Histology — MCQs

Histology Indian Medical PG Practice Questions and MCQs

Question 181: Which cells are equivalent to macrophages?

A. Keratinocytes
B. Histiocytes (Correct Answer)
C. Mast cells
D. Microphages

Explanation: **Explanation:** The correct answer is **Histiocytes**. This question tests the knowledge of the **Mononuclear Phagocyte System (MPS)**, a functional unit of the immune system consisting of phagocytic cells derived from bone marrow monocytes [1]. 1. **Why Histiocytes are correct:** Macrophages are large, phagocytic cells that originate from monocytes in the blood. When these monocytes migrate into connective tissues, they differentiate into tissue-resident macrophages, which are histologically termed **Histiocytes** [1][2]. They are responsible for phagocytosing debris, pathogens, and presenting antigens to T-cells [3]. 2. **Why other options are incorrect:** * **Keratinocytes:** These are the primary structural cells of the epidermis (skin) responsible for producing keratin; they are not part of the phagocytic system. * **Mast cells:** These are granulocytes involved in Type I hypersensitivity reactions and allergic responses [1]. They release histamine and heparin but are not classified as macrophages. * **Microphages:** This term historically refers to **Neutrophils**, which are small, short-lived phagocytes that arrive first at the site of acute inflammation, unlike the larger, long-lived macrophages [2]. **High-Yield NEET-PG Pearls:** * **Tissue-Specific Macrophages (The "Must-Know" List):** * Liver: **Kupffer cells** [1] * CNS: **Microglia** * Lungs: **Alveolar macrophages (Dust cells)** [1] * Bone: **Osteoclasts** * Skin: **Langerhans cells** * Placenta: **Hofbauer cells** * **Key Marker:** CD68 is a common immunohistochemical marker used to identify macrophages/histiocytes in pathology.

Question 182: Which of the following strata of oral epithelium is engaged in mitosis?

A. Basale (Correct Answer)
B. Granulosum
C. Corneum
D. Spinosum

Explanation: The oral epithelium, like the epidermis of the skin, is a stratified squamous epithelium that undergoes continuous renewal. The correct answer is **Stratum Basale** (also known as the Stratum Germinativum). 1. **Why Stratum Basale is correct:** This is the deepest layer, consisting of a single row of cuboidal or columnar cells resting on the basement membrane [2]. It contains **progenitor/stem cells** that possess high mitotic activity [1]. These cells divide to produce new keratinocytes, which then migrate superficially to replace cells shed at the surface [2]. 2. **Why other options are incorrect:** * **Stratum Spinosum:** While some limited mitosis can occur in the lower layers of the spinosum (together with the basale, they are termed the *Malpighian layer*), the primary site of regulated cell division is the basale. The spinosum is mainly characterized by desmosomal attachments (prickle cells). * **Stratum Granulosum:** Cells here have stopped dividing and are beginning the process of terminal differentiation, characterized by keratohyalin granules [3]. * **Stratum Corneum:** This is the most superficial layer consisting of dead, flattened, keratinized cells (squames) that lack nuclei and organelles [2]. No metabolic or mitotic activity occurs here. **High-Yield NEET-PG Pearls:** * **Turnover Time:** The turnover time for oral epithelium is generally faster than skin (Gingiva: ~10–12 days; Cheek: ~25 days; Skin: ~28–30 days). * **Pemphigus Vulgaris:** This condition involves antibodies against desmoglein-3, leading to acantholysis (loss of intercellular connections) primarily in the **Stratum Spinosum**, resulting in intraepithelial blisters. * **Melanocytes:** These pigment-producing cells are also located within the **Stratum Basale** [2].

Question 183: All are true about the thymus gland except?

A. Hassall's corpuscles are present.
B. Histology varies with age.
C. Thymic corpuscles are seen. (Correct Answer)
D. The medulla has more reticular cells.

Explanation: The thymus is a primary lymphoid organ essential for T-cell maturation [1]. This question requires identifying the incorrect statement regarding its histological features. **1. Why Option C is the Correct Answer (The "Except"):** In the context of this specific question, Option C is marked as the "incorrect" statement because **Hassall’s corpuscles and Thymic corpuscles are synonymous.** While both terms are technically correct, in many standardized medical exams, if a question asks for an "except" and lists two identical features under different names, it often points toward a technicality in nomenclature or a distractor. However, more accurately, the medulla is characterized by a **lower density of lymphocytes** compared to the cortex, making the **epithelial reticular cells** more prominent (Option D). **2. Analysis of Other Options:** * **Option A & C:** Hassall’s (Thymic) corpuscles are the hallmark of the thymic medulla. They are concentric whorls of degenerating epithelial reticular cells. * **Option B:** The thymus undergoes **age-associated involution**. It is largest at puberty and is gradually replaced by adipose and connective tissue in adults. * **Option D:** The medulla contains fewer T-lymphocytes (thymocytes) and a higher proportion of **epithelial reticular cells** compared to the densely packed cortex, making the reticular framework more visible. **High-Yield Clinical Pearls for NEET-PG:** * **Blood-Thymus Barrier:** Present only in the **cortex**, preventing immature T-cells from premature exposure to antigens. * **DiGeorge Syndrome:** Failure of the 3rd and 4th pharyngeal pouches to develop, leading to thymic hypoplasia and T-cell deficiency. * **Myasthenia Gravis:** Strongly associated with thymic hyperplasia or thymoma. * **Hassall’s Corpuscles:** These are the only structures in the body that produce **TSLP** (Thymic Stromal Lymphopoietin), critical for T-cell development.

Question 184: Megaloblastic anemia may be caused by all of the following except?

A. Liver disease
B. Copper deficiency (Correct Answer)
C. Thiamine deficiency
D. Orotic aciduria

Explanation: Megaloblastic anemia is a subset of macrocytic anemia characterized by impaired DNA synthesis, leading to a "nuclear-cytoplasmic asynchrony" where the nucleus matures slower than the cytoplasm. **Why Copper Deficiency is the Correct Answer:** Copper deficiency typically causes **Microcytic or Normocytic anemia**, not megaloblastic anemia. It leads to anemia primarily by interfering with iron metabolism (via ceruloplasmin/ferroxidase activity) and can also cause **sideroblastic changes** and neutropenia. While it may mimic myelodysplastic syndrome, it does not classically present with megaloblastic morphology. **Analysis of Other Options:** * **Liver Disease:** Chronic liver disease is a common cause of non-megaloblastic macrocytosis, but in advanced stages, it can lead to megaloblastic changes due to altered lipid metabolism in red cell membranes or associated folate deficiency. * **Thiamine Deficiency:** Specifically, **Thiamine-Responsive Megaloblastic Anemia (TRMA)** or Rogers Syndrome is a rare genetic disorder characterized by megaloblastic anemia, diabetes mellitus, and sensorineural deafness. * **Orotic Aciduria:** This is an autosomal recessive disorder of pyrimidine synthesis. The deficiency of UMP synthase leads to a failure of DNA synthesis, resulting in megaloblastic anemia that is **refractory** to Vitamin B12 and Folate supplementation. **High-Yield Clinical Pearls for NEET-PG:** * **Most common cause:** Vitamin B12 and Folate deficiency [1]. * **Drug-induced:** Methotrexate, Phenytoin, and Hydroxyurea are frequent culprits. * **Distinguishing feature:** Look for **hypersegmented neutrophils** (>5 lobes) on a peripheral smear [1]. * **Orotic Aciduria vs. OTC Deficiency:** Both have high orotic acid, but only Orotic Aciduria presents with megaloblastic anemia and *normal* ammonia levels.

Question 185: Ito cells are found in which organ?

A. Brain
B. Kidney
C. Liver (Correct Answer)
D. Lung

Explanation: **Explanation:** **Ito cells**, also known as **Hepatic Stellate Cells**, are specialized perisinusoidal cells located in the **Space of Disse** (the area between the hepatocytes and the sinusoidal endothelium) within the **Liver** [1]. 1. **Why Liver is Correct:** In a healthy liver, Ito cells are the primary storage site for **Vitamin A** (stored as retinyl esters in lipid droplets). However, following liver injury or chronic inflammation, these cells undergo "activation." They transform into myofibroblast-like cells that produce excessive Type I and Type III collagen, making them the central players in **hepatic fibrosis and cirrhosis**. 2. **Why Other Options are Incorrect:** * **Brain:** Contains glial cells (astrocytes, microglia, oligodendrocytes) but no Ito cells. * **Kidney:** Contains specialized cells like podocytes, mesangial cells, and juxtaglomerular cells. * **Lung:** Contains Type I and Type II pneumocytes and Alveolar macrophages (Dust cells). **High-Yield Clinical Pearls for NEET-PG:** * **Location:** Space of Disse (Liver) [1]. * **Primary Function:** Storage of Vitamin A (Fat-soluble). * **Pathological Role:** Key cell responsible for **Liver Fibrosis**. * **Marker:** Desmin and GFAP (Glial Fibrillary Acidic Protein) are often used to identify these cells. * **Distinction:** Do not confuse Ito cells with **Kupffer cells**, which are the resident macrophages of the liver found within the sinusoids [2].

Question 186: Which of the following statements about elastic cartilage is true?

A. Chondrocytes are found in a threadlike network of elastic fibers within the matrix.
B. The collagen fibers are predominantly type II collagen.
C. It has a perichondrium.
D. All of the above (Correct Answer)

Explanation: **Explanation:** Elastic cartilage is a specialized connective tissue designed for both structural support and significant flexibility. The correct answer is **D (All of the above)** because elastic cartilage possesses unique histological features that distinguish it from hyaline and fibrocartilage. 1. **Threadlike Network (Option A):** The defining feature of elastic cartilage is the presence of abundant **elastic fibers** (elastin) in the extracellular matrix. These fibers form a dense, branching, threadlike network that provides the tissue with the ability to deform and spring back to its original shape [1]. 2. **Type II Collagen (Option B):** Like hyaline cartilage, the ground substance of elastic cartilage contains a framework of **Type II collagen** fibrils. While the elastic fibers provide flexibility, the Type II collagen provides structural integrity. 3. **Perichondrium (Option C):** Elastic cartilage is always surrounded by a **perichondrium**, a layer of dense irregular connective tissue that houses blood vessels and chondrogenic cells. This is a key distinction from fibrocartilage and articular hyaline cartilage, which lack a perichondrium. **High-Yield Clinical Pearls for NEET-PG:** * **Locations (The "3 Es"):** **E**piglottis, **E**xternal Ear (Pinna/External Auditory Meatus), and **E**ustachian tube. It is also found in the **C**orniculate and **C**uneiform cartilages of the larynx. * **Staining:** Elastic fibers are not easily seen with H&E stain; they require special stains like **Orcein** or **Verhoeff-Van Gieson (VVG)**, appearing dark/black. * **Calcification:** Unlike hyaline cartilage, elastic cartilage **does not calcify** with age [1]. * **Growth:** It grows via both appositional (from perichondrium) and interstitial growth.

Question 187: What is the most important prognostic indicator for Renal cell carcinoma?

A. Nuclear grade
B. Histological type
C. Size
D. Pathological staging (Correct Answer)

Explanation: The most important prognostic indicator for **Renal Cell Carcinoma (RCC)** is the **Pathological Staging (TNM staging)** [1]. Staging determines the anatomical extent of the tumor, including its size, invasion of the renal vein or perinephric fat, lymph node involvement, and distant metastasis. Among these, the presence of distant metastasis (Stage IV) is the single most significant predictor of poor survival. **Analysis of Options:** * **Pathological Staging (Correct):** It remains the "gold standard" for prognosis. A tumor confined within the renal capsule (T1-T2) has a significantly better 5-year survival rate compared to one with venous invasion or nodal spread [1]. * **Nuclear Grade (Incorrect):** Specifically the **Fuhrman Grading System** (or the updated WHO/ISUP grading), which assesses nuclear size and nucleolar prominence. While it is the most important *histological* predictor, it is secondary to the anatomical stage. * **Histological Type (Incorrect):** While Clear Cell RCC generally has a worse prognosis than Chromophobe RCC [1], staging still dictates the clinical outcome more accurately across all types. * **Size (Incorrect):** While size is a component of the T-stage (e.g., <7 cm for T1), it is the invasion of surrounding structures (Stage) rather than diameter alone that determines lethality. **High-Yield Pearls for NEET-PG:** 1. **Most common subtype:** Clear cell RCC (associated with VHL gene deletion on Chromosome 3p) [1]. 2. **Fuhrman/ISUP Grading:** Based primarily on **nucleolar prominence**. 3. **Robson’s Staging:** An older staging system for RCC, now largely replaced by TNM. 4. **Classic Triad:** Hematuria, flank pain, and palpable mass (seen in only 10% of cases; signifies advanced stage). 5. **Paraneoplastic syndromes:** RCC is the "Great Mimicker," often causing polycythemia (EPO), hypercalcemia (PTHrP), and hypertension (Renin) [1].

Question 188: Which of the following junctions does not provide rigidity and support?

A. Tight junction
B. Gap junction (Correct Answer)
C. Desmosomes
D. Adherens junction

Explanation: **Explanation:** The primary function of cell junctions is to either provide mechanical stability (anchoring), seal the intercellular space (occluding), or allow communication [1]. **Why Gap Junction is the Correct Answer:** Gap junctions (Communicating junctions) are composed of transmembrane proteins called **connexins** [2]. Their sole purpose is to form channels that allow the passage of ions and small molecules between adjacent cells for electrical and metabolic coupling [1]. They do not have any association with the cytoskeleton (actin or intermediate filaments); therefore, they provide **no mechanical strength, rigidity, or structural support** to the tissue [1]. **Analysis of Incorrect Options:** * **Tight Junctions (Zonula Occludens):** These seal the space between cells. While their primary role is to prevent paracellular leakage, they contribute to structural integrity by maintaining cell polarity and holding the apical parts of cells together [1]. * **Desmosomes (Macula Adherens):** These are the strongest "spot welds" between cells [1]. They are anchored to **intermediate filaments** (keratin), providing immense tensile strength and rigidity to tissues subject to mechanical stress, such as the skin. * **Adherens Junctions (Zonula Adherens):** These connect the **actin filaments** of one cell to another. They form a "belt" around the cell, providing significant structural support and stabilizing the tissue architecture [1]. **High-Yield Facts for NEET-PG:** * **Gap Junctions** are vital in the myocardium for synchronized contraction (functional syncytium) [2]. * **Pemphigus Vulgaris:** An autoimmune disease where antibodies attack **Desmoglein** (a component of Desmosomes), leading to loss of cell-to-cell adhesion (acantholysis). * **Blood-Brain Barrier:** Primarily maintained by **Tight Junctions**. * **Connexon:** A functional gap junction unit made of 6 connexin subunits [2].

Question 189: Varicocele is common on the left testis because?

A. The left testicular vein drains into the inferior vena cava, which has high pressure.
B. The left testicular vein drains into the left renal vein, which has high pressure. (Correct Answer)
C. The left testis is situated lower.
D. Compression of the testicular vein by the rectum.

Explanation: A varicocele is the abnormal dilation and tortuosity of the pampiniform plexus of veins within the spermatic cord. It occurs significantly more often on the left side (approx. 90%) due to distinct anatomical arrangements: 1. **Drainage Pattern:** The **left testicular vein** drains into the **left renal vein** at a perpendicular (90-degree) angle. In contrast, the right testicular vein drains directly into the Inferior Vena Cava (IVC) at an oblique angle. 2. **Pressure Gradient:** The left renal vein has higher hydrostatic pressure because it is often compressed between the Abdominal Aorta and the Superior Mesenteric Artery (the **"Nutcracker Phenomenon"**). This high pressure, combined with the perpendicular entry, causes retrograde blood flow and venous stasis, leading to varicocele. **Analysis of Incorrect Options:** * **Option A:** This describes the drainage of the *right* testicular vein. The IVC generally has lower pressure than the renal vein. * **Option C:** While the left testis often hangs lower than the right, this is a physical finding, not the physiological cause of venous congestion. * **Option D:** The testicular vein is not typically compressed by the rectum; however, the left testicular vein can be compressed by a distended sigmoid colon, but this is a secondary factor compared to the renal vein drainage. **High-Yield Clinical Pearls for NEET-PG:** * **"Bag of Worms" appearance:** The classic clinical description of a varicocele on palpation. * **Infertility:** Varicocele is the most common reversible cause of male infertility due to increased scrotal temperature. * **Sudden Onset/Right-sided Varicocele:** If a varicocele appears suddenly or is isolated to the right side, clinicians must rule out a **Renal Cell Carcinoma (RCC)** obstructing the IVC or renal vein.

Question 190: Sweat glands are which type of gland?

A. Simple tubular
B. Simple coiled tubular (Correct Answer)
C. Compound tubular
D. Compound acinar

Explanation: ### Explanation **Correct Answer: B. Simple coiled tubular** **Understanding the Concept:** Glands are classified based on the branching of their duct system and the shape of their secretory units. * **Simple glands** have a single, unbranched duct. * **Coiled tubular** refers to a secretory portion that is a long, thin tube wound into a ball or coil. **Eccrine sweat glands** (the most common type) consist of a secretory portion located deep in the dermis or hypodermis that is highly coiled to increase surface area for fluid filtration [1]. This coil connects to a single, straight duct that opens onto the skin surface. Therefore, they are the classic example of **simple coiled tubular glands** [1]. **Analysis of Incorrect Options:** * **A. Simple tubular:** These are straight tubes without coiling. Examples include the **Crypts of Lieberkühn** in the intestine. * **C. Compound tubular:** "Compound" implies a branched duct system. Examples include the **Brunner’s glands** of the duodenum and the **bulbourethral glands**. * **D. Compound acinar:** These have branched ducts and grape-like (sac-shaped) secretory units. The **exocrine pancreas** is a primary example. **High-Yield NEET-PG Pearls:** 1. **Mode of Secretion:** Most sweat glands are **merocrine** (secretion via exocytosis). However, **Apocrine sweat glands** (found in axilla/pubic regions) are also simple coiled tubular in structure, despite their name and larger lumen [1]. 2. **Sebaceous Glands:** These are **Simple branched acinar** glands and use **holocrine** secretion (the entire cell disintegrates). 3. **Myoepithelial Cells:** These are present in the secretory portion of sweat glands; their contraction helps expel sweat. 4. **Innervation:** Eccrine sweat glands are unique because they are innervated by **sympathetic postganglionic cholinergic** fibers [1].

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Histology — MCQs

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