Histology Practice Questions

Q: Which of the following is a characteristic feature of the axon hillock that distinguishes it from the neuronal cell body?

Contains no Nissl granules. Correct: Contains no Nissl granules - The **axon hillock** is a specialized region of the neuron that is devoid of rough endoplasmic reticulum and free ribosomes, which constitute **Nissl granules (Nissl substance)** [1] - This absence of Nissl granules distinguishes it from the cell body and dendrites where active protein synthesis occurs [1] - Its primary function is **action potential generation** and initiation, requiring a specific distribution of voltage-gated sodium channels rather than protein synthesis machinery [1] - This is the key **cytological feature** that differentiates the axon hillock from the soma [1] *Incorrect: Contains dense Nissl granules* - **Nissl granules** are abundant in the neuronal cell body (soma) and proximal dendrites, indicating active protein synthesis for neuronal maintenance and function [1] - The axon hillock specifically **lacks** these structures, which is one of its defining histological characteristics [1] - This absence can be demonstrated with Nissl staining (cresyl violet or toluidine blue) *Incorrect: Is located at the beginning of dendrites* - The **axon hillock** is located at the junction of the **cell body (soma)** and the **axon**, not at the beginning of dendrites [1] - Dendrites are receptive regions that receive synaptic input and extend from the cell body in multiple directions [1] - The axon hillock integrates inputs to determine whether an action potential will be initiated *Incorrect: Has a conical shape leading into the axon* - While the axon hillock does have a conical/funnel shape tapering into the axon, this is a **morphological description** rather than a distinguishing characteristic [1] - Many neuronal structures have specific shapes, but the **absence of Nissl granules** is the specific cytological feature that functionally distinguishes the axon hillock - The shape facilitates efficient action potential propagation but is not the defining histological feature

Q: Which of the following is an example of a sebaceous gland that opens directly to the surface of the skin?

Fordyce's spots. ***Fordyce's spots*** - These are **ectopic sebaceous glands** that are not associated with hair follicles and open directly onto the surface of the skin or mucous membranes. - They are commonly found on the lips, buccal mucosa, and genitalia, appearing as small, painless, yellowish or whitish papules. *Meibomian glands of the eyelids* - These are modified **sebaceous glands** located within the eyelids that produce the oily layer of the tear film. - They open onto the margin of the eyelids, not directly onto the skin surface in the same manner as Fordyce's spots. *Tyson's glands of the prepuce* - These are modified **sebaceous glands** found on the inner surface of the preputial folds and the corona of the glans penis. - They secrete **smegma**, a lubricating substance, but are generally considered a variant of sebaceous glands associated with genital structures, not opening widely on the general skin surface. *Koplik's spots (lesions, not glands)* - **Koplik's spots** are pathognomonic **mucosal lesions** associated with **measles (rubeola)**, appearing as small, white spots with a red halo on the buccal mucosa. - They are not glands but rather an inflammatory sign of viral infection, and therefore, not relevant to the question of sebaceous glands opening to the skin surface.

Q: Which layer of the epidermis is known as the stratum germinatum?

Stratum germinatum. ***Stratum germinatum*** - This term is often used synonymously with the **stratum basale** (or basal layer) of the epidermis. [1] - It is where continuous cell **division (mitosis)** occurs, germinating new keratinocytes to replenish the layers above. [1] *Stratum corneum* - This is the **outermost layer** of the epidermis, composed of flattened, dead keratinocytes. [1] - Its primary function is to provide a **protective barrier** against the environment. [1] *Stratum spinosum* - Known for its **spiny appearance** due to desmosomal junctions that hold the keratinocytes together. - Cells in this layer are still live and actively produce **keratin**. *Stratum granulosum* - Characterized by the presence of **keratohyalin granules** and lamellar granules within the cells. - This layer is involved in the formation of the **skin barrier** and waterproofing.

Q: What are gap junctions composed of?

Connexins. ***Connexins*** - **Gap junctions** are intercellular channels that permit the passage of ions and small molecules between adjacent cells [1], and they are primarily formed by proteins called **connexins** [1]. - Six connexin proteins assemble to form a **connexon**, also known as a hemichannel, which then docks with a connexon from an adjacent cell to create a complete gap junction channel [1]. *Catenins* - **Catenins** are a group of proteins involved in cell adhesion by linking cadherins to the **actin cytoskeleton**. - They are crucial for the stability and function of **adherens junctions**, not gap junctions [2]. *Cadherins* - **Cadherins** are transmembrane proteins that mediate **calcium-dependent cell-cell adhesion** in adherens junctions and desmosomes. - They are responsible for homophilic binding between cells, playing a key role in tissue segregation and morphogenesis, but do not form channels [2]. *Claudin* - **Claudins** are a family of proteins that are essential components of **tight junctions** [2]. - They help to form the primary seal of tight junctions, regulating paracellular permeability and maintaining cell polarity [2].

Q: Follicles are present in which part of lymph nodes?

Cortex. ***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.

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

Vimentin. ***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.

Q: Barr bodies are not present in which individuals?

XO. ***XO*** - Individuals with an **XO karyotype** (Turner syndrome) have only one X chromosome and therefore lack an additional X chromosome to be inactivated and form a Barr body. - A Barr body is formed from the **inactivated X chromosome**, and since only one X chromosome is present, no inactivation occurs. *XXY* - Individuals with an **XXY karyotype** (Klinefelter syndrome) will have **one Barr body** because one of their two X chromosomes will be inactivated. - The number of Barr bodies is typically **N-1**, where N is the number of X chromosomes. *XX* - Individuals with a normal female **XX karyotype** will have **one Barr body**, as one of the two X chromosomes is randomly inactivated during development. - X-inactivation ensures proper gene dosage compensation between males and females. *XXX* - Individuals with an **XXX karyotype** (Triple X syndrome) will have **two Barr bodies**, as two of their three X chromosomes will be inactivated. - This follows the N-1 rule, where N=3, so 3-1=2 Barr bodies.

Q: The thin limbs of the ansa nephroni are primarily lined by what?

Squamous epithelium. Squamous epithelium - The thin limbs of the loop of Henle (ansa nephroni) are characterized by their simple, flattened squamous epithelial cells [1]. - This thin lining facilitates efficient passive diffusion of water and solutes, crucial for urine concentration [2]. Columnar - Columnar epithelial cells are typically found in regions involved in secretion and absorption, such as the gastrointestinal tract, not the thin limbs of the ansa nephroni. - Their tall, cylindrical shape is suited for active transport processes rather than passive diffusion. Cuboidal epithelium - Cuboidal epithelium lines the proximal and distal convoluted tubules and the thick ascending limb of the loop of Henle, where active transport of ions and reabsorption of water occur [1]. - These cells have abundant mitochondria to support their metabolic activity, which is not characteristic of the thin limbs. Stratified squamous epithelium - Stratified squamous epithelium is a protective lining found in areas subject to abrasion, such as the skin and mucosa of the mouth and esophagus. - It is not found in the kidney tubules, which are involved in filtration and reabsorption.

Q: Which of the following statements about the periosteum is false?

It is insensitive to pain. ***It is insensitive to pain*** - The periosteum is, in fact, **highly sensitive to pain** due to its rich nerve supply. - This rich innervation contributes significantly to the pain experienced in **fractures** and **bone bruises**. *It is highly vascular* - The periosteum is indeed **highly vascular**, containing numerous blood vessels that supply nutrients to the underlying bone [1]. - This extensive blood supply is crucial for **bone health**, maintenance, and repair, especially after injury. *It does not cover the articular surface of the bones* - This statement is correct; the periosteum **does not cover the articular surfaces** of bones. - Articular surfaces are instead covered by **articular cartilage**, which provides a smooth, low-friction surface for joint movement [2]. *It is pierced by the fibers of Sharpey's* - This statement is correct; **Sharpey's fibers** are collagenous fibers that extend from the periosteum into the outer circumferential lamellae of the bone. - These fibers serve to **anchor the periosteum firmly** to the bone, providing structural integrity.

Q: What is the primary organic component of bone?

90% collagen protein. ***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 1

Which of the following is a characteristic feature of the axon hillock that distinguishes it from the neuronal cell body?

Accepted Answer

Contains no Nissl granules

Answer

Has a conical shape leading into the axon

Answer

Contains dense Nissl granules

Answer

Is located at the beginning of dendrites

Question 2

Which of the following is an example of a sebaceous gland that opens directly to the surface of the skin?

Accepted Answer

Fordyce's spots

Answer

Meibomian glands of the eyelids

Answer

Koplik's spots

Answer

Tyson's glands of the prepuce

Question 3

Which layer of the epidermis is known as the stratum germinatum?

Accepted Answer

Stratum germinatum

Answer

Stratum corneum

Answer

Stratum spinosum

Answer

Stratum granulosum

Question 4

What are gap junctions composed of?

Accepted Answer

Connexins

Answer

Catenins

Answer

Cadherins

Answer

Claudin

Question 5

Follicles are present in which part of lymph nodes?

Accepted Answer

Cortex

Answer

Red pulp

Answer

White pulp

Answer

Medulla

Question 6

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

Accepted Answer

Vimentin

Answer

Keratin

Answer

Lamin

Answer

Desmin

Question 7

Barr bodies are not present in which individuals?

Accepted Answer

XO

Answer

XX

Answer

XXY

Answer

XXX

Question 8

The thin limbs of the ansa nephroni are primarily lined by what?

Accepted Answer

Squamous epithelium

Answer

Cuboidal epithelium

Answer

Columnar epithelium

Answer

Stratified squamous epithelium

Question 9

Which of the following statements about the periosteum is false?

Accepted Answer

It is insensitive to pain

Answer

It does not cover the articular surface of the bones

Answer

It is pierced by the fibers of Sharpey's

Answer

It is highly vascular

Question 10

What is the primary organic component of bone?

Accepted Answer

90% collagen protein

Answer

10% collagen

Answer

10% noncollagenous protein

Answer

20% noncollagenous protein

Histology — MCQs

Histology — MCQs

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