Anatomy
1 questionsB cells are located in which region of lymph nodes?
NEET-PG 2015 - Anatomy NEET-PG Practice Questions and MCQs
Question 381: B cells are located in which region of lymph nodes?
- A. Paracortical region
- B. Cortical follicles (Correct Answer)
- C. Subcapsular region
- D. Medullary sinuses
Explanation: ***Cortical follicles*** - **B cells** are predominantly found within the **cortical follicles** of lymph nodes, where they mature and become activated upon encountering antigens [2]. - These follicles can be primary (inactive) or secondary (active, containing **germinal centers** for B cell proliferation and differentiation). *Paracortical region* - The **paracortical region** is primarily occupied by **T cells** and is the site where T cells interact with antigen-presenting cells [1]. - While it's adjacent to B cell areas, it's not the primary location for B cells. *Medullary sinuses* - **Medullary sinuses** are channels in the medulla of the lymph node, containing macrophages and plasma cells, which are *differentiated B cells*. - They are not the primary residence for undifferentiated B cells. *Subcapsular region* - **Subcapsular region** is the space immediately beneath the capsule of the lymph node where lymph initially enters. - It contains macrophages and dendritic cells that sample antigens but is not a primary B cell zone.
Biochemistry
5 questionsBile acids are synthesized from ?
Most abundant source of fuel in starvation -
Most important carbohydrate store for maintaining blood glucose homeostasis -
Which of the following statements about the enzymes involved in the conversion of glucose to glucose-6-phosphate in glycolysis is true?
Enzyme deficient in Hers disease -
NEET-PG 2015 - Biochemistry NEET-PG Practice Questions and MCQs
Question 381: Bile acids are synthesized from ?
- A. Heme
- B. Ribulose
- C. Arachidonic acid
- D. Cholesterol (Correct Answer)
Explanation: ***Cholesterol*** - **Bile acids** are derivatives of **cholesterol**, synthesized in the liver through a multi-step enzymatic pathway. - The conversion of cholesterol to bile acids is a primary mechanism for the excretion and transport of cholesterol from the body. *Heme* - **Heme** is a component of hemoglobin and myoglobin, primarily involved in oxygen transport and storage. - Its degradation product is **bilirubin**, which forms part of bile but is distinct from bile acids. *Ribulose* - **Ribulose** is a 5-carbon sugar, playing a key role in the **pentose phosphate pathway** and the **Calvin cycle** in photosynthesis. - It is not a precursor for bile acid synthesis. *Arachidonic acid* - **Arachidonic acid** is a polyunsaturated fatty acid that serves as a precursor for **eicosanoids** (prostaglandins, thromboxanes, and leukotrienes). - These molecules are involved in inflammation and immune responses but are unrelated to bile acid synthesis.
Question 382: Most abundant source of fuel in starvation -
- A. Liver glycogen
- B. Muscle glycogen
- C. Adipose tissue (Correct Answer)
- D. Blood glucose
Explanation: ***Adipose tissue*** - **Adipose tissue** stores **triglycerides**, which are hydrolyzed into fatty acids and glycerol to serve as the body's primary energy source during prolonged starvation. - The energy reserve in adipose tissue is significantly larger than glycogen stores, providing **sustained fuel** for days or weeks. *Liver glycogen* - **Liver glycogen** is a readily available source of glucose but is rapidly depleted within **12-24 hours** during starvation. - Its primary role is to maintain **blood glucose levels** for glucose-dependent tissues like the brain. *Muscle glycogen* - **Muscle glycogen** is used primarily for **muscle contraction** and cannot be directly released into the bloodstream to maintain blood glucose levels. - While it's a significant energy reserve for working muscles, it does not contribute to systemic fuel needs during starvation. *Blood glucose* - **Blood glucose** is the immediate circulating fuel, but it is tightly regulated and its levels decrease during starvation as glycogen stores are depleted. - It is not an abundant stored source of fuel but rather a transport form of energy.
Question 383: Most important carbohydrate store for maintaining blood glucose homeostasis -
- A. Blood glucose
- B. Glycogen in adipose tissue
- C. Hepatic glycogen (Correct Answer)
- D. None of the options
Explanation: ***Hepatic glycogen*** - The liver contains **100-120g of glycogen**, which is the most crucial carbohydrate store for **maintaining blood glucose homeostasis**. - **Hepatic glycogen** can be mobilized and released as glucose into the bloodstream to supply all body tissues, especially during fasting. - Although muscle glycogen is quantitatively larger (~400-500g), it cannot contribute to blood glucose as muscle lacks glucose-6-phosphatase. - The liver's unique ability to release free glucose makes hepatic glycogen the **most metabolically important** carbohydrate store. *Blood glucose* - **Blood glucose** (~5g total in circulation) represents carbohydrates available for immediate energy, not a storage form. - This is far too small to be considered a major carbohydrate reserve. *Glycogen in adipose tissue* - **Adipose tissue** primarily stores **fat (triglycerides)**, with negligible glycogen content. - Adipose tissue plays virtually no role in carbohydrate storage. *None of the options* - This is incorrect because **hepatic glycogen** is indeed the most important carbohydrate store for glucose homeostasis.
Question 384: Which of the following statements about the enzymes involved in the conversion of glucose to glucose-6-phosphate in glycolysis is true?
- A. Glucokinase is induced by insulin. (Correct Answer)
- B. Hexokinase is specific for glucose.
- C. Glucokinase is inhibited by glucose-6-phosphate.
- D. Hexokinase has a high Km for glucose.
Explanation: ***Glucokinase is induced by insulin.*** - **Insulin** promotes glucose uptake and utilization in the liver and pancreatic beta cells, where glucokinase is primarily expressed. - Induction of **glucokinase** by insulin ensures that glucose is efficiently phosphorylated and trapped within hepatocytes when blood glucose levels are high. - This is a key mechanism for postprandial glucose homeostasis. *Incorrect: Hexokinase is specific for glucose.* - **Hexokinase** is NOT specific for glucose; it can phosphorylate various hexoses including **fructose**, **mannose**, and **galactose**. - Its broad substrate specificity distinguishes it from glucokinase, which has greater specificity for glucose. *Incorrect: Glucokinase is inhibited by glucose-6-phosphate.* - Unlike **hexokinase**, which is subject to product inhibition by glucose-6-phosphate, **glucokinase is NOT inhibited** by its product. - This lack of feedback inhibition allows glucokinase to continue phosphorylating glucose even when glucose-6-phosphate levels are elevated, which is appropriate for its role as a glucose sensor in liver and pancreatic beta cells. *Incorrect: Hexokinase has a high Km for glucose.* - **Hexokinase** has a **low Km** (~0.1 mM) for glucose, meaning it has high affinity and is saturated at normal blood glucose levels. - In contrast, **glucokinase** has a high Km (~10 mM), allowing it to respond proportionally to changes in blood glucose concentration.
Question 385: Enzyme deficient in Hers disease -
- A. Muscle phosphorylase
- B. Liver phosphorylase (Correct Answer)
- C. Acid maltase
- D. Debranching enzyme
Explanation: ***Liver phosphorylase*** - Hers disease, also known as Glycogen Storage Disease Type VI, is specifically caused by a deficiency of **liver phosphorylase**. - This enzyme is crucial for the breakdown of **glycogen in the liver**, leading to an inability to release glucose into the bloodstream during fasting. *Muscle phosphorylase* - Deficiency of **muscle phosphorylase** (myophosphorylase) causes **McArdle disease** (Glycogen Storage Disease Type V), which primarily affects muscle energy. - Patients typically present with exercise intolerance, muscle pain, and cramps, not the hepatic symptoms seen in Hers disease. *Acid maltase* - Deficiency of **acid maltase** (also known as alpha-glucosidase) is responsible for **Pompe disease** (Glycogen Storage Disease Type II), a lysosomal storage disorder. - This enzyme deficiency leads to glycogen accumulation in lysosomes in various tissues, including muscle, liver, and heart, causing muscle weakness and cardiomyopathy. *Debranching enzyme* - A deficiency in the **debranching enzyme** (amylo-1,6-glucosidase) causes **Cori disease** or **Forbes disease** (Glycogen Storage Disease Type III). - This results in the accumulation of abnormally structured glycogen with short outer branches in the liver, muscle, and heart.
Microbiology
2 questionsThe process by which antigen-specific B lymphocytes are selected and activated to proliferate and produce antibodies is called:
In the context of immune response, which of the following cell types does not express MHC class II molecules?
NEET-PG 2015 - Microbiology NEET-PG Practice Questions and MCQs
Question 381: The process by which antigen-specific B lymphocytes are selected and activated to proliferate and produce antibodies is called:
- A. Clonal selection (Correct Answer)
- B. Class switching
- C. Group switching
- D. Hybridisation
Explanation: ***Clonal selection*** - **Clonal selection** is the fundamental process by which an antigen-specific B lymphocyte is **selected** when its B cell receptor (BCR) recognizes and binds to a matching antigen. - This binding triggers the B cell to become **activated**, **proliferate** (undergo clonal expansion), and **differentiate** into plasma cells that produce antibodies specific to that antigen. - This process is the cornerstone of **adaptive immunity**, ensuring that only B cells with receptors matching the encountered antigen are stimulated to respond. *Class switching* - **Class switching** (isotype switching) occurs AFTER clonal selection and activation. - It allows already-activated B cells to change the **antibody class** they produce (from IgM to IgG, IgA, or IgE) while maintaining the **same antigen specificity**. - This process modifies effector functions but does NOT involve the initial selection and activation of antigen-specific B cells. *Group switching* - This is not a recognized term in immunology. - It does not describe any standard process of B cell activation or antibody production. *Hybridisation* - **Hybridization** refers to the formation of double-stranded nucleic acids from complementary strands or the creation of hybrid cells (e.g., hybridomas for monoclonal antibody production). - It is not the physiological process by which B lymphocytes are selected and activated in response to antigen exposure.
Question 382: In the context of immune response, which of the following cell types does not express MHC class II molecules?
- A. Cortical macrophages
- B. Neutrophils
- C. Medullary macrophages
- D. NK cells (Correct Answer)
Explanation: ***NK cells*** - **Natural Killer (NK) cells)** are innate lymphocytes that do **NOT express MHC class II molecules** under any circumstances. - NK cells use alternative recognition mechanisms (KIRs, activating receptors) to detect target cells, primarily recognizing the **absence of MHC class I** or stress-induced ligands. - They function in innate immunity without antigen presentation capability. - **This is the best answer** as NK cells never express MHC class II, making them distinctly different from professional APCs. *Cortical macrophages* - **Cortical macrophages** in lymphoid organs are professional **antigen-presenting cells (APCs)** that constitutively express **MHC class II molecules**. - They present processed antigens to CD4+ T helper cells, playing a crucial role in initiating adaptive immune responses. *Medullary macrophages* - **Medullary macrophages** are also professional APCs that constitutively express **MHC class II molecules**. - They participate in antigen presentation and immune surveillance within the medullary regions of lymphoid tissues. *Neutrophils* - Neutrophils are granulocytes that **typically do not constitutively express MHC class II molecules** in their resting state. - However, under certain inflammatory conditions with prolonged stimulation (IFN-γ, GM-CSF), neutrophils can be induced to express low levels of MHC class II. - While neutrophils generally lack MHC class II, **NK cells are the more definitive answer** as they never express MHC class II under any physiological or pathological conditions.
Pathology
1 questionsPost-streptococcal glomerulonephritis (PSGN) is an example of which type of hypersensitivity?
NEET-PG 2015 - Pathology NEET-PG Practice Questions and MCQs
Question 381: Post-streptococcal glomerulonephritis (PSGN) is an example of which type of hypersensitivity?
- A. Type -1 hypersensitivity
- B. Type -2 hypersensitivity
- C. Type -3 hypersensitivity (Correct Answer)
- D. Type -4 hypersensitivity
Explanation: ***Type -3 hypersensitivity*** - Post-streptococcal glomerulonephritis (PSGN) is caused by **immune complex deposition**, a hallmark of type III hypersensitivity reactions [1][2][3]. - It involves the formation of **antigen-antibody complexes** following a streptococcal infection, leading to inflammation in the kidneys [1][2]. *Type -1 hypersensitivity* - Characterized by **IgE-mediated** reactions, such as allergies and anaphylaxis, which do not apply to PSGN. - It typically involves **mast cells** and histamine release, notably absent in PSGN cases. *Type -4 hypersensitivity* - Involves **T-cell mediated** responses and is related to delayed-type reactions, not applicable to PSGN. - Common examples include **contact dermatitis** and graft-versus-host disease, differing fundamentally from PSGN's mechanism. *Type -2 hypersensitivity* - Characterized by **antibody-mediated cytotoxicity**, such as in hemolytic anemia, unrelated to immune complexes in PSGN. - Typically involves direct damage to cells, contrasting with the immune complex mechanism observed in PSGN [2]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 214-215. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Kidney, pp. 910-915. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 215-216.
Surgery
1 questionsWhich solid organ is considered to have the lowest risk of rejection during transplantation?
NEET-PG 2015 - Surgery NEET-PG Practice Questions and MCQs
Question 381: Which solid organ is considered to have the lowest risk of rejection during transplantation?
- A. Pancreas
- B. Kidney
- C. Heart
- D. Liver (Correct Answer)
Explanation: ***Liver*** - The liver has a unique immunologic environment, often referred to as **immunologic privilege**, which contributes to its lower rates of rejection compared to other transplanted solid organs. - It produces various **immunosuppressive factors** and has a high capacity for regeneration and repair, adapting more readily to the recipient's immune system. - The liver's **dual blood supply** (hepatic artery and portal vein) and tolerogenic properties make it the most immunologically privileged solid organ. *Pancreas* - **Pancreas transplantation** carries a high risk of rejection, with rejection rates significantly higher than liver transplantation. - Pancreatic tissue is highly **immunogenic** due to its endocrine and exocrine functions, requiring aggressive immunosuppression. - Often transplanted with kidney in diabetic patients, and rejection episodes are common. *Kidney* - Kidney transplantation is common, but it carries a significant risk of both **acute and chronic rejection**, requiring lifelong immunosuppression. - The kidney expresses various **MHC antigens** that are readily recognized by the recipient's immune system, making it more immunogenic than the liver. *Heart* - **Heart transplantation** is associated with a high risk of rejection due to the rich vascularity and immunogenicity of cardiac tissue. - It often requires aggressive immunosuppressive regimens to prevent both **acute cellular rejection** and **antibody-mediated rejection**.