Histology — MCQs

Histology Indian Medical PG Practice Questions and MCQs

Question 161: Intercalated discs are present in which type of muscle cell?

A. Smooth muscle cell
B. Skeletal muscle cell
C. Cardiac myocytes (Correct Answer)
D. Adipose tissue

Explanation: ### Explanation **Correct Answer: C. Cardiac myocytes** **Underlying Medical Concept:** Intercalated discs are specialized junctional complexes found exclusively in **cardiac muscle**. They represent the interface between adjacent cardiac myocytes and are essential for the heart to function as a **functional syncytium** [1]. These discs contain three types of cell-to-cell junctions: 1. **Fascia adherens:** Anchors actin filaments and transmits contractile forces. 2. **Desmosomes (Macula adherens):** Provide structural stability by preventing cells from pulling apart during contraction. 3. **Gap junctions:** Facilitate low-resistance electrical coupling, allowing rapid spread of action potentials across the myocardium [2]. **Analysis of Incorrect Options:** * **A. Smooth muscle cell:** These are non-striated, spindle-shaped cells. They lack intercalated discs and instead use **dense bodies** (analogous to Z-discs) and gap junctions for communication [3]. * **B. Skeletal muscle cell:** These are long, multinucleated cylinders. While they are striated, they lack intercalated discs because each fiber is an independent structural unit stimulated by a motor neuron [1]. * **C. Adipose tissue:** This is a connective tissue composed of adipocytes (fat cells) characterized by a "signet ring" appearance. It does not possess contractile properties or intercalated discs. **High-Yield Facts for NEET-PG:** * **Microscopic Appearance:** Intercalated discs appear as dark, transverse lines under light microscopy (H&E stain). * **Step-like Pattern:** They have a "staircase" appearance with transverse (horizontal) and longitudinal (vertical) components. * **Clinical Pearl:** Mutations in proteins of the intercalated disc (e.g., desmoplakin) are linked to **Arrhythmogenic Right Ventricular Dysplasia (ARVD)**, a common cause of sudden cardiac death in young athletes.

Question 162: In Genitourinary Tuberculosis, which of the following statements is true?

A. Sterile pyuria is a consistent finding. (Correct Answer)
B. AFB in an early morning urine sample is always positive.
C. The most common site involved is the pelvis.
D. It is the commonest cause of pyelonephritis.

Explanation: ### Explanation **1. Why Option A is Correct:** **Sterile pyuria** (the presence of white blood cells in the urine with negative routine bacterial cultures) is the hallmark of Genitourinary Tuberculosis (GUTB). In GUTB, the inflammation caused by *Mycobacterium tuberculosis* leads to the shedding of leukocytes into the urine. However, because *M. tuberculosis* does not grow on standard culture media (like Blood Agar or MacConkey), the routine culture remains "sterile." This is a classic high-yield finding for NEET-PG. **2. Why the Other Options are Incorrect:** * **Option B:** While an early morning urine sample is the preferred specimen, AFB (Acid-Fast Bacilli) staining is **not always positive**. The sensitivity of a single urine smear is low (approx. 30-50%) due to the intermittent shedding of the bacilli. Multiple samples (usually three to five) are required to increase the yield. * **Option C:** The **kidney** (specifically the renal cortex) is the most common site of initial involvement in GUTB, following hematogenous spread. The infection then spreads downstream to the ureters and bladder. * **Option D:** GUTB is a specific infection, but it is **not** the commonest cause of pyelonephritis. The most common cause of pyelonephritis is ascending bacterial infection, primarily by *Escherichia coli*. **3. Clinical Pearls for NEET-PG:** * **Pathogenesis:** Always starts as a hematogenous spread from a primary pulmonary focus (often dormant). * **Radiology:** Look for the **"Putty Kidney"** (autonephrectomy due to caseous necrosis and calcification) and **"Thimble Bladder"** (small, fibrotic, contracted bladder). * **Gold Standard Diagnosis:** Culture on **Lowenstein-Jensen (LJ) medium**, though PCR is now frequently used for rapid detection. * **Ureteric involvement:** Often leads to multiple strictures, giving a **"Beaded Ureter"** appearance.

Question 163: Which of the following is not a component of the buffer system in embalming fluid?

A. Sodium borate
B. Sodium bicarbonate
C. Sodium chloride (Correct Answer)
D. Sodium carbonate

Explanation: ### Explanation **Concept Overview:** Embalming fluid is a complex mixture of preservatives, germicides, buffers, wetting agents, and dyes. The **buffer system** is critical because it maintains the pH of the fluid (ideally between 7.2 and 7.4). Maintaining an alkaline pH is essential to prevent the polymerization of formaldehyde and to ensure that the formaldehyde reacts optimally with tissue proteins to achieve preservation. **Why Sodium Chloride is the Correct Answer:** * **Sodium Chloride (NaCl):** This is an **osmotic agent** (crystalloid), not a buffer. It is added to embalming fluid to adjust the tonicity (osmolarity) of the solution. It helps in drawing excess fluid out of edematous tissues or maintaining osmotic balance to prevent tissue swelling [1]. It does not possess the chemical capacity to resist changes in pH. **Analysis of Incorrect Options (Buffers):** * **Sodium Borate (Borax):** A classic alkaline buffer used in embalming to stabilize the pH and reduce the hardening effect of aldehydes. * **Sodium Carbonate and Sodium Bicarbonate:** These are common inorganic salts used to maintain the alkalinity of the solution [2]. They prevent the solution from becoming too acidic, which would otherwise lead to "formaldehyde gray" (discoloration of the body). **High-Yield Facts for NEET-PG:** * **Primary Preservative:** Formalin (37%–40% solution of formaldehyde gas in water). * **Humectants:** Glycerin and Sorbitol (added to prevent excessive dehydration of the cadaver). * **Anticoagulants:** Sodium citrate and Sodium oxalate (used to prevent blood clotting, ensuring better fluid distribution). * **The "Buffer Goal":** Embalming fluid must be slightly alkaline to mimic physiological pH and ensure the best cosmetic result for the cadaver.

Question 164: All of the following cells are found in the small intestine, EXCEPT:

A. Enterochromaffin cells
B. Goblet cells
C. Neck cells (Correct Answer)
D. Paneth cells

Explanation: The small intestine is characterized by a specialized mucosal lining designed for digestion and absorption. The correct answer is **Neck cells (Mucous Neck Cells)**, as these are specific to the **stomach**. **1. Why Neck Cells are the Correct Answer:** Mucous neck cells are located in the neck region of the **gastric glands** (fundus and body of the stomach). They secrete a soluble, acidic mucus that is distinct from the thick, alkaline mucus produced by surface mucous cells. They are not found in the intestinal mucosa. **2. Analysis of Incorrect Options:** * **Enterochromaffin (EC) cells:** These are a type of enteroendocrine cell found throughout the gastrointestinal tract, including the small intestine [2]. They secrete **serotonin**, which regulates intestinal motility [2]. * **Goblet cells:** These are unicellular glands interspersed among enterocytes [1]. Their density increases distally (Duodenum < Jejunum < Ileum). They secrete mucin to lubricate the intestinal wall. * **Paneth cells:** These are hallmark cells of the small intestine, located at the **base of the Crypts of Lieberkühn** [1]. They contain eosinophilic granules and secrete antimicrobial substances like **lysozyme**, defensins, and TNF-α [1]. **3. High-Yield Clinical Pearls for NEET-PG:** * **Paneth Cells:** Essential for mucosal immunity; they are absent in the large intestine (except in pathological conditions like "Paneth cell metaplasia" in IBD) [1]. * **M-cells (Microfold cells):** Found in the ileum overlying Peyer's patches; they are specialized for antigen sampling. * **Brunner’s Glands:** Found exclusively in the **submucosa of the Duodenum**; they secrete alkaline fluid to neutralize gastric acid. * **Stem Cells:** In the small intestine, stem cells are located at the **base of the crypts**, whereas in the stomach, they are located in the **isthmus/neck region** [1].

Question 165: Which of the following is present in cartilage but not in bone tissue?

A. Type 1 collagen
B. Blood
C. Nerves
D. Chondroitin sulfate (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. Chondroitin sulfate** The fundamental difference between bone and cartilage lies in their matrix composition and vascularity. **Cartilage** is a specialized, avascular connective tissue [1]. Its extracellular matrix is rich in **Chondroitin sulfate**, a sulfated glycosaminoglycan (GAG) that provides structural support and allows the tissue to withstand compression [1]. While bone matrix also contains GAGs [2], Chondroitin sulfate is the hallmark and predominant ground substance of cartilage. **Analysis of Incorrect Options:** * **A. Type 1 Collagen:** This is the primary structural protein of **bone** (making up 90% of the organic matrix) [2]. In contrast, the predominant collagen in hyaline and elastic cartilage is **Type 2** [1]. (Mnemonic: *Type "B-one" for Bone; Type "Two" for Car-two-lage*). * **B. Blood:** Bone is a highly vascularized tissue containing a rich network of vessels (Haversian and Volkmann canals). Cartilage is **avascular**; it receives nutrients via diffusion from the perichondrium or synovial fluid [1]. * **C. Nerves:** Bone is richly innervated (especially the periosteum), which is why fractures are extremely painful. Cartilage is **aneural** (lacks nerve supply) [1]. **High-Yield Clinical Pearls for NEET-PG:** 1. **Avascularity:** Because cartilage lacks blood vessels (Option B) and nerves (Option C), it has a very limited capacity for regeneration and repair compared to bone [1]. 2. **Growth Patterns:** Cartilage grows by both **interstitial** (from within) and **appositional** (from the periphery) growth. Bone grows **only by appositional growth** because its calcified matrix is too rigid for interstitial expansion. 3. **Cartilage Types:** * **Hyaline:** Type 2 Collagen (Most common, e.g., articular surfaces) [1]. * **Fibrocartilage:** Type 1 + Type 2 Collagen (Strongest, e.g., Intervertebral discs). * **Elastic:** Type 2 + Elastic fibers (e.g., Pinna, Epiglottis).

Question 166: Blistering of skin is common in the presence of abnormal what?

A. Intermediate filaments (Correct Answer)
B. Centrosomes
C. Microfilaments
D. Microtubules

Explanation: **Explanation:** The correct answer is **Intermediate filaments (Option A)**. These cytoskeletal elements provide mechanical strength to cells and tissues, particularly the skin. In the epidermis, specific intermediate filaments called **Keratins** (K5 and K14 in the basal layer) are essential for maintaining structural integrity. They anchor cells to each other via **desmosomes** and to the basement membrane via **hemidesmosomes**. When these filaments are defective or absent, the mechanical bond between cells or layers is lost, leading to fluid accumulation and the formation of blisters [1]. **Why the other options are incorrect:** * **Centrosomes (Option B):** These are the primary microtubule-organizing centers (MTOCs) involved in cell division and spindle formation. Defects here typically lead to mitotic errors or ciliopathies, not skin blistering. * **Microfilaments (Option C):** Composed of actin, these are primarily involved in cell motility, cytokinesis, and muscle contraction. While they contribute to the cell cortex, they do not provide the high-tensile strength required to prevent blistering. * **Microtubules (Option D):** Composed of tubulin, these act as "tracks" for intracellular transport and form the structure of cilia and flagella. They are not the primary structural anchors for dermo-epidermal stability. **Clinical Pearls for NEET-PG:** * **Epidermolysis Bullosa Simplex (EBS):** A classic clinical example caused by mutations in **Keratin 5 or 14**, leading to blistering after minor mechanical trauma. * **Pemphigus Vulgaris:** An autoimmune condition where antibodies attack **Desmoglein** (part of the desmosome complex that anchors intermediate filaments), causing intraepidermal blistering [1]. * **Bullous Pemphigoid:** Antibodies attack **Hemidesmosomes**, leading to subepidermal blistering [1].

Question 167: Goblet cells are present in all of the following except?

A. Small intestine
B. Large intestine
C. Oesophagus
D. Stomach (Correct Answer)

Explanation: **Explanation:** The correct answer is **Stomach (Option D)**. Goblet cells are specialized unicellular glands that secrete mucin. While the stomach is lined by a mucus-secreting epithelium, it consists of **Simple Columnar Mucous Surface Cells**, not Goblet cells. The presence of Goblet cells in the stomach is a pathological finding known as **Intestinal Metaplasia**, often associated with chronic gastritis or *H. pylori* infection, which is a precursor to gastric adenocarcinoma. **Analysis of other options:** * **Small Intestine (Option A):** Goblet cells are abundant here, increasing in number from the duodenum to the ileum [1]. They provide lubrication and protect the lining from digestive enzymes. * **Large Intestine (Option B):** The density of Goblet cells is highest in the colon and rectum to facilitate the passage of increasingly solid fecal matter. * **Oesophagus (Option C):** While the normal esophagus is lined by non-keratinized stratified squamous epithelium (lacking Goblet cells), the question asks where they are *normally* present in the GI tract. However, in the context of NEET-PG, the stomach is the classic "except" answer because the stomach has its own unique secretory cells (Mucous Neck Cells). *Note: The presence of Goblet cells in the esophagus is the hallmark of Barrett’s Esophagus.* **High-Yield NEET-PG Pearls:** 1. **Staining:** Goblet cells stain positive with **PAS (Periodic Acid-Schiff)** and **Alcian Blue** due to their carbohydrate-rich mucin content. 2. **Respiratory System:** Goblet cells are also found in the trachea and bronchi but disappear at the level of the **Terminal Bronchioles**. 3. **Key Distinction:** The stomach secretes "visible mucus" (alkaline), whereas Goblet cells secrete "acidic mucin."

Question 168: Which of the following is NOT a type of elastic cartilage?

A. Pinna
B. Epiglottis
C. Tip of arytenoid cartilage
D. Thyroid cartilage (Correct Answer)

Explanation: The correct answer is **Thyroid cartilage** because it is composed of **Hyaline cartilage**, not elastic cartilage. In the human body, cartilages are classified into three types—Hyaline, Elastic, and Fibrocartilage—based on the composition of their extracellular matrix [1]. **1. Why Thyroid Cartilage is the correct answer:** The thyroid, cricoid, and the base of the arytenoid cartilages are all **Hyaline** in nature. A high-yield characteristic of hyaline cartilage in the larynx is its tendency to **calcify and ossify** with advancing age, a feature not seen in elastic cartilage. **2. Why the other options are incorrect:** Elastic cartilage contains a dense network of branching elastic fibers (elastin), providing flexibility and the ability to recoil. * **Pinna (Auricle):** Along with the external auditory canal and the Eustachian tube, the pinna is a classic example of elastic cartilage. * **Epiglottis:** This leaf-shaped structure must be flexible to seal the laryngeal inlet during swallowing; hence, it is elastic. * **Tip of Arytenoid:** While the base of the arytenoid is hyaline, the **apex (tip)**, along with the **corniculate** and **cuneiform** cartilages, consists of elastic cartilage. **High-Yield NEET-PG Pearls:** * **Mnemonic for Elastic Cartilage:** Remember the **"6 Es"**: **E**piglottis, **E**xternal Ear (Pinna), **E**xternal Auditory Meatus, **E**ustachian Tube, and the small laryngeal cartilages—corniculat**E** and cun**E**iform (plus the apex of arytenoid). * **Key Distinction:** Hyaline cartilage has a "glassy" appearance and lacks visible fibers under standard H&E staining, whereas elastic cartilage requires special stains (like Verhoeff’s) to highlight the dark elastic fibers.

Question 169: Collagen present in skin is?

A. Type I (Correct Answer)
B. Type II
C. Type IV
D. Type V

Explanation: **Explanation:** The correct answer is **Type I Collagen**. Collagen is the most abundant protein in the human body, providing structural integrity to various tissues. **1. Why Type I is correct:** Type I collagen is the most prevalent type (constituting about 90% of the body's collagen). It forms thick, robust fibers that provide high tensile strength [1]. It is the primary structural component of the **dermis of the skin**, as well as **bone, tendons, ligaments, and cornea** [1]. In the skin, it provides the necessary resistance to stretching and tearing. **2. Why other options are incorrect:** * **Type II:** Found primarily in **cartilage** (hyaline and elastic) and the vitreous humor [1]. It forms thinner fibrils compared to Type I. (Mnemonic: "Type **Two** is for Car-**two**-lage"). * **Type IV:** This type does not form fibrils; instead, it forms a mesh-like network. It is a key component of the **Basal Lamina** (Basement membrane) and the lens capsule [2], [3]. * **Type V:** Typically found in the placenta, fetal membranes, and hair. It often co-distributes with Type I collagen to regulate fiber diameter. **High-Yield Clinical Pearls for NEET-PG:** * **Type III Collagen:** Also known as **Reticular fibers**. It is found in extensible organs like blood vessels, uterus, and during the early stages of **wound healing** (later replaced by Type I) [2]. * **Osteogenesis Imperfecta:** Caused by a defect in **Type I** collagen (presents with blue sclera and brittle bones) [1]. * **Alport Syndrome:** Caused by a defect in **Type IV** collagen (presents with nephritis and sensorineural deafness). * **Ehlers-Danlos Syndrome (Vascular type):** Associated with a deficiency in **Type III** collagen.

Question 170: All of the following are features of exstrophy of the bladder except?

A. Epispadias
B. Cloacal membrane is present (Correct Answer)
C. Posterior bladder wall protrudes through the defect
D. Umbilical and inguinal hernia

Explanation: **Explanation:** **Exstrophy of the Bladder** is a complex congenital malformation resulting from a failure of the lateral body wall folds to fuse in the midline. **1. Why "Cloacal membrane is present" is the correct answer:** In normal development, the cloacal membrane is a transient structure that is later reinforced by the migration of mesoderm. Bladder exstrophy occurs specifically because of the **premature rupture or failure of the cloacal membrane to be reinforced by mesoderm**. Therefore, the cloacal membrane is **absent** (ruptured) in the affected area, allowing the bladder mucosa to be exposed to the exterior. **2. Analysis of Incorrect Options:** * **Epispadias (Option A):** This is a hallmark association. Since the defect involves the anterior abdominal wall and the dorsal aspect of the urogenital sinus, the urethra opens on the dorsal surface of the penis. * **Posterior bladder wall protrudes (Option C):** Due to the defect in the anterior abdominal wall and the anterior wall of the bladder, the internal (posterior) surface of the bladder mucosa is exposed and protrudes through the opening. * **Umbilical and Inguinal Hernia (Option D):** The structural weakness of the lower abdominal wall and the separation of the pubic symphysis (diastasis) frequently lead to associated hernias. **Clinical Pearls for NEET-PG:** * **Embryological Basis:** Failure of mesenchymal cells to migrate between the ectoderm and endoderm of the cloacal membrane. * **Classic Triad:** Exstrophy of bladder, Epispadias, and Wide separation of pubic symphysis. * **Risk:** Long-term exposure of the bladder mucosa increases the risk of **Adenocarcinoma** of the bladder (due to glandular metaplasia). * **Cloacal Exstrophy:** A more severe form involving the failure of the urorectal septum to divide the cloaca, leading to exposed bowel and bladder.

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Histology — MCQs

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