Blood and Immunity Practice Questions

Q: The least marked function of a human spleen is

reservoir function. ***Reservoir Function*** - In **humans**, the spleen stores only a **minimal amount of blood** (~30-40 ml of RBCs), unlike in animals like dogs and horses where it serves as a major blood reservoir - While it does store some **platelets and monocytes**, the reservoir function is the **least marked** among the spleen's primary functions in humans - This function is relatively insignificant compared to the spleen's other critical roles *Filter Function* - The spleen is a **major blood filter**, removing **old and damaged red blood cells**, bacteria, and cellular debris - Removes approximately **20-30 ml of aged RBCs daily** through selective filtration in the red pulp - This is one of the **most important** and highly marked functions of the spleen *Immune Function* - The spleen is a **major secondary lymphoid organ** containing **25% of the body's lymphocytes** - Produces **antibodies** (IgM and IgG) and responds to blood-borne antigens - Critical for fighting **encapsulated organisms** (Streptococcus pneumoniae, Haemophilus influenzae, Neisseria meningitidis) - Post-splenectomy patients face risk of **OPSI** (overwhelming post-splenectomy infection), highlighting its crucial immune role *Pitting Function* - The spleen performs the unique **pitting function** by selectively removing intracellular inclusions (**Howell-Jolly bodies, Pappenheimer bodies, Heinz bodies**) from RBCs without destroying the entire cell - This specialized function helps maintain RBC quality and is particularly evident in splenectomized patients who show these inclusions in peripheral blood

Q: Stored blood which has been preserved in a blood bank is deficient in which of the following coagulation factors?

V and VIII. ***V and VIII*** - **Factors V and VIII** are **labile coagulation factors** that degrade quickly during blood storage, making them deficient in stored blood. - This lability is due to their protein structure, which is sensitive to breakdown at refrigerated temperatures over time. *IX and X* - **Factors IX and X** are relatively stable and **vitamin K-dependent factors** that maintain their activity well in stored blood. - They are not significantly depleted during standard blood bank storage periods. *II and VII* - **Factors II (prothrombin) and VII** are also **vitamin K-dependent factors** known for their stability in stored blood. - Their levels remain largely preserved for typical blood storage durations. *II only* - **Factor II (prothrombin)** is a **stable, vitamin K-dependent factor**, and its levels are well-preserved in stored blood. - Therefore, stating only factor II is deficient is incorrect, as it is one of the more stable factors.

Q: The removal of malarial parasites from the blood is called

Phagocytosis. ***Phagocytosis*** - **Phagocytosis** is the process by which specialized cells, such as **macrophages** and **neutrophils**, engulf and digest foreign particles, including malarial parasites in the blood. - This is a crucial immune mechanism for clearing infected red blood cells and free parasites from the body. - Phagocytosis occurs primarily in the **spleen, liver, and bone marrow**, where macrophages recognize and destroy parasitized RBCs. *Binding* - **Binding** refers to the initial attachment of parasites or infected cells to host cells or tissues. - While binding is a step in the parasitic lifecycle and influences sequestration, it is not the process of *removal* from the blood. *Culling* - **Culling** refers to the selective removal of damaged, aged, or parasitized red blood cells by the spleen. - In malaria, the spleen does "cull" infected RBCs through mechanical filtration and phagocytic clearance. - However, **phagocytosis** is the broader immunological term that describes the cellular mechanism of engulfment and destruction, making it the more appropriate general answer. *Sequestration* - **Sequestration** is the process by which malarial parasites (specifically *Plasmodium falciparum*) in infected red blood cells adhere to the endothelium of capillaries and venules, especially in vital organs. - This mechanism allows parasites to **avoid clearance** by the spleen, representing a process of *retention* or *hiding* rather than removal from the circulation.

Q: The immunoglobulins that can be transported across the placenta include:

IgG only. ***IgG only*** - **IgG** is the only class of immunoglobulin that can actively be transported across the **placental barrier** from mother to fetus, providing passive immunity. - This transport is mediated by specialized receptors (FcRn) on placental cells, ensuring the fetus receives protection against pathogens. *IgA only* - **IgA** is primarily found in **mucosal secretions** (e.g., breast milk, tears, saliva) and plays a crucial role in mucosal immunity. - It does not significantly cross the placenta and therefore does not contribute to fetal immunity in utero. *Neither IgG nor IgA* - This statement is incorrect because **IgG** is well-established as being transported across the placenta. - Such an absence of maternal antibodies would leave the fetus highly vulnerable to infections during development and early life. *Both IgG and IgA* - While **IgG** readily crosses the placenta, **IgA** does not, making this option incorrect. - The primary route for IgA transfer to the infant is through **breast milk** after birth, providing crucial immunity for the newborn's gastrointestinal tract.

Q: What is the ratio of T cells to B cells in a healthy adult?

3:1. ***3:1*** - In healthy adults, a typical peripheral blood sample shows a **predominance of T cells** over B cells. - This ratio reflects the differing roles and distributions of these lymphocytes; **T cells are more numerous** in circulation. *1:3* - This ratio would indicate **more B cells than T cells**, which is not typical for peripheral blood in a healthy individual. - An inversion of the usual T:B cell ratio could suggest certain disease states, such as specific **lymphoid malignancies**. *1:1* - While possible in some specific lymphoid tissues, a **1:1 ratio is not the standard** for circulating T and B cells in healthy adults. - This ratio would represent a **significantly higher proportion of B cells** than usually found in peripheral blood. *1:2* - This ratio implies **twice as many B cells as T cells**, which is significantly skewed compared to normal physiological levels in peripheral blood. - Such a high proportion of B cells is typically observed in states of **B-cell proliferation** or specific immune dysregulation.

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

Myoglobin. ***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).

Q: What is needed for prothrombin to thrombin conversion?

Calcium. ***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.

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

C: Eosinophil. ***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.

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

Vitamin K. ***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 1

The least marked function of a human spleen is

Accepted Answer

reservoir function

Answer

filter function

Answer

immune function

Answer

pitting function

Question 2

Stored blood which has been preserved in a blood bank is deficient in which of the following coagulation factors?

Accepted Answer

V and VIII

Answer

IX and X

Answer

II and VII

Answer

II only

Question 3

The removal of malarial parasites from the blood is called

Accepted Answer

Phagocytosis

Answer

Binding

Answer

Culling

Answer

Sequestration

Question 4

The immunoglobulins that can be transported across the placenta include:

Accepted Answer

IgG only

Answer

IgA only

Answer

Neither IgG nor IgA

Answer

Both IgG and IgA

Question 5

What is the ratio of T cells to B cells in a healthy adult?

Accepted Answer

3:1

Answer

1:3

Answer

1:1

Answer

1:2

Question 6

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

Accepted Answer

Myoglobin

Answer

Methemoglobin

Answer

Carboxyhemoglobinemia

Answer

Fetal hemoglobin

Question 7

What is needed for prothrombin to thrombin conversion?

Accepted Answer

Calcium

Answer

Magnesium

Answer

Sodium

Answer

Potassium

Question 8

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?

Accepted Answer

Fetal hemoglobin binds 2,3-BPG with fewer ionic bonds than the adult form.

Answer

There is less 2,3-BPG in the fetal circulation as compared to maternal circulation

Answer

The tense form of hemoglobin is more prevalent in the circulation of the fetus

Answer

The oxygen-binding curve of fetal hemoglobin is shifted to the right.

Question 9

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

Accepted Answer

C: Eosinophil

Answer

A: Lymphocyte

Answer

D: Basophil

Answer

B: Neutrophil

Question 10

Which of the following is not involved in local hemostasis?

Accepted Answer

Vitamin K

Answer

Fibrinogen

Answer

Collagen

Answer

Calcium

Blood and Immunity — MCQs

Blood and Immunity — MCQs

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