- Gametogenesis is the formation of gametes in the gonads.
- It is of 2 types: Spermatogenesis and Oogenesis.
Spermatogenesis
- It is the process of formation of sperms (spermatozoa) in seminiferous tubules of testis. It has 2 stages:
- Formation of spermatids: In this, Sperm mother cells (Spermatogonia or male germ cells) produce spermatids.
- Spermiogenesis: Spermatids transform into sperm.
Schematic Representation of Spermatogenesis
- 4 spermatids are formed from each primary spermatocyte.
- After spermiogenesis, sperm heads are embedded in Sertoli cells to get nourishment. Then they are released to the lumen of seminiferous tubules. It is called spermiation.
Diagrammatic sectional view of a seminiferous tubule
Role of Hormones in Spermatogenesis
- Hypothalamus releases Gonadotropin releasing hormone (GnRH).
- GnRH stimulates the anterior pituitary gland to secrete 2 gonadotropins such as Luteinizing hormone (LH) and follicle stimulating hormone (FSH).
- LH acts on the Leydig cells and stimulates secretion of androgens. Androgens stimulate spermatogenesis.
- FSH acts on the Sertoli cells and stimulates secretion of some factors for spermiogenesis.
Structure of Spermatozoa (Sperm)
- A mature sperm is about 60 µ (0.06 mm) long.
- A plasma membrane envelops the whole body of sperm.
- A sperm has 3 regions:
- Head: Oval shaped. Formed of nucleus and acrosome. Acrosome is formed from Golgi complex. It contains lytic enzymes. Behind the head is a neck.
- Middle piece: Composed of axial filament surrounded by mitochondria & cytoplasm. Mitochondria produce energy for sperm motility.
- Tail: Consists of a central axial filament. The sperm moves in fluid medium and female genital tract by the undulating movement of the tail.
- Man ejaculates 200–300 million sperms during a coitus.
- For normal fertility, at least 60% sperms must have normal shape and size. 40% of them must show vigorous motility.