SPERMATOGENESIS

 

 

INTRODUCTION:

     The germ cells are the one which helps in fertilization and forms into foetus. The production of these germline cells is held in reproductive system of humans. For male the germ cells are produced in testis and for female the cells are produced in ovary. The production of these germline cells(gametes) is known as gametogenesis. In male the production process is known as spermatogenesis and in female the process is known as oogenesis.in this upcoming blog the spermatogenesis is explained in detail.

SPERMATOGENESIS:

 Spermatogenesis is the process by which primordial germ cells produce male gametes. the beginning and growth of sperm cells in the testes, which are male reproductive organs. Spermatozoa are the completely developed sperm cells. Although the testes continuously create sperm cells, not every region of the seminiferous tubules produces sperm cells simultaneously. It can take up to 74 days for a single immature germ cell to reach full maturity.

NOTE: per day approximately 100 million sperm cells were produced.

  The spermatogenesis has two major phases, namely.

·         Spermato cytogenesis: one primordial cell undergoes mitotic division to form 4 spermatids.

·         Spermiogenesis: it is the maturation phase from spermatids to sperm.

The walls of seminiferous tubules are the place were primary spermatogonia gets produced and gets mature into spermatids. The two major cells found in the walls of seminiferous tubules are,

·         Sertoli cells: its is the cell which producing energy for division and maturation of spermatogonium.

·         Leydig cells: it is the primary source cell in production of testosterone in males.

PHASES OF SPERMATOZOA:

PHASE-1: SPERMATOCYTOGENESIS

The primordial germ cells are type-A spermatogonia, where it undergoes mitotic division to produce two different cells which are type-A & type-B spermatogonia. These type-B spermatogonia helps to auto reproduce type-A cells.

        The primary spermatogonium undergoes mitotic division to form primary spermatocyte. It is the diploid cell where presence of 2N-nucleus.

         The primary spermatocyte undergoes meiosis-1 where diploid cell equally divides in nucleic material & forms secondary spermatocyte which is haploid (N) in nature.

         This secondary spermatocytes undergoes meiosis-2 where these immature cells are gets developed into spermatids which is a partially matured sperm cells.

With this the phase-1 spermatocytogenesis has come to an end and the phase-2 spermiogenesis gets begin.

PHASE-2: SPERMIOGENESIS

   It is the phase where maturation of sperm cell occur. where this phase has 4 stages, namely

·         Golgi phase: golgi body produces enzyme  to form acrosome.

·         Acrosomal phase: acrosome gets condense around the nucleus.

·         Tail phase: centrioles gets elongated to form tail.

·         Maturation phase: its is the final phase where loss of excess cytoplasm occurs.

The first steps involve the construction of the acrosomal vesicle from the Golgi apparatus. The acrosome forms a cap that covers the sperm nucleus. As the acrosomal cap is formed, the nucleus rotates so that the cap will be facing the basal membrane of the seminiferous tubule. This rotation is necessary because the flagellum is beginning to form from the centriole on the other side of the nucleus, and this flagellum will extend into the lumen. During the last stage of spermiogenesis, the nucleus flattens and condenses, the remaining cytoplasm (the “cytoplasmic droplet”) is jettisoned, and the mitochondria form a ring around the base of the flagellum.

Yet, these mature sperms are non-motile and these mature spermatozoa are released in lumen of seminiferous tubules. This process is known as spermiation.

The released sperms moved towards epididymis where the sperms gets motility & capable for fertilization.

CONCLUSION:

    In the mouse, the entire development process from stem cell to spermatozoon takes 34.5 days. The spermatogonial stages last 8 days, meiosis lasts 13 days, and spermiogenesis takes up another 13.5 days. In humans, spermatic development takes nearly twice as long to complete. Because the type A₁ spermatogonia are stem cells, spermatogenesis can occur continuously. Each day, some 100 million sperm are made in each human testicle, and each ejaculation releases 200 million sperm. Unused sperm are either resorbed or passed out of the body in urine. During his lifetime, a human male can produce 10¹² to 10¹³ sperm.