Histology — MCQs

Histology Indian Medical PG Practice Questions and MCQs

Question 271: Which cells in the gastrointestinal tract sample antigens to Peyer's patches?

A. Microfold cells (Correct Answer)
B. G cells
C. Langerhans cells
D. T cells

Explanation: ### Explanation **Correct Answer: A. Microfold cells (M cells)** **Mechanism:** Microfold cells (M cells) are specialized epithelial cells located within the **Follicle-Associated Epithelium (FAE)** that overlies Peyer’s patches in the ileum [2]. Unlike typical enterocytes, M cells lack a well-developed brush border (microvilli) and a thick glycocalyx. Their primary function is **transcytosis**: they sample luminal antigens, bacteria, and viruses, transporting them across the epithelial barrier to underlying dendritic cells and lymphocytes within the Peyer’s patch [2]. This initiates the mucosal immune response. **Analysis of Incorrect Options:** * **B. G cells:** These are enteroendocrine cells located primarily in the antrum of the stomach. They secrete **gastrin**, which stimulates gastric acid secretion, but they do not have an immune-sampling role [1]. * **C. Langerhans cells:** These are dendritic (antigen-presenting) cells found in the **stratum spinosum of the epidermis** and squamous epithelium (e.g., esophagus). While they sample antigens, they are not the primary cells associated with Peyer's patches in the intestinal mucosa. * **D. T cells:** These are effector lymphocytes of the adaptive immune system. While T cells are found *within* Peyer’s patches to receive presented antigens, they do not perform the initial sampling/transport from the intestinal lumen [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Pathogen Entry:** Certain pathogens exploit M cells as a portal of entry into the body, most notably ***Salmonella typhi***, *Shigella*, and Poliovirus [2]. * **Histology:** M cells are characterized by a "pocket" on their basolateral surface which houses B-lymphocytes, T-lymphocytes, and macrophages. * **Peyer’s Patches:** These are macroscopic lymphoid aggregates found predominantly in the **lamina propria and submucosa of the ileum** [1]. They are a key component of GALT (Gut-Associated Lymphoid Tissue).

Question 272: Which one of the following statements concerning Loose Connective Tissue is true?

A. It is less abundant than Dense Connective Tissue.
B. It has a lower proportion of cells to fibers than does Dense Connective Tissue.
C. It acts as a medium for exchange of nutrients and wastes between the blood and tissues. (Correct Answer)
D. It provides structural support for organs.

Explanation: ### Explanation **Correct Answer: C. It acts as a medium for exchange of nutrients and wastes between the blood and tissues.** **1. Why Option C is Correct:** Loose Connective Tissue (also known as **Areolar Tissue**) is characterized by a high proportion of **ground substance** relative to fibers. This ground substance is a viscous, gel-like matrix rich in glycosaminoglycans (GAGs) and water. Because it is highly vascularized and contains a large volume of interstitial fluid, it serves as the primary site for the diffusion of oxygen, nutrients, and metabolic wastes between the capillaries and the parenchymal cells of organs [1]. **2. Why Other Options are Incorrect:** * **Option A:** Loose connective tissue is actually the **most abundant** type of connective tissue in the body, found beneath almost every epithelium and surrounding most blood vessels and nerves. * **Option B:** Loose connective tissue has a **higher proportion of cells** (such as fibroblasts, macrophages, and mast cells) and a **lower proportion of fibers** (collagen, elastic, and reticular) compared to dense connective tissue, which is dominated by tightly packed collagen fibers. * **Option D:** While it provides a flexible framework, **structural support** is the primary function of **Dense Connective Tissue** (regular/irregular) or specialized tissues like bone and cartilage, which are designed to resist mechanical stress [2]. **3. NEET-PG High-Yield Clinical Pearls:** * **Site of Inflammation:** Loose connective tissue is the primary site where immune cells (leukocytes) leave the blood to fight pathogens. It is the major site for **inflammatory and immune responses** [1]. * **Lamina Propria:** The loose connective tissue found beneath the epithelial lining of the digestive and respiratory tracts is specifically called the *lamina propria*. * **Edema:** Because of its loose nature and high ground substance content, this tissue is the most common site for the accumulation of excess interstitial fluid, leading to **edema**.

Question 273: Which one of the following statements concerning liver sinusoids is true?

A. Their lining includes Ito cells.
B. They receive bile from the hepatocytes.
C. They are lined by fenestrated endothelial cells.
D. The space of Disse is located between sinusoidal cells and hepatocytes. (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. The space of Disse is located between sinusoidal cells and hepatocytes.** The **Space of Disse** (perisinusoidal space) is a narrow gap located between the fenestrated endothelium of the liver sinusoids and the microvilli-covered surface of the hepatocytes [1]. It is a crucial site for metabolic exchange between the blood and the liver cells [1]. It contains the blood plasma that filters through the sinusoidal fenestrae, allowing hepatocytes to absorb nutrients and secrete proteins (like albumin) directly into the plasma. **Analysis of Incorrect Options:** * **A. Their lining includes Ito cells:** Ito cells (Stellate cells) are located **within the Space of Disse**, not in the sinusoidal lining. Their primary role is Vitamin A storage; however, in chronic liver injury, they transform into myofibroblasts and produce collagen, leading to liver fibrosis. * **B. They receive bile from the hepatocytes:** This is anatomically incorrect. Hepatocytes secrete bile into **bile canaliculi** [4], which flow in the opposite direction of sinusoidal blood (centrifugal vs. centripetal flow) [3]. Sinusoids carry a mixture of portal venous and hepatic arterial blood [2]. * **C. They are lined by fenestrated endothelial cells:** While liver sinusoids are indeed lined by fenestrated endothelial cells, these cells are unique because they **lack a continuous basal lamina** (basement membrane) [1]. This lack of a basement membrane is a high-yield distinction that facilitates rapid exchange. **NEET-PG High-Yield Pearls:** * **Kupffer Cells:** These are specialized macrophages found **within** the sinusoidal lumen, attached to the endothelial surface. * **Blood Flow:** In a liver lobule, blood flows from the periphery (Portal triad) to the center (Central vein) [3]. * **Zone 3 of Rappaport:** The area around the central vein is most susceptible to ischemia and "nutmeg liver" changes in congestive heart failure [5].

Question 274: Anemia which is associated with pancytopenia is?

A. Hemolytic
B. Iron deficiency
C. Megaloblastic (Correct Answer)
D. All

Explanation: **Explanation:** **Megaloblastic Anemia** is the correct answer because it is characterized by a defect in **DNA synthesis**, most commonly due to Vitamin B12 or Folic acid deficiency [1]. This defect does not just affect red blood cells; it affects all rapidly dividing cells in the bone marrow. When DNA synthesis is impaired, the maturation of the nucleus lags behind the cytoplasm (**nuclear-cytoplasmic asynchrony**), leading to ineffective hematopoiesis. This results in the premature destruction of precursors within the marrow (intramedullary hemolysis), leading to a reduction in all three cell lines: anemia (RBCs), leukopenia (WBCs), and thrombocytopenia (platelets)—a condition known as **pancytopenia**. **Why other options are incorrect:** * **Hemolytic Anemia:** This involves the premature destruction of mature red blood cells in the peripheral circulation or spleen. While RBC counts drop, the bone marrow is typically hyperactive and compensates by increasing the production of WBCs and platelets. * **Iron Deficiency Anemia:** This is a defect in **hemoglobin synthesis** (heme part), not DNA synthesis. It specifically affects the erythroid lineage, leading to microcytic hypochromic anemia. Platelet counts are often normal or even elevated (reactive thrombocytosis). **NEET-PG High-Yield Pearls:** * **Peripheral Smear:** Look for **hypersegmented neutrophils** (early sign) [1] and macro-ovalocytes. * **Bone Marrow:** Shows "megaloblastic" changes with open, lacy chromatin [1]. * **Pancytopenia Differential:** Always consider Aplastic Anemia (hypocellular marrow) vs. Megaloblastic Anemia (hypercellular marrow). * **MCV:** Typically >100 fL in megaloblastic anemia.

Question 275: Halocrine secretion is characteristic of which type of gland?

A. Salivary gland
B. Mammary gland
C. Sebaceous gland (Correct Answer)
D. Gastric gland

Explanation: ### Explanation Glands are classified based on their **mode of secretion** (how the secretory product is released from the cell). **1. Why Sebaceous Gland is Correct:** **Holocrine secretion** (derived from the Greek *holos*, meaning "whole") occurs when the entire secretory cell matures, dies, and ruptures to release its contents. The **Sebaceous gland** is the classic example; the oily secretion (sebum) consists of the disintegrated remains of the glandular cells themselves. These cells are continuously replaced by rapid mitotic division of basal cells. **2. Analysis of Incorrect Options:** * **Salivary Glands (Merocrine):** These glands use exocytosis. The secretory vesicles fuse with the plasma membrane and release their contents without any loss of cellular cytoplasm or membrane. Most sweat glands and the pancreas also follow this mode. * **Mammary Glands (Apocrine):** In apocrine secretion, the apical portion of the cell cytoplasm is pinched off along with the secretory product. * **Gastric Glands (Merocrine):** Cells like Chief cells (pepsinogen) and Parietal cells (HCl) release their secretions via exocytosis (merocrine) without cell destruction. **3. High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Holocrine:** "**H**olocrine = **H**ole" (The whole cell is lost). * **Mnemonic for Apocrine:** "**A**pocrine = **A**pical" (Only the apex is lost). * **Clinical Correlation:** Acne vulgaris is a disorder of the pilosebaceous unit where holocrine debris and sebum become trapped, leading to inflammation. * **Meibomian Glands:** These are modified sebaceous glands in the tarsal plate of the eye and are also **holocrine**.

Question 276: All of the following are components of the white pulp of the spleen, except?

A. Periaeriolar lymphoid sheath
B. Lymphatic follicle
C. B lymphocytes
D. Vascular sinus (Correct Answer)

Explanation: The spleen is divided into two distinct functional regions: the **White Pulp** (immune function) and the **Red Pulp** (blood filtration) [1]. ### Why "Vascular Sinus" is the Correct Answer **Vascular sinuses** (or splenic sinusoids) are the hallmark of the **Red Pulp**. They are wide, thin-walled blood vessels lined by specialized "stave cells." Their primary role is to filter aged or damaged red blood cells from the circulation [1]. Since they are structural components of the red pulp, they are not found within the white pulp. ### Explanation of Incorrect Options (Components of White Pulp) The white pulp is organized around the **Central Artery** and consists of: * **A. Periarteriolar Lymphoid Sheath (PALS):** A cylindrical collection of lymphocytes surrounding the central artery. It is primarily composed of **T-lymphocytes**. * **B & C. Lymphatic Follicles and B-lymphocytes:** At intervals, the PALS expands to form lymphoid follicles (Malpighian corpuscles). These follicles are rich in **B-lymphocytes** and may contain germinal centers for antibody production. ### NEET-PG High-Yield Pearls * **Marginal Zone:** The boundary between red and white pulp. It is the site where antigen-presenting cells (macrophages and dendritic cells) capture blood-borne antigens. * **Open vs. Closed Circulation:** Humans primarily have "open circulation" where blood from penicillar arterioles empties into the splenic cords before entering the sinuses. * **Stave Cells:** The endothelial cells lining the vascular sinuses. They have slit-like gaps that act as a physical filter for RBCs (testing their deformability) [1]. * **PALS = T-cells; Follicles = B-cells.** (Memory aid: **P**ALS has **T**'s).

Question 277: What is the most abundant fibrillary collagen found in the basement membrane?

A. Type 1
B. Type 2
C. Type 3
D. Type 4 (Correct Answer)

Explanation: The correct answer is **Type 4 Collagen**. The basement membrane is a specialized form of extracellular matrix that underlies all epithelia and surrounds muscle cells and peripheral nerves [1]. Unlike fibrillar collagens that form long, rope-like structures, **Type 4 Collagen** is a **network-forming (non-fibrillar) collagen**. It forms a multi-layered, scaffold-like meshwork that provides structural support and acts as a selective filtration barrier. It is the primary structural component of the *lamina densa* within the basal lamina. **Analysis of Incorrect Options:** * **Type 1:** The most abundant collagen in the human body [2]. It forms thick fibers and is found in high-tension areas like **bone, skin, tendons, and late scars**. * **Type 2:** Primarily found in **cartilage** (hyaline and elastic) and the vitreous humor. It provides resistance to pressure. * **Type 3 (Reticulin):** Forms thin, branching fibers that create a supportive framework for highly cellular organs like the **liver, spleen, and lymph nodes**. It is also prominent in early wound healing (granulation tissue). **High-Yield Clinical Pearls for NEET-PG:** * **Goodpasture Syndrome:** Autoantibodies are directed against the alpha-3 chain of Type 4 Collagen, leading to glomerulonephritis and pulmonary hemorrhage. * **Alport Syndrome:** A genetic defect in Type 4 Collagen synthesis resulting in hereditary nephritis, sensorineural deafness, and ocular defects ("Can't see, can't pee, can't hear high C"). * **Mnemonic for Collagen Types:** * Type **1**: **B**one (and Skin) * Type **2**: **C**artilage * Type **3**: **R**eticular fibers * Type **4**: **F**loor (Basement membrane)

Question 278: Hyaline cartilage is located at all sites except?

A. Costal cartilage
B. Menisci of Knee joint (Correct Answer)
C. Articular cartilage
D. Epiphyseal plate

Explanation: ### Explanation The correct answer is **B. Menisci of Knee joint**. **1. Why Menisci of Knee joint is correct:** The menisci of the knee joint are composed of **Fibrocartilage**, not hyaline cartilage. Fibrocartilage is characterized by dense bundles of Type I collagen fibers, providing high tensile strength and shock absorption. It lacks a perichondrium and is found in areas subject to heavy pressure and stretch, such as the intervertebral discs, pubic symphysis, and intra-articular discs (menisci). **2. Why the other options are incorrect:** * **Costal cartilage (A):** These connect the ribs to the sternum and are classic examples of hyaline cartilage. * **Articular cartilage (C):** The smooth, glass-like surface covering the ends of bones in synovial joints is hyaline cartilage [1]. Note: It is unique because it lacks a perichondrium. * **Epiphyseal plate (D):** Also known as the growth plate, it consists of hyaline cartilage and is responsible for the longitudinal growth of long bones via endochondral ossification [2]. **3. High-Yield Clinical Pearls for NEET-PG:** * **Hyaline Cartilage:** Most common type; contains **Type II collagen** [1]. Locations include the nose, larynx (thyroid, cricoid), trachea, bronchi, and fetal skeleton [2]. * **Elastic Cartilage:** Contains Type II collagen + Elastic fibers. Locations (The "E"s): **E**xternal ear, **E**ustachian tube, and **E**piglottis. * **Fibrocartilage:** Contains **Type I collagen**. It is the strongest type of cartilage. * **Regeneration:** Cartilage has limited repair capacity because it is **avascular** (receives nutrients via diffusion) [1].

Question 279: What is the most common presenting sign of carcinoma of the urinary bladder?

A. Dysuria
B. Hematuria (Correct Answer)
C. Frequency
D. Abdominal lump

Explanation: **Explanation:** **Carcinoma of the urinary bladder** (most commonly Urothelial/Transitional Cell Carcinoma) typically presents in older adults, often with a history of smoking or occupational exposure to aniline dyes. **1. Why Hematuria is Correct:** The hallmark clinical presentation of bladder cancer is **painless, gross (macroscopic) hematuria** throughout the urinary stream. This occurs because the neoplastic tissue is highly vascular and friable; as the tumor grows, surface vessels rupture easily, leading to bleeding into the bladder lumen. In NEET-PG, any elderly patient presenting with painless hematuria should be considered to have a malignancy until proven otherwise. **2. Analysis of Incorrect Options:** * **A & C (Dysuria and Frequency):** These are symptoms of bladder irritation (cystitis). While they can occur if the tumor is large, necrotic, or associated with an infection, they are secondary symptoms and far less common as the *initial* presenting sign compared to hematuria. * **D (Abdominal Lump):** A palpable mass is a late-stage finding indicating advanced, muscle-invasive disease or regional spread. It is rarely the presenting sign in early-stage carcinoma. **3. NEET-PG High-Yield Pearls:** * **Gold Standard Investigation:** Cystoscopy with biopsy is the definitive diagnostic tool. * **Most Common Type:** Transitional Cell Carcinoma (TCC) / Urothelial Carcinoma (>90%). * **Risk Factors:** Smoking (most common), exposure to 2-Naphthylamine (aniline dyes), and *Schistosoma haematobium* (specifically associated with **Squamous Cell Carcinoma**). * **Classic Triad:** Painless hematuria, frequency, and dysuria (though hematuria remains the most common).

Question 280: From which structure are fibroblasts derived?

A. Local mesenchyme (Correct Answer)
B. Macrophage
C. Endothelium
D. Vessels

Explanation: ### Explanation **Correct Option: A. Local mesenchyme** Fibroblasts are the most common cells found in connective tissue [3]. They are derived from **primitive mesenchymal cells** (undifferentiated mesoderm). Mesenchymal cells are multipotent stem cells that migrate throughout the developing embryo and differentiate into various connective tissue components, including fibroblasts, chondroblasts, osteoblasts, and adipocytes. In adults, fibroblasts primarily proliferate through local cell division or by the differentiation of resident mesenchymal stem cells in response to tissue injury (wound healing) [2]. **Why other options are incorrect:** * **B. Macrophage:** Macrophages are derived from **monocytes**, which originate in the bone marrow (hematopoietic lineage). While both are found in connective tissue, they have distinct lineages [2]. * **C. Endothelium:** Endothelial cells are specialized epithelial cells lining blood vessels. While they also share a mesodermal origin, they are a differentiated cell type and do not typically transform into fibroblasts under normal physiological conditions. * **D. Vessels:** Vessels are complex structures composed of endothelium, smooth muscle, and adventitia. While fibroblasts are found *within* the vessel wall (adventitia), the vessels themselves are not the progenitor source for fibroblasts. **High-Yield Clinical Pearls for NEET-PG:** * **Function:** Fibroblasts synthesize the extracellular matrix (ECM), including **collagen, elastin, and glycosaminoglycans** [1]. * **Myofibroblasts:** These are modified fibroblasts containing actin filaments (similar to smooth muscle) [4]. They are crucial for **wound contraction**. * **Active vs. Inactive:** Active cells are called **fibroblasts** (abundant cytoplasm, RER, and large nuclei), while inactive/resting cells are called **fibrocytes** (spindle-shaped, dark heterochromatic nuclei). * **Vitamin C:** Essential for the hydroxylation of proline and lysine during collagen synthesis by fibroblasts; deficiency leads to Scurvy (poor wound healing) [1].

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Histology — MCQs

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