Histology Practice Questions

Q: Purkinje fibres are:

Modified cardiac muscle. **Explanation:** **Why Option C is Correct:** Purkinje fibers are specialized **modified cardiac muscle cells** (myocytes) that form the terminal portion of the heart's conduction system. Although they function to conduct electrical impulses, they are embryologically derived from cardiogenic mesoderm, not neural tissue. Structurally, they are larger than typical ventricular myocytes, contain fewer myofibrils, and are rich in glycogen, which allows them to conduct action potentials at the highest velocity in the heart (approx. 1.5–4.0 m/s). **Why Other Options are Incorrect:** * **Option A:** While they conduct impulses like nerves, they lack the histological characteristics of neurons (e.g., axons, dendrites). They are "myogenic," not "neurogenic." * **Option B:** Smooth muscle is found in hollow organs and blood vessels; the conduction system is strictly a specialization of the myocardium (striated muscle). * **Option D:** Fibrous tissue (like the Annulus Fibrosus) acts as an electrical insulator in the heart. Purkinje fibers are excitable tissues, the opposite of inert fibrous tissue. **High-Yield NEET-PG Pearls:** 1. **Conduction Velocity:** Purkinje fibers have the **fastest conduction velocity** in the heart, while the AV node has the slowest (AV nodal delay). 2. **Pacemaker Hierarchy:** Purkinje fibers act as tertiary pacemakers with an intrinsic firing rate of **15–40 bpm**. 3. **Histology:** They appear "pale" under a microscope due to high glycogen content and fewer contractile filaments. 4. **Location:** They are located in the **subendocardial** layer of the ventricular walls.

Q: Microscopic examination of the articular surface of a synovial joint demonstrates the following histology representing:

Hyaline cartilage. ***Hyaline cartilage*** - The articular surface of synovial joints is covered by **hyaline cartilage**, which provides a smooth, low-friction surface for joint movement and acts as a **shock absorber**. - Histologically, it shows **chondrocytes** residing in **lacunae** within a homogeneous **basophilic matrix** rich in **type II collagen** and **proteoglycans**, with no **perichondrium** at the articular surface. *Adipocytes* - **Fat cells** are not found on the articular surface but may be present in the **synovial membrane** and **joint capsule**. - They appear as large cells with **peripheral nuclei** and **clear cytoplasm** due to lipid content, which is distinctly different from cartilage matrix. *Endothelial cells* - These **flat, elongated cells** line blood vessels and are not present on the **avascular** articular cartilage surface. - They form the **tunica intima** of blood vessels and have a characteristic **cobblestone appearance** when viewed en face. *Periosteum* - This is a **fibrous membrane** covering bone surfaces, not the articular cartilage of joints. - It consists of an outer **fibrous layer** and inner **cambium layer** with **osteoprogenitor cells**, and is absent from articular surfaces.

Q: B-cells are dispersed in which part of the spleen?

White pulp. **Explanation:** The spleen is divided into two distinct functional components: the **White Pulp** and the **Red Pulp**. **Why White Pulp is correct:** The white pulp represents the lymphoid tissue of the spleen and is responsible for the immune response. It is organized around the central arterioles. B-cells are primarily located within the **lymphatic follicles** (or Malpighian corpuscles) of the white pulp. When activated, these follicles develop germinal centers where B-cells proliferate. In contrast, T-cells are mainly found in the **Periarteriolar Lymphoid Sheath (PALS)** surrounding the central artery. **Why other options are incorrect:** * **Red pulp:** This area consists of splenic sinusoids and Cords of Billroth. Its primary function is the filtration of blood, removal of aged/damaged erythrocytes, and storage of platelets [1]. While some lymphocytes pass through, it is not the site where B-cells are "dispersed" or organized. * **Capsule:** The capsule is a thick connective tissue covering composed of collagen and elastic fibers. It provides structural integrity but does not contain functional lymphoid aggregates like B-cells. **NEET-PG High-Yield Pearls:** * **PALS (Periarteriolar Lymphoid Sheath):** Specifically contains **T-cells** (CD4+ and CD8+). * **Marginal Zone:** The interface between red and white pulp; it contains specialized macrophages and B-cells that respond to encapsulated bacteria (e.g., *S. pneumoniae*, *H. influenzae*). * **Splenectomy Risk:** Patients are at high risk for **OPSI** (Overwhelming Post-Splenectomy Infection) due to the loss of these B-cell-rich follicles and marginal zone macrophages which produce IgM against encapsulated organisms [2].

Q: Which of the following cell types are NOT found in the stomach?

Goblet cells. ### Explanation The stomach mucosa is characterized by gastric pits and glands lined by specific secretory cells. The correct answer is **Goblet cells**, as these are characteristic of the **intestinal mucosa** (small and large intestine), not the stomach. **1. Why Goblet Cells are the correct answer:** Goblet cells are unicellular mucous glands found interspersed among the enterocytes of the intestines. In the stomach, surface protection is provided by **surface mucous cells** and **mucous neck cells**, which form a continuous epithelial sheet [3]. The presence of Goblet cells in the stomach is a pathological finding known as **Intestinal Metaplasia**, often a precursor to gastric adenocarcinoma, usually resulting from chronic irritation (e.g., H. pylori infection). **2. Why the other options are incorrect:** * **Chief (Zymogenic) Cells:** Located in the base of gastric glands, they secrete pepsinogen and gastric lipase [3], [1]. * **Parietal (Oxyntic) Cells:** Located in the neck/body of gastric glands, they secrete Hydrochloric acid (HCl) and Intrinsic Factor (essential for Vitamin B12 absorption) [3], [1]. * **Argentaffin (Enteroendocrine) Cells:** These are part of the APUD system found throughout the GI tract, including the stomach (e.g., G-cells secreting Gastrin, ECL cells secreting Histamine) [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Parietal Cells:** Characterized by an abundance of mitochondria and intracellular canaliculi [2]. They are targeted by Proton Pump Inhibitors (PPIs) [2]. * **Vitamin B12:** Deficiency of Intrinsic Factor (due to parietal cell atrophy in Pernicious Anemia) leads to Megaloblastic Anemia. * **Histology Marker:** The presence of "PAS-positive" Goblet cells in a gastric biopsy is the diagnostic hallmark of intestinal metaplasia.

Q: The receptor cells of the olfactory epithelium are?

Bipolar neurons. ### Explanation **1. Why Bipolar Neurons are Correct:** The olfactory receptor cells are unique because they are **primary sensory neurons** located directly within the olfactory epithelium. They are classic examples of **bipolar neurons**, characterized by a single dendrite extending to the epithelial surface (ending in an olfactory vesicle with cilia) and a single unmyelinated axon that penetrates the cribriform plate to reach the olfactory bulb. Notably, these are among the few neurons in the human body that undergo continuous turnover and replacement throughout life from basal stem cells. **2. Why Other Options are Incorrect:** * **Unipolar/Pseudounipolar neurons:** These are typically found in the dorsal root ganglia of spinal nerves and sensory ganglia of cranial nerves. They have a single process that divides into peripheral and central branches. * **Multipolar neurons:** These are the most common type of neurons in the CNS (e.g., motor neurons, pyramidal cells). They possess one axon and multiple dendrites, which is not the morphology of olfactory receptors. * **Stellate cells:** These are star-shaped interneurons found in the cerebral cortex and cerebellum (molecular layer). They serve inhibitory functions rather than primary sensory transduction. **3. High-Yield Clinical Pearls for NEET-PG:** * **First-order neurons:** The olfactory bipolar cells themselves are the first-order neurons (unlike the visual system where photoreceptors are not neurons). * **Regeneration:** Olfactory neurons have a lifespan of about 30–60 days and are replaced by **Basal cells**. * **Anosmia:** Fracture of the **cribriform plate** of the ethmoid bone can shear these bipolar axons, leading to a loss of smell (anosmia) and potentially CSF rhinorrhea. * **Bowman’s Glands:** Located in the olfactory mucosa, they secrete mucus to dissolve odorants; they are *not* the receptors themselves.

Q: Lymphocytes are located in each of the following tissues or organs EXCEPT one. What is the exception?

Brain. The correct answer is **A. Brain**. **1. Why the Brain is the Exception:** The brain is considered an **immunologically privileged site**. Under normal physiological conditions, the **Blood-Brain Barrier (BBB)**—composed of tight junctions between endothelial cells, a thick basement membrane, and astrocyte foot processes—prevents the free entry of peripheral immune cells, including lymphocytes, into the central nervous system (CNS) parenchyma. While the brain has its own resident immune cells called **microglia** (derived from yolk sac macrophages), it lacks organized lymphatic tissue and a resident lymphocyte population [1]. **2. Analysis of Incorrect Options:** * **B. Spleen:** This is the largest secondary lymphoid organ. The **White Pulp** of the spleen specifically contains the Periarteriolar Lymphoid Sheaths (PALS) rich in T-cells and lymphoid follicles rich in B-cells [2]. * **C. Lymph Nodes:** These are secondary lymphoid organs designed to filter lymph. They contain distinct regions for lymphocytes: the **cortex** (B-cells) and the **paracortex** (T-cells) [1]. * **D. Thymus Gland:** This is a primary lymphoid organ. It is the site of **T-cell maturation** and differentiation, where thymocytes (immature lymphocytes) undergo positive and negative selection [1]. **3. NEET-PG High-Yield Pearls:** * **Microglia:** The only immune cells resident in the brain; they are of mesenchymal origin, unlike neurons/glia which are neuroectodermal [1]. * **MALT:** Lymphocytes are also found in Mucosa-Associated Lymphoid Tissue (e.g., Peyer’s patches in the ileum, tonsils). * **Glymphatic System:** While the brain lacks traditional lymphatics, the "glymphatic system" facilitates waste clearance via CSF and interstitial fluid exchange. * **Virchow-Robin Spaces:** Small numbers of lymphocytes may be found in these perivascular spaces, but not within the brain tissue itself.

Q: Birbeck granules are seen in the cytoplasm of which of the following cells?

Langerhans cells. **Explanation:** **Langerhans cells (Option B)** are the correct answer. These are dendritic, antigen-presenting cells (APCs) located primarily in the **stratum spinosum** of the epidermis. Under electron microscopy, they exhibit characteristic rod-shaped or "tennis-racket" shaped cytoplasmic organelles known as **Birbeck granules**. These granules contain a protein called **Langerin (CD207)**, which is involved in the endocytosis and degradation of viruses. **Analysis of Incorrect Options:** * **Mast cells (Option A):** These contain coarse basophilic granules filled with histamine and heparin. They are involved in Type I hypersensitivity reactions but do not possess Birbeck granules. * **Thrombocytes (Option C):** Also known as platelets, they contain alpha and dense granules involved in coagulation, but lack Birbeck granules. * **Myelocytes (Option D):** These are precursors in granulopoiesis (white blood cell formation) and contain primary (azurophilic) and secondary (specific) granules, but not Birbeck granules. **High-Yield Clinical Pearls for NEET-PG:** * **Origin:** Langerhans cells are derived from the **bone marrow** (monocyte-macrophage lineage). * **Immunohistochemistry (IHC) Markers:** They are positive for **S-100**, **CD1a**, and **CD207 (Langerin)**. * **Clinical Correlation:** Proliferation of these cells leads to **Langerhans Cell Histiocytosis (LCH)**. On imaging, LCH often presents with "punched-out" lytic bone lesions (especially in the skull) and a "floating-in-air" appearance of teeth on dental X-rays. * **Stain:** Gold chloride stain is used to visualize them under light microscopy.

Q: Which of the following is associated with ependymal cells rather than microglial cells?

Blepharoplasts. **Explanation:** **1. Why Blepharoplasts are the correct answer:** Ependymal cells are simple cuboidal-to-columnar epithelial cells that line the ventricles of the brain and the central canal of the spinal cord. Many ependymal cells possess **cilia** to facilitate the movement of cerebrospinal fluid (CSF). **Blepharoplasts** (also known as basal bodies) are the specialized centriole-derived structures located at the base of these cilia that anchor them to the cytoskeleton. Their presence is a characteristic histological feature of ependymal cells, especially in the choroid plexus [3]. **2. Why the other options are incorrect:** * **B. Rod cells:** These are elongated, activated forms of **microglia** seen in pathological states like neurosyphilis or viral encephalitis [1]. * **C. Gitter cells:** These are "compound granular corpuscles" or lipid-laden macrophages derived from **microglia** after they have phagocytosed necrotic neural tissue (seen in liquefactive necrosis/infarcts) [2]. * **D. Reservoir for HIV:** In the Central Nervous System, **microglia** (and macrophages) are the primary targets and reservoirs for HIV, as they possess CD4 receptors and CCR5/CXCR4 co-receptors [2]. **Clinical Pearls & High-Yield Facts for NEET-PG:** * **Origin:** Ependymal cells are derived from the **neuroectoderm**, whereas microglia are the only glial cells derived from the **mesoderm** (monocyte-macrophage lineage) [2]. * **Tanycytes:** Specialized ependymal cells found in the floor of the 3rd ventricle that transport hormones from CSF to the hypophyseal portal system. * **Ependymoma:** A common pediatric CNS tumor; histologically characterized by **perivascular pseudorosettes** and blepharoplasts (visible on electron microscopy) [3].

Q: The type of cartilage shown in the color plate is:

Hyaline cartilage. ***Hyaline cartilage*** - Characterized by a **homogeneous, glassy matrix** with evenly distributed **chondrocytes** in lacunae, appearing translucent under microscopy. - Most common type found in **articular surfaces**, **tracheal rings**, **costal cartilages**, and **nasal septum**. *Elastic cartilage* - Contains abundant **elastic fibers** in the matrix, giving it a yellowish appearance and greater flexibility. - Primarily found in the **external ear (auricle)**, **epiglottis**, and **auditory tube**, not matching typical hyaline cartilage locations. *Fibrocartilage* - Distinguished by dense bundles of **collagen fibers** arranged in parallel rows between chondrocytes. - Found in **intervertebral discs**, **menisci**, and **pubic symphysis** where tensile strength is required. *Mixed cartilage* - This is not a recognized histological classification of cartilage tissue. - Cartilage is categorized into only **three main types**: hyaline, elastic, and fibrocartilage based on matrix composition.

Q: Which of the following cells is NOT present in the parathyroid gland?

Parietal cells. The parathyroid gland is an endocrine organ responsible for calcium homeostasis [1]. To identify the correct answer, one must distinguish between the cellular components of the endocrine system and the gastrointestinal system. **Why Parietal Cells is the correct answer:** **Parietal cells** (also known as oxyntic cells) are located in the **gastric glands of the stomach**, not the parathyroid gland. Their primary function is the secretion of hydrochloric acid (HCl) and intrinsic factor. Confusingly, "oxyntic" sounds similar to "oxyphil," which is a common trap in histology questions. **Analysis of Incorrect Options:** * **Chief cells:** These are the most numerous cells in the parathyroid gland [1][2]. They are small, polygonal cells with central nuclei that secrete **Parathyroid Hormone (PTH)** in response to low serum calcium [3]. * **Oxyphil cells:** These are larger, acidophilic cells that appear after puberty [2]. They contain abundant mitochondria [1]. While their exact function is unclear, they increase in number with age [2]. * **Water-clear cells (Wasserhelle cells):** These are rare cells with abundant cytoplasmic glycogen, giving them a "clear" appearance [1]. They are considered a variant of chief cells and are often prominent in cases of parathyroid hyperplasia. **High-Yield Clinical Pearls for NEET-PG:** * **Embryology:** The superior parathyroids develop from the **4th pharyngeal pouch**, while the inferior parathyroids develop from the **3rd pharyngeal pouch** (along with the thymus). * **PTH Action:** PTH increases bone resorption, increases renal calcium reabsorption, and stimulates the synthesis of active Vitamin D (1,25-dihydroxycholecalciferol) in the kidneys [3]. * **Histology Tip:** If a question mentions "nests of cells" with "adipocytes" in an endocrine gland, think Parathyroid. In older adults, adipose tissue can make up to 50% of the gland [1].

Question 1

Purkinje fibres are:

Accepted Answer

Modified cardiac muscle

Answer

Modified nerve fibres

Answer

Modified smooth muscle

Answer

Fibrous tissue

Question 2

Microscopic examination of the articular surface of a synovial joint demonstrates the following histology representing:

Accepted Answer

Hyaline cartilage

Answer

Adipocytes

Answer

Endothelial cells

Answer

Periosteum

Question 3

B-cells are dispersed in which part of the spleen?

Accepted Answer

White pulp

Answer

Red pulp

Answer

Capsule

Answer

None

Question 4

Which of the following cell types are NOT found in the stomach?

Accepted Answer

Goblet cells

Answer

Chief cells

Answer

Parietal cells

Answer

Argentaffin cells

Question 5

The receptor cells of the olfactory epithelium are?

Accepted Answer

Bipolar neurons

Answer

Unipolar neurons

Answer

Multipolar neurons

Answer

Stellate cells

Question 6

Lymphocytes are located in each of the following tissues or organs EXCEPT one. What is the exception?

Accepted Answer

Brain

Answer

Spleen

Answer

Lymph nodes

Answer

Thymus gland

Question 7

Birbeck granules are seen in the cytoplasm of which of the following cells?

Accepted Answer

Langerhans cells

Answer

Mast cells

Answer

Thrombocytes

Answer

Myelocytes

Question 8

Which of the following is associated with ependymal cells rather than microglial cells?

Accepted Answer

Blepharoplasts

Answer

Rod cells

Answer

Gitter cells

Answer

Reservoir for HIV

Question 9

The type of cartilage shown in the color plate is:

Accepted Answer

Hyaline cartilage

Answer

Elastic cartilage

Answer

Fibrocartilage

Answer

Mixed cartilage

Question 10

Which of the following cells is NOT present in the parathyroid gland?

Accepted Answer

Parietal cells

Answer

Chief cells

Answer

Oxyphil cells

Answer

Water-clear cells

Histology — MCQs

Histology — MCQs

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