Histology Practice Questions

Q: Glomus cells are found in which of the following locations or structures?

Chemoreceptors. **Explanation:** **Glomus cells** (Type I cells) are specialized peripheral chemoreceptors primarily located in the **Carotid Body** (at the bifurcation of the common carotid artery) and the **Aortic Bodies** (along the aortic arch) [1]. 1. **Why Chemoreceptors is correct:** Glomus cells act as sensory receptors that monitor changes in arterial blood. They are specifically sensitive to **hypoxia** (decreased $PaO_2$), **hypercapnia** (increased $PaCO_2$), and **acidosis** (decreased pH) [1], [2]. When triggered, they release neurotransmitters (like dopamine and acetylcholine) to stimulate the glossopharyngeal (CN IX) and vagus (CN X) nerves, which signal the brainstem to increase the respiratory rate. 2. **Why other options are incorrect:** * **Bladder:** The bladder contains transitional epithelium and detrusor muscle; it does not house glomus cells. * **Brain:** While the brain contains *central* chemoreceptors (in the medulla), these are sensitive to pH/CO2 changes in the CSF, not glomus cells. * **Kidney:** The kidney contains **Juxtaglomerular (JG) cells**, which secrete renin [3]. Though the names sound similar, their functions are entirely different. **High-Yield Clinical Pearls for NEET-PG:** * **Embryology:** Glomus cells are derived from the **Neural Crest**. * **Glomus Tumor (Paraganglioma):** A highly vascular tumor arising from these cells. A common site is the **Glomus Jugulare** (near the jugular bulb), often presenting with pulsatile tinnitus and cranial nerve palsies. * **Histology:** On H&E stain, they appear as clusters of cells called **"Zellballen"** surrounded by a rich vascular network and sustentacular (Type II) cells.

Q: Which of the following is the epithelial lining of the vagina?

Stratified squamous non-keratinized. The vagina is a muscular canal lined by **Stratified Squamous Non-keratinized Epithelium**. This histological structure is specifically adapted to withstand mechanical stress and friction during coitus and childbirth. **Why Option A is correct:** The multiple layers of squamous cells provide a protective barrier. Under the influence of estrogen, these cells accumulate **glycogen**. When these cells desquamate, the glycogen is fermented by commensal bacteria (*Döderlein’s bacilli* / Lactobacillus) into **lactic acid**, maintaining an acidic vaginal pH (3.8–4.5), which inhibits the growth of pathogens. **Why other options are incorrect:** * **B. Columnar:** This lining is found in the endocervix and the rest of the female reproductive tract (uterus and fallopian tubes) [1]. The transition from columnar to squamous epithelium occurs at the **Squamocolumnar Junction** (Transformation Zone) of the cervix [1]. * **C. Stratified squamous keratinized:** This is found in the skin (epidermis) [2]. Keratin provides a waterproof, protective layer against desiccation, which is unnecessary in the moist environment of the vagina. * **D. Cuboidal:** Simple cuboidal epithelium is typically found in glandular ducts or the germinal epithelium of the ovary, not in areas prone to high friction. **High-Yield Clinical Pearls for NEET-PG:** * **Embryology:** The upper 1/3rd of the vagina is derived from **Müllerian ducts** (Mesoderm), while the lower 2/3rds is derived from the **Urogenital sinus** (Endoderm) [2]. * **Vaginal pH:** It is acidic during reproductive years but becomes neutral/alkaline before puberty and after menopause due to low estrogen levels. * **Cytology:** The cells seen on a Pap smear from the ectocervix/vagina are these stratified squamous cells [2].

Q: What are the transmembrane adhesive molecules present in hemidesmosomes that specifically bind to the basal lamina glycoprotein laminin?

integrin α6-β4. **Explanation:** **1. Why Option A is Correct:** Hemidesmosomes are specialized junctional complexes that anchor the basal surface of epithelial cells to the underlying basement membrane (basal lamina). The primary transmembrane proteins in hemidesmosomes are **integrins**, specifically **integrin α6β4**. Unlike other integrins that bind to the extracellular matrix via actin filaments, α6β4 connects intracellularly to **keratin intermediate filaments** (via plectin and BP180) and extracellularly to **laminin-332** in the basal lamina. This linkage is crucial for maintaining dermo-epidermal stability. **2. Why Other Options are Incorrect:** * **Option B (Desmoplakin):** This is an intracellular **plaque protein** found in desmosomes (not hemidesmosomes) that links cadherins to intermediate filaments. It is not a transmembrane molecule. * **Option C (Desmoglein):** This is a transmembrane protein belonging to the **cadherin** family. It is found in **desmosomes** (cell-to-cell junctions), not hemidesmosomes, and mediates adhesion between adjacent keratinocytes. * **Option D (α and β catenin):** These are intracellular signaling and anchoring proteins found in **Adherens junctions** (Zonula adherens). They link transmembrane E-cadherin to the **actin cytoskeleton**, not the basal lamina. **3. Clinical Pearls for NEET-PG:** * **Bullous Pemphigoid:** An autoimmune blistering disease where antibodies target **BP180 (Type XVII Collagen)** or **BP230** within the hemidesmosomes. It results in subepidermal blisters. * **Pemphigus Vulgaris:** Antibodies target **Desmoglein 3** (desmosomes), leading to intraepidermal blisters (acantholysis). * **Mnemonic:** **H**emidesmosomes help cells stick to the **H**ypodermis (basal lamina); **D**esmosomes stick **D**ouble cells together.

Q: What type of epithelium lines the cornea?

Stratified squamous non-keratinizing. **Explanation:** The **cornea** is the transparent anterior part of the eye [1]. Its outermost layer, the corneal epithelium, is composed of **Stratified Squamous Non-Keratinizing Epithelium**. **Why Option A is Correct:** The corneal epithelium consists of 5–6 layers of cells. The basal layer is columnar, the middle layers are wing cells, and the superficial layers are flattened (squamous). It is **non-keratinizing** to maintain transparency and ensure a smooth, moist refractive surface [1]. The presence of keratin would make the cornea opaque and dry, obstructing vision [2]. **Why the Other Options are Incorrect:** * **Option B (Stratified squamous keratinizing):** This is found in the **epidermis of the skin**. Keratin provides a waterproof, protective barrier but is opaque. If the cornea undergoes keratinization (e.g., in severe Vitamin A deficiency), it leads to blindness [2]. * **Options C & D (Columnar):** While the basal layer of the cornea is columnar (for regeneration), the overall classification of a stratified epithelium is always based on the shape of the **superficial layer**, which is squamous in the cornea. **High-Yield NEET-PG Pearls:** 1. **Regeneration:** The corneal epithelium has a high turnover rate (approx. 7 days). It is replenished by stem cells located at the **Limbal Basal Layer** [2] (the junction between the cornea and sclera). 2. **Bowman’s Membrane:** Located just beneath the epithelium; it does not regenerate if damaged, leading to permanent scarring [2]. 3. **Clinical Correlation:** **Vitamin A deficiency** causes squamous metaplasia and keratinization of the cornea (Xerophthalmia), leading to Bitot’s spots and eventually keratomalacia. 4. **Nerve Supply:** The cornea is one of the most sensitive tissues in the body, supplied by the **Ophthalmic nerve (V1)** via long ciliary nerves.

Q: Which of the following are neuroendocrine cells found in the lungs?

APUD cells. **Explanation:** The correct answer is **D. APUD cells**. **Why APUD cells are correct:** APUD (Amine Precursor Uptake and Decarboxylation) cells, also known as **Kulchitsky cells** or Pulmonary Neuroendocrine Cells (PNECs), are specialized cells located within the bronchial epithelium. They function as "chemoreceptors" that sense hypoxia and release bioactive amines and peptides (such as serotonin, calcitonin, and bombesin). These cells are part of the diffuse neuroendocrine system and play a crucial role in lung development and the regulation of airway tone. **Why other options are incorrect:** * **A. Dendritic cells:** These are professional antigen-presenting cells (APCs) of the immune system. They reside in the respiratory epithelium to capture pathogens but do not have neuroendocrine functions. * **B. Type I pneumocytes:** These are thin, squamous cells covering ~95% of the alveolar surface area. Their primary function is to facilitate gas exchange. * **C. Type II pneumocytes:** These are cuboidal cells that act as the "caretakers" of the alveoli. Their primary roles are the secretion of **surfactant** and acting as stem cells to regenerate Type I pneumocytes after injury. **High-Yield Clinical Pearls for NEET-PG:** * **Small Cell Carcinoma of the Lung:** This highly malignant tumor originates from the **Kulchitsky (APUD) cells**. This explains why it is frequently associated with paraneoplastic syndromes (e.g., SIADH, ectopic ACTH). * **Carcinoid Tumor:** This is another neuroendocrine tumor of the lung derived from these cells, typically presenting with serotonin secretion. * **Location:** APUD cells are most numerous in the fetal lung and decrease in number after birth.

Q: Transitional epithelium is present in which of the following locations?

Renal pelvis. **Explanation:** **Transitional epithelium (Urothelium)** is a specialized stratified epithelium unique to the urinary tract [1]. Its primary function is to provide a waterproof barrier while allowing for significant distension and contraction as the volume of urine changes. **Why the Correct Answer is Right:** The **Renal Pelvis** is the beginning of the "excretory" portion of the urinary system. Transitional epithelium lines the entire urinary tract from the **renal calyces** (major and minor) to the **renal pelvis**, **ureters**, **urinary bladder**, and the **proximal part of the urethra** [1]. Its "umbrella cells" (superficial layer) are specifically adapted to resist the osmotic pressure of concentrated urine. **Analysis of Incorrect Options:** * **Loop of Henle:** Lined by **simple squamous epithelium** (thin limbs) and **simple cuboidal epithelium** (thick limbs). These are involved in active transport and passive diffusion, not distension. * **Terminal part of urethra:** In both males and females, the distal-most part of the urethra transitions from transitional/pseudostratified columnar to **non-keratinized stratified squamous epithelium** as it nears the external orifice. * **Proximal Convoluted Tubule (PCT):** Lined by **simple cuboidal epithelium with a prominent brush border** (microvilli) to maximize surface area for reabsorption. **High-Yield Clinical Pearls for NEET-PG:** * **Umbrella Cells:** The topmost layer of transitional epithelium contains "facet cells" or "umbrella cells," which may be binucleated and contain **uroplakin** proteins that form a barrier against urine toxicity [1]. * **Schistosomiasis:** Chronic infection can cause squamous metaplasia of the bladder's transitional epithelium, leading to **Squamous Cell Carcinoma**. * **Key Locations:** Remember the "Calyces to Urethra" rule—if it stores or transports urine (but doesn't filter/modify it), it is likely transitional.

Q: Haversian system is seen in which type of bone tissue?

Cortical bone. The **Haversian system**, also known as an **Osteon**, is the fundamental functional unit of **compact (cortical) bone**. It consists of a central Haversian canal containing blood vessels and nerves, surrounded by concentric layers of mineralized matrix called lamellae [2]. Between these lamellae are lacunae containing osteocytes, which communicate via tiny channels called canaliculi. This dense, organized arrangement provides the structural strength required for the outer shell of long bones [1]. **Analysis of Options:** * **Cortical bone (Correct):** This is the dense outer layer of bone where Haversian systems are tightly packed to withstand mechanical stress [1]. * **Cancellous bone (Incorrect):** Also known as spongy or trabecular bone, it lacks true Haversian systems. Instead, it is composed of an irregular lattice of **trabeculae** [1]. Nutrients are absorbed via diffusion from the surrounding bone marrow spaces. * **Teeth (Incorrect):** While teeth contain mineralized tissues (enamel, dentin, cementum), they do not possess Haversian systems. Dentin contains "dentinal tubules," which are structurally distinct. * **Nail (Incorrect):** Nails are composed of hard **keratin** (a protein), not mineralized bone tissue, and thus have no cellular or vascular organization resembling an osteon. **High-Yield Clinical Pearls for NEET-PG:** * **Volkmann’s Canals:** These are horizontal canals that connect adjacent Haversian systems and carry blood vessels from the periosteum. * **Interstitial Lamellae:** These are the remnants of old Haversian systems found between intact osteons, representing the result of continuous bone remodeling. * **Woven Bone:** This is immature bone where collagen fibers are randomly arranged; it lacks Haversian systems and is seen during fetal development or fracture healing [2].

Q: Which cells are located outside the blood-testis barrier?

Leydig cells. ### Explanation The **Blood-Testis Barrier (BTB)** is a physical barrier formed by **tight junctions (zonula occludens)** between adjacent **Sertoli cells**. Its primary function is to divide the seminiferous epithelium into a basal compartment and an adluminal compartment, protecting developing germ cells from the immune system. **Why Leydig Cells are the Correct Answer:** Leydig cells are located in the **interstitial space** (the connective tissue between seminiferous tubules). Since the BTB is formed within the walls of the seminiferous tubules themselves, any cell located in the interstitium is outside this barrier. Leydig cells are exposed to systemic circulation, allowing them to respond to Luteinizing Hormone (LH) and secrete testosterone directly into the bloodstream. **Analysis of Incorrect Options:** * **Sertoli cells:** These cells actually **form** the barrier. While their nuclei are in the basal compartment, their tight junctions create the seal that defines the BTB. * **Spermatocytes:** Primary spermatocytes must cross the BTB to enter the adluminal compartment for meiosis. Once they transition, they are protected inside the barrier. * **Spermatids:** These are mature haploid cells located in the adluminal compartment, deep within the protection of the BTB, to prevent an autoimmune response against "foreign" haploid antigens. **High-Yield Clinical Pearls for NEET-PG:** * **Basal Compartment:** Contains Spermatogonia and pre-leptotene spermatocytes. * **Adluminal Compartment:** Contains Spermatocytes, Spermatids, and Spermatozoa. * **Function:** The BTB prevents **anti-sperm antibodies** from forming. Disruption of this barrier (via trauma, infection, or vasectomy) can lead to immune-mediated infertility. * **Testosterone Paradox:** While Leydig cells are outside the barrier, the testosterone they produce must cross into the tubules (aided by Androgen Binding Protein) to support spermatogenesis.

Question 1

Glomus cells are found in which of the following locations or structures?

Accepted Answer

Chemoreceptors

Answer

Bladder

Answer

Brain

Answer

Kidney

Question 2

Which of the following is the epithelial lining of the vagina?

Accepted Answer

Stratified squamous non-keratinized

Answer

Columnar

Answer

Stratified squamous keratinized

Answer

Cuboidal

Question 3

Which cells secrete the basal lamina of blood vessels in the CNS?

Accepted Answer

Endothelial cells

Answer

Oligodendrocytes

Answer

Microglia

Answer

Astrocytes

Question 4

What are the transmembrane adhesive molecules present in hemidesmosomes that specifically bind to the basal lamina glycoprotein laminin?

Accepted Answer

integrin α6-β4

Answer

the catenins desmoplakin

Answer

cadherins desmoglein

Answer

α and β catenin

Question 5

What type of epithelium lines the cornea?

Accepted Answer

Stratified squamous non-keratinizing

Answer

Stratified squamous keratinizing

Answer

Columnar keratinized

Answer

Columnar non-keratinized

Question 6

Which of the following are neuroendocrine cells found in the lungs?

Accepted Answer

APUD cells

Answer

Dendritic cells

Answer

Type I pneumocytes

Answer

Type II pneumocytes

Question 7

Transitional epithelium is present in which of the following locations?

Accepted Answer

Renal pelvis

Answer

Loop of Henle

Answer

Terminal part of urethra

Answer

Proximal convoluted tubule (PCT)

Question 8

Haversian system is seen in which type of bone tissue?

Accepted Answer

Cortical bone

Answer

Cancellous bone

Answer

Teeth

Answer

Nail

Question 9

A 35-year-old male presents for an infertility evaluation. A biopsy of his testis is performed to assess sperm production and maturation. A microscopic section reveals only a few germ cells near the basal lamina in the seminiferous tubule. Which of the following cells is the germ cell closest to the basal lamina in the seminiferous tubule?

Accepted Answer

Spermatogonia

Answer

Primary spermatocyte

Answer

Secondary spermatocyte

Answer

Spermatid

Question 10

Which cells are located outside the blood-testis barrier?

Accepted Answer

Leydig cells

Answer

Sertoli cells

Answer

Spermatocyte

Answer

Spermatid

Histology — MCQs

Histology — MCQs

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