1. **Vascular Endothelial Cells:** Here, it is stored in specialized secretory organelles called **Weibel-Palade bodies**. 2. **Megakaryocytes:** It is synthesized here and subsequently stored in the **$\alpha$-granules of platelets**. Upon vascular injury, vWF is released from these sites to initiate platelet adhesion. **Why Other Options are Incorrect:** * **Macrophages:** These are phagocytic cells of the immune system and do not synthesize clotting factors. * **Liver:** While the liver is the primary site for the synthesis of most coagulation factors (like Fibrinogen, Prothrombin, and Factors VII, IX, X), it is **not** the source of vWF. This is a common "trap" in exams. * **Eosinophils:** These are granulocytes involved in allergic reactions and parasitic infections; they have no role in vWF production. **High-Yield Clinical Pearls for NEET-PG:** * **vWF and Factor VIII:** vWF stabilizes Factor VIII in circulation, increasing its half-life. In von Willebrand Disease (vWD), Factor VIII levels may also be low. * **Ristocetin Cofactor Assay:** This is the gold standard test for vWF function; Ristocetin induces platelet agglutination only in the presence of vWF. * **Desmopressin (DDAVP):** Used in treatment as it stimulates the release of vWF from Weibel-Palade bodies. * **vWD:** It is the most common inherited bleeding disorder.

Q: What is not caused by platelet activating factor?

Bronchodilation. **Explanation:** Platelet Activating Factor (PAF) is a potent phospholipid-derived mediator released by various cells, including platelets, neutrophils, monocytes, and endothelial cells. It plays a central role in inflammation and allergic responses. **Why Bronchodilation is the correct answer:** PAF is a powerful **bronchoconstrictor**, not a bronchodilator. In the lungs, it induces contraction of airway smooth muscle and increases mucus secretion. It is significantly more potent than histamine in inducing bronchial hyperreactivity, making it a key mediator in the pathogenesis of asthma and anaphylaxis. **Analysis of Incorrect Options:** * **A. Vasoconstriction:** While PAF causes systemic vasodilation (leading to hypotension), it can cause localized vasoconstriction in specific vascular beds, such as the pulmonary and coronary arteries. * **C. Causes platelet aggregation:** This is the primary function for which it was named. PAF binds to G-protein-coupled receptors on platelets, leading to shape change, granule release, and aggregation. * **D. Transmits signals between cells:** PAF acts as a signaling molecule (intercellular mediator) that coordinates the response between inflammatory cells and the vascular endothelium. **High-Yield Clinical Pearls for NEET-PG:** * **Potency:** PAF is roughly 1,000 to 10,000 times more potent than histamine in causing bronchospasm and increasing vascular permeability. * **Vascular Effect:** It causes increased capillary permeability (edema) by inducing endothelial cell contraction. * **Chemotaxis:** It is a strong chemoattractant for neutrophils and eosinophils. * **Inhibitors:** PAF receptor antagonists are being studied for the treatment of inflammatory conditions and septic shock.

Question 1

What is the primary determinant of colloidal osmotic pressure of plasma?

Accepted Answer

Albumin

Answer

Fibrinogen

Answer

Globulin

Answer

Prothrombin

Question 2

In which of the following conditions is the synthesis of hepcidin not reduced?

Accepted Answer

Hemosiderosis

Answer

Hypoxia

Answer

Anemia

Answer

Hemorrhage

Question 3

2,3-DPG levels are decreased in which of the following conditions?

Accepted Answer

Acidosis

Answer

Anemia

Answer

High altitude

Answer

Exercise

Question 4

Regarding the oxygen-hemoglobin dissociation curve, which statement is true?

Accepted Answer

Oxygen affinity will be equal in both HbF and HbA in the absence of 2,3-DPG.

Answer

The affinity of oxygen with hemoglobin decreases as hemoglobin attaches to oxygen in a linear fashion.

Answer

One hemoglobin molecule attaches to two molecules of 2,3-DPG.

Answer

Carboxyhemoglobin increases the release of oxygen in the blood, causing a rightward shift of the oxygen dissociation curve.

Question 5

What is the half-life of monocytes in circulation?

Accepted Answer

1-3 days

Answer

6 hours

Answer

12 hours

Answer

24 hours

Question 6

Which enzyme is responsible for the respiratory burst reaction?

Accepted Answer

NADPH-oxidase

Answer

Dehydrogenase

Answer

Peroxidase

Answer

Hydroxylase

Question 7

What is the typical volume of blood per kilogram of body weight in a child?

Accepted Answer

60-70 ml

Answer

100-150 ml

Answer

150-200 ml

Answer

200-250 ml

Question 8

In an adult man, what is the approximate total amount of hemoglobin in the circulating blood in grams?

Accepted Answer

900

Answer

350

Answer

500

Answer

1000

Question 9

Von Willebrand's factor is synthesized in which one of the following?

Accepted Answer

Vascular endothelium

Answer

Macrophages

Answer

Liver

Answer

Eosinophils

Question 10

What is not caused by platelet activating factor?

Accepted Answer

Bronchodilation

Answer

Vasoconstriction

Answer

Causes platelet aggregation

Answer

Transmits signals between cells

Blood and Immunity — MCQs

Blood and Immunity — MCQs

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