Histology — MCQs

Histology Indian Medical PG Practice Questions and MCQs

Question 101: Which of the following statements about osteoclasts is not true?

A. They have acidophilic cytoplasm
B. They stain strongly with alkaline phosphatase (Correct Answer)
C. The cytoplasmic surface that abuts the bone being resorbed is characterized by a clear zone and a ruffled border
D. They are found in Howship's lacunae

Explanation: The correct answer is **B**, as osteoclasts do not stain for alkaline phosphatase; instead, they are characterized by high levels of **Acid Phosphatase**, specifically the isoenzyme **Tartrate-Resistant Acid Phosphatase (TRAP)**. **Why Option B is the correct choice (False statement):** Alkaline phosphatase (ALP) is a marker of **osteoblast** activity (bone formation) [1]. Osteoclasts are bone-resorbing cells that function in an acidic environment to dissolve bone minerals. Therefore, they express TRAP, which serves as a definitive histological marker for identifying osteoclasts [2]. **Analysis of other options (True statements):** * **Option A:** Osteoclasts have **acidophilic (eosinophilic) cytoplasm** due to an abundance of lysosomes and mitochondria required for active transport and enzymatic degradation [2]. * **Option C:** The **ruffled border** consists of deep plasma membrane infoldings that increase surface area for proton pumps ($H^+$-ATPase) to acidify the resorption pit [2]. The **clear zone** (sealing zone) contains actin filaments that anchor the cell to the bone matrix, creating an isolated microenvironment for resorption [2]. * **Option D:** Osteoclasts reside in shallow enzymatic pits on the bone surface known as **Howship’s lacunae** [2]. **High-Yield NEET-PG Pearls:** * **Origin:** Osteoclasts are derived from the **Monocyte-Macrophage lineage** (GM-CFU), not osteoprogenitor cells. * **Regulation:** Stimulated by **RANKL** (secreted by osteoblasts) and inhibited by **Osteoprotegerin (OPG)** and **Calcitonin**. * **Clinical Correlation:** In **Osteopetrosis** (marble bone disease), osteoclast function is defective (often due to carbonic anhydrase II deficiency), leading to increased bone density but high fragility [3].

Question 102: Which of the following statements is true about the histology of the small intestine?

A. The zone of replication is in the lower half of the gland.
B. M cells convey microorganisms to Peyer's patches.
C. GALT is absent in the lamina propria. (Correct Answer)
D. Secretory IgA (SIgA) provides mucosal immunity.

Explanation: **Explanation:** **1. Understanding the Correct Answer (Option C):** In the histology of the small intestine, **GALT (Gut-Associated Lymphoid Tissue)** is a prominent feature. It is primarily located in the **lamina propria** [1] and the submucosa. GALT includes diffuse lymphoid tissue, isolated lymphoid follicles, and aggregated lymphoid follicles (Peyer’s patches). Therefore, the statement "GALT is absent in the lamina propria" is **incorrect** (Note: In the context of this question format, if Option C is marked as the "correct" answer to select, it is likely identifying the *false* statement among the options). **2. Analysis of Other Options:** * **Option A:** The **zone of replication** (stem cell niche) is indeed located in the **lower half/base** of the Crypts of Lieberkühn [2]. From here, cells migrate upward to replace the villous epithelium every 3–6 days. * **Option B:** **M cells (Microfold cells)** are specialized epithelial cells overlying Peyer's patches [3]. They lack microvilli and function to sample antigens/microorganisms from the lumen and transport them via transcytosis to underlying lymphoid tissue. * **Option C:** **Secretory IgA (sIgA)** is the primary immunoglobulin of the mucosal immune system. It is produced by plasma cells in the lamina propria and transported across the epithelium to neutralize pathogens [3]. **High-Yield NEET-PG Pearls:** * **Peyer’s Patches:** Most numerous in the **Ileum**; they are a hallmark histological feature. * **Brunner’s Glands:** Located in the **Duodenum** (submucosa); they secrete alkaline mucus to neutralize gastric acid. * **Paneth Cells:** Found at the base of crypts [2]; they contain eosinophilic granules and secrete **Lysozyme** and **Defensins** (innate immunity). * **Stem Cell Marker:** Lgr5+ is a specific marker for intestinal stem cells.

Question 103: A patient presented with a hard swelling in his right testis. All are true statements except?

A. Inguinal exploration is performed.
B. Trans-scrotal biopsy is needed. (Correct Answer)
C. High inguinal exploration is performed.
D. Scrotal ultrasound is performed.

Explanation: In the evaluation of a hard testicular swelling, the primary concern is **Testicular Germ Cell Tumor (TGCT)**. **Why "Trans-scrotal biopsy is needed" is the correct (False) statement:** A trans-scrotal biopsy is strictly **contraindicated** in suspected testicular cancer. The lymphatic drainage of the testis follows the testicular arteries to the **Para-aortic lymph nodes**, whereas the scrotum drains into the **Superficial Inguinal lymph nodes**. Performing a biopsy through the scrotal skin risks "seeding" the tumor cells into a different lymphatic territory (scrotal contamination), which alters the clinical stage [1] and complicates the surgical management. [2] **Explanation of other options:** * **High Inguinal Exploration (Options A & C):** This is the standard surgical approach for a suspected testicular malignancy. The surgeon accesses the testis through the inguinal canal to perform a **Radical Orchidectomy**. This allows for the ligation of the spermatic cord at the level of the internal inguinal ring before manipulating the tumor, preventing hematogenous and lymphatic spread. * **Scrotal Ultrasound (Option D):** This is the initial investigation of choice. It is highly sensitive (nearly 100%) for distinguishing between intra-testicular and extra-testicular masses and confirming the presence of a solid tumor. **Clinical Pearls for NEET-PG:** * **Lymphatic Drainage:** Testis → Para-aortic nodes; Scrotum → Superficial Inguinal nodes. * **Tumor Markers:** Always check AFP, beta-hCG, and LDH before surgery. * **Rule of Thumb:** Any solid, painless intra-testicular mass is malignant until proven otherwise. * **Management:** Never biopsy; always perform a Radical Inguinal Orchidectomy.

Question 104: Stratum lucidum is present between which two epidermal layers?

A. Stratum corneum and stratum granulosum (Correct Answer)
B. Stratum granulosum and stratum spinosum
C. Stratum spinosum and stratum basale
D. Stratum basale and stratum subbasale

Explanation: The epidermis is composed of keratinized stratified squamous epithelium, organized into five distinct layers (strata) in thick skin. The correct sequence from superficial to deep is: **Stratum Corneum → Stratum Lucidum → Stratum Granulosum → Stratum Spinosum → Stratum Basale.** [1] 1. **Why Option A is correct:** The **Stratum Lucidum** is a thin, clear, translucent layer of dead keratinocytes. It acts as a transitional zone where cells lose their nuclei and organelles before becoming the fully keratinized cells of the stratum corneum. Therefore, it is anatomically situated between the **Stratum Corneum** (most superficial) and the **Stratum Granulosum**. 2. **Why Option B is incorrect:** The Stratum Granulosum sits directly above the Stratum Spinosum. There is no intervening layer between them. 3. **Why Option C is incorrect:** The Stratum Spinosum (prickle cell layer) is located immediately above the Stratum Basale (the germinal layer). 4. **Why Option D is incorrect:** "Stratum subbasale" is not a recognized histological layer of the epidermis. The layer deep to the stratum basale is the papillary dermis. **High-Yield NEET-PG Pearls:** * **Mnemonic:** "**C**ome **L**et's **G**et **S**un **B**urnt" (Corneum, Lucidum, Granulosum, Spinosum, Basale). * **Location:** Stratum lucidum is **only present in thick skin** (palms and soles); it is absent in thin skin. * **Eleidin:** The translucency of the stratum lucidum is due to **eleidin**, an intermediate transformation product of keratohyalin. * **Keratohyalin Granules:** These are the hallmark of the Stratum Granulosum. * **Desmosomes:** These are most prominent in the Stratum Spinosum, giving the cells their "spiny" appearance.

Question 105: Hassall's corpuscles are observed in which anatomical structure?

A. Thymus (Correct Answer)
B. Spleen
C. Lymph node
D. Appendix

Explanation: **Explanation:** **Hassall’s corpuscles** (also known as thymic corpuscles) are the pathognomonic histological feature of the **Thymus**. They are located exclusively in the **medulla** of the thymic lobules. [1] Structurally, they consist of concentric layers of flattened epithelial reticular cells that have undergone keratinization and sometimes calcification. Their primary function is the production of cytokines (like TSLP) that aid in the development of regulatory T-cells. **Analysis of Incorrect Options:** * **B. Spleen:** Characterized by White Pulp (containing PALS and Malpighian corpuscles) and Red Pulp (containing splenic cords and sinusoids). [2] It does not contain Hassall’s corpuscles. * **C. Lymph Node:** Distinguished by an outer cortex containing lymphoid follicles (B-cells) and an inner medulla with medullary cords and sinuses. [2] * **D. Appendix:** A part of the GALT (Gut-Associated Lymphoid Tissue), it is identified by a continuous ring of lymphoid follicles in the submucosa and the absence of a distinct medulla. **High-Yield Clinical Pearls for NEET-PG:** * **Location:** Hassall's corpuscles are found only in the **Medulla**, never the cortex. * **Origin:** They are derived from the **3rd pharyngeal pouch** (endoderm). * **Ageing:** As the thymus undergoes "age involution" post-puberty, the number of Hassall’s corpuscles may actually increase or become more prominent as the lymphoid tissue is replaced by fat. * **DiGeorge Syndrome:** Characterized by the absence of the thymus (and Hassall’s corpuscles) due to the failure of the 3rd and 4th pharyngeal pouches to develop.

Question 106: Hyaline cartilage is found in all of the following locations except?

A. Costal Cartilage
B. Thyroid Cartilage
C. Foetal Skeleton
D. External Ear (Correct Answer)

Explanation: The correct answer is **D. External Ear**. **1. Why External Ear is the Correct Answer:** The external ear (pinna) is composed of **Elastic Cartilage**, not hyaline cartilage. Elastic cartilage is characterized by a dense network of branching elastic fibers (elastin) within its matrix, providing the flexibility and structural resilience required for the ear to maintain its shape after being bent. **2. Analysis of Incorrect Options:** * **Costal Cartilage:** These connect the ribs to the sternum and are classic examples of hyaline cartilage. They provide semi-rigid support and allow for chest wall expansion. * **Thyroid Cartilage:** Most of the laryngeal cartilages (Thyroid, Cricoid, and the base of Arytenoids) are **Hyaline**. Note: The Epiglottis and the tips of the Arytenoids are Elastic. * **Foetal Skeleton:** Hyaline cartilage serves as the temporary "model" for the embryonic skeleton before it undergoes endochondral ossification to become bone [2]. **3. High-Yield Clinical Pearls for NEET-PG:** * **Hyaline Cartilage (Most Common):** Found in Articular surfaces (except TMJ), Tracheal rings, Bronchi, Larynx (Thyroid/Cricoid), and Nasal septum. It contains Type II Collagen [1]. * **Elastic Cartilage (The "E" Rule):** Found in **E**xternal ear, **E**ustachian tube, and **E**piglottis. * **Fibrocartilage (Strongest):** Found in Intervertebral discs, Pubic symphysis, and Menisci. It contains Type I Collagen. * **Calcification:** Hyaline and Fibrocartilage can calcify with age; Elastic cartilage **never** calcifies. * **Articular Cartilage:** A unique type of hyaline cartilage that lacks a perichondrium [1].

Question 107: Which marker is indicative of myeloid malignancies?

A. S100
B. HMB45
C. Common leukocyte antigen (Correct Answer)
D. Cytokeratin

Explanation: The correct answer is **Common Leukocyte Antigen (CLA)**, also known as **CD45**. ### **Explanation** **Common Leukocyte Antigen (CD45)** is a transmembrane protein tyrosine phosphatase expressed on almost all hematolymphoid cells, including granulocytes, monocytes, and lymphocytes. In the context of Immunohistochemistry (IHC), CD45 is the primary screening marker used to differentiate **hematologic malignancies** (like myeloid leukemias or lymphomas) from non-hematologic tumors (carcinomas or sarcomas). Since myeloid cells are of leukocyte lineage, they stain positive for CLA. ### **Analysis of Incorrect Options** * **S100:** This is a marker for cells derived from the **neural crest**. It is highly sensitive for **Melanoma**, Schwannomas, and Neurofibromas. It is also found in Langerhans cell histiocytosis. * **HMB45:** This is a highly specific marker for **Melanoma**. It reacts against gp100, a protein found in melanosomes. It is not expressed in myeloid cells. * **Cytokeratin:** This is the hallmark marker for **Epithelial cells**. It is used to diagnose **Carcinomas**. Myeloid cells, being mesenchymal/hematopoietic in origin, are cytokeratin-negative. ### **High-Yield NEET-PG Pearls** * **CD45 (CLA):** The "Pan-leukocyte" marker. If a tumor is CD45+, think Lymphoma/Leukemia. * **Specific Myeloid Markers:** While CLA is a general marker, more specific markers for myeloid differentiation include **Myeloperoxidase (MPO)**, **CD13**, **CD33**, and **CD117** (c-kit). * **Vimentin:** The general marker for **Mesenchymal tumors** (Sarcomas). * **Desmin:** Marker for **Muscle** tumors (Rhabdomyosarcoma/Leiomyosarcoma).

Question 108: In the treatment of varicocele, at what level is the testicular vein ligated?

A. Above the inguinal ligament (Correct Answer)
B. Below the inguinal ligament
C. At the neck of the sac
D. In the scrotum

Explanation: The surgical treatment of varicocele (Palomo’s or Ivanissevich procedure) involves the high ligation of the testicular (spermatic) veins. **Why "Above the Inguinal Ligament" is correct:** The testicular vein originates from the pampiniform plexus in the scrotum. As it ascends through the inguinal canal, it consists of multiple anastomosing branches. However, **above the internal inguinal ring** (retroperitoneally, above the inguinal ligament), these branches usually coalesce into one or two main trunks. Ligating the vein at this higher level is preferred because it ensures all collateral venous channels contributing to the varicocele are intercepted, significantly reducing the risk of recurrence. **Analysis of Incorrect Options:** * **Below the inguinal ligament:** At this level (within the inguinal canal or just outside the external ring), the veins are numerous and thin-walled. Ligating here increases the risk of missing small collateral branches and carries a higher risk of accidental injury to the testicular artery or vas deferens. * **At the neck of the sac:** This terminology refers to inguinal hernia repair, not the standard anatomical landmark for varicocele ligation. [1] * **In the scrotum:** Ligation here is avoided due to the extreme complexity of the pampiniform plexus and the high risk of postoperative hematoma and testicular atrophy. **High-Yield Clinical Pearls for NEET-PG:** * **Anatomy:** The **Left** testicular vein drains into the **Left Renal Vein** at a right angle (explaining why varicoceles are more common on the left). The **Right** testicular vein drains directly into the **IVC**. * **"Bag of Worms":** The classic clinical description of a varicocele. * **Complication:** The most common complication of high ligation is **hydrocele** (due to accidental ligation of lymphatic vessels). * **Sudden Right-sided Varicocele:** In an older patient, this is a red flag for **Renal Cell Carcinoma (RCC)** obstructing the IVC.

Question 109: Stave cells are seen in which organ?

A. Liver
B. Spleen (Correct Answer)
C. Pancreas
D. Gall bladder

Explanation: Stave cells are specialized endothelial cells found exclusively in the Spleen [1]. They line the walls of the splenic sinusoids (venous sinuses) in the red pulp. 1. Why Spleen is correct: Stave cells are elongated, spindle-shaped cells arranged longitudinally like the wooden staves of a barrel. They are supported by incomplete basement membranes and transverse reticular fibers (hoops). This unique "slat-like" arrangement creates narrow intercellular slits. For older or damaged red blood cells (RBCs) to return to circulation, they must undergo extreme deformation to squeeze through these slits [1]. This serves as a mechanical filter; rigid or parasitized RBCs (e.g., in Spherocytosis or Malaria) fail to pass and are subsequently removed by splenic macrophages [1]. 2. Why other options are incorrect: - Liver: Contains Kupffer cells (macrophages) and Ito cells (fat-storing cells), but the sinusoids are lined by typical fenestrated endothelium, not stave cells [2]. - Pancreas: Characterized by acini (exocrine) and Islets of Langerhans (endocrine). It does not possess a filtration sinusoidal system. - Gall bladder: Lined by simple columnar epithelium with microvilli (striated border) for bile concentration; it lacks sinusoids. High-Yield Clinical Pearls for NEET-PG: - Open vs. Closed Circulation: Stave cells are the "gatekeepers" in the open circulation model of the splenic red pulp. - Culling and Pitting: The process of removing aged RBCs is "culling," while removing inclusions (like Heinz bodies) without destroying the cell is "pitting"—both occur at the stave cell interface [1]. - Littoral Cells: Another name sometimes used for these specialized lining cells of the splenic sinusoids.

Question 110: Capillary invasion of corpus luteum begins?

A. One day after ovulation
B. 2 days after ovulation (Correct Answer)
C. 3 days after ovulation
D. 4 days after ovulation

Explanation: The formation of the **Corpus Luteum** is a dynamic process involving the transformation of the ruptured Graafian follicle. Following ovulation (Day 14 of a typical cycle), the basement membrane between the granulosa and theca cells breaks down. **Why Option B is correct:** The process of **luteinization** begins immediately after ovulation, but significant **vascularization (capillary invasion)** specifically occurs on **Day 2 after ovulation** (Day 16 of the cycle). Angiogenic factors (like VEGF) stimulate the vessels from the theca interna to sprout and invade the granulosa layer, which was previously avascular. This rapid vascularization is essential to deliver cholesterol to the lutein cells for the massive production of progesterone. **Analysis of Incorrect Options:** * **Option A (1 day after):** On the first day, the follicle collapses and forms the *corpus hemorrhagicum*. While the basement membrane begins to disrupt, the organized invasion of capillaries is not yet established. * **Option C & D (3 & 4 days after):** By this time, the capillary network is already well-established. The peak vascularity and peak progesterone production usually occur around Day 7–8 post-ovulation (Day 21–22 of the cycle). **NEET-PG High-Yield Pearls:** * **Granulosa Lutein Cells:** Derived from granulosa cells; produce Progesterone and Inhibin A. * **Theca Lutein Cells:** Derived from theca interna; produce Estrogen and Androgens. * **Life Span:** If fertilization does not occur, the corpus luteum degenerates into the **Corpus Albicans** after approximately 14 days due to a drop in LH. * **HCG Role:** If pregnancy occurs, HCG (produced by syncytiotrophoblast) rescues the corpus luteum to maintain progesterone levels until the placenta takes over (around 8–10 weeks). [1]

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Histology — MCQs

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