Histology Practice Questions

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.

Q: In a sperm cell, where are the mitochondria located?

Body. ### Explanation The mature human spermatozoon is divided into three main parts: the head, the neck, and the tail (which includes the middle piece, principal piece, and end piece) [1]. **Why the "Body" (Middle Piece) is correct:** The **Middle Piece** (often referred to as the **Body**) contains a central core of longitudinal microtubules (the axoneme) surrounded by a spiral column of **mitochondria** (mitochondrial sheath). These mitochondria are essential for aerobic metabolism, providing the **ATP (Adenosine Triphosphate)** required for the motility of the flagellum [1], [3]. **Analysis of Incorrect Options:** * **Head:** Primarily contains the **haploid nucleus** (condensed genetic material) and the **acrosome** [1]. The acrosome is a lysosome-like organelle containing enzymes (hyaluronidase and acrosin) necessary for penetrating the ovum’s zona pellucida [2]. * **Neck:** This is the constricted region containing the **centrioles** (proximal and distal). * **Tail:** While the middle piece is technically the proximal part of the tail, the **Principal Piece** and **End Piece** consist mainly of the axoneme and fibrous sheath, lacking mitochondria. **High-Yield NEET-PG Pearls:** 1. **Mitochondrial Inheritance:** All mitochondria in a sperm cell are located in the middle piece. During fertilization, this part usually does not enter the oocyte, or if it does, the paternal mitochondria are selectively degraded. Thus, **mitochondrial DNA is inherited exclusively from the mother**. 2. **Kartagener Syndrome:** A clinical condition involving dynein arm defects in the sperm tail (and cilia), leading to **immotile spermatozoa** and male infertility [3]. 3. **Acrosome Origin:** The acrosome is derived from the **Golgi apparatus** during spermiogenesis.

Q: What is the germinal cell layer surrounding the oocyte before ovulation called?

Cumulous oophorus. **Explanation:** The correct answer is **Cumulus oophorus**. In the developing ovarian follicle (Graafian follicle), the oocyte is surrounded by a specialized cluster of granulosa cells. As the antrum (fluid-filled cavity) enlarges, the oocyte is pushed to one side and remains connected to the peripheral granulosa cells by a mound or "pedicle" of cells known as the **cumulus oophorus**. The innermost layer of these cells, which are in direct contact with the zona pellucida, is termed the *corona radiata*. **Analysis of Incorrect Options:** * **A. Zona pellucida:** This is a thick, transparent, acellular glycoprotein membrane secreted by the oocyte itself. While it surrounds the oocyte, it is not a "germinal cell layer." * **B. Zona reticularis:** This is the innermost layer of the **adrenal cortex**, responsible for producing androgens (e.g., DHEA). It is unrelated to ovarian folliculogenesis. * **D. Zona glomerulosa:** This is the outermost layer of the **adrenal cortex**, responsible for the synthesis of mineralocorticoids (aldosterone). **NEET-PG High-Yield Pearls:** * **Stigma:** The small area on the ovarian surface that thins out and ruptures during ovulation to release the oocyte. * **Meiotic Status:** At the time of ovulation, the oocyte is arrested in **Metaphase of Meiosis II**. It only completes meiosis II if fertilization occurs. * **Call-Exner Bodies:** Small fluid-filled spaces between granulosa cells, characteristic of Granulosa Cell Tumors (and seen in normal developing follicles). * **Theca Interna:** The vascularized layer of the follicle that produces androstenedione under the influence of LH.

Q: Histological section is given below. Identify the marked cell.

Purkinje cell. ***Purkinje cell*** - The image displays a histological section of the **cerebellar cortex**. The arrow points to a large, flask-shaped neuron situated in a single layer between the outer molecular layer and the inner granular layer, which is characteristic of a **Purkinje cell**. - These cells are the primary output neurons of the cerebellar cortex, utilizing **GABA** as their neurotransmitter to exert an inhibitory effect on the deep cerebellar nuclei. *Stellate cell* - Stellate cells are small, star-shaped inhibitory interneurons located in the superficial part of the **molecular layer** of the cerebellar cortex. - They are significantly smaller than the cell indicated and are not organized into the distinct single-cell layer where the marked neuron is found. *Basket cell* - Basket cells are inhibitory interneurons found in the deeper part of the **molecular layer**, close to the Purkinje cell layer. - While they synapse on Purkinje cells, they are themselves much smaller and are not the large, flask-shaped cell bodies pointed to by the arrow. *Granular cell* - Granular cells are very small, densely packed excitatory neurons that constitute the **granular layer**, the innermost and most cellular layer of the cerebellar cortex (visible as the dark purple area at the bottom). - The marked cell is located in the layer just above the granular layer and is morphologically distinct, being much larger than a single granular cell.

Q: Histological section is given below. Identify the marked cell. ![img-34.jpeg](img-34.jpeg)

Purkinje cell. ***Purkinje cell*** - The marked cell is a **Purkinje cell**, identified by its large, **flask-shaped** (pyriform) body and its characteristic location in the cerebellar cortex. - These neurons form a distinct single layer, the **Purkinje cell layer**, situated between the outer, less cellular **molecular layer** and the inner, densely packed **granular layer**. *Stellate cell* - **Stellate cells** are small, star-shaped inhibitory interneurons located within the superficial part of the **molecular layer**; they are not the large, flask-shaped cells shown. - They are significantly smaller than Purkinje cells and do not form a distinct, single-cell-thick layer. *Basket cell* - **Basket cells** are inhibitory interneurons found in the deeper part of the **molecular layer**, close to the Purkinje cells. - Although they synapse on Purkinje cells by forming a 'basket' of fibers around the soma, the arrow is pointing to the large Purkinje cell body itself, not the smaller basket cell. *Granular cell* - **Granular cells** are the very small, densely packed neurons with dark-staining nuclei that form the **granular layer**, which is the dark purple layer at the bottom of the image. - The marked cell is clearly much larger than a granular cell and is located in the layer just above the granular layer.

Q: Which of the following images displays the characteristic histology of the Thymus?

Image of Thymus. ***Image of Thymus*** - The image correctly illustrates the key histological features of the thymus, including the division of thymic lobules into a dark outer **cortex** and a lighter inner **medulla**. - A pathognomonic feature shown is the presence of **Hassall's (thymic) corpuscles**, which are whorls of epithelial reticular cells found exclusively in the thymic medulla. *Image of Tonsil* - Tonsillar histology is characterized by deep invaginations called **tonsillar crypts** and numerous **lymphoid follicles** with prominent germinal centers, neither of which are depicted in the image. - Tonsils are covered by **stratified squamous epithelium** (in palatine and lingual tonsils) or pseudostratified columnar epithelium (in pharyngeal tonsils), a feature not seen in the thymus. *Image of Lymph node* - A lymph node has a distinct architecture with a **cortex** containing **lymphoid follicles**, a **paracortex**, and a **medulla** with medullary cords and sinuses, which is structurally different from the image provided. - Lymph nodes are surrounded by a capsule with afferent lymphatic vessels and a **subcapsular sinus**, features that are absent in the thymus. *Image of Spleen* - Splenic histology is organized into **red pulp** and **white pulp**. The white pulp consists of **lymphoid follicles** and **periarteriolar lymphoid sheaths (PALS)** surrounding a central arteriole, which is not shown. - The red pulp, which makes up the majority of the spleen, contains **splenic sinusoids** and the **cords of Billroth**, structures for filtering blood that are absent in the thymus.

Q: Identify the lymphatic structure from the histology section given below?

Thymus. ***Thymus*** - The histology shows lymphoid tissue organized into **lobules** separated by connective tissue septa, with each lobule having a darkly stained outer **cortex** and a paler inner **medulla**. - The medulla contains **Hassall's corpuscles**, which are pathognomonic for the thymus, and the cortex lacks the germinal centers found in other lymphoid organs. *Tonsil* - Tonsils are characterized by an overlying **stratified squamous epithelium** that invaginates to form deep **tonsillar crypts**, neither of which is present in this image. - They contain numerous lymphoid follicles with prominent germinal centers but lack the distinct lobulated cortico-medullary architecture of the thymus. *Lymph node* - A lymph node has a distinct architecture with a **subcapsular sinus**, a cortex with B-cell follicles, a paracortex, and a medulla with medullary cords and sinuses, which is structurally different from the image provided. - The lobulated pattern with clear cortico-medullary differentiation within each lobule is a key feature of the thymus, not a lymph node. *Spleen* - The spleen's parenchyma is divided into **red pulp** (containing sinusoids) and **white pulp** (lymphoid tissue), an organization not seen in this section. - Splenic white pulp is characterized by a **central arteriole** surrounded by a **periarteriolar lymphoid sheath (PALS)**, a feature absent in the image.

Q: A renal biopsy image is shown. Identify the cells marked in the histological section.

Lacis cells. ***Lacis cells*** - The highlighted cells are **extraglomerular mesangial cells**, also known as Lacis cells, located in the triangular space between the afferent arteriole, efferent arteriole, and macula densa at the vascular pole of the glomerulus. - They are part of the **juxtaglomerular apparatus (JGA)** and are thought to play a role in transmitting signals from the macula densa to the juxtaglomerular cells, contributing to **tubuloglomerular feedback**. *Macula densa* - These are specialized, densely packed epithelial cells in the wall of the **distal convoluted tubule** where it contacts the glomerulus. The highlighted cells are situated outside of any tubule. - Macula densa cells function as **chemoreceptors** that monitor the **sodium chloride** concentration in the tubular fluid, regulating renin release and glomerular filtration rate. *Juxtaglomerular (JG) cells* - These are modified smooth muscle cells located primarily in the wall of the **afferent arteriole**. The cells in the image are not within an arteriolar wall. - JG cells synthesize, store, and secrete **renin**, and they function as **mechanoreceptors** by sensing changes in blood pressure within the afferent arteriole. *Podocytes* - These are specialized cells located **inside Bowman's capsule**, wrapping around the glomerular capillaries. The highlighted cells are distinctly **extraglomerular** (outside the glomerulus). - Podocytes form **filtration slits** with their interdigitating foot processes (**pedicels**), which are a critical component of the glomerular filtration barrier.

Question 1

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 2

Which cells are located outside the blood-testis barrier?

Accepted Answer

Leydig cells

Answer

Sertoli cells

Answer

Spermatocyte

Answer

Spermatid

Question 3

In a sperm cell, where are the mitochondria located?

Accepted Answer

Body

Answer

Head

Answer

Neck

Answer

Tail

Question 4

What is the germinal cell layer surrounding the oocyte before ovulation called?

Accepted Answer

Cumulous oophorus

Answer

Zona pellucida

Answer

Zona reticularis

Answer

Zona glomerulosa

Question 5

A 70-year-old man presents with urinary retention and back pain. Which investigation should be performed?

Accepted Answer

Serum acid phosphatase

Answer

Serum calcium

Answer

Serum alkaline phosphatase

Answer

Serum electrophoresis

Question 6

Histological section is given below. Identify the marked cell.

Accepted Answer

Purkinje cell

Answer

Granular cell

Answer

Stellate cell

Answer

Basket cell

Question 7

Histological section is given below. Identify the marked cell. ![img-34.jpeg](img-34.jpeg)

Accepted Answer

Purkinje cell

Answer

Granular cell

Answer

Stellate cell

Answer

Basket cell

Question 8

Which of the following images displays the characteristic histology of the Thymus?

Accepted Answer

Image of Thymus

Answer

Image of Spleen

Answer

Image of Lymph node

Answer

Image of Tonsil

Question 9

Identify the lymphatic structure from the histology section given below?

Accepted Answer

Thymus

Answer

Spleen

Answer

Lymph node

Answer

Tonsil

Question 10

A renal biopsy image is shown. Identify the cells marked in the histological section.

Accepted Answer

Lacis cells

Answer

Podocytes

Answer

Juxtaglomerular (JG) cells

Answer

Macula densa

Histology — MCQs

Histology — MCQs

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