Microscopic Anatomy — MCQs

Microscopic Anatomy Indian Medical PG Practice Questions and MCQs

Question 231: Where is the density of the parafollicular cells (C-cells) in the thyroid gland at its maximum?

A. Isthmus
B. Upper one-third of the gland
C. Juncture of the upper one-third and lower two-thirds of the gland (Correct Answer)
D. Posterior part

Explanation: ***Juncture of the upper one-third and lower two-thirds of the gland*** - **Parafollicular cells** (C-cells) are neuroectodermal cells derived from the **ultimobranchial body** that migrate into the thyroid during embryological development. - They are maximally concentrated at the **junction of the upper and middle thirds** of the lateral lobes, particularly in the **interfollicular spaces**. - This anatomical distribution is clinically significant as **medullary thyroid carcinoma**, which originates from C-cells, is most commonly found in this region [1]. - The C-cells are responsible for **calcitonin secretion**, which regulates calcium homeostasis [1]. *Upper one-third of the gland* - While C-cells are present in the upper portion of the thyroid, they are not maximally concentrated here. - The peak density occurs more at the **junction zone** rather than exclusively in the upper third. *Isthmus* - The **isthmus** contains relatively **fewer C-cells** compared to the lateral lobes [2]. - The isthmus is primarily composed of follicular thyroid tissue with lower parafollicular cell density. *Posterior part* - While C-cells are distributed throughout the thyroid gland, the **posterior aspect** does not represent the site of maximal concentration. - The **lateral lobes at the junction of upper and middle thirds** have the highest C-cell density.

Question 232: Which of the following structures contains subcapsular sinuses?

A. Spleen
B. Thymus
C. Thyroid
D. Lymph node (Correct Answer)

Explanation: ***Lymph node*** - The **subcapsular sinus** is the space immediately beneath the capsule of a lymph node, where **afferent lymphatic vessels** drain. [1] - This sinus is the initial site where lymph percolates through the node, allowing surveillance by **immune cells**. *Spleen* - The spleen has a complex vascular structure with **red pulp** (involved in filtering blood) and **white pulp** (immune function), but it lacks subcapsular sinuses. [2] - Its primary function is blood filtration and removal of old red blood cells, not lymph filtration. *Thymus* - The thymus is an organ involved in **T-cell maturation** and does not filter lymph. [2] - It is encapsulated but lacks subcapsular sinuses, as its primary role is not to filter afferent lymph. *Thyroid* - The thyroid gland is an **endocrine gland** responsible for producing hormones, not an immune organ involved in filtering lymph. [3] - It consists of follicles and parafollicular cells and does not possess subcapsular sinuses.

Question 233: Follicles are present in which part of lymph nodes?

A. Red pulp
B. White pulp
C. Medulla
D. Cortex (Correct Answer)

Explanation: ***Cortex*** - The **cortex** of a lymph node contains lymphoid follicles, which are sites of **B cell proliferation** and differentiation. - These follicles can be primary (inactive) or secondary (active, with a **germinal center**) based on ongoing immune responses. *Red pulp* - The **red pulp** is a component of the **spleen**, not lymph nodes. - It is primarily involved in filtering blood, removing old or damaged red blood cells, and storing monocytes. *White pulp* - The **white pulp** is also a component of the **spleen**, organized around central arterioles. - It contains periarteriolar lymphoid sheaths (PALS) with T cells and lymphoid follicles with B cells. *Medulla* - The **medulla** of a lymph node is the central region, rich in **medullary cords** (containing plasma cells, macrophages, and B cells) and **medullary sinuses**. - While lymphocytes are present, the organized structures of follicles are characteristic of the cortex.

Question 234: Intermediate filaments in connective tissue are which type of structural component?

A. Keratin
B. Vimentin (Correct Answer)
C. Lamin
D. Desmin

Explanation: ***Vimentin*** - **Vimentin** is the most common intermediate filament found in cells of **mesenchymal origin**, including those in connective tissue (e.g., fibroblasts) [1]. - It plays a crucial role in maintaining **cell shape**, integrity, and in processes like cell migration and adhesion within connective tissue [1]. *Keratin* - **Keratins** (also known as cytokeratins) are the primary intermediate filaments found in **epithelial cells**, providing structural integrity to tissues like skin, hair, and nails [1]. - They are not typically found in connective tissue cells, which have different structural requirements. *Desmin* - **Desmin** is an intermediate filament predominantly found in **muscle cells** (skeletal, cardiac, and smooth muscle). - It helps in maintaining the structural and mechanical integrity of the **sarcomere** and muscle fibers. *Lamin* - **Lamins** are unique intermediate filaments that form the **nuclear lamina**, a fibrous network underlying the inner nuclear membrane found in almost all nucleated cells. - They provide structural support to the nucleus and are involved in chromatin organization and gene regulation.

Question 235: In which of the following organs is the Space of Disse found?

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

Explanation: ***Liver*** - The **Space of Disse**, also known as the perisinusoidal space, is a crucial area located in the **liver** between the sinusoidal endothelial cells and the hepatocytes [1]. - This space is involved in the exchange of substances between the blood and liver cells, and it contains **hepatic stellate cells** (Ito cells) which play a role in retinoid storage and liver fibrosis [1]. *Bone* - Bone tissue contains various spaces like bone marrow cavities and lacunae, but not the **Space of Disse**. - Its primary functions are structural support, hematopoiesis, and mineral storage. *Lymph node* - Lymph nodes are part of the immune system and contain sinuses for lymph flow, but not the **Space of Disse**. - They function in filtering lymph and initiating immune responses. *Spleen* - The spleen is involved in filtering blood and immune surveillance, containing red and white pulp, but lacks the **Space of Disse**. - It plays a role in red blood cell turnover and immune responses.

Question 236: Elongated rete pegs are seen in:

A. Alveolar mucosa
B. Floor of the mouth
C. Attached gingiva (Correct Answer)
D. Buccal mucosa

Explanation: ***Attached gingiva*** - The **attached gingiva** is characterized by a **keratinized stratified squamous epithelium** with prominent, **elongated rete pegs** that interdigitate with the underlying connective tissue. - This anatomical feature provides a strong attachment to the underlying bone, contributing to its immobility and resistance to functional stress. *Alveolar mucosa* - The **alveolar mucosa** is composed of a **non-keratinized stratified squamous epithelium** with a relatively smooth interface between the epithelium and connective tissue, exhibiting short or absent rete pegs. - Its loose connective tissue and lack of keratinization make it highly movable and less resistant to abrasion compared to attached gingiva. *Floor of the mouth* - The epithelium of the **floor of the mouth** is typically **non-keratinized**, thin, and relatively smooth, featuring **short or flattened rete pegs**. - This characteristic allows for flexibility and is involved in salivary gland secretions, lacking the robust interdigitations seen in attached gingiva. *Buccal mucosa* - **Buccal mucosa** is lined by **non-keratinized stratified squamous epithelium** with **short, irregular rete pegs**, making it flexible and well-adapted for chewing and speech. - It serves as a protective lining for the inner cheek and lacks the tightly interdigitated, elongated rete pegs characteristic of keratinized tissues like attached gingiva.

Question 237: Which one of the following possesses a distinct internal elastic lamina?

A. Arteriole
B. Capillary
C. Metarteriole
D. Muscular artery (Correct Answer)

Explanation: ***Muscular artery*** - **Muscular arteries** have a well-developed, distinct **internal elastic lamina** [1] between the tunica intima and tunica media. - This lamina helps to maintain blood pressure and regulate blood flow to various organs. *Capillary* - **Capillaries** are the smallest blood vessels, consisting only of an **endothelial layer** [1] and basement membrane. - They lack a distinct internal elastic lamina, as their primary function is efficient **exchange of nutrients** [2] and waste products. *Metarteriole* - **Metarterioles** are small-diameter vessels leading to capillaries, characterized by scattered **smooth muscle cells** [1] rather than a continuous muscular layer. - They do not possess a distinct internal elastic lamina; their structure is transitional between arterioles and capillaries. *Arteriole* - **Arterioles** generally have a thinner and less distinct elastic lamina compared to muscular arteries [1], or it may be entirely absent in the smallest arterioles. - Their primary role is to regulate **blood flow** and **peripheral resistance** through constriction and dilation of their smooth muscles.

Question 238: Which laryngeal cartilage is elastic?

A. Cuneiform
B. Epiglottis (Correct Answer)
C. Corniculate
D. Thyroid

Explanation: ***Epiglottis*** - The **epiglottis** is the **largest** laryngeal cartilage composed of **elastic cartilage**, which allows it to be flexible and return to its original shape after bending. - This flexibility is crucial for its function in covering the laryngeal opening during swallowing, preventing food and liquids from entering the trachea. - It is the **most clinically significant** elastic cartilage of the larynx and the primary answer when asked about elastic laryngeal cartilages. *Corniculate* - **Corniculate cartilages** are small, paired cartilages also composed of **elastic cartilage** (not hyaline). - They are located at the apex of the arytenoid cartilages. - While elastic, they are much smaller and less significant than the epiglottis. *Cuneiform* - **Cuneiform cartilages** are also composed of **elastic cartilage** (not hyaline). - They are small, rod-shaped cartilages located within the aryepiglottic folds. - Like the corniculate cartilages, they are minor elastic cartilages compared to the epiglottis. *Thyroid* - The **thyroid cartilage**, the largest laryngeal cartilage overall, is composed of **hyaline cartilage**. - Its rigid structure provides protection for the vocal cords and forms the anterior wall of the larynx.

Question 239: What is the primary organic component of bone?

A. 10% collagen
B. 10% noncollagenous protein
C. 20% noncollagenous protein
D. 90% collagen protein (Correct Answer)

Explanation: ***90% collagen protein*** - **Type I collagen** constitutes around 90% of the organic matrix of bone, providing its tensile strength and flexibility [1]. - This extensive collagen network forms the framework upon which **mineral crystals** (hydroxyapatite) are deposited [1]. *10% collagen* - This percentage is significantly lower than the actual proportion of collagen in the organic matrix of bone. - If collagen only represented 10%, bone would lack its characteristic **tensile strength** and elasticity [2]. *10% noncollagenous protein* - While noncollagenous proteins like **osteocalcin** and **osteonectin** are important for bone mineralization and cell signaling, they only constitute about 10% of the *organic matrix*, not the entire bone, and are not the *primary organic component* [1]. - The dominant organic component is collagen, which provides the structural scaffold [1]. *20% noncollagenous protein* - This percentage is inaccurate; **noncollagenous proteins** typically make up about 10% of the bone's organic matrix [1]. - A higher proportion of noncollagenous proteins would alter the bone's mechanical properties, potentially making it more brittle.

Question 240: Capsule of the crystalline lens is thinnest at:

A. Anterior pole
B. Equator
C. Posterior pole (Correct Answer)
D. None of the options

Explanation: ***Posterior pole*** - The **lens capsule** is a basement membrane that completely encloses the lens. It is thinnest at the **posterior pole**, measuring about 2-4 μm. - Its thinness in this region explains why **posterior subcapsular cataracts** are common and why a posterior capsule rupture is a significant complication during cataract surgery. *Anterior pole* - The **anterior capsule** is generally thicker than the posterior capsule, with the thickest part being near the **anterior pole** (around 13-16 μm). - This region is exposed to the aqueous humor and plays a role in the lens's metabolism and protection. *Equator* - The capsule at the **equator** of the lens has an intermediate thickness, typically around 10-12 μm. - This area is where the **zonular fibers** attach, supporting the lens and facilitating accommodation. *None of the options* - This option is incorrect because the lens capsule does exhibit varying thickness, with specific regions being distinctly thinner or thicker than others.

Practice by Chapter

Cellular Ultrastructure

Practice Questions

Microscopic Anatomy of Epithelial Tissues

Practice Questions

Microscopic Anatomy of Connective Tissues

Practice Questions

Microscopic Anatomy of Muscle Tissues

Practice Questions

Microscopic Anatomy of Nervous Tissues

Practice Questions

Microscopic Anatomy of Blood and Immune System

Practice Questions

Microscopic Anatomy of Endocrine Glands

Practice Questions

Microscopic Anatomy of Digestive System

Practice Questions

Microscopic Anatomy of Respiratory System

Practice Questions

Microscopic Anatomy of Urinary System

Practice Questions

Microscopic Anatomy of Reproductive System

Practice Questions

Techniques in Microscopic Anatomy

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free