The process of formation of sperm from diploid spermatogonia is called spermatogenesis.
Process of spermatogenesis:
(1) Spermatogonaia & primary spermatocytes are diploid.
(2) Secondary spermatocytes, spermatids & sperms are haploid.
(3) The spermatids are fransformed into spermatozoa (sperm) by the process of spermiogenesis.
(4) The sperms lead get embedded into the sertoli cells to take nourishment from them & finally released from seminiferous tubules by a process called spermiation.
Structure of a sperm:
- A sperm consist of a head, neck, a middle piece and a tail. A plasma membrane envelops the whole body of sperm.
- The sperm head contains an elongated haploid nucleus whichnis is covered by a cap-like structure, acrosome. The acrosome is filled with enzymes that help fertilisation of the ovum.
- The middle piece possesses numerous mitochondria, which produce energy for the movement of tail.
- The human male ejaculates about 200 to 300 million sperms during a coitus.
- Secretions of epididymis, vas deferens, seminal vesicle and prostate are essential for maturation and motility of sperms. The seminal plasma along with the sperms constitute the semen.
Hormonal control of spermatogenesis:
- Spermatogenesis starts at the age of puberty due to significant increase in the secretion of gonadotropin releasing hormone (GnRH), a hypothalamic hormone.
- The increased levels of GnRH then acts at the anterior pituitary gland and stimulates secretion of two gonadotropins – luteinising hormone (LH) and follicle stimulating hormone (FSH).
- LH acts at the Leydig cells and stimulates synthesis and secretion of androgens. Androgens, in turn, stimulate the process of spermatogenesis.
- FSH acts on the Sertoli cells and stimulates secretion of some factors which help in the process of spermiogenesis.
Flow chart of hormonal control during spermatogenesis: