Histology Practice Questions

Q: Which of the following is correct about the type of neuron shown below?

Pseudo-unipolar cell. ***Pseudo-unipolar cell*** - The image shows a neuron with a **single process** emerging from the cell body that then **divides into two branches** (one leading to dendrites and the other to the axon terminal), which is characteristic of a pseudo-unipolar neuron. - These neurons are typically found in **sensory ganglia**, such as the dorsal root ganglia, where they transmit sensory information. *Bipolar neuron* - A bipolar neuron has **two distinct processes** extending from the cell body: one axon and one dendrite. - Examples include neurons found in the **retina** and **olfactory epithelium**. *Unipolar cell* - A unipolar neuron has a **single process** extending from the cell body, which serves as both the dendrite and the axon. - These are typically found in **invertebrates**, though the term can sometimes be confusingly used for pseudo-unipolar neurons in some contexts. *All of the above* - This is incorrect because the neuron depicted specifically matches the morphology of a pseudo-unipolar cell, not all the listed types. - Each neuron type has distinct morphological features (number of poles/processes from the cell body).

Q: Which of the following is correct about the image shown below?

A=Hemidesmosomes, B=Desmosomes, C=Tight junctions. ***Correct: A=Hemidesmosomes, B=Desmosomes, C=Tight junctions*** - Structure **A** is located at the **basal side** of the cell, anchoring the cell to the **basement membrane**, which is the characteristic function of **hemidesmosomes** - Structure **B** connects two adjacent cells and is associated with **intermediate filaments** (keratin), which is typical of **desmosomes** - Structure **C** is at the **apical side** of the lateral membrane, forming a **sealing barrier** between cells, representing **tight junctions (zonula occludens)** *Incorrect: A=Desmosomes, B=Hemidesmosomes, C=Tight junctions* - This incorrectly identifies **A** as desmosomes, which connect adjacent cells laterally via intermediate filaments, not cells to the basement membrane - It also incorrectly identifies **B** as hemidesmosomes, which should be located at the basal surface anchoring to the basement membrane, not between adjacent cells *Incorrect: A=Desmosomes, B=Hemidesmosomes, C=Zona Occludens* - While this correctly uses **"Zona Occludens"** as a synonym for tight junctions for structure **C**, it incorrectly identifies structures **A** and **B** - **Desmosomes** are cell-to-cell junctions found laterally, not at the basal surface where structure A is located - **Hemidesmosomes** anchor to the basal lamina, not between two adjacent cells where structure B is shown *Incorrect: A=Desmosomes, B=Hemidesmosomes, C=Gap junctions* - This incorrectly identifies **A** as desmosomes and **B** as hemidesmosomes for the same reasons as above - Furthermore, **gap junctions** facilitate direct cell-to-cell communication via **connexons**, allowing passage of small molecules and ions, which is functionally different from structure **C** that acts as a sealing barrier preventing paracellular transport

Q: Identify the cells marked X in the image shown below.

Mesangial cells. ***Mesangial cells*** - The cells labeled 'X' are situated within the **glomerular tuft**, between the capillaries of the glomerulus. - These cells provide **structural support** to the glomerulus and have contractile, phagocytic, and proliferative properties. *Lacis cells* - Lacis cells, or **extraglomerular mesangial cells**, are part of the juxtaglomerular apparatus but are typically located outside the glomerulus, between the afferent and efferent arterioles and the macula densa. - They are primarily involved in **regulating glomerular filtration rate** and modulating renin release. *Macula densa* - The macula densa consists of **specialized columnar cells** lining the wall of the distal convoluted tubule where it contacts the afferent and efferent arterioles. - Its main function is to **sense sodium chloride concentration** in the filtrate, thereby regulating renin secretion and glomerular filtration. *Podocytes* - Podocytes are highly specialized **epithelial cells** that form the visceral layer of Bowman's capsule, directly wrapping around the glomerular capillaries. - They contribute to the **filtration barrier** through their foot processes and slit diaphragms.

Q: The fiber marked as X is:

Modified cardiac muscle. ***Modified cardiac muscle*** - The fiber marked as X represents **Purkinje fibers**, which are part of the cardiac conduction system consisting of **specialized cardiac muscle cells** (modified cardiomyocytes). - These cells have **lost most of their contractile elements** and have developed specialized properties for **rapid electrical impulse conduction** throughout the ventricles. - Histologically, they are **larger and paler** than regular cardiac muscle cells, with abundant glycogen and fewer myofibrils, but they retain their cardiac muscle origin and characteristics. - Found in the **subendocardial layer** of the ventricles, they are the terminal component of the cardiac conduction system. *Modified nerve fiber* - This is a **common misconception**. While Purkinje fibers conduct electrical impulses rapidly (similar to nerve fibers), they are **not nerve tissue**. - The cardiac conduction system consists entirely of **modified cardiac muscle cells**, not neurons or nerve fibers. - True nerve fibers (autonomic nervous system) modulate the heart rate but are **separate from the conduction system**. *Nerve fiber* - **Nerve fibers** are axons of neurons and are part of the nervous system. - The cardiac conduction system, including Purkinje fibers, is **not composed of nervous tissue** but rather specialized cardiac muscle. - Autonomic nerve fibers do innervate the heart but are distinct from the conduction system structures. *Modified connective tissue* - **Connective tissue** provides structural support but does not have the ability to generate or conduct electrical impulses. - Purkinje fibers are **specialized cardiac muscle cells**, not connective tissue derivatives.

Q: In this electron micrograph, identify the structure marked with arrow.

Smooth endoplasmic reticulum. ***Smooth endoplasmic reticulum*** - The image shows a network of **tubular structures** that are interconnected and lack ribosomes, which is characteristic of the smooth endoplasmic reticulum. - The smooth endoplasmic reticulum is involved in various metabolic processes, including **lipid synthesis**, detoxification, and calcium storage. *Trans Golgi network* - The trans Golgi network consists of **flattened sacs (cisternae)** and is the exit face of the Golgi apparatus, where proteins are sorted and packaged into vesicles. - It would appear as a series of stacked, flattened membranes, often associated with budding vesicles, which is not what the arrow indicates. *Cis Golgi network* - The cis Golgi network is the entry face of the Golgi apparatus, receiving proteins from the ER. It also consists of **flattened cisternae**. - It is located closest to the endoplasmic reticulum and looks like flattened sacs rather than a tubular network. *Medial Golgi network* - The medial Golgi network comprises the cisternae located between the cis and trans faces, involved in further processing and modification of proteins. - Like the cis and trans networks, it is composed of **flattened, stacked cisternae**, distinct from the tubular appearance of the structure pointed to by the arrow.

Q: Which of the following is the constituent of the marked area in the given electron microscope picture of the muscle?

$\alpha$-actinin. ***$\alpha$-actinin*** - The image highlights the **Z-disc**, which is primarily composed of **$\alpha$-actinin**. - **$\alpha$-actinin** anchors the **thin filaments (actin)** at the Z-disc and helps maintain the structural integrity of the sarcomere. *Nebulin* - **Nebulin** is a large protein associated with thin filaments, regulating their **length** and contributing to their **stability**, but it is not the main constituent of the Z-disc. - It extends along the entire length of the thin filament, rather than forming the Z-disc itself. *Titin* - **Titin** is the largest known protein, responsible for the **elasticity** of muscle and connecting the Z-disc to the M-line. - While it associates with the Z-disc, it does not constitute the primary structural component of the Z-disc itself. *Tropomodulin* - **Tropomodulin** caps the **pointed (minus) end** of the **actin filaments**, regulating their length and ensuring stability in the sarcomere. - It is located at the ends of the thin filaments, away from the Z-disc.

Q: Which of the following proteins are not seen in the region marked in the image?

Zona occludens. ***Zona occludens*** - The image shows **cardiac muscle** tissue, and the arrow points to an **intercalated disc**. - Intercalated discs are primarily composed of **fascia adherens**, **maculae adherentes (desmosomes)**, and **gap junctions (connexons)**, but not tight junctions (zona occludens). *Macula adherens* - **Maculae adherentes**, also known as **desmosomes**, are abundant in intercalated discs. - They provide **strong adhesion** between cardiac muscle cells and are crucial for resisting mechanical stress. *Fascia adherens* - **Fascia adherens** are the most extensive type of junction in the transverse portion of the intercalated disc. - They anchor the **actin filaments** of the terminal sarcomeres to the plasma membrane. *Connexions* - **Connexons** are the structural proteins that form **gap junctions**. - Gap junctions in intercalated discs allow for the rapid **passage of ions** and small molecules, facilitating electrical coupling and coordinated contraction.

Q: Which of the following has maximum smooth muscle as compared to wall thickness?

A. ***A*** - Structure A represents a **terminal bronchiole**, which has the **maximum proportion of smooth muscle relative to wall thickness** among all respiratory structures. - Terminal bronchioles lack cartilage and respiratory epithelium (no alveoli), making smooth muscle the dominant structural component of their walls, comprising a high percentage of the total wall thickness. - This abundant smooth muscle allows for precise control of **bronchoconstriction** and **bronchodilation**, which is crucial for regulating air distribution to the respiratory zones. *B* - Structure B appears to be a **respiratory bronchiole** or an **alveolar duct**, which is more distal than terminal bronchioles and has less smooth muscle relative to its wall thickness. - As airways progress distally from terminal bronchioles toward the alveoli, smooth muscle gradually decreases as the primary function shifts from conduction and airflow regulation to gas exchange. - Respiratory bronchioles have alveoli budding from their walls, which reduces the proportion of smooth muscle in the overall wall structure. *C* - Structure C points to an **alveolar sac**, which is composed primarily of **alveoli** clustered together. Alveolar walls are extremely thin to facilitate efficient gas exchange and contain very little to no smooth muscle. - The function of alveoli is gas exchange, not airflow regulation, hence they lack the contractile elements like smooth muscle that are abundant in conducting airways. *D* - Structure D points to an **individual alveolus**, which is the primary site of gas exchange. Alveolar walls are extremely thin and consist of type I pneumocytes (for gas exchange), type II pneumocytes (surfactant production), and alveolar macrophages. - **Alveoli** lack smooth muscle entirely, as their structure is optimized for diffusion and not for active constriction or dilation.

Q: Which is correct about structures marked as "X" found in smooth muscle?

Dense bodies. ***Dense bodies*** - The structures marked "X" are **dense bodies**, which are analogous to **Z-discs** in skeletal muscle, serving as attachment points for **actin filaments**. - They are crucial for transmitting the contractile force generated by the **actin-myosin bundles** to the cell membrane, leading to the characteristic corkscrew-like contraction of smooth muscle cells. *A band* - The **A band** is a region found in **striated muscle** (skeletal and cardiac muscle) where thick and thin filaments overlap, corresponding to the length of the myosin filaments. - Smooth muscle lacks the organized sarcomeric structure, and thus, **A bands** are not present. *Calmodulin* - **Calmodulin** is a calcium-binding protein that plays a key role in smooth muscle contraction by activating **myosin light chain kinase (MLCK)**. - However, it is a soluble protein involved in signaling, not a structural component like the dense bodies shown in the image. *H band* - The **H band** is located within the **A band** of a **sarcomere** in striated muscle, representing the central region where only thick (myosin) filaments are present. - Similar to the **A band**, the **H band** is a feature of striated muscle and is not found in the unstriated smooth muscle cells.

Question 1

Which of the following is correct about the type of neuron shown below?

Accepted Answer

Pseudo-unipolar cell

Answer

Bipolar neuron

Answer

Unipolar cell

Answer

All of the above

Question 2

Which of the following is correct about the image shown below?

Accepted Answer

A=Hemidesmosomes, B=Desmosomes, C=Tight junctions

Answer

A=Desmosomes, B=Hemidesmosomes, C=Tight junctions

Answer

A=Desmosomes, B=Hemidesmosomes, C=Zona Occludens

Answer

A=Desmosomes, B=Hemidesmosomes, C=Gap junctions

Question 3

Identify the cells marked X in the image shown below.

Accepted Answer

Mesangial cells

Answer

Lacis cells

Answer

Macula densa

Answer

Podocytes

Question 4

The fiber marked as X is:

Accepted Answer

Modified cardiac muscle

Answer

Nerve fiber

Answer

Modified nerve fiber

Answer

Modified connective tissue

Question 5

In this electron micrograph, identify the structure marked with arrow.

Accepted Answer

Smooth endoplasmic reticulum

Answer

Trans Golgi network

Answer

Cis Golgi network

Answer

Medial Golgi network

Question 6

Which of the following is the constituent of the marked area in the given electron microscope picture of the muscle?

Accepted Answer

$\alpha$-actinin

Answer

Nebulin

Answer

Titin

Answer

Tropomodulin

Question 7

What is incorrect about the shown basement membrane?

Accepted Answer

Only molecules which are larger than 50,000 Daltons can traverse the filtration barrier

Answer

Part of filtration barrier

Answer

Stained with PAS

Answer

It has Lamina Densa and Lamina Rara

Question 8

Which of the following proteins are not seen in the region marked in the image?

Accepted Answer

Zona occludens

Answer

Macula adherens

Answer

Fascia adherens

Answer

Connexons

Question 9

Which of the following has maximum smooth muscle as compared to wall thickness?

Accepted Answer

A

Answer

B

Answer

C

Answer

D

Question 10

Which is correct about structures marked as "X" found in smooth muscle?

Accepted Answer

Dense bodies

Answer

A band

Answer

Calmodulin

Answer

H band

Histology — MCQs

Histology — MCQs

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