Spermatogenesis

• The primary function of the male reproductive system is the production of spermatozoa, the transportation of spermatozoa from the testes out of the male body, the secretion by glands, and the placement of spermatozoa in the female reproductive tract.
• Spermatogenesis is the formation of the male gametes, the spermatozoa.
• Each lobule of the testes contains one to four blindly ending seminiferous tubules, which are highly convoluted hollow tubules.
• The spermatogenic epithelium consists of spermatogonia, primary spermatocytes, secondary spermatocytes, spermatids, and spermatozoa.
• Spermatogonia are stem cells which proliferate by mitosis.
• In oogenesis one large gamete and three polar bodies are conserved in the final gamete.
• One gamete from each primary oocyte is used in fertilization.
• Abnormal sperms are seen more frequently than oocytes.
• Oogenesis often functions in fertilization before meiosis is complete.
• Spermatogenesis functions in fertilization only after meiosis is complete.
• The leydig cells secrete testosterone from the testis.
• The process by which spherical spermatids become elongated spermatozoa is called spermiogenesis.
• Spermatogenesis requires about 64 days to produce four gametes from each primary spermatocyte
• Spermatogonia come in two types, type A and type B.
• Some of the progeny cells of spermatogonia differentiate into sperm.
• These differentiating cells first undergo meiosis then undergo a morphological change to become spermatozoa.
• The spermatogonia, type A are pale, type A dark, and type B are pale and preleptotene spermatocytes located in the basal compartment of the seminiferous epithelium below the junctional complex, between adjacent Sertoli cells.
• At puberty, FSH stimulating, spermatogenic cells differentiate to spermatozoa.
• Spermatogenesis includes three phases: Spermatocytogenesis, Meiosis, and Spermiogenesis.
• Spermatocytogenesis is the phase where spermatogonia become primary spermatocytes by mitosis.
• Two spermatids bear X chromosome complement and other two bear Y chromosome complement.
• Sertoli Cells prevent some physical and chemical factors from damaging germ cells, such as radiation, body temperature, and infection.
• All the spermatocytes are not in the same stage of development in the different seminiferous tubules.
• As steps of spermatogenesis continue, the spermatocytes progressively move from basement membrane to the luminal side of seminiferous tubule.
• Only 23 double structured chromosomes are involved in spermatogenesis.
• The function of Sertoli Cells is to support and nourish spermatogenic cells, secrete fluid to help the sperm moving, phagocytize and digest the residual bodies, and synthesize and secrete ABP (androgen binding protein) which combines androgen in seminiferous tubule to stimulate spermatogenesis.
• All dividing spermatogonia and spermatocytes are connected by means of cytoplasmic bridges.
• Groups of connected spermatogonia divide synchronously and proceed into meiosis together.
• Mature sperm arise synchronously in any given area of a seminiferous tubule.
• The cells of Sertoli provide nutrition and pockets of support to developing spermatocytes.
• The process of modification of spermatids to assume the specific shape of the sperm is called Spermiogenesis.
• The cytoplasmic bridges persist until the end of sperm differentiation.
• Sertoli Cells form the blood-testis barrier, which separates germ cells from the immune system and prevents auto-immune reaction.
• Two secondary spermatocytes quickly undergo meiosis, resulting in the formation of four spermatids each with 23 single structured chromosomes and 1N DNA.
• Meiosis is the phase where spermatocytes undergo two successive meiosis, reducing the number of chromosomes and half the amount of DNA per cell.
• Spermiogenesis is the phase where spermatids become spermatozoa by modifying their structures and shape, with no division.
• In prophase1 of meiosis, pairing and crossing over of chromosomal segments takes place and genetic recombination occurs.
• In metaphase1 of meiosis, homologous pairs arrange on the equator.
• In anaphase1 of meiosis, homologous pairs separate to go to opposite poles.
• After telophase1 of meiosis, meiosis1 ends and two secondary spermatocytes form each with 23 double structured chromosomes with X or Y sex chromosome complement.