Histology — MCQs

Histology Indian Medical PG Practice Questions and MCQs

Question 151: Canals of Hering are present in which organ?

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

Explanation: The **Canals of Hering** (also known as intrahepatic bile ductules) are anatomical structures located in the **Liver**. They serve as the physiological link between the bile canaliculi (formed by hepatocytes) and the interlobular bile ducts located in the portal triads [1]. **Why Liver is Correct:** The Canals of Hering are lined partially by hepatocytes and partially by specialized epithelial cells called **cholangiocytes**. Their primary function is to transport bile out of the liver lobule [1]. Crucially, for NEET-PG, they are recognized as the **niche for hepatic stem cells** (oval cells), which proliferate during significant liver injury to regenerate hepatocytes or bile duct cells. **Why Other Options are Incorrect:** * **Spleen:** Contains red pulp, white pulp, and sinusoids, but no biliary structures. * **Lymph node:** Characterized by a cortex (follicles), paracortex, and medulla; it contains lymphatic sinuses, not bile canals. * **Bone marrow:** Composed of hematopoietic cords and venous sinusoids; it is the site of blood cell production, unrelated to the biliary system. **High-Yield Clinical Pearls for NEET-PG:** * **Location:** They are found at the periphery of the liver lobule, crossing the limiting plate. * **Stem Cell Niche:** They contain "Oval cells," which are bipotential stem cells. * **Pathology:** In Primary Biliary Cholangitis (PBC), the small bile ductules including the Canals of Hering are often the target of immunological destruction. * **Direction of Flow:** Remember that in a liver lobule, **blood flows centripetally** (toward the central vein), while **bile flows centrifugally** (toward the portal triad via Canals of Hering) [1].

Question 152: What are the most predominant cells found in the pars nervosa?

A. Basophilic cells
B. Acidophilic cells
C. Pituicytes (Correct Answer)
D. Chromatophobe cells

Explanation: The pituitary gland (hypophysis) is divided into the **Adenohypophysis** (Anterior Pituitary) and the **Neurohypophysis** (Posterior Pituitary). The **Pars Nervosa** is the main bulk of the neurohypophysis. **Why Pituicytes are correct:** Unlike the anterior pituitary, the pars nervosa does not contain glandular secretory cells. Instead, it consists of unmyelinated axons of neurosecretory neurons (whose cell bodies reside in the hypothalamus) and specialized glial cells called **Pituicytes** [1]. Pituicytes are the most predominant cell type in this region; they are star-shaped (astrocytic) cells that provide structural support and regulate the release of hormones (Oxytocin and ADH) from the axonal terminals [3]. **Analysis of Incorrect Options:** * **Options A, B, and D (Basophils, Acidophils, and Chromophobes):** These cells are found exclusively in the **Pars Distalis** (Anterior Pituitary) [2]. * **Acidophils** include Somatotrophs (GH) and Lactotrophs (Prolactin) [2]. * **Basophils** include Corticotrophs (ACTH), Thyrotrophs (TSH), and Gonadotrophs (FSH/LH) [2]. * **Chromatophobes** are cells that have depleted their granules or are undifferentiated stem cells. **High-Yield Facts for NEET-PG:** * **Herring Bodies:** These are dilated terminal portions of axons in the pars nervosa containing neurosecretory granules (ADH and Oxytocin). * **Origin:** The Pars Nervosa develops from **neuroectoderm** (down-growth of the hypothalamus), whereas the Adenohypophysis develops from **Rathke’s pouch** (oral ectoderm). * **Hormone Storage:** The posterior pituitary does *not* synthesize hormones; it only stores and releases hormones produced in the Supraoptic and Paraventricular nuclei of the hypothalamus [1].

Question 153: Paneth cells are characterized by which of the following?

A. A higher number of lysosomal enzymes
B. A high concentration of zinc (Correct Answer)
C. A higher concentration of EFR
D. Foamy cells

Explanation: **Explanation:** Paneth cells are specialized secretory epithelial cells located at the base of the **Crypts of Lieberkühn** in the small intestine [1]. They play a critical role in innate mucosal immunity. **Why Option B is Correct:** Paneth cells contain prominent, acidophilic (eosinophilic) apical secretory granules. These granules are unique because they contain a **high concentration of Zinc**, which acts as a cofactor for various enzymes and stabilizes the storage of antimicrobial peptides like **defensins (cryptidins)** and **lysozyme**. This high zinc content is a classic histological hallmark used to identify these cells. **Analysis of Incorrect Options:** * **Option A:** While Paneth cells do contain lysozyme (an antibacterial enzyme), they are not primarily characterized by "lysosomal enzymes" in the way macrophages or neutrophils are. Their primary secretion consists of antimicrobial peptides. * **Option C:** "EFR" is not a standard histological term associated with Paneth cells. If referring to Rough Endoplasmic Reticulum (RER), Paneth cells do have an extensive RER for protein synthesis, but the high zinc concentration is the more specific distinguishing feature. * **Option D:** **Foamy cells** are lipid-laden macrophages typically seen in atherosclerosis or certain infections (like Leprosy). They are not a feature of the intestinal mucosa. **High-Yield Clinical Pearls for NEET-PG:** * **Location:** Most numerous in the **ileum**; absent in the large intestine (except in pathological "Paneth cell metaplasia"). Paneth cells remain in the crypt bases where they protect intestinal stem cells [1]. * **Function:** They secrete **Lysozyme**, **Alpha-defensins**, and **Zinc**, providing a barrier against enteric pathogens [1]. * **Stem Cell Niche:** Paneth cells provide essential growth factors (like Wnt) to the neighboring intestinal stem cells [1]. * **Staining:** Their granules are strongly **acidophilic** (stain bright red/pink with H&E).

Question 154: All are true about bulbar urethral rupture, except?

A. Perineal hematoma
B. Floating prostate on per rectal examination (Correct Answer)
C. Collection of urine in the perineum
D. Bleeding per urethra

Explanation: To understand urethral injuries, it is crucial to distinguish between **Anterior** and **Posterior** urethral ruptures based on their anatomical location relative to the perineal membrane [1]. ### Why "Floating Prostate" is the Correct Answer (The Exception) A **"Floating Prostate"** on digital rectal examination (DRE) is the hallmark sign of a **Posterior Urethral Injury** (specifically the membranous urethra), usually associated with pelvic fractures [1]. In these cases, the puboprostatic ligaments are torn, allowing the prostate to be displaced superiorly by a pelvic hematoma, which may appear as a "pie in the sky" bladder on imaging [2]. In contrast, the **Bulbar Urethra** is part of the **Anterior Urethra**. A rupture here (typically due to a "straddle injury") occurs below the urogenital diaphragm; therefore, the prostate remains in its normal anatomical position and is not "floating." ### Analysis of Other Options * **A & C. Perineal Hematoma and Collection of Urine:** In a bulbar rupture, if **Buck’s fascia** is torn, urine and blood extravasate into the superficial perineal pouch. Due to the attachments of **Colles' fascia**, this collection is confined to the perineum, scrotum, and penis, and may extend to the abdominal wall, but it cannot track into the thighs. * **D. Bleeding per Urethra:** This is the most common clinical sign of any urethral injury, whether anterior or posterior. Blood at the external meatus indicates a breach in the urethral mucosa. ### Clinical Pearls for NEET-PG * **Mechanism:** Bulbar rupture = Straddle injury (falling onto a fence/manhole); Membranous rupture = Pelvic fracture (RTA) [1]. * **Extravasation Limits:** Colles' fascia is continuous with Scarpa’s fascia of the abdomen but fuses with the fascia lata of the thigh and the perineal body, explaining why urine doesn't track into the legs. * **Gold Standard Investigation:** Retrograde Urethrogram (RUG) must be performed before any catheterization attempt if a urethral injury is suspected [2].

Question 155: Plasma cells are a constituent of which type of tissue?

A. Nervous tissue
B. Muscular tissue
C. Epithelial tissue
D. Connective tissue (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. Connective tissue** **1. Why Connective Tissue is Correct:** Plasma cells are specialized immune cells derived from **B-lymphocytes** [2]. They are a key component of the **Connective Tissue Proper**, specifically categorized as "wandering" or "transient" cells [3]. Their primary function is the synthesis and secretion of large quantities of antibodies (immunoglobulins) into the extracellular matrix to combat pathogens [1]. Histologically, they are easily identified by their eccentric nucleus and a "cartwheel" or "clock-face" chromatin pattern. **2. Why Other Options are Incorrect:** * **A. Nervous tissue:** Composed primarily of neurons and neuroglia (astrocytes, oligodendrocytes, etc.). While the CNS has specialized immune cells (microglia), plasma cells are not native constituents. * **B. Muscular tissue:** Consists of specialized contractile cells (myocytes). Its primary function is movement and thermogenesis, not immune secretion. * **C. Epithelial tissue:** Characterized by closely packed cells with minimal extracellular matrix. While plasma cells are often found in the *Lamina Propria* (the connective tissue layer immediately beneath the epithelium), they are not part of the epithelium itself [1]. **3. NEET-PG High-Yield Clinical Pearls:** * **Histological Hallmark:** Plasma cells exhibit a prominent **perinuclear halo** (clear zone), which represents a highly developed Golgi apparatus required for antibody packaging. * **Russell Bodies:** These are eosinophilic, large cytoplasmic inclusions representing accumulated immunoglobulins within a plasma cell. * **Clinical Correlation:** A malignancy of plasma cells is known as **Multiple Myeloma**, characterized by the "M-spike" on serum electrophoresis and "punched-out" lytic lesions on X-ray. * **Location:** They are most abundant in the connective tissue of the gastrointestinal and respiratory tracts (sites of pathogen entry) [1].

Question 156: A 15-year-old girl presents with a sore throat. She is prescribed an antibiotic that can enter most body tissues but cannot penetrate the blood-brain barrier. Which cell type is primarily responsible for the blood-brain barrier?

A. Astrocyte
B. Endothelial cell (Correct Answer)
C. Glial cell
D. Macrophage

Explanation: The **Blood-Brain Barrier (BBB)** is a highly selective semipermeable border that prevents solutes in the circulating blood from non-selectively crossing into the extracellular fluid of the central nervous system. **Why Endothelial Cells are the Correct Answer:** The structural and functional basis of the BBB is the **non-fenestrated capillary endothelial cells**. These cells are unique because they are fused together by **tight junctions (Zonula occludens)**, which eliminate intercellular clefts [1]. This forces substances to travel *through* the cell membrane (transcellularly) rather than between cells (paracellularly), effectively blocking large or hydrophilic molecules (like many antibiotics) from entering the brain [2]. **Analysis of Incorrect Options:** * **Astrocyte:** While astrocytes are crucial for the BBB, they are not the primary barrier. Their cytoplasmic processes (**perivascular feet**) surround the capillaries and induce/maintain the tight junctions in the endothelial cells, but they do not form the physical seal themselves [3]. * **Glial cell:** This is a general category of support cells (including astrocytes, oligodendrocytes, and microglia) [3]. It is too non-specific to be the primary structural component of the barrier. * **Macrophage:** In the CNS, these are known as **Microglia**. Their role is immunological (phagocytosis) and they do not contribute to the structural integrity of the BBB [3]. **High-Yield NEET-PG Pearls:** 1. **Components of the BBB:** (1) Tight junctions of non-fenestrated endothelial cells (Primary), (2) Thick basement membrane, (3) Astrocyte foot processes. 2. **Circumventricular Organs (CVOs):** Areas where the BBB is **absent** to allow for sensing of blood chemistry (e.g., Area Postrema/Chemoreceptor Trigger Zone, Posterior Pituitary, OVLT) [1]. 3. **Transport:** Only lipid-soluble substances (O2, CO2, alcohol) and those with specific carrier-mediated transport (Glucose via GLUT-1) cross the BBB easily [1].

Question 157: Tattooing colors the skin permanently because pigmented dyes are injected into which layer of the skin?

A. Stratum Lucidum
B. Stratum Granulosum
C. Stratum Corneum
D. Dermis (Reticular layer) (Correct Answer)

Explanation: The permanence of a tattoo depends entirely on the depth at which the pigment is deposited. For a tattoo to be lasting, the dye must reach the **Dermis**, specifically the **Reticular layer**. [1] **Why the Dermis is the correct answer:** The epidermis undergoes constant renewal through a process called desquamation, where cells move from the basal layer to the surface and are shed every 28–30 days. [1] If ink were placed in the epidermis, it would disappear within a month. In contrast, the dermis does not shed. When ink is injected into the dermis, it is engulfed by **dermal macrophages** and fibroblasts or trapped within the dense network of collagen fibers in the reticular layer. [1] Because these cells and fibers are stable, the pigment remains visible through the translucent epidermis permanently. **Why the other options are incorrect:** * **Stratum Corneum:** This is the outermost layer of dead, keratinized cells. It is constantly sloughing off; ink here would wash away in days. [1] * **Stratum Lucidum:** This layer is only found in thick skin (palms and soles). Like all epidermal layers, it is subject to turnover and shedding. * **Stratum Granulosum:** This is a middle layer of the epidermis. Cells here are destined to become keratinized and shed, making it unsuitable for permanent pigmentation. **NEET-PG High-Yield Pearls:** * **Skin Layers:** Remember the mnemonic **"C**ome **L**et's **G**et **S**un **B**urned" (Corneum, Lucidum, Granulosum, Spinosum, Basale). [1] * **Dermal Anatomy:** The dermis has two layers: the superficial **Papillary layer** (loose CT) and the deeper, thicker **Reticular layer** (dense irregular CT). Tattoo ink resides primarily in the reticular layer. [1] * **Clinical Correlation:** Laser tattoo removal works by breaking down these large ink particles into smaller fragments that the lymphatic system can finally carry away.

Question 158: What is the best marker for iron deficiency?

A. Serum iron
B. Serum ferritin (Correct Answer)
C. Total iron binding capacity
D. Transferrin saturation

Explanation: **Explanation:** **Serum ferritin** is considered the most reliable and sensitive biochemical marker for diagnosing iron deficiency. Ferritin is the primary intracellular storage protein for iron. Since serum ferritin levels are directly proportional to total body iron stores, a low level is highly specific for iron deficiency anemia (IDA), often decreasing before changes in hemoglobin or red cell morphology occur. [1] **Analysis of Incorrect Options:** * **Serum Iron:** This measures the amount of iron circulating in the blood bound to transferrin. It is a poor marker because it fluctuates significantly throughout the day (diurnal variation) and can be affected by recent dietary intake or infection. * **Total Iron Binding Capacity (TIBC):** This measures the blood's capacity to bind iron with transferrin. While TIBC increases in iron deficiency, it is an indirect measure and can be influenced by liver function and nutritional status (e.g., pregnancy or oral contraceptives). * **Transferrin Saturation:** This is the ratio of serum iron to TIBC. While it decreases in IDA, it is less sensitive than ferritin because it relies on serum iron levels, which are inherently unstable. **NEET-PG High-Yield Pearls:** * **Gold Standard:** While serum ferritin is the best *non-invasive* test, the absolute gold standard for assessing iron stores is a **Bone Marrow Aspiration** (Prussian Blue staining), though it is rarely performed for simple IDA. * **The "Acute Phase" Caveat:** Ferritin is an **acute-phase reactant**. In the presence of inflammation, malignancy, or liver disease, ferritin levels may be falsely elevated even if the patient is iron deficient. * **Early Marker:** The very first biochemical change in developing iron deficiency is a **decrease in serum ferritin**. [1]

Question 159: Which one of the following statements about cilia is true?

A. They possess a 9 + 0 configuration of microtubules.
B. They do not contain an axoneme.
C. They contain ciliary dynein arms. (Correct Answer)
D. They are nearly identical to centrioles.

Explanation: ### Explanation **1. Why the Correct Answer is Right:** Cilia are motile, hair-like projections of the plasma membrane. The core of a motile cilium is the **axoneme**, which consists of a central pair of microtubules surrounded by nine peripheral doublets (**9 + 2 arrangement**) [2]. The movement of cilia is powered by **ciliary dynein arms** (adenosine triphosphatase/ATPase) [1]. These arms are attached to the 'A' microtubule of each doublet and reach out to the 'B' microtubule of the adjacent doublet, facilitating the sliding motion required for ciliary beating. **2. Analysis of Incorrect Options:** * **Option A:** Motile cilia have a **9 + 2** configuration [2]. A **9 + 0** configuration is characteristic of **primary (non-motile) cilia**, which lack the central pair and function as sensory receptors. * **Option B:** The **axoneme** is the structural backbone of the cilium; saying they do not contain one is anatomically incorrect. * **Option D:** Cilia are structurally distinct from centrioles. While the **basal body** (which anchors the cilium) has a 9 + 0 triplet arrangement similar to a centriole, the cilium itself has a doublet arrangement (9 + 2 or 9 + 0). **3. Clinical Pearls & High-Yield Facts:** * **Kartagener Syndrome:** A subset of Primary Ciliary Dyskinesia (PCD) caused by a **deficiency in dynein arms**. Clinical triad: *Situs inversus, chronic sinusitis, and bronchiectasis* [3]. * **Infertility:** Ciliary dysfunction leads to male infertility (immotile spermatozoa) and female subfertility (impaired ovum transport in fallopian tubes). * **Location:** Motile cilia are primarily found in the respiratory epithelium (mucociliary escalator) and the female reproductive tract [3].

Question 160: Which of the following is NOT a feature found in the cerebellum?

A. Betz cells (Correct Answer)
B. Climbing fibers
C. Mossy fibers
D. Purkinje cells

Explanation: **Explanation:** The correct answer is **Betz cells** because these are characteristic features of the **Cerebrum**, not the Cerebellum. **1. Why Betz cells is the correct answer:** Betz cells are giant pyramidal neurons located in **Layer V (Internal Pyramidal Layer)** of the primary motor cortex (Brodmann area 4) of the cerebrum. They are the largest neurons in the central nervous system and their axons form part of the corticospinal tract. **2. Why the other options are incorrect:** The cerebellum has a highly organized three-layered cortex (Molecular, Purkinje, and Granular layers) containing specific fibers and cells [1]: * **Purkinje cells:** These are the large, flask-shaped inhibitory neurons found in the middle layer of the cerebellar cortex [1]. They represent the sole output from the cerebellar cortex to the deep cerebellar nuclei [1]. * **Climbing fibers:** These originate from the **inferior olivary nucleus** and wrap around the dendrites of Purkinje cells, providing powerful excitatory input [2]. * **Mossy fibers:** These are the main afferent inputs to the cerebellum (from the spinal cord and pons). They synapse with **granule cells** in specialized structures called cerebellar glomeruli [1]. **High-Yield Facts for NEET-PG:** * **Layers of Cerebellar Cortex (Outer to Inner):** Molecular layer $\rightarrow$ Purkinje cell layer $\rightarrow$ Granular layer [1]. * **Inhibitory Cells:** All cells in the cerebellar cortex are inhibitory (GABAergic) EXCEPT for **Granule cells**, which are excitatory (Glutamatergic) [1]. * **Cerebellar Glomerulus:** A complex synaptic junction consisting of a Mossy fiber terminal, Golgi cell axon, and Granule cell dendrites [1]. * **Clinical Correlation:** Damage to the cerebellum leads to **ipsilateral** symptoms like ataxia, intention tremors, and dysmetria (DANISH mnemonic) [2].

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Histology — MCQs

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