(a) Draw a sectional view of seminiferous tubule of a human. Label the following cells in the seminiferous tubule: (i) Cells that divide by mitosis to increase their number, (ii) Cells that undergo meiosis I, (iii) Cells that undergo meiosis II, (iv) Cells that help in the process of spermiogenesis.
(b) Mention the role of Leydig cells.
Show Hint
- Mitosis cells = Spermatogonia
- Meiosis I cells = Primary spermatocytes
- Meiosis II cells = Secondary spermatocytes
- Spermiogenesis helper cells = Sertoli cells
- Leydig cells sit outside the tubules and produce testosterone under LH stimulation.
Concept:
The testes are filled with highly coiled structures called seminiferous tubules, which serve as the site for human spermatogenesis. A cross-sectional view of a tubule reveals an outer germinal epithelium lined with developing germ cells alongside specialized supporting cells, while the surrounding interstitial spaces contain endocrine cells.
Step 1: Functional Mapping and Identification of the Required Labels (Part a).
To fulfill the specific labeling criteria, we match the physiological descriptions given in the prompt to their precise cytological identities within the seminiferous tubule:
• (i) Cells that divide by mitosis to increase their number $\longrightarrow$ Spermatogonia: These are the diploid ($2n$), undifferentiated stem cells situated directly along the basement membrane of the tubule. They undergo continuous mitotic divisions to maintain the stem cell pool and provide cells that differentiate into spermatocytes.
• (ii) Cells that undergo meiosis I $\longrightarrow$ Primary Spermatocytes: These large diploid ($2n$) cells develop from modified spermatogonia. They undergo the first meiotic division (reductional division) to produce two haploid secondary spermatocytes.
• (iii) Cells that undergo meiosis II $\longrightarrow$ Secondary Spermatocytes: These are haploid ($n$) cells resulting from meiosis I. They rapidly undergo the second meiotic division (equational division) to form four haploid spermatids.
• (iv) Cells that help in the process of spermiogenesis $\longrightarrow$ Sertoli Cells (Nurse Cells): These large, elongated, pyramidal cells extend from the basement membrane toward the lumen. During spermiogenesis (the transformation of spherical spermatids into elongated, motile spermatozoa), the spermatids embed their heads into the Sertoli cells to obtain essential nutrients and structural support.
Step 2: Detailed Explanation of the Role of Leydig Cells (Part b).
The interstitial spaces located outside the seminiferous tubules contain connective tissue, blood vessels, and clusters of endocrine cells called Leydig cells (or interstitial cells).
• Endocrine Function: The primary role of Leydig cells is the biosynthesis, storage, and secretion of testicular hormones collectively termed androgens, principal among which is testosterone.
• Hormonal Regulation: This secretory activity is stimulated by Luteinizing Hormone (LH), a gonadotropin released from the anterior pituitary gland.
• Physiological Impact: Testosterone secreted by Leydig cells is essential for stimulating and maintaining spermatogenesis within the adjacent seminiferous tubules. It also drives the development, maturation, and maintenance of male secondary sexual characteristics and accessory reproductive organs (such as the epididymis, vas deferens, and prostate gland).
