Histology — MCQs

Histology Indian Medical PG Practice Questions and MCQs

Question 281: Which of the following cell types is NOT present in the lungs?

A. Clara cells
B. Langerhans cells (Correct Answer)
C. Brush cells
D. Klutischky cells

Explanation: The correct answer is **Langerhans cells**. These are specialized dendritic (antigen-presenting) cells found primarily in the **stratum spinosum of the epidermis**. [2] While the lungs contain "Alveolar Macrophages" (Dust cells), [3] Langerhans cells are specific to the skin and should not be confused with "Langhans giant cells" (seen in tuberculosis) or "Langerhans islets" (pancreas). **Analysis of Options:** * **Clara Cells (Club Cells):** These are non-ciliated, dome-shaped cells found in the terminal and respiratory bronchioles. They secrete surfactant-like lipoproteins and act as stem cells to regenerate the bronchiolar epithelium. * **Brush Cells (Type III Pneumocytes):** These are chemoreceptor cells found throughout the tracheobronchial tree. They have short, blunt microvilli and are involved in monitoring air quality. * **Kultschitksy Cells (K-cells):** These are enteroendocrine cells of the bronchial tree belonging to the APUD system. They secrete hormones like serotonin and calcitonin. Clinically, they are the cells of origin for **Small Cell Carcinoma** and **Carcinoid tumors** of the lung. [4] **High-Yield Clinical Pearls for NEET-PG:** * **Blood-Air Barrier:** Formed by Type I Pneumocytes, fused basal laminae, and capillary endothelial cells. * **Surfactant:** Produced by **Type II Pneumocytes** (contain lamellar bodies). * **Pneumoconiosis:** Alveolar macrophages (Dust cells) are the primary cells involved in the pathogenesis of occupational lung diseases by phagocytosing silica or asbestos particles. [1] * **Langerhans Cell Histiocytosis (LCH):** While Langerhans cells are skin cells, LCH can involve the lungs in adults (strongly associated with smoking), but these cells are not part of the *normal* lung histology.

Question 282: The ducts of all the following glands consist of stratified cuboidal epithelium EXCEPT:

A. Sweat gland
B. Sebaceous glands (Correct Answer)
C. Salivary glands
D. Pancreas

Explanation: **Explanation:** The core concept tested here is the histological classification of glandular ducts. **Stratified cuboidal epithelium** is a relatively rare tissue type in the human body, primarily functioning as a robust lining for the larger excretory ducts of exocrine glands. **Why Sebaceous Glands are the Exception:** Sebaceous glands are **holocrine glands**, meaning the entire cell disintegrates to release its lipid-rich secretion (sebum). Unlike other exocrine glands, sebaceous glands typically lack a long, independent duct system lined by specialized epithelium. Instead, they usually open directly into the upper portion of a hair follicle via a short canal lined by **stratified squamous epithelium** (continuous with the follicular wall and skin surface). **Analysis of Incorrect Options:** * **Sweat Glands:** The secretory portion is simple cuboidal, but the **ductal portion** (specifically the double-layered part in the dermis) is the classic textbook example of **stratified cuboidal epithelium** [1]. * **Salivary Glands & Pancreas:** Both are complex tubuloacinar glands. While their smallest ducts (intercalated) are simple cuboidal, their **larger excretory ducts** (interlobular ducts) are characteristically lined by stratified cuboidal or stratified columnar epithelium to provide structural integrity. **High-Yield NEET-PG Pearls:** 1. **Stratified Cuboidal Locations:** Remember the "Big Three"—Ducts of sweat glands, large ducts of salivary glands, and large ducts of the pancreas [1]. 2. **Holocrine Secretion:** Sebaceous glands are the only major holocrine glands; "Whole cell dies" = Holocrine. 3. **Transitional Epithelium:** Often confused with stratified cuboidal; it is unique to the urinary tract (Urothelium) and allows for distension.

Question 283: Which of the following is an example of a sesamoid bone?

A. Rider's bone in adductor magnus
B. Pisiform in flexor carpi ulnaris (Correct Answer)
C. Fabella in medial head of gastrocnemius
D. One bone in peronius teius

Explanation: **Explanation:** **Sesamoid bones** are unique ossicles embedded within tendons or joint capsules [1]. They lack a periosteum and function primarily to reduce friction, modify pressure, and alter the direction of muscle pull, acting as anatomical pulleys. **Why Option B is Correct:** The **Pisiform** is a classic example of a sesamoid bone. It develops within the tendon of the **Flexor Carpi Ulnaris (FCU)** muscle. It is unique because it is the only carpal bone that is also a sesamoid bone, articulating only with the triquetral bone. **Analysis of Incorrect Options:** * **Option A:** **Rider’s bone** is an example of **heterotopic (ectopic) ossification**. It occurs due to chronic trauma and calcification within the tendon of the **adductor longus** (not magnus) in horseback riders. It is a pathological calcification, not a true physiological sesamoid bone. * **Option C:** The **Fabella** is indeed a sesamoid bone, but it is located in the **lateral head** of the gastrocnemius, not the medial head. This makes the option factually incorrect. * **Option D:** The sesamoid bone in the foot is found within the tendon of the **Peroneus Longus** (as it crosses the cuboid), not the "peronius teius" (which is not a standard anatomical term). **High-Yield NEET-PG Pearls:** 1. **Patella:** The largest sesamoid bone in the body (embedded in the Quadriceps femoris tendon). 2. **Ossification:** Sesamoid bones typically ossify after birth [1]. 3. **Other Examples:** Two sesamoids are consistently found under the head of the **1st metatarsal** (in the Flexor hallucis brevis tendon). 4. **Clinical Significance:** Inflammation of these bones (Sesamoiditis) is a common cause of forefoot pain in athletes.

Question 284: The mammary gland is which type of gland?

A. Apocrine (Correct Answer)
B. Merocrine
C. Holocrine
D. Endocrine

Explanation: The mammary gland is classified as an **apocrine gland** based on its mode of secretion. In apocrine secretion, the apical portion of the secretory cell cytoplasm is pinched off along with the secretory product [1]. In the case of the mammary gland, while the protein component (casein) is secreted via exocytosis (merocrine), the **lipid/fat component** is released via the apocrine mechanism. For competitive exams like NEET-PG, the mammary gland is the classic textbook example of an apocrine gland. **Analysis of Options:** * **A. Apocrine (Correct):** The secretory process involves the loss of the apical cell membrane. Other examples include modified sweat glands in the axilla, areola, and perianal region. * **B. Merocrine:** This is the most common type of secretion where products are released via exocytosis without any loss of cell substance (e.g., salivary glands, pancreas, and most eccrine sweat glands). * **C. Holocrine:** The entire cell disintegrates to release its secretion. The classic example is the **Sebaceous gland**. * **D. Endocrine:** These are ductless glands that secrete hormones directly into the bloodstream (e.g., Thyroid, Adrenal glands). The mammary gland is an exocrine gland as it uses a duct system. **High-Yield Clinical Pearls for NEET-PG:** * **Embryology:** Mammary glands are modified **apocrine sweat glands** [1]. They develop from the **milk line** (ectodermal thickening). * **Histology:** The functional unit is the Terminal Duct Lobular Unit (TDLU) [2]. * **Hormonal Control:** Prolactin stimulates milk production (alveolar cells), while Oxytocin stimulates milk ejection (contraction of myoepithelial cells).

Question 285: Respiratory epithelium (i.e., ciliated pseudostratified columnar) is found in all of the following structures, EXCEPT:

A. Nasal cavity
B. Trachea
C. Extrapulmonary bronchi
D. Alveoli (Correct Answer)

Explanation: The respiratory tract is lined by different types of epithelium depending on the function of the specific segment. **Respiratory epithelium** is defined as **ciliated pseudostratified columnar epithelium with goblet cells** [1]. Its primary role is to warm, humidify, and filter air (the mucociliary escalator) [1]. **1. Why Alveoli is the Correct Answer:** The alveoli are the primary sites of gas exchange. For efficient diffusion of oxygen and carbon dioxide, the barrier must be extremely thin. Therefore, the thick respiratory epithelium is replaced by **Simple Squamous Epithelium** (Type I pneumocytes) and surfactant-secreting Type II pneumocytes [2], [3]. Cilia and goblet cells are absent here to prevent fluid accumulation and obstruction of gas exchange. **2. Analysis of Incorrect Options:** * **Nasal Cavity:** Most of the nasal cavity (except the vestibule and olfactory region) is lined by respiratory epithelium to filter incoming dust [1]. * **Trachea:** This is the classic site for ciliated pseudostratified columnar epithelium, containing numerous goblet cells and a thick basement membrane [1]. * **Extrapulmonary Bronchi:** These structures maintain the same histological profile as the trachea before entering the lungs. **High-Yield NEET-PG Pearls:** * **Transition Point:** The epithelium gradually thins as we move down the tract: Pseudostratified Columnar (Trachea/Bronchi) → Simple Columnar (Large Bronchioles) → Simple Cuboidal (Terminal Bronchioles) → Simple Squamous (Alveoli) [2]. * **Goblet Cells:** These disappear first (at the level of terminal bronchioles), followed by cilia. * **Kartagener Syndrome:** A high-yield clinical correlation where dynein arm defects lead to immobile cilia, causing recurrent respiratory infections and situs inversus [2].

Question 286: Which stain is used for glycogen?

A. PAS (Periodic Acid-Schiff) (Correct Answer)
B. Congo red
C. Prussian blue
D. Alcian blue

Explanation: **Explanation:** **PAS (Periodic Acid-Schiff)** is the correct answer because it is the gold-standard histochemical stain for detecting carbohydrates, specifically **glycogen**, glycoproteins, and mucins. The mechanism involves periodic acid oxidizing the carbon-carbon bonds in glucose residues to form aldehydes, which then react with the Schiff reagent to produce a characteristic **magenta/deep pink** color. **Analysis of Incorrect Options:** * **Congo Red:** This is the specific stain for **Amyloid**. Under polarized microscopy, amyloid stained with Congo red exhibits a pathognomonic "apple-green birefringence." * **Prussian Blue (Perl’s Stain):** This is used to detect **Ferric iron ($Fe^{3+}$)**. It is clinically significant in diagnosing conditions like hemochromatosis or identifying sideroblasts and hemosiderin-laden macrophages ("heart failure cells"). * **Alcian Blue:** This stain is used for **acidic mucopolysaccharides** (glycosaminoglycans). It is frequently used to identify intestinal metaplasia (Barrett’s esophagus) where it stains goblet cells blue. **Clinical Pearls for NEET-PG:** * **Diastase Sensitivity:** To confirm that PAS-positive staining is specifically due to glycogen (and not other carbohydrates), a **Diastase** test is performed. Diastase digests glycogen; if the staining disappears after treatment, it confirms the presence of glycogen. * **PAS-Positive Structures:** Basement membranes, fungal hyphae (e.g., Candida, Histoplasma), and the thick secretions in Whipple’s disease (Tropheryma whipplei) are all PAS-positive. * **Best’s Carmine:** An older, highly specific stain for glycogen, though less commonly used today than PAS.

Question 287: Which stain is used to stain the X chromosome?

A. Quinacrine
B. Acriflavin Schiff reagent (Correct Answer)
C. Methylene blue
D. Fluorescent green

Explanation: **Explanation:** The correct answer is **Acriflavin Schiff reagent**. This stain is a fluorescent variant of the traditional Feulgen reaction used to detect DNA. In the context of cytogenetics and histology, Acriflavin Schiff is specifically utilized to visualize the **X-chromatin (Barr body)** in interphase nuclei, such as those found in buccal smears or hair root cells. The reagent binds to the deoxyribonucleic acid of the condensed X chromosome [1], allowing it to be identified under a fluorescence microscope. [1] **Analysis of Options:** * **A. Quinacrine:** This is a fluorescent stain primarily used for **Q-banding** of chromosomes [1]. It has a high affinity for the **Y-chromosome** (specifically the long arm), making it the gold standard for identifying the "Y-body" rather than the X-body. * **C. Methylene blue:** This is a basic dye used for general morphology to highlight nuclei and acidic components (like RNA). While it stains the nucleus, it is not specific for identifying the X chromosome or Barr bodies. * **D. Fluorescent green:** This is a general description of a signal (like FITC) rather than a specific histological stain used for sex chromatin identification. **High-Yield Clinical Pearls for NEET-PG:** * **Barr Body:** It represents the inactivated X chromosome (Lyon’s hypothesis) found in females. The number of Barr bodies = (Total number of X chromosomes – 1). * **Drumstick Appearance:** In neutrophils, the inactivated X chromosome appears as a "drumstick" appendage on the nucleus. * **Y-Body:** Identified using **Quinacrine Mustard**; it appears as a bright fluorescent dot in the interphase nucleus of males. * **Feulgen Stain:** The parent reaction for Acriflavin Schiff, specific for DNA (stains it magenta/red).

Question 288: White fibrocartilage is present in all EXCEPT:

A. Acetabular labrum
B. Intervertebral disc
C. Meniscus
D. Pinna (Correct Answer)

Explanation: **Explanation:** The question tests the ability to differentiate between types of cartilage based on their histological composition and anatomical location. **1. Why Pinna is the Correct Answer:** The **Pinna (Auricle)** of the ear is composed of **Elastic Cartilage**, not white fibrocartilage. Elastic cartilage contains a dense network of elastic fibers (elastin), which provides the flexibility and resilience required for the ear to maintain its shape after being bent. Other sites for elastic cartilage include the External Auditory Meatus, Eustachian tube, and Epiglottis (the "4 Es"). **2. Analysis of Incorrect Options (Where White Fibrocartilage is present):** White fibrocartilage is characterized by thick bundles of **Type I Collagen**, making it the strongest type of cartilage, designed to act as a shock absorber and provide tensile strength. [3] * **Intervertebral Disc:** The *annulus fibrosus* is a classic example of fibrocartilage, resisting multi-directional compressive forces. * **Acetabular Labrum:** This fibrocartilaginous rim deepens the hip socket, providing stability and load distribution. * **Meniscus:** The medial and lateral menisci of the knee are fibrocartilaginous structures that facilitate weight-bearing and reduce friction. **3. Clinical Pearls & High-Yield Facts:** * **Perichondrium:** Fibrocartilage is unique because it **lacks a perichondrium** (unlike elastic and most hyaline cartilage). * **Collagen Types:** Hyaline and Elastic cartilage primarily contain **Type II collagen** [1], whereas Fibrocartilage is dominant in **Type I collagen** [3]. * **Secondary Cartilaginous Joints:** All symphyses (e.g., Pubic symphysis, Manubriosternal joint) contain fibrocartilage. [2] * **NEET-PG Tip:** If a structure needs to be "stretchy," think Elastic. If it needs to "withstand heavy pressure," think Fibrocartilage.

Question 289: Tear drop bladder is seen in which condition?

A. Hunner's ulcer
B. Tuberculosis
C. Perivisceral hemorrhage with rupture (Correct Answer)
D. Perivisceral hemorrhage without rupture

Explanation: ### Explanation **Correct Answer: C. Perivisceral hemorrhage with rupture** The **"Tear-drop bladder"** is a classic radiological sign seen on a cystogram or CT scan. It occurs when the urinary bladder is compressed from both sides (extrinsic compression), causing it to elongate vertically and narrow horizontally, resembling a teardrop or a pear. The most common cause is a **pelvic hematoma** resulting from a pelvic fracture (perivisceral hemorrhage) [1]. While a hematoma without rupture can cause compression, the sign is most classically associated with significant trauma involving **pelvic floor disruption and hemorrhage**, often accompanied by bladder or urethral injury [1]. The accumulation of blood and fluid in the extraperitoneal space (Cave of Retzius) squeezes the bladder into this characteristic shape. [3, 4] **Analysis of Incorrect Options:** * **A. Hunner’s Ulcer:** This is a feature of Interstitial Cystitis. It is characterized by mucosal lesions and a "thimble bladder" (small capacity) due to chronic inflammation, not extrinsic compression. * **B. Tuberculosis:** Renal/Bladder TB leads to extensive fibrosis, resulting in a small, shrunken, and non-compliant bladder known as a **"Thimble bladder"** or "Golf-hole ureter." * **D. Perivisceral hemorrhage without rupture:** While any pelvic collection can compress the bladder, the classic "tear-drop" description in trauma surgery and radiology is most frequently linked to major pelvic ring disruptions where rupture/extravasation is a high-risk factor. **NEET-PG High-Yield Pearls:** * **Tear-drop Bladder:** Pelvic hematoma, pelvic lipomatosis, or bilateral iliac artery aneurysms. * **Thimble Bladder:** Tuberculosis, Schistosomiasis, or Radiation cystitis. * **Christmas Tree Bladder:** Neurogenic bladder (seen in Voiding Cystourethrogram - VCUG). * **Hourglass Bladder:** Congenital urachal diverticulum or sliding inguinal hernia containing the bladder.

Question 290: Which of the following statements is not true regarding type-II pneumocytes?

A. Secrete surfactant
B. Are epithelial cells
C. Secrete by endocytosis (Correct Answer)
D. Lamellar bodies are formed

Explanation: The correct answer is **C (Secrete by endocytosis)** because Type-II pneumocytes secrete pulmonary surfactant via **exocytosis**, not endocytosis [1]. Endocytosis is the process of taking substances *into* the cell, whereas secretion involves releasing substances *out* of the cell. **Analysis of Options:** * **Option A (Secrete surfactant):** This is a primary function. Type-II pneumocytes produce surfactant (mainly dipalmitoylphosphatidylcholine), which reduces surface tension and prevents alveolar collapse (atelectasis) [1]. * **Option B (Are epithelial cells):** This is true. The alveolar epithelium is composed of two main types: Type-I (95% of surface area, thin for gas exchange) and Type-II (cuboidal cells that act as "stem cells" for the epithelium) [1],[2]. * **Option D (Lamellar bodies are formed):** This is true. Surfactant is stored in specialized intracellular organelles called **lamellar bodies**, which appear as membrane-bound stacks of parallel lamellae under electron microscopy [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Stem Cell Function:** Type-II pneumocytes are the progenitors for both Type-I and Type-II cells; they proliferate to repair the alveolar wall after injury [1]. * **Development:** Surfactant production begins around **24–28 weeks** of gestation, but adequate levels are often not reached until **35 weeks**. * **Clinical Correlation:** Deficiency of surfactant in premature neonates leads to **Infant Respiratory Distress Syndrome (IRDS)** or Hyaline Membrane Disease. * **Histology Hint:** Type-II cells are **cuboidal** and located at the alveolar septal junctions, whereas Type-I cells are **squamous** [2].

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Histology — MCQs

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