Spermatogenesis in Human - Process and Description

• The process by which male gametes  or sperms are formed from the primary germ cells inside the male  gonads or testes is called spermatogenesis.

• Spermatogenesis is a type  of gametogenesis in male. Spermatozoa are the mature male gametes.

• In mammals spermatozoa  are formed  in the male Testes but maturation of male gamete takes place in Epididymis.

• 👌👌Remember - The process of spermatogenesis takes approximately 74 days in male humans.

• Spermatogenesis starts at puberty and generally continues uninterrupted until death. There could be a slight decrease in the quantity of sperm with increase in age.

Site of Spermatogenesis

• The site  of the spermatogenesis  is male gonad or testes. The initial stages of this process occur inside the testes and further progress to the epididymis.

• In epididymis, the male  gametes mature and are stored till ejaculation. Process of Spermatogenesis include Spermatocytogenesis, Spermatidogenesis and Spermiogenesis

Spermatocytogenesis 

• It is the type of gametocytogenesis that takes place in male and results in the formation of spermatocytes.

• In spermatocytogenesis, a diploid spermatogonium which is present   in the compartment of seminiferous tubules, divides mitosis division and  to form  two diploid  cells called primary spermatocytes.

• Each primary spermatocyte duplicates its DNA and undergoes meiosis-I  or reduction division to produce two equal and haploid secondary spermatocytes.

• This division involves genetic variations. These variations occur due to  either parental chromosomes or chromosomal crossover.
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• Spermatidogenesis
• Spermatidogenesis is the process of formation of spermatids from secondary spermatocytes. 

• Secondary spermatocytes rapidly enter meiosis-II  or equational division and divide to produce four equal and haploid spermatids. 
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• Spermiogenesis
• During this process of spermiogenesis, the spermatids develop a tail and  middle piece.

• In this middle piece, the mitochondria  are accumulated to form an axoneme. During this process, spermatid DNA is  packed and  condensed.
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• 👌👌 Remember -The Golgi apparatus surrounds the condensed nucleus and forms a cap-like structure called acrosome.  Acrosome has Hyaluronidase enzyme.
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• Proximal and distal centriole also develops in sperm. Maturation of sperm is triggered by testosterone Although spermatozoa are  matured but they lack motility.

• These spermatozoa are released from seminiferous tubules of testes  through a process called spermiation. Sperm heads become embedded in the Sertoli cells after spermiogensis.

• The non-motile spermatozoa are transported to the epididymis with the help of testicular fluid secreted by the Sertoli cells with peristaltic contraction.

• The spermatozoa gain motility and become capable of fertilization in the epididymis.
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• Factors  affecting Spermatogenesis
• The process of spermatogenesis is highly influenced by hormones and temperature. Testosterone is required to maintain the process of spermatogenesis. 

• Testosterone is produced by interstitial cells, also known as Leydig cells, which reside adjacent to the seminiferous tubules.

• Temperature is another factor that affects the process of spermatogenesis. So the testes are located outside the body in the scrotum.

• The optimal temperature is maintained at 2°C  below body temperature.

• Dietary deficiencies like vitamins B, E and A  x-ray exposure, alcohol, and infectious diseases will also adversely affect the rate of spermatogenesis.
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• Hormonal control of Spermatogenesis
• Spermatogenesis occurs at puberty due to the interaction of the hypothalamus, pituitary gland and Leydig cells.

• Gonadotropin releasing hormone is secreted  by the hypothalamus and released by the anterior pituitary.

• This Gonadotropin releasing hormone stimulates. luteinizing hormone and Sertoli cells to secrete testosterone  Hormone and Follicle stimulating hormonal

• The Sertoli cells provide nourishment for the complete process of spermatogenesis under Follicle stimulating Hormone  production.

• The Leydig cells are also capable of producing Androgen in addition to their main product testosterone.

Structure of Sperm :

• Sperm is a microscopic structure and contain four parts - head, neck, a middle piece and tail.

• Sperm is a gametic cell so plasma membrane envelops the whole body of sperm. 

• The sperm head contains haploid nucleus which is covered by a cap-like structure, acrosome.

• The acrosome is filled with enzymes that help fertilisation of the ovum. 

• The middle piece has numerous mitochondria, which produce energy for the movement of tail .

• Tail facilitate sperm motility which is  essential for fertilisation.

• The human male ejaculates about 200 to 300 million sperms during a coitus.

• For the normal fertility, at least 60 per cent sperms must have normal shape and size and at least 40 per cent of them must show vigorous motility.