Histology — MCQs

Histology Indian Medical PG Practice Questions and MCQs

Question 331: Intercalated discs have all of the following except:

A. Zona occludens (Correct Answer)
B. Macula adherens
C. Fascia adherens
D. Gap junctions

Explanation: Intercalated discs are specialized cell-to-cell junctions found in **cardiac muscle** that allow the myocardium to function as a functional syncytium [2]. They consist of three distinct types of cell junctions, each serving a specific mechanical or electrical purpose. **Why Zona Occludens is the correct answer:** **Zona occludens (Tight junctions)** are typically found in epithelial tissues (like the intestinal lining or the blood-brain barrier) where they seal the intercellular space to prevent the passage of molecules [1]. They are **not** present in intercalated discs. Cardiac muscle requires mechanical strength and electrical communication, not a waterproof seal between cells. **Why the other options are incorrect:** * **Fascia Adherens (Option C):** This is the most prominent component of the transverse portion of the disc. It anchors actin filaments of the terminal sarcomeres to the plasma membrane, transmitting contractile forces between cells. * **Macula Adherens / Desmosomes (Option B):** These provide strong mechanical attachment and prevent the myocytes from pulling apart during explosive contractions [1]. * **Gap Junctions / Nexus (Option D):** Located primarily in the longitudinal portion of the disc, these provide low-resistance electrical coupling, allowing action potentials to spread rapidly across the heart [3]. **High-Yield NEET-PG Pearls:** * **Functional Syncytium:** The combination of mechanical (desmosomes) and electrical (gap junctions) coupling allows the heart to contract as a single unit. * **Location:** Intercalated discs always coincide with the **Z-lines** of the cardiac muscle sarcomere [2]. * **Microscopy:** Under light microscopy, they appear as dark-staining transverse lines; under EM, they show a "staircase" appearance with transverse and longitudinal components.

Question 332: Which of the following surface glycoproteins is most often expressed in human hematopoietic stem cells?

A. CD22
B. CD40
C. CD15
D. CD34 (Correct Answer)

Explanation: **Explanation:** **CD34** is the hallmark surface marker for **Hematopoietic Stem Cells (HSCs)** and progenitor cells. It is a transmembrane phosphoglycoprotein that facilitates cell-cell adhesion and allows stem cells to attach to the bone marrow extracellular matrix. In clinical practice, CD34 expression is the gold standard used to identify, quantify, and isolate stem cells for **bone marrow transplantation** [1], [3]. **Analysis of Incorrect Options:** * **CD22:** This is a regulatory marker specifically expressed on the surface of **mature B-lymphocytes**. It is not found on hematopoietic stem cells. * **CD40:** This is a costimulatory protein found on **Antigen-Presenting Cells (APCs)** like B-cells, macrophages, and dendritic cells. It is crucial for T-cell dependent B-cell activation. * **CD15:** Also known as Lewis X, this is a carbohydrate adhesion molecule primarily expressed on **Granulocytes** (neutrophils) and is a classic marker for **Reed-Sternberg cells** in Hodgkin Lymphoma [2]. **High-Yield Clinical Pearls for NEET-PG:** * **Stem Cell Harvesting:** A minimum dose of $2 \times 10^6$ CD34+ cells/kg is typically required for successful engraftment in autologous transplants. * **Negative Markers:** True HSCs are often described as **CD34+ and CD38–** (the absence of CD38 indicates a more primitive, undifferentiated state). * **Acute Leukemia:** CD34 is frequently used in flow cytometry to differentiate **blasts** (which are CD34+) from mature cells in the diagnosis of Acute Myeloid Leukemia (AML).

Question 333: Thyroid follicles are lined by which type of epithelium?

A. Squamous
B. Cuboidal (Correct Answer)
C. Transitional
D. None

Explanation: **Explanation:** The thyroid gland is composed of functional units called **thyroid follicles**. These follicles are typically lined by a **Simple Cuboidal Epithelium** (follicular cells) which rests on a basement membrane and surrounds a central lumen filled with colloid (thyroglobulin) [1], [2]. **Why Cuboidal is Correct:** The height of the follicular epithelium reflects the **functional state** of the gland. In a normal, euthyroid state, the cells are cuboidal [2]. However, this epithelium is unique because it is highly dynamic: * **Active State (TSH stimulation):** Cells become **Columnar** as they actively synthesize and secrete hormones [2]. * **Inactive/Resting State:** Cells become **Squamous** (flat) as the follicle distends with stored colloid. For examination purposes, the standard histological classification for the thyroid follicle is **Simple Cuboidal**. **Analysis of Incorrect Options:** * **A. Squamous:** Simple squamous epithelium lines structures requiring rapid diffusion (e.g., alveoli, endothelium). In the thyroid, it only indicates an inactive/hypofunctioning follicle. * **C. Transitional:** This is a specialized "stretchable" epithelium (urothelium) found exclusively in the urinary tract (e.g., bladder, ureters). * **D. None:** Incorrect, as the thyroid has a distinct epithelial lining. **High-Yield NEET-PG Pearls:** 1. **Parafollicular Cells (C-cells):** Located between follicles; they secrete **Calcitonin** and are derived from the **Ultimobranchial body** (Neural crest cells). 2. **Origin:** The thyroid gland is the first endocrine gland to develop (24th day) from the **endoderm** of the floor of the primitive pharynx [1]. 3. **Colloid Scalloping:** In Graves' disease (hyperthyroidism), the epithelium becomes tall columnar, and "scalloping" or "moth-eaten" edges are seen in the colloid due to rapid reabsorption.

Question 334: What is the type of cell lining the small intestine?

A. Simple squamous
B. Stratified squamous
C. Simple columnar (Correct Answer)
D. Stratified columnar

Explanation: **Explanation:** The primary function of the small intestine is the **absorption** of nutrients and the **secretion** of digestive enzymes [2]. To facilitate these processes, the intestinal mucosa is lined by a **Simple Columnar Epithelium**. **Why Simple Columnar is correct:** * **Surface Area:** These tall, rectangular cells provide ample cytoplasmic volume for organelles involved in processing absorbed nutrients [1]. * **Microvilli:** The apical surface features a "striated border" (microvilli), which dramatically increases the surface area for absorption [2]. * **Specialized Cells:** This layer includes enterocytes (absorptive) and goblet cells (mucus-secreting), which are characteristic of the gastrointestinal tract from the stomach to the rectum [1]. **Why other options are incorrect:** * **Simple Squamous:** These thin, flat cells are designed for rapid diffusion (e.g., alveoli of lungs, endothelium of blood vessels) and lack the machinery for active absorption/secretion. * **Stratified Squamous:** This multi-layered epithelium is designed for protection against mechanical stress (e.g., esophagus, skin). It is too thick for efficient nutrient absorption. * **Stratified Columnar:** This is a rare tissue type found only in specific areas like the large ducts of salivary glands or the conjunctiva; it does not serve an absorptive function. **High-Yield Clinical Pearls for NEET-PG:** * **Celiac Disease:** Characterized by "villous atrophy," where the simple columnar lining flattens, leading to malabsorption. * **Goblet Cells:** Their number increases distally along the small intestine, being most numerous in the ileum [1]. * **Crypts of Lieberkühn:** These are simple tubular glands located between the bases of the villi, containing Paneth cells (secreting lysozymes) and stem cells [1].

Question 335: Which of the following conditions cannot be prevented by orchiopexy in cryptorchidism?

A. Testicular tumor (Correct Answer)
B. Epididymo-orchitis
C. Torsion of the testis
D. Sexual ambiguity

Explanation: The primary goal of **orchiopexy** (surgical repositioning of the testis into the scrotum) is to preserve fertility and facilitate clinical examination. However, it does **not** eliminate the increased risk of malignancy associated with cryptorchidism. [1] **1. Why "Testicular Tumor" is the correct answer:** Cryptorchidism is a major risk factor for testicular germ cell tumors (especially seminomas). While orchiopexy performed before puberty (ideally before age 1) may slightly reduce the risk, it **cannot prevent** it. The optimal recommended timing for this procedure is 6 months to 1 year of age [1]. The increased risk is believed to be due to underlying dysgenetic changes in the germ cells that exist regardless of the anatomical position. The main benefit of orchiopexy regarding malignancy is that it brings the testis to a palpable location, allowing for early detection via physical examination. **2. Why the other options are incorrect:** * **Torsion of the testis:** Orchiopexy involves fixing the testis to the scrotal wall (tunica vaginalis), which anatomically prevents the testis from twisting on its spermatic cord. * **Epididymo-orchitis:** By placing the testis in its normal anatomical position and correcting associated patent processus vaginalis (often done during the same surgery), the risk of certain inflammatory complications and associated inguinal hernias is reduced. * **Sexual ambiguity:** Cryptorchidism is a physical finding, not a cause of intersex disorders. However, early surgical correction and diagnosis help in the management of cases where undescended testes are part of a broader DSD (Disorders of Sex Development) profile, ensuring appropriate phenotypic alignment. **High-Yield Clinical Pearls for NEET-PG:** * **Most common site** of an undescended testis: **Inguinal canal**. * **Most common tumor** in an undescended testis: **Seminoma**. * **Optimal age for Orchiopexy:** Between **6 to 12 months** of age to preserve spermatogenesis (Sertoli and Leydig cells are heat-sensitive) [1]. * **Risk factor:** The risk of malignancy is also increased in the contralateral, normally descended testis.

Question 336: Which of the following conditions is associated with microcytic hypochromic anemia?

A. Sickle cell anemia
B. Thalassemia (Correct Answer)
C. Fanconi's anemia
D. Hereditary spherocytosis

Explanation: **Explanation:** The classification of anemia is primarily based on the **Mean Corpuscular Volume (MCV)**. Microcytic hypochromic anemia (MCV < 80 fL) occurs when there is a defect in hemoglobin synthesis, either in heme (Iron Deficiency Anemia, Sideroblastic Anemia) or globin chains (**Thalassemia**) [1]. **Why Thalassemia is Correct:** Thalassemia is a quantitative defect in globin chain synthesis ($\alpha$ or $\beta$). [1] This reduction in hemoglobin production leads to smaller (microcytic) and paler (hypochromic) red blood cells. On a peripheral smear, it is classically associated with **Target cells** and a low Mentzer Index (MCV/RBC count < 13). **Analysis of Incorrect Options:** * **Sickle Cell Anemia:** This is a qualitative defect (point mutation) in the globin chain. It typically presents as a **normocytic normochronic anemia** with characteristic sickle-shaped cells on a peripheral smear. * **Fanconi’s Anemia:** This is an inherited form of aplastic anemia characterized by DNA repair defects. It typically presents as **macrocytic anemia** (MCV > 100 fL) associated with pancytopenia and physical anomalies (e.g., absent thumb). * **Hereditary Spherocytosis:** This is a red cell membrane defect (ankyrin or spectrin deficiency). It presents as a **normocytic hyperchromic anemia** (due to increased MCHC) with spherical RBCs lacking central pallor. **High-Yield Clinical Pearls for NEET-PG:** * **Differential Diagnosis of Microcytic Anemia (SITA):** **S**ideroblastic anemia, **I**ron deficiency (most common), **T**halassemia, **A**nemia of chronic disease (late stage). * **Mentzer Index:** Useful to differentiate Iron Deficiency (>13) from Thalassemia (<13). * **Iron Deficiency Anemia:** Characterized by increased Total Iron Binding Capacity (TIBC) and decreased Ferritin.

Question 337: Stratum germinativum is synonymous to which layer of the epidermis?

A. Stratum Basale (Correct Answer)
B. Stratum Spinosum
C. Stratum granulosum
D. Stratum corneum

Explanation: The epidermis is a keratinized stratified squamous epithelium composed of five distinct layers [1]. The **Stratum Basale** (the deepest layer) is synonymous with **Stratum Germinativum** because it contains the mitotically active stem cells (keratinocytes) responsible for the continuous "germination" or regeneration of the skin [1]. These cells divide and migrate superficially to replenish the upper layers. **Analysis of Options:** * **Stratum Basale (Correct):** It consists of a single layer of columnar or cuboidal cells resting on the basement membrane [1]. It is the site of active cell division and contains melanocytes and Merkel cells [1]. * **Stratum Spinosum:** Also known as the "prickle cell layer" due to the prominent desmosomal attachments (nodes of Bizzozero) that appear as spines under microscopy. * **Stratum Granulosum:** Characterized by cells containing basophilic keratohyalin granules and lamellar bodies (Odland bodies), which provide the water-impermeable lipid barrier. * **Stratum Corneum:** The outermost layer consisting of dead, flattened, enucleated cells (corneocytes) filled with keratin [1]. **High-Yield NEET-PG Pearls:** 1. **Mnemonic for layers (Deep to Superficial):** **B**asale, **S**pinosum, **G**ranulosum, **L**ucidum, **C**orneum (**B**ritish **S**pies **G**et **L**ucky **C**harms). 2. **Stratum Lucidum:** A clear, translucent layer found **only in thick skin** (palms and soles). 3. **Clinical Correlation:** Psoriasis involves an accelerated cell cycle in the stratum germinativum, leading to a thickened epidermis (acanthosis) and retained nuclei in the stratum corneum (parakeratosis). 4. **Bullous Pemphigoid:** Targets hemidesmosomes, which anchor the stratum basale to the basement membrane.

Question 338: Progressive transformation of germinal centres is a precursor lesion of which condition?

A. Hodgkin's lymphoma, nodular sclerosis (Correct Answer)
B. Hodgkin's lymphoma, mixed cellularity
C. Anaplastic large cell lymphoma
D. Peripheral T cell lymphoma

Explanation: **Explanation:** **Progressive Transformation of Germinal Centres (PTGC)** is a reactive lymphadenopathy characterized by the enlargement of germinal centres due to an influx of mantle zone B-cells into the follicle. 1. **Why Option A is Correct:** PTGC is clinically significant because it is most frequently associated with **Nodular Lymphocyte Predominant Hodgkin Lymphoma (NLPHL)**. However, in the context of classical Hodgkin Lymphoma (cHL) subtypes, it is specifically linked as a precursor or a concurrent finding in **Nodular Sclerosis Hodgkin Lymphoma (NSHL)**. Histologically, both conditions involve follicular architectural changes and a background of reactive inflammatory cells. PTGC can precede, coexist with, or follow the development of Hodgkin lymphoma. 2. **Why Other Options are Incorrect:** * **Option B (Mixed Cellularity):** This subtype is associated with EBV infection and an abundant inflammatory background (eosinophils, plasma cells) but does not typically arise from PTGC. * **Option C & D (ALCL & PTCL):** These are T-cell lymphomas. PTGC is a B-cell follicular process and is not a precursor to T-cell malignancies. **High-Yield Facts for NEET-PG:** * **PTGC Histology:** Large "transformed" follicles (3–5 times normal size) with indistinct borders between the germinal centre and mantle zone. * **NLPHL vs. PTGC:** PTGC is often seen in the same lymph nodes as NLPHL. The "Popcorn cells" (L&H cells) of NLPHL are the key diagnostic differentiator. * **Nodular Sclerosis HL:** The most common subtype of HL; characterized by **Lacunar cells** and collagen bands (fibrosis) encircling lymphoid nodules. * **Clinical Pearl:** PTGC is usually asymptomatic and occurs more commonly in young males. While benign, it necessitates close follow-up due to the risk of synchronous or metachronous Hodgkin lymphoma.

Question 339: What is the relative size of a small lymphocyte compared to a red blood cell?

A. Bigger than an RBC
B. The same size as an RBC
C. Smaller than an RBC (Correct Answer)
D. None of these

Explanation: **Explanation:** In histology, the **Red Blood Cell (RBC)** is often referred to as the "histological ruler" because of its consistent size [2]. A mature RBC typically measures **7.2 to 7.5 µm** in diameter. **1. Why the correct answer is right:** A **small lymphocyte** is the smallest type of white blood cell. It typically measures between **6 to 8 µm** in diameter [1]. In most standard histological preparations (like a peripheral blood smear), the majority of small lymphocytes appear slightly smaller than or nearly equal to the size of a resting RBC. Specifically, the nucleus of a small lymphocyte is roughly the same size as an RBC, but because the cytoplasm is minimal, the overall cell profile often appears more compact or slightly **smaller than an RBC**. **2. Why the incorrect options are wrong:** * **Option A (Bigger than an RBC):** Large lymphocytes (10–15 µm), monocytes, and granulocytes (neutrophils, eosinophils, basophils) are all significantly larger than an RBC. However, the question specifically specifies a *small* lymphocyte. * **Option B (The same size as an RBC):** While the nucleus of the lymphocyte is often used as a reference for a ~7 µm structure, the total cell diameter of a "small" lymphocyte is frequently on the lower end of the spectrum (6 µm), making "smaller" the more precise histological distinction. **3. NEET-PG High-Yield Pearls:** * **Histological Ruler:** Always remember the RBC diameter (7.2 µm) to estimate the size of other structures in a biopsy [2]. * **Small Lymphocyte:** Characterized by a high N:C (Nucleus-to-Cytoplasm) ratio; the nucleus is dense, heterochromatic, and occupies nearly the entire cell. * **Clinical Correlation:** An increase in the size of lymphocytes (atypical lymphocytes) is a hallmark of viral infections like **Infectious Mononucleosis** (EBV), where they become much larger than RBCs.

Question 340: Which of the following are features of membranous urethral injury?

A. Blood at meatus
B. Extravasation of urine
C. Retention of urine
D. All of the above (Correct Answer)

Explanation: ### Explanation The **membranous urethra** is the shortest and least dilatable part of the male urethra, located within the **deep perineal pouch** where it is surrounded by the external urethral sphincter. Injury to this segment most commonly occurs due to **fracture of the bony pelvis** (e.g., road traffic accidents), leading to a partial or complete transection at the puboprostatic ligament [1]. **Why "All of the above" is correct:** 1. **Blood at the meatus:** This is the most important clinical sign of urethral injury. Disruption of the urethral mucosa leads to bleeding that tracks distally to the external urethral orifice. 2. **Extravasation of urine:** When the membranous urethra is ruptured, urine leaks into the **deep perineal pouch**. If the perineal membrane is also torn, urine can track superiorly into the prevesical space (Space of Retzius) or around the prostate [1]. 3. **Retention of urine:** The physical disruption of the urethral continuity, combined with pain and reflex spasm of the sphincters, prevents the patient from voiding, leading to acute urinary retention and a palpable bladder. **Clinical Pearls for NEET-PG:** * **High-riding Prostate:** On Digital Rectal Examination (DRE), the prostate may be non-palpable or "floating" because the puboprostatic ligaments are torn and the prostate is displaced superiorly by a pelvic hematoma, often referred to as a "pie in the sky" bladder [1]. * **Gold Standard Investigation:** **Retrograde Urethrogram (RUG)** must be performed *before* attempting catheterization to avoid converting a partial tear into a complete one [1]. * **Anatomical Landmark:** The membranous urethra is the part that pierces the **urogenital diaphragm**. * **Bulbar vs. Membranous:** While membranous injury is associated with pelvic fractures, **bulbar urethral injury** is typically caused by "straddle injuries" (falling astride) and results in a "butterfly-shaped" hematoma in the perineum [1].

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Histology — MCQs

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