Histology — MCQs

Histology Indian Medical PG Practice Questions and MCQs

Question 131: Which of the following pairs of structures have similar types of epithelium?

A. Alveoli and olfactory epithelium
B. Olfactory epithelium and skin
C. Esophagus and urinary bladder
D. Lung alveoli and Bowman's capsule (Correct Answer)

Explanation: ### Explanation The correct answer is **D. Lung alveoli and Bowman's capsule**. Both structures are lined by **Simple Squamous Epithelium**. #### 1. Why the Correct Answer is Right Simple squamous epithelium consists of a single layer of flat, scale-like cells [2]. This morphology is ideal for sites where **rapid diffusion or filtration** is required. * **Lung Alveoli:** The thin barrier (Type I pneumocytes) allows for efficient gas exchange between the air and blood [1], [2]. * **Bowman’s Capsule:** The parietal layer is composed of simple squamous cells, facilitating the filtration of blood into the nephron. #### 2. Analysis of Incorrect Options * **A. Alveoli and Olfactory Epithelium:** Alveoli are simple squamous, whereas olfactory epithelium is **Pseudostratified Ciliated Columnar Epithelium** (specialized sensory type) [2]. * **B. Olfactory Epithelium and Skin:** Olfactory epithelium is pseudostratified columnar, while skin (epidermis) is **Keratinized Stratified Squamous Epithelium**, designed for protection against mechanical stress and dehydration. * **C. Esophagus and Urinary Bladder:** The esophagus is lined by **Non-keratinized Stratified Squamous Epithelium** (for protection during swallowing), while the urinary bladder is lined by **Transitional Epithelium (Urothelium)**, which allows for distension. #### 3. High-Yield Clinical Pearls for NEET-PG * **Endothelium vs. Mesothelium:** Both are simple squamous. Endothelium lines blood vessels; Mesothelium lines serous cavities (pleura, pericardium, peritoneum). * **Microvilli vs. Cilia:** Remember that the **Proximal Convoluted Tubule (PCT)** has a "brush border" (microvilli) for absorption, while the **Fallopian tube** has cilia for ovum transport. * **Metaplasia:** In chronic smokers, the ciliated columnar epithelium of the airways can undergo **squamous metaplasia**, a common high-yield pathology concept [2].

Question 132: The presence of small-sized platelets on the peripheral smear is characteristic of which of the following conditions?

A. Idiopathic thrombocytopenic purpura
B. Bernard-Soulier syndrome
C. Disseminated intravascular coagulation
D. Wiskott-Aldrich syndrome (Correct Answer)

Explanation: **Explanation:** The size of platelets on a peripheral smear is a crucial diagnostic clue in hematology. In **Wiskott-Aldrich Syndrome (WAS)**, the hallmark finding is the triad of **thrombocytopenia with small-sized platelets (microthrombocytes)**, eczema, and recurrent infections due to immunodeficiency. This condition is caused by a mutation in the *WAS* gene, which leads to defects in the actin cytoskeleton of hematopoietic cells, resulting in the production of abnormally small and dysfunctional platelets. **Analysis of Incorrect Options:** * **Idiopathic Thrombocytopenic Purpura (ITP):** Characterized by increased peripheral destruction of platelets. The bone marrow compensates by releasing immature, **large-sized platelets (megathrombocytes)**. * **Bernard-Soulier Syndrome:** This is a qualitative platelet disorder (deficiency of GpIb-IX-V) classically associated with **giant platelets** (often as large as red blood cells). * **Disseminated Intravascular Coagulation (DIC):** While it causes thrombocytopenia due to consumption, the remaining platelets are typically normal in size or slightly larger if there is rapid bone marrow turnover; they are never characteristically small. **High-Yield Facts for NEET-PG:** * **Wiskott-Aldrich Syndrome:** X-linked recessive inheritance; low IgM, high IgA and IgE levels. * **Giant Platelets:** Seen in Bernard-Soulier syndrome, May-Hegglin anomaly, and Gray platelet syndrome. * **Mean Platelet Volume (MPV):** This is the laboratory parameter used to quantify platelet size; it is significantly decreased in WAS and increased in ITP and Bernard-Soulier.

Question 133: In an adult man, approximately how many grams of hemoglobin are present in the circulating blood?

A. 350 grams
B. 500 grams
C. 900 grams (Correct Answer)
D. 1000 grams

Explanation: To determine the total mass of hemoglobin in the body, we apply a simple physiological calculation based on average adult male values. [1] ### **Explanation of the Correct Answer** The total hemoglobin (Hb) mass is calculated using two variables: **Total Blood Volume** and **Hemoglobin Concentration**. [1] 1. **Average Blood Volume:** In an adult male weighing 70 kg, the blood volume is approximately 5 liters (70 ml/kg). 2. **Average Hb Concentration:** The normal range is 14–16 g/dL. Taking an average of **15 g/dL** (which is 150 g/L). [1] 3. **Calculation:** $150 \text{ g/L} \times 5 \text{ L} = \mathbf{750 \text{ to } 900 \text{ grams}}$. While 750g is a baseline, standard medical textbooks (like Guyton and Ganong) often cite the upper range or a slightly higher blood volume (up to 6L) for healthy adult males, making **900 grams** the most accurate representative value among the choices. [1] ### **Analysis of Incorrect Options** * **A (350g) & B (500g):** These values are too low. 350g would imply a life-threatening state of anemia or a very small pediatric blood volume. * **D (1000g):** While closer than the others, 1 kg of hemoglobin would require either polycythemia or a significantly larger body mass/blood volume than the average reference man. ### **High-Yield Clinical Pearls for NEET-PG** * **Hb Structure:** A tetramer consisting of 4 globin chains and 4 heme groups. Each heme group contains one iron atom in the **ferrous state ($Fe^{2+}$)**. * **Oxygen Carrying Capacity:** 1 gram of Hb carries **1.34 ml** of oxygen. * **Life Span:** RBCs circulate for **120 days**; the iron from degraded Hb is recycled via the mononuclear phagocyte system. * **Reference Range:** Adult Male: 13–17 g/dL; Adult Female: 12–15 g/dL. [1]

Question 134: What type of cartilage is found in the trachea?

A. Hyaline (Correct Answer)
B. Elastic
C. Articular
D. Fibro

Explanation: ### Explanation **1. Why Hyaline Cartilage is Correct:** The trachea contains 16–20 C-shaped rings of **hyaline cartilage**. This type of cartilage is characterized by a glassy, translucent matrix rich in Type II collagen and chondroitin sulfate [1]. Its primary function in the trachea is to provide structural rigidity, ensuring the airway remains patent (open) despite the negative pressure generated during inspiration, while still allowing for flexibility during neck movement [1]. **2. Why the Other Options are Incorrect:** * **Elastic Cartilage:** Contains abundant elastic fibers. It is found in structures requiring high flexibility and shape retention, such as the **epiglottis**, pinna of the ear, and Eustachian tube. * **Articular Cartilage:** While this is a subtype of hyaline cartilage, it specifically refers to the cartilage covering the **ends of long bones** in synovial joints [1]. It lacks a perichondrium, whereas tracheal hyaline cartilage possesses one. * **Fibrocartilage:** Contains thick bundles of Type I collagen. It is designed to withstand heavy pressure and tension. Examples include **intervertebral discs**, pubic symphysis, and the TMJ. **3. NEET-PG High-Yield Pearls:** * **The "C-shape" Rule:** Tracheal rings are incomplete posteriorly. This gap is bridged by the **trachealis muscle** (smooth muscle), which allows the esophagus to expand during swallowing. * **Laryngeal Cartilages:** Remember the "3P" rule for Elastic cartilage: **P**inna, **P**haryngotympanic tube, and **P**liable laryngeal parts (Epiglottis, Corniculate, Cuneiform). The rest (Thyroid, Cricoid, and base of Arytenoid) are **Hyaline**. * **Calcification:** Hyaline cartilage has a tendency to calcify with age, whereas elastic cartilage does not.

Question 135: What best describes myoepithelium?

A. Epithelial cells covering muscle tissue
B. Muscle cells
C. Epithelial cells with contractile units (Correct Answer)
D. None of the above

Explanation: **Explanation:** **Myoepithelial cells** are unique cells found in glandular epithelium. Despite their name, they are **epithelial in origin** (derived from the ectoderm) but possess functional characteristics of smooth muscle cells. **1. Why Option C is Correct:** Myoepithelial cells contain **contractile units** consisting of actin and myosin filaments (specifically alpha-smooth muscle actin) [2]. They are located between the basal plasma membrane of the secretory cells and the basal lamina. When these cells contract, they squeeze the acini or ducts of glands, facilitating the expulsion of secretory products into the ductal system. **2. Why Other Options are Incorrect:** * **Option A:** Epithelial cells covering muscle tissue refers to general connective tissue sheaths (like endomysium) or serous membranes, not a specific cell type with contractile properties. * **Option B:** While they share contractile proteins with muscle cells, myoepithelial cells are histologically distinct. They are joined by desmosomes and contain cytokeratin filaments, which are hallmarks of epithelial cells, not myocytes. **3. NEET-PG High-Yield Facts & Clinical Pearls:** * **Location:** Commonly found in the **mammary glands** (stimulated by oxytocin), **salivary glands**, **sweat glands**, and **lacrimal glands**. * **Staining:** They are identified immunohistochemically using markers like **p63**, **S-100**, and **Smooth Muscle Actin (SMA)**. * **Clinical Significance:** In breast pathology, the presence of a preserved myoepithelial layer is a key diagnostic feature used to differentiate **benign/in-situ lesions** from **invasive carcinoma** (where the myoepithelial layer is typically lost) [1]. * **Origin:** Unlike most muscle (mesodermal), myoepithelial cells are **ectodermal** in origin.

Question 136: The inner surface of the labia minora medial to the Hart line is lined by which of the following type of epithelium?

A. Cuboidal epithelium
B. Columnar epithelium
C. Squamous epithelium (Correct Answer)
D. Stratified squamous epithelium

Explanation: **Explanation:** The **Hart line** is a critical anatomical landmark on the inner surface of the labia minora. It represents the transition zone where the keratinized stratified squamous epithelium of the outer labia becomes non-keratinized. **Why the correct answer is right:** The area medial to the Hart line (the inner surface of the labia minora) is lined by **non-keratinized stratified squamous epithelium**. In the context of the options provided, **Squamous epithelium** is the most accurate histological classification [2]. This tissue is rich in glycogen and lacks hair follicles or sweat glands, providing a smooth, moist surface that transitions into the vaginal mucosa at the vestibule. **Analysis of Incorrect Options:** * **Cuboidal & Columnar Epithelium (A & B):** These are typically found in secretory or absorptive surfaces (e.g., renal tubules or the gastrointestinal tract). While the endocervix is columnar [1], the vulva and vagina are strictly squamous to withstand mechanical friction [2]. * **Stratified Squamous Epithelium (D):** While technically more descriptive, in many standardized exams (including NEET-PG), "Squamous epithelium" is often used as the broad correct category for this region. However, if "Non-keratinized stratified squamous" were an option, it would be the most specific. **High-Yield Clinical Pearls for NEET-PG:** * **Hart Line:** Marks the boundary between the skin-like outer surface (keratinized) and the mucosal-like inner surface (non-keratinized) of the labia minora. * **Embryology:** The labia minora develop from the **urethral folds** (genital folds). * **Sebaceous Glands:** Unlike the outer surface, the area medial to the Hart line contains sebaceous glands that open directly onto the surface (Fordyce spots) but lacks hair follicles. * **Vulvar Histology:** Always remember that the vulva is primarily squamous; any malignancy arising here is most commonly **Squamous Cell Carcinoma** [2].

Question 137: The 40 nm gap between tropocollagen molecules in collagen, which serves as the site for initiation of mineralization, is occupied by which of the following?

A. Carbohydrate
B. Ligand moiety
C. Ca++ (Correct Answer)
D. Fe++

Explanation: The structural integrity of collagen fibers is based on the staggered arrangement of **tropocollagen** molecules. These molecules align in a "head-to-tail" fashion with a specific overlap, creating distinct **"gap regions"** (also known as hole zones) measuring approximately 40 nm. **Why Ca++ is the correct answer:** In mineralized tissues like bone and dentin, these 40 nm gaps serve as the primary sites for the **initiation of calcification**. Calcium ions (**Ca++**) and phosphate accumulate within these gaps to form hydroxyapatite crystals [3]. The gap provides the necessary microenvironment for the nucleation of these minerals, which eventually spread to occupy the entire collagen matrix. **Analysis of Incorrect Options:** * **A. Carbohydrate:** While collagen is a glycoprotein and contains glucose/galactose side chains, these are covalently bound to hydroxylysine residues and do not specifically "occupy" the 40 nm mineralization gap [2]. * **B. Ligand moiety:** This is a generic term. While various proteins (like osteonectin) act as ligands to bind calcium to collagen, the gap itself is functionally defined by the mineral ions it houses. * **D. Fe++:** Iron is not involved in the primary mineralization of the collagen matrix. Its presence in high amounts in bone is usually pathological (e.g., hemosiderosis). **High-Yield Facts for NEET-PG:** * **D-spacing:** The staggered arrangement results in a characteristic banding pattern with a periodicity of **67 nm** under electron microscopy [2]. * **Vitamin C Requirement:** Prolyl and lysyl hydroxylase (enzymes that stabilize tropocollagen) require Vitamin C as a cofactor; deficiency leads to Scurvy [1]. * **Type I Collagen:** The most abundant type, found in bone, skin, and tendons. It is the specific template for the mineralization described above [3].

Question 138: True about hyaline cartilage?

A. Hyaline cartilage covers the articular surface of synovial joints. (Correct Answer)
B. Hyaline cartilage is present in all synovial joints.
C. Articular cartilage may undergo ossification with aging.
D. Articular cartilage limits the mobility of the joint.

Explanation: Explanation: Correct Option (A): Hyaline cartilage is the most abundant type of cartilage in the body. Its primary function at synovial joints is to provide a smooth, low-friction surface for movement and to act as a shock absorber [1]. It covers the epiphyses of long bones within the joint capsule, forming the articular cartilage. Analysis of Incorrect Options: * Option B: While most synovial joints feature hyaline cartilage, there are notable exceptions. The Temporomandibular Joint (TMJ) and the Sternoclavicular joint are lined with fibrocartilage rather than hyaline cartilage. * Option C: Unlike other hyaline cartilages (like costal or laryngeal cartilage) which tend to calcify and ossify with age, articular cartilage does not undergo ossification under normal physiological aging. Its persistence is vital for joint function. * Option D: Articular cartilage is designed to facilitate and enhance mobility by reducing friction (its coefficient of friction is lower than ice on ice) [1]. It does not limit joint movement; limitations are typically due to ligaments, capsules, or bony morphology. High-Yield NEET-PG Pearls: * Composition: Hyaline cartilage consists primarily of Type II collagen [1]. * Perichondrium: It is generally covered by perichondrium EXCEPT at articular surfaces and the epiphyseal plate. * Nutrition: Articular cartilage is avascular, aneural, and alymphatic [1]. It receives nutrition via diffusion from the synovial fluid [1]. * Locations: Remember the mnemonic "ART": Articular cartilage, Respiratory tract (Trachea, Bronchi, Larynx—except epiglottis), and Tip of nose/Costal cartilages.

Question 139: The Space of Disse is a potential space located between which structures?

A. Bone
B. Lymph node
C. Spleen
D. Liver (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. Liver** The **Space of Disse** (also known as the perisinusoidal space) is a critical anatomical landmark in the microscopic structure of the **liver** [1]. It is a narrow gap located between the **basal surface of hepatocytes** and the **fenestrated endothelial cells** of the hepatic sinusoids [1]. **Why it is correct:** The primary function of the Space of Disse is to facilitate the exchange of nutrients and metabolites between the blood flowing in the sinusoids and the hepatocytes [1]. It contains blood plasma that filters through the sinusoidal fenestrations [2]. Crucially, it also houses **Ito cells (Stellate cells)**, which store Vitamin A and can transform into myofibroblasts during liver injury, leading to fibrosis. **Why incorrect options are wrong:** * **A. Bone:** The microscopic spaces in bone include the Lacunae (housing osteocytes) and Canaliculi, but no "Space of Disse." * **B. Lymph node:** Lymph nodes contain subcapsular, cortical, and medullary sinuses, but the cellular arrangement does not involve a perisinusoidal space of this nomenclature. * **C. Spleen:** While the spleen contains venous sinuses and the "Cords of Billroth," the specific anatomical arrangement of the Space of Disse is unique to the hepatic architecture. **High-Yield Clinical Pearls for NEET-PG:** * **Lymph Formation:** Approximately 50% of the body’s lymph is formed within the Space of Disse. * **Ito Cells:** These are the primary cells involved in **hepatic fibrosis** (cirrhosis). When activated, they secrete excess collagen into the Space of Disse. * **Microvilli:** Hepatocytes extend microvilli into this space to increase the surface area for protein and glucose transport [1].

Question 140: Acanthocytes are seen in which of the following conditions?

A. Abetalipoproteinemia (Correct Answer)
B. Hampy's disease
C. Whipple disease
D. None of the above

Explanation: **Explanation:** **Acanthocytes** (also known as spur cells) are red blood cells with irregularly spaced, thorny, or spiked cytoplasmic projections of varying lengths [2]. **1. Why Abetalipoproteinemia is correct:** Abetalipoproteinemia is an autosomal recessive disorder caused by a mutation in the **MTTP gene**, leading to a deficiency in Apolipoprotein B-48 and B-100. This results in an inability to synthesize chylomicrons and VLDLs. The lack of these lipoproteins leads to an abnormal lipid composition in the RBC membrane (specifically an accumulation of sphingomyelin), which decreases membrane fluidity and causes the characteristic "spiked" acanthocyte morphology. **2. Why other options are incorrect:** * **Hampy’s disease:** This is not a standard medical term associated with hematological or histological pathology. It may be a distractor for Hartnup disease (a disorder of amino acid transport) or simply a "filler" option. * **Whipple disease:** Caused by the bacterium *Tropheryma whipplei*, this is a systemic infectious disease primarily affecting the small intestine. Histologically, it is characterized by **PAS-positive macrophages** in the lamina propria, not acanthocytes. **3. High-Yield Clinical Pearls for NEET-PG:** * **Acanthocytes** are also seen in: Severe liver disease (Spur cell anemia), McLeod syndrome, and Post-splenectomy states [2]. * **Abetalipoproteinemia Triad:** Acanthocytosis, Steatorrhea (malabsorption of fat-soluble vitamins A, D, E, K), and Retinitis pigmentosa/Ataxia [1]. * **Differentiate from Echinocytes (Burr cells):** These have *regularly* spaced, shorter projections and are seen in Uremia, Pyruvate kinase deficiency, and Gastric cancer.

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Histology — MCQs

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