Spermatogenesis, its hormonal control and the sperm
From puberty, spermatogonia multiply, and primary spermatocytes divide by meiosis to form spermatids. These become sperms by spermiogenesis. GnRH, LH and FSH control it.
Draw it: spermatogenesis
After spermiogenesis, the sperm heads stay embedded in Sertoli cells. They are finally released from the tubules by spermiation.
Hormonal control of spermatogenesis
- 1At puberty, the hypothalamus greatly increases its secretion of GnRH (gonadotropin releasing hormone).
- 2GnRH acts on the anterior pituitary, which secretes two gonadotropins: LH (luteinising hormone) and FSH (follicle stimulating hormone).
- 3★LH acts on Leydig cells, which make and secrete androgens. Androgens stimulate spermatogenesis.
- 4★FSH acts on Sertoli cells, which secrete factors that help spermiogenesis.
- 5Androgens also keep the accessory ducts and glands working.
★ key step
Structure of a sperm
| Part | Features | Role |
|---|---|---|
| Head | Elongated haploid nucleus; its front is covered by a cap, the acrosome | Acrosome enzymes help the sperm fertilise the ovum |
| Neck | Short region just behind the head | Joins the head to the middle piece |
| Middle piece | Has numerous mitochondria | Make energy for the movement of the tail |
| Tail | Long and whip-like | Moves the sperm; motility is essential for fertilisation |
How to draw a human sperm
- Draw an oval head with a large nucleus; cap its front with a thin acrosome.
- Draw a short neck below the head.
- Draw a slightly wider middle piece; show coiled mitochondria inside it.
- Draw a long, thin tail.
- Draw a thin outline around the whole cell and label it plasma membrane. Title: Structure of a sperm.
Activity: spotting meiosis (onion bud cells or grasshopper testis, permanent slides)
- Extra reading for the practical: the stages below come from the cell division chapter of Class XI, not from this chapter's text.
- Prophase I: long, thread-like chromosomes in homologous pairs (bivalents); points of crossing over (chiasmata) may be seen.
- Metaphase I: the bivalents line up at the equator of the cell.
- Anaphase I: homologous chromosomes move to opposite poles; each still has two chromatids.
- Telophase II or a tetrad: four groups of chromosomes or four cells, each haploid.
- Record: meiosis halves the chromosome number. In the testis, it happens in primary and secondary spermatocytes and gives haploid sperms.
A semen analysis at an Indian infertility clinic checks exactly what your textbook lists: sperm count, shape and motility. Smoking, alcohol and heat can lower these, so doctors advise healthy habits.
3 marks: “Draw a flow chart of spermatogenesis in humans, showing the number of chromosomes at each stage.” Spermatogonium (46) → mitosis → primary spermatocyte (46) → meiosis I → 2 secondary spermatocytes (23) → meiosis II → 4 spermatids (23) → spermiogenesis → 4 sperms (23).
2 marks: “Distinguish between spermiogenesis and spermiation.” Spermiogenesis: transformation of spermatids into sperms. Spermiation: release of sperms from the seminiferous tubules after their heads were embedded in Sertoli cells.
1 marks: “What is the role of the acrosome?” Its enzymes help the sperm enter and fertilise the ovum.
LH goes to Leydig; FSH goes to Sertoli.