Blood and Immunity Practice Questions

Q: A 15-year-old girl incurs a cut to the sole of her foot after stepping on a piece of broken glass. On examination, a superficial 0.5-cm laceration ceases to bleed within 5 minutes after application of local pressure. Which of the following substances is released by endothelium and is most likely to counteract platelet aggregation near this site of injury?

Prostacyclin. ### Explanation The correct answer is **Prostacyclin (PGI₂)**. **Why it is correct:** In the event of vascular injury, the goal of the body is to form a localized clot to stop bleeding (hemostasis) while preventing the clot from spreading to healthy, uninjured vessel segments. **Prostacyclin (PGI₂)** is a prostaglandin synthesized by healthy endothelial cells. It acts as a potent **vasodilator** and **inhibitor of platelet aggregation**. It increases intracellular cAMP levels in platelets, effectively counteracting the effects of Thromboxane A₂ (TXA₂), thereby ensuring the platelet plug remains localized only to the site of injury. **Analysis of Incorrect Options:** * **A. Glycoprotein IIb/IIIa:** This is a surface receptor found on platelets. When activated, it binds to fibrinogen to facilitate **platelet aggregation** (clumping). It promotes clot formation rather than counteracting it. * **B. Platelet-activating factor (PAF):** This is a potent phospholipid mediator derived from various cells (including neutrophils and endothelium) that **induces** platelet aggregation and degranulation. * **D. Tissue-type plasminogen activator (tPA):** While released by the endothelium, tPA is involved in **fibrinolysis** (breaking down an existing fibrin clot) by converting plasminogen to plasmin. It does not directly inhibit the initial stage of platelet aggregation. **NEET-PG High-Yield Pearls:** * **The Balance:** Hemostasis is a balance between **TXA₂** (from platelets; causes vasoconstriction/aggregation) and **PGI₂** (from endothelium; causes vasodilation/anti-aggregation). * **Aspirin Mechanism:** Low-dose aspirin irreversibly inhibits COX-1, shifting the balance in favor of PGI₂ because endothelial cells can regenerate the enzyme while platelets cannot. * **Nitric Oxide (NO):** Along with PGI₂, NO is another major substance released by healthy endothelium to inhibit platelet adhesion and promote vasodilation.

Q: Which factor is essential for the prothrombin time test?

Thromboplastin. **Explanation:** The **Prothrombin Time (PT)** test evaluates the **Extrinsic** and **Common pathways** of the coagulation cascade. To perform this test, citrated plasma is added to a reagent containing **Tissue Factor (Factor III)** and **Calcium ions**. This reagent is collectively known as **Thromboplastin**. 1. **Why Thromboplastin is correct:** Thromboplastin acts as the external trigger that activates Factor VII, initiating the extrinsic pathway. Without the addition of exogenous thromboplastin, the extrinsic pathway cannot be assessed in a laboratory setting. 2. **Why other options are incorrect:** * **Prothrombin (Factor II) and Fibrinogen (Factor I):** These are clotting factors already present in the patient's plasma. They are the *substrates* being tested, not the essential reagent added to initiate the reaction. * **Fibrin:** This is the end-product of the coagulation cascade. The PT test measures the time it takes for a fibrin clot to form; it is not a factor required to start the test. **High-Yield Clinical Pearls for NEET-PG:** * **PT/INR** is specifically used to monitor **Warfarin (Oral Anticoagulant)** therapy because Warfarin inhibits Vitamin K-dependent factors (II, VII, IX, X), and Factor VII has the shortest half-life. * **Normal PT Range:** 11–13.5 seconds. * **Prolonged PT** is seen in Vitamin K deficiency, liver disease, and DIC. * **Mnemonic:** "PET" – **P**T measures the **E**xtrinsic pathway and is used for **T**houmadin (Warfarin). Conversely, **aPTT** measures the **I**ntrinsic pathway and is used for **H**eparin.

Q: Serum does not contain which of the following?

Fibrinogen. **Explanation:** The fundamental difference between plasma and serum lies in the process of **coagulation**. **1. Why Fibrinogen is the Correct Answer:** Serum is defined as the liquid portion of blood that remains after the blood has been allowed to clot. During the clotting process, the soluble protein **fibrinogen** (Factor I) is converted into an insoluble mesh of **fibrin** by the action of thrombin. This fibrin mesh traps blood cells to form a clot. Consequently, because fibrinogen is consumed and used up to form the clot, it is absent in the resulting serum. * **Formula to remember:** Serum = Plasma – Clotting Factors (specifically Fibrinogen, Factors II, V, VIII, and XIII). **2. Why the Other Options are Incorrect:** * **Albumin (C) and Globulin (D):** These are the major plasma proteins. Unlike clotting factors, they do not participate in the formation of a fibrin clot. Therefore, they remain in the liquid portion and are present in both plasma and serum. * **Ceruloplasmin (B):** This is an alpha-2 globulin that carries copper in the blood. As a transport protein that does not participate in coagulation, it remains present in the serum. **3. High-Yield Clinical Pearls for NEET-PG:** * **Plasma vs. Serum:** Plasma is obtained by adding an anticoagulant (like Heparin or EDTA) and centrifuging; Serum is obtained by allowing blood to clot naturally without anticoagulants. * **Electrophoresis:** Serum is preferred over plasma for protein electrophoresis because the fibrinogen peak in plasma can mask or be confused with monoclonal spikes (M-protein). * **Serology:** Most biochemical and serological tests are performed on **serum** because the absence of fibrinogen prevents interference with chemical reagents and avoids clogging automated analyzers.

Q: A 40-year-old female patient complains of excessive bleeding. She has a history of a road traffic accident 5 hours ago with a lacerated wound on the lower back region. Blood grouping reveals the presence of antigen A and antigen B. This system for blood grouping consists of 3 major allelic genes which are located on which chromosome?

Chromosome 9. ### Explanation **1. Why Chromosome 9 is Correct:** The patient’s blood group is **AB**, as indicated by the presence of both Antigen A and Antigen B on the red cell surface. This is determined by the **ABO blood group system**, which is governed by a single gene locus (the *ABO* gene) located on the **long arm of Chromosome 9 (9q34.2)**. The system follows the principle of **multiple allelism** (three alleles: $I^A$, $I^B$, and $i$) and **codominance** (where $I^A$ and $I^B$ are both expressed). These alleles encode specific glycosyltransferases that add sugar molecules to the H-substance to form A or B antigens. **2. Why Other Options are Incorrect:** * **Chromosome 8:** Does not harbor major blood group genes. It is clinically significant in hematology for the *c-myc* proto-oncogene (associated with Burkitt lymphoma). * **Chromosome 10:** Not associated with the ABO system. It contains genes like *RET* (associated with MEN 2) and *PTEN*. * **Chromosome 7:** While it carries the gene for the **Kell blood group system**, it is not responsible for the ABO system. **3. High-Yield Clinical Pearls for NEET-PG:** * **Rh Blood Group:** The genes for the Rh system (*RHD* and *RHCE*) are located on **Chromosome 1**. * **H-Substance:** The *H* gene (FUT1), which is the precursor for A and B antigens, is located on **Chromosome 19**. A deficiency in this leads to the rare **Bombay Blood Group**. * **Inheritance:** ABO inheritance is a classic example of **Mendelian genetics** involving codominance ($I^A$ and $I^B$) and complete dominance over the recessive allele ($i$). * **Universal Recipient:** AB positive; **Universal Donor:** O negative.

Q: Which of the following is NOT a function of plasmin?

Stabilization of fibrin. **Explanation:** The core concept tested here is the distinction between the **Fibrinolytic System** (which breaks down clots) and the **Coagulation Cascade** (which forms clots). **Why Option D is the Correct Answer:** **Stabilization of fibrin** is a function of **Factor XIII (Fibrin Stabilizing Factor)**, not plasmin. Factor XIII is a transglutaminase that creates covalent cross-links between fibrin strands to form a stable, insoluble mesh. **Plasmin**, conversely, is the primary enzyme of the fibrinolytic system; its role is to dissolve clots, not stabilize them. **Analysis of Other Options:** * **A. Fibrinolysis:** This is the primary function of plasmin. It proteolytically cleaves fibrin and fibrinogen into soluble Fibrin Degradation Products (FDPs), such as D-dimers. * **B. Activation of collagenase:** Plasmin plays a role in tissue remodeling and wound healing by activating latent matrix metalloproteinases, specifically **pro-collagenase**, into active collagenase. * **C. Destruction of vWF:** Plasmin is a relatively non-specific serine protease. In addition to fibrin, it can degrade several clotting factors, including **Factors V, VIII, XII, and von Willebrand Factor (vWF)**, thereby exerting an anticoagulant effect. **High-Yield NEET-PG Pearls:** * **Plasminogen Activation:** Plasminogen is converted to active Plasmin by **tPA** (Tissue Plasminogen Activator) and **Urokinase**. * **Inhibitor:** The primary physiological inhibitor of plasmin is **$\alpha$2-antiplasmin**. * **Clinical Link:** Tranexamic acid (an antifibrinolytic) works by inhibiting the binding of plasminogen/plasmin to fibrin, preventing clot breakdown. * **D-Dimer:** A specific marker of fibrinolysis; it indicates that both thrombin (to form the clot) and plasmin (to break it) have been active.

Q: The major regulator of platelet production is the hormone thrombopoietin (THPO), which is produced by which organ(s)?

Liver and kidneys. **Explanation:** **Thrombopoietin (THPO)** is a glycoprotein hormone that serves as the primary regulator of megakaryocyte differentiation and platelet production. It acts by binding to the **c-Mpl receptor** on the surface of hematopoietic stem cells and megakaryocytes. 1. **Why Option C is correct:** The **liver** is the primary site of thrombopoietin production (constituting approximately 90% of the circulating levels), where it is produced constitutively by parenchymal cells and sinusoidal endothelial cells. The **kidneys** (specifically the proximal convoluted tubule cells) act as the secondary site of production. Small amounts are also produced by the smooth muscle of the bone marrow. 2. **Why other options are incorrect:** * **Option A & B:** While both organs produce THPO, selecting only one is incomplete. The liver is the dominant source, but the renal contribution is physiologically significant. * **Option D:** The spleen and lymph nodes are involved in platelet storage and immune function, respectively, but they do not synthesize thrombopoietin. **High-Yield Clinical Pearls for NEET-PG:** * **Regulation:** Unlike Erythropoietin (which is regulated by hypoxia/gene transcription), THPO levels are largely regulated by **platelet mass**. Platelets have c-Mpl receptors that internalize and degrade THPO; thus, in thrombocytopenia, less THPO is degraded, leading to higher circulating levels that stimulate the bone marrow. * **Clinical Correlation:** In **liver cirrhosis**, decreased THPO production is a major cause of thrombocytopenia. * **Drug Link:** **Romiplostim** and **Eltrombopag** are TPO receptor agonists used to treat ITP and aplastic anemia.

Q: Which white blood cell is considered the "second line of defense"?

Monocyte. **Explanation:** In the context of the cellular response to infection, white blood cells are categorized based on their arrival time and function at the site of injury or inflammation. **Why Monocytes are the "Second Line of Defense":** While **Neutrophils** are the first to arrive, they are short-lived and often die after phagocytosing a few bacteria. **Monocytes** (which circulate in the blood) migrate into the tissues and transform into **Macrophages**. These macrophages are larger, more powerful, and longer-lived than neutrophils. They arrive slightly later but are capable of engulfing much larger quantities of debris and pathogens, effectively taking over the defense once neutrophils are exhausted. Thus, the Monocyte-Macrophage system is termed the "second line of defense." **Analysis of Incorrect Options:** * **A. Neutrophils:** These are the **"first line of defense"** among WBCs. They are the most numerous and the first to reach the site of acute inflammation via chemotaxis. * **B. Eosinophils:** These are primarily involved in allergic reactions and defense against **parasitic infections** (e.g., helminths) by releasing major basic protein. * **C. Basophils:** These play a role in immediate hypersensitivity reactions. They contain histamine and heparin and are functionally similar to mast cells. **NEET-PG High-Yield Pearls:** * **First Line of Defense (General):** Physical and chemical barriers (Skin, Mucus, Gastric acid). * **First Line of Defense (Cellular):** Neutrophils. * **Second Line of Defense (Cellular):** Monocytes/Macrophages. * **Third Line of Defense:** Specific immunity involving **Lymphocytes** (T-cells and B-cells). * **Kupffer cells** (Liver) and **Microglia** (CNS) are specialized tissue macrophages derived from monocytes.

Q: Which of the following organs is a primary lymphoid organ?

Thymus. ***Thymus***- **Primary lymphoid organs** are the sites where lymphocytes are generated and mature into immunocompetent cells.- The **thymus** is essential for the maturation, selection, and central tolerance of **T lymphocytes**.*Lymph node*- Lymph nodes are classified as **secondary lymphoid organs** where matured lymphocytes activate and proliferate upon encountering specific antigens.- They serve as critical filters for **lymph**, organizing immune responses against pathogens draining from local tissues.*Spleen*- The spleen is a major **secondary lymphoid organ** responsible for filtering **blood** and mounting immune responses to systemic infections.- The **white pulp** contains T and B cell zones that are crucial for activating adaptive immunity against blood-borne pathogens.*MALT*- MALT (Mucosa-Associated Lymphoid Tissue) represents **secondary lymphoid tissues** found beneath epithelial surfaces.- It is responsible for initiating local immune responses at mucosal sites (e.g., **Peyer's patches** in the intestine).

Q: Which of the following clotting factor participates in the extrinsic pathway of coagulation?

Factor VII. ***Factor VII***- This factor is the key component initiating the **extrinsic pathway** when complexed with **Tissue Factor (TF)**.- The TF-Factor VIIa complex activates Factor X, linking the extrinsic pathway to the **common pathway**.*Factor VIII*- Factor VIII is a crucial component of the **intrinsic pathway**, where it acts as a cofactor for Factor IXa to activate Factor X.- Deficiency of Factor VIII causes **Hemophilia A**, a common inherited bleeding disorder.*Factor XI*- Factor XI is involved in the initial steps of the **intrinsic pathway**, typically activated by Factor XIIa.- Its main function is to activate Factor IX, continuing the cascade in the intrinsic pathway.*Factor IX*- Factor IX is part of the **intrinsic pathway**; when activated (IXa), it forms the tenase complex with Factor VIIIa to activate Factor X.- Deficiency of Factor IX leads to **Hemophilia B** (Christmas disease).

Question 1

A 15-year-old girl incurs a cut to the sole of her foot after stepping on a piece of broken glass. On examination, a superficial 0.5-cm laceration ceases to bleed within 5 minutes after application of local pressure. Which of the following substances is released by endothelium and is most likely to counteract platelet aggregation near this site of injury?

Accepted Answer

Prostacyclin

Answer

Glycoprotein IIb/IIIa

Answer

Platelet-activating factor

Answer

Tissue-type plasminogen activator

Question 2

Which factor is essential for the prothrombin time test?

Accepted Answer

Thromboplastin

Answer

Prothrombin

Answer

Fibrinogen

Answer

Fibrin

Question 3

Serum does not contain which of the following?

Accepted Answer

Fibrinogen

Answer

Cerruloplasmin

Answer

Albumin

Answer

Globulin

Question 4

A 40-year-old female patient complains of excessive bleeding. She has a history of a road traffic accident 5 hours ago with a lacerated wound on the lower back region. Blood grouping reveals the presence of antigen A and antigen B. This system for blood grouping consists of 3 major allelic genes which are located on which chromosome?

Accepted Answer

Chromosome 9

Answer

Chromosome 8

Answer

Chromosome 10

Answer

Chromosome 7

Question 5

Which of the following is NOT a function of plasmin?

Accepted Answer

Stabilization of fibrin

Answer

Fibrinolysis

Answer

Activation of collagenase

Answer

Destruction of von Willebrand Factor (vWF)

Question 6

The major regulator of platelet production is the hormone thrombopoietin (THPO), which is produced by which organ(s)?

Accepted Answer

Liver and kidneys

Answer

Kidneys

Answer

Liver

Answer

Spleen and lymph nodes

Question 7

Which white blood cell is considered the "second line of defense"?

Accepted Answer

Monocyte

Answer

Neutrophil

Answer

Eosinophil

Answer

Basophil

Question 8

Which of the following organs is a primary lymphoid organ?

Accepted Answer

Thymus

Answer

Lymph node

Answer

MALT

Answer

Spleen

Question 9

Which of the following clotting factor participates in the extrinsic pathway of coagulation?

Accepted Answer

Factor VII

Answer

Factor VIII

Answer

Factor XI

Answer

Factor IX

Question 10

A 35-year-old woman with menorrhagia presents with pallor, fatigue, and koilonychia. Laboratory findings show hemoglobin 8.2 g/dL, MCV 68 fL, serum iron 25 μg/dL, TIBC 450 μg/dL, and serum ferritin 10 ng/mL. Which of the following best explains the increased TIBC in this patient?

Accepted Answer

Upregulation of transferrin synthesis by the liver in response to iron deficiency

Answer

Increased transferrin degradation in iron overload state

Answer

Increased erythropoietin production stimulating iron mobilization

Answer

Decreased hepcidin production leading to increased iron absorption

Blood and Immunity — MCQs

Blood and Immunity — MCQs

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