Q.Read the following passage and answer the questions that follow. Spermatogenesis is an important primary sex characteristic in humans and all other vertebrates. The process is coordinated and controlled under the influence of hormones. It starts with the onset of puberty in humans and thereafter continues. The primordial cells within the embryonic testis which differentiate into spermatogonia are the precursors of the sperms. These are located at the outer walls of the seminiferous tubules where the process of spermatogenesis proceeds.
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Start your 14-day free trial to unlock the full solution →Concept understanding — Hormonal Regulation Spermatogenesis
Let’s begin with an everyday picture. Think of a factory that produces a specific product — say, a car factory. The factory doesn’t just run on its own; it needs a central command centre that sends signals to start production, keep it steady, and stop it when enough cars are made. In the male body, the “factory” is the testes, and the “product” is sperm. The command centre is the brain — specifically two tiny glands: the hypothalamus and the pituitary gland. The signals they send are hormones (chemical messengers that travel through the blood).
Hormonal regulation of spermatogenesis means that the entire process of sperm production is controlled by a chain of hormones, each one triggering or suppressing the next. This ensures that sperm are made at the right time, in the right quantity, and that the body doesn’t overproduce them.
The Hormonal Chain (Step by Step)
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Hypothalamus releases GnRH
The hypothalamus, a region at the base of the brain, secretes Gonadotropin-Releasing Hormone (GnRH). This is the “start” signal. GnRH travels a short distance to the pituitary gland, telling it to get ready.
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Pituitary releases two key hormones
In response to GnRH, the anterior pituitary releases two hormones into the bloodstream:
- LH (Luteinizing Hormone) — targets the Leydig cells in the testes.
- FSH (Follicle-Stimulating Hormone) — targets the Sertoli cells in the seminiferous tubules (the actual “assembly line” where sperm are made).
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LH stimulates testosterone production
Leydig cells, when activated by LH, produce testosterone. Testosterone is the main male sex hormone and is absolutely essential for spermatogenesis. It acts directly on the seminiferous tubules to drive sperm production.
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FSH supports the Sertoli cells
Sertoli cells are like the “nourishers” and “quality controllers” inside the tubules. FSH makes them produce nutrients and other factors that help developing sperm cells survive and mature. Sertoli cells also convert some testosterone into a more active form.
Both LH and FSH are needed for normal sperm production. LH provides the fuel (testosterone), and FSH ensures the assembly line runs smoothly. If either is missing, spermatogenesis slows down or stops.
The Feedback Loop (Why It Doesn’t Go Wild)
The body hates waste. If too much testosterone is produced, it sends a message back to the brain to slow down. This is called negative feedback.
- High testosterone in the blood signals the hypothalamus to reduce GnRH release, and the pituitary to reduce LH and FSH release.
- Low testosterone does the opposite — the brain increases GnRH, LH, and FSH to boost production.
This keeps testosterone levels within a narrow, healthy range. Sertoli cells also produce a hormone called inhibin, which specifically suppresses FSH when sperm production is adequate.
Think of it like a thermostat: when the room gets warm enough, the heater turns off. When it cools, the heater turns back on. The hypothalamus and pituitary are the thermostat; testosterone is the heat.
Why This Matters (Even for a Commerce/Humanities Student) …
Part (a): FSH acts on Sertoli cells (→ ABP, inhibin); spermatogonia→mitosis→primary spermatocytes; Meiosis I gives secondary spermatocytes, Meiosis II gives spermatids; ducts = rete testis then vasa efferentia.
Part (b): LH acts on Leydig cells → testosterone, essential for spermatogenesis; the same cell divisions and the same ducts apply.
Spermatogenesis begins at puberty and continues through reproductive life. Primordial germ cells at the outer wall of the seminiferous tubules differentiate into spermatogonia, and the whole process is hormonally controlled. Sub-part (a) is answered two ways (FSH or LH); sub-parts (b) and (c) are common.
- FSH — site and action. Follicle-stimulating hormone acts on the Sertoli cells located within the seminiferous tubules. These nurse cells nourish the developing germ cells. On FSH stimulation they secrete Androgen Binding Protein (ABP), which binds and concentrates testosterone within the tubule (essential for spermatid maturation), and inhibin, which exerts negative feedback on the pituitary to regulate FSH.
- Cells and their products.
- (i) Mitosis and differentiation: Spermatogonia (diploid, 2n) multiply by mitosis and some enlarge into primary spermatocytes (2n). Separately, spermatids (n) undergo differentiation — spermiogenesis — to become spermatozoa.
- (ii) Meiosis I and II: Each primary spermatocyte (2n) undergoes the reductional Meiosis I to form two haploid secondary spermatocytes (n). Each secondary spermatocyte rapidly undergoes the equational Meiosis II to form spermatids (n).
(c) Accessory ducts. After release into the tubule lumen, sperms pass through the rete testis, then the vasa efferentia, to reach the epididymis.
Part (a): FSH acts on Sertoli cells (→ ABP, inhibin); spermatogonia→mitosis→primary spermatocytes; Meiosis I gives secondary spermatocytes, Meiosis II gives spermatids; ducts = rete testis then vasa efferentia.
Part (b): LH acts on Leydig cells → testosterone, essential for spermatogenesis; the same cell divisions and the same ducts apply.
Spermatogenesis begins at puberty and continues through reproductive life. Primordial germ cells at the outer wall of the seminiferous tubules differentiate into spermatogonia, and the whole process is hormonally controlled. Sub-part (a) is answered two ways (FSH or LH); sub-parts (b) and (c) are common.
Part (b) …
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