Anatomy
1 questionsT cells in lymph node are present in:
NEET-PG 2013 - Anatomy NEET-PG Practice Questions and MCQs
Question 621: T cells in lymph node are present in:
- A. Paracortical area (Correct Answer)
- B. Mantle layer
- C. Medullary cords
- D. Cortical follicles
Explanation: ***Paracortical area*** - The **paracortical area** contains a high concentration of **T cells**, particularly activated T cells in response to antigenic stimulation [1]. - It plays a crucial role in **immune responses**, bridging the cortex and medulla of the lymph node [1]. *Mantle layer* - The **mantle layer** surrounds the follicles and primarily consists of **B cells**, not T cells. - It is involved in the initial immune response but does not contain a significant number of T lymphocytes. *Medullary cords* - **Medullary cords** mainly contain **plasma cells** and macrophages, with very few T cells present. - Their primary function is the secretion of antibodies rather than T cell activation or response. *Cortical follicles* - **Cortical follicles** are primarily sites for **B cell activation and proliferation**. - While they may have some T cells at their periphery, the majority of T cells are located in the paracortical area.
Biochemistry
2 questionsWhich immunoglobulin is known to be heat-labile?
What is the number of variable regions present on each light and heavy chain of an antibody?
NEET-PG 2013 - Biochemistry NEET-PG Practice Questions and MCQs
Question 621: Which immunoglobulin is known to be heat-labile?
- A. IgA
- B. IgG
- C. IgM (Correct Answer)
- D. IgE
Explanation: ***IgM*** - **IgM** is known for its **heat lability** and is readily denatured at 56°C within a few minutes. - This characteristic is due to its **pentameric structure** held together by disulfide bonds and J chains, which are sensitive to thermal denaturation. - Heat lability of IgM is clinically important in complement fixation tests and other laboratory assays where heat inactivation is performed. - IgM is the first antibody produced in primary immune response and its heat sensitivity distinguishes it from other immunoglobulins. *IgA* - **IgA** exists in monomeric (serum) and dimeric (secretory) forms and shows moderate stability to heat. - Secretory IgA is relatively stable as it needs to function in harsh mucosal environments, though not as heat-resistant as IgG. - Does not exhibit the pronounced heat lability characteristic of IgM. *IgG* - **IgG** is the most stable immunoglobulin and is highly resistant to heat denaturation. - Can withstand temperatures up to 60-70°C without significant loss of activity. - Its monomeric structure with strong intramolecular bonds provides exceptional thermal stability. - Most abundant antibody in serum and has the longest half-life. *IgE* - **IgE** is actually quite stable to heat and can withstand 56°C for extended periods. - While it has a short half-life in serum (2-3 days), this is due to receptor binding rather than heat instability. - Important in type I hypersensitivity reactions and parasitic infections. - Does not show the characteristic heat lability that defines IgM.
Question 622: What is the number of variable regions present on each light and heavy chain of an antibody?
- A. 1 (Correct Answer)
- B. 2
- C. 3
- D. 4
Explanation: ***1*** - Each **light chain** and **heavy chain** within an antibody molecule contains **one variable region (V domain)**. - These variable regions are crucial for **antigen binding specificity**, as they combine to form the antigen-binding site. - The variable domain is located at the **N-terminal end** of each chain. *2* - While a complete antibody molecule has **two antigen-binding sites** (bivalent), each formed by pairing of VH and VL domains, individual chains possess only **one variable region each**. - The number '2' refers to the total number of identical binding sites on the intact antibody, not the number of variable regions per chain. *3* - The number **3** does not correspond to the number of variable regions on individual chains. - This might be confused with the **three complementarity-determining regions (CDRs)** present within each variable domain (CDR1, CDR2, CDR3), which are hypervariable loops that directly contact the antigen. *4* - The number **4** is incorrect for variable regions. - This number corresponds to the total number of **polypeptide chains** in a complete IgG antibody (2 heavy + 2 light chains), or the number of **constant domains** in some heavy chain isotypes (IgM, IgE have 4 CH domains).
Forensic Medicine
1 questionsMiscarriage due to medical negligence is seen under which IPC?
NEET-PG 2013 - Forensic Medicine NEET-PG Practice Questions and MCQs
Question 621: Miscarriage due to medical negligence is seen under which IPC?
- A. Sec 304A IPC (Correct Answer)
- B. Sec 310 IPC
- C. Sec 312 IPC
- D. Sec 314 IPC
Explanation: ***Sec 304A IPC*** - This section specifically deals with **causing death by negligence** (rash or negligent acts not amounting to culpable homicide). - **Medical negligence causing miscarriage** falls under this section as it involves an unintentional harm due to negligent medical practice. - This is the appropriate section when there is no voluntary intent to cause miscarriage, but harm results from professional negligence. *Sec 312 IPC* - This section deals with **voluntarily causing miscarriage**, requiring intentional/voluntary act. - It applies when a person **intentionally** causes a woman to miscarry (criminal abortion). - Medical **negligence** does not constitute a voluntary act in the legal sense, so Sec 312 does not apply to negligence cases. *Sec 310 IPC* - This section is related to **thuggee**, defining someone who habitually commits robbery or child-stealing by murder. - It has no relevance to medical negligence or miscarriage. *Sec 314 IPC* - This section deals with **death caused by an act done with intent to cause miscarriage**. - It applies when an intentional act to cause miscarriage results in the death of the woman. - This requires criminal intent, not negligence.
Microbiology
4 questionsRosette formation with sheep RBCs (SRBCs) indicates functioning of -
All are true regarding the development of T-cells, except?
Cytolytic activity of membrane attack complex is modulated by ?
Prions are best killed by
NEET-PG 2013 - Microbiology NEET-PG Practice Questions and MCQs
Question 621: Rosette formation with sheep RBCs (SRBCs) indicates functioning of -
- A. T-cells (Correct Answer)
- B. B-cells
- C. Neutrophils
- D. Monocytes
Explanation: ***T-cells*** - **T-cells** possess specific receptors, like **CD2** on their surface, that can bind to ligands on sheep red blood cells (SRBCs). - This binding leads to the formation of characteristic **rosettes**, where SRBCs cluster around the T-lymphocytes, indicating functional T-cells. *B-cells* - **B-cells** primarily function in **humoral immunity** by producing antibodies and do not typically form rosettes with sheep RBCs. - While B-cells have surface receptors, they are not CD2 and thus do not facilitate this specific type of rosette formation. *Neutrophils* - **Neutrophils** are **phagocytic cells** involved in innate immunity, primarily combating bacterial and fungal infections. - They lack the specific surface receptors (like CD2) required to form rosettes with sheep RBCs. *Monocytes* - **Monocytes** are precursors to macrophages and dendritic cells, involved in phagocytosis and antigen presentation. - They do not possess the necessary surface markers to form rosettes with sheep RBCs.
Question 622: All are true regarding the development of T-cells, except?
- A. T-cells are formed in bone marrow
- B. In lymph nodes, T-cells are found in paracortical area
- C. Maturation of T-cells take place in thymus
- D. T-cells are located in mantle layer of spleen (Correct Answer)
Explanation: ***T-cells are located in mantle layer of spleen*** - The **mantle layer** (or marginal zone) of the spleen is primarily associated with **B-lymphocytes**, which are involved in antibody production. - While T-cells are present in the spleen, they are predominantly found in the **periarteriolar lymphoid sheath (PALS)**, which is part of the white pulp, rather than the mantle layer. *T-cells are formed in bone marrow* - **Hematopoietic stem cells** in the **bone marrow** are the progenitors of all blood cells, including lymphocytes. - These stem cells differentiate into **lymphoid stem cells**, which then travel to the thymus to become T-cells. *Maturation of T-cells take place in thymus* - **T-cell precursors** migrate from the bone marrow to the **thymus**, where they undergo a complex process of differentiation and selection. - In the thymus, T-cells acquire their **T-cell receptors (TCRs)** and undergo positive and negative selection to ensure they are self-MHC restricted and tolerant to self-antigens. *In lymph nodes, T-cells are found in paracortical area* - The **paracortical area** (or paracortex) of the lymph node is the **T-cell zone**, rich in T-lymphocytes and dendritic cells. - This region is crucial for the interaction between T-cells and antigen-presenting cells, initiating adaptive immune responses.
Question 623: Cytolytic activity of membrane attack complex is modulated by ?
- A. Factor I
- B. Factor B
- C. Factor S (vitronectin) (Correct Answer)
- D. Factor H
Explanation: ***Correct Option: Factor S (vitronectin)*** - Vitronectin (S-protein) is a **plasma protein** that directly modulates the **cytolytic activity of the membrane attack complex (MAC)**. - It binds to the **C5b-7 complex** in the fluid phase, preventing its insertion into target cell membranes and thereby blocking the formation of the complete, functional MAC. - By inhibiting membrane insertion of C5b-7, vitronectin prevents the subsequent binding of **C8 and C9**, which are essential for the cytolytic pore formation. - This is a **direct modulation** of MAC's cytolytic activity at the MAC assembly stage. *Incorrect Option: Factor H* - Factor H is a regulatory protein that controls the **alternative pathway** of complement activation by promoting degradation of **C3b**. - By degrading C3b, Factor H prevents formation of **C5 convertase**, thereby reducing downstream MAC formation. - However, Factor H acts **early in the complement cascade** and does not directly modulate the cytolytic activity of already-formed MAC components. - Its effect is on **preventing MAC formation**, not on modulating MAC's cytolytic function itself. *Incorrect Option: Factor I* - Factor I is a **serine protease** that cleaves and inactivates C3b and C4b, requiring cofactors like Factor H or C4bp. - Like Factor H, it regulates complement activation **upstream** of MAC formation. - It does not directly interact with or modulate the cytolytic activity of the MAC. *Incorrect Option: Factor B* - Factor B is a component of the **alternative pathway C3 convertase** (C3bBb). - It **promotes complement activation** rather than modulating MAC's cytolytic activity. - Factor B functions early in the cascade and has no direct role in regulating MAC function.
Question 624: Prions are best killed by
- A. Incineration at high temperatures
- B. Autoclaving at 134°C (for 18 minutes) (Correct Answer)
- C. 5% formalin solution
- D. Sodium hypochlorite solution
Explanation: ***Autoclaving at 134°C (for 18 minutes)*** - **Prions** are highly resistant to conventional sterilization methods, and **autoclaving at 134°C for at least 18 minutes** is the **most effective method for sterilizing reusable medical instruments** contaminated with prions. - This high temperature and pressure protocol (WHO/CDC recommended) helps to denature the misfolded protein structure of prions, reducing their infectivity to safe levels. - **In the context of sterilization and disinfection**, this is the best practical method for surgical instruments that cannot be discarded. *Incineration at high temperatures* - **Incineration at 800-1000°C** achieves complete combustion and is **highly effective** at destroying prions. - However, incineration is used only for **single-use disposable items** and prion-contaminated waste, not for reusable surgical instruments. - In the clinical context of sterilization (implied by this topic), autoclaving is the preferred answer as it applies to reusable equipment. *Sodium hypochlorite solution* - **Sodium hypochlorite** (bleach) at **high concentrations** (20,000 ppm or 2% available chlorine) for extended contact times (1+ hours) can inactivate prions. - However, it is **corrosive to instruments**, damages tissue samples, and requires precise concentration and exposure conditions, making it less practical than autoclaving. *5% formalin solution* - Formalin is **not effective at inactivating prions**; it can actually **preserve and stabilize** prion infectivity. - Formalin cross-links proteins and preserves tissue morphology but does not reliably break down the highly stable **beta-sheet structures** characteristic of prions.
Pharmacology
1 questionsWhich of the following conditions is not treated by penicillin G?
NEET-PG 2013 - Pharmacology NEET-PG Practice Questions and MCQs
Question 621: Which of the following conditions is not treated by penicillin G?
- A. Bacterial meningitis
- B. Syphilis
- C. Anthrax
- D. Rickettsial infection (Correct Answer)
Explanation: ***Rickettsial infection*** - **Rickettsial infections**, such as Rocky Mountain spotted fever or typhus, are caused by **obligate intracellular bacteria** that are not susceptible to penicillin G. - The primary treatment for rickettsial infections is **doxycycline**, due to its ability to penetrate host cells and inhibit bacterial protein synthesis. *Bacterial meningitis* - **Bacterial meningitis**, particularly caused by susceptible strains of *Neisseria meningitidis*, *Streptococcus pneumoniae*, and *Haemophilus influenzae*, can be effectively treated with **high-dose intravenous penicillin G** [1]. - Penicillin G's ability to cross the **blood-brain barrier** in inflamed meninges makes it a suitable option, though ceftriaxone is now more commonly used empirically due to resistance concerns [2]. *Syphilis* - **Penicillin G** remains the **drug of choice** for all stages of syphilis, caused by *Treponema pallidum*. - For primary, secondary, and early latent syphilis, a **single intramuscular dose of benzathine penicillin G** is curative. *Anthrax* - While **ciprofloxacin** and **doxycycline** are often considered first-line for anthrax, **penicillin G** can also be an effective treatment for susceptible strains of *Bacillus anthracis*. - It is particularly used in cases of less severe cutaneous anthrax or to de-escalate treatment once susceptibility is confirmed.
Physiology
1 questionsWhich immunoglobulin is primarily secreted by the intestine?
NEET-PG 2013 - Physiology NEET-PG Practice Questions and MCQs
Question 621: Which immunoglobulin is primarily secreted by the intestine?
- A. IgG
- B. IgM
- C. IgA (Correct Answer)
- D. IgD
Explanation: **IgA** - **Secretory IgA** is the dominant immunoglobulin in mucosal secretions, including those of the intestine. - It plays a crucial role in providing **local immunity** by preventing microbial adherence and neutralizing toxins on mucosal surfaces. *IgG* - **IgG** is the most abundant immunoglobulin in serum and plays a major role in systemic immunity, including opsonization and complement activation. - While some IgG is found in secretions, it is not the primary immunoglobulin secreted by the intestine. *IgM* - **IgM** is a pentameric immunoglobulin, primarily found in blood and lymph, where it is very effective in activating the complement system and agglutinating antigens. - Although it can be found at mucosal surfaces in small amounts, it is not the principal secreted antibody in the intestine. *IgD* - **IgD** is primarily found on the surface of naive B lymphocytes, where it functions as a B cell receptor. - Its role in secreted form is minimal, and it is not significantly secreted into the intestine or other bodily fluids.