Note that half of the spermatids will development into spermatozoa carrying an X chromosome and half will develop into spermatozoa carrying a Y chromosome. During spermiogenesis , the morphology of the spermatid radically changes.
The cell develops the acrosome , which covers the sperm head and contains enzymes that assist in penetrating the zona pellucida during fertilization. The cell becomes elongated forming a neck, connecting the head to the middle piece and tail.
The middle piece contains mitochondria for generating energy to propel the cell through the female reproductive tract by action of the flagellum in the tail. The cell loses most of its cytoplasm and must depend on secretions in the semen for sustenance on its journey through the female reproductive tract.
Endogenous damage to the the genetic material eg. Throughout spermatocytogenesis cells retain a rounded configuration Figure Spermatids undergo a dramatic change in form during spermiogenesis - into the streamline spermatozoa adapted for fertilization. Spermiogenesis involves nuclear condensation, formation of the acrosomal cap, and development of a tail.
The acrosome is derived from the Golgi apparatus. Centrioles points of organization of spindle fibers migrate to a postnuclear region after the completion of meiosis.
The distal centriole provides a template for accretion of cytoskeletal elements comprising the contractile lattice of the tail. Mitochondria become concentrated into the sheath of the middle piece. Cells do not divide during spermiogenesis Figure Spermatogenic cycle and wave. If one closely examines serial cross-sections of a seminiferous tubule you will discover that sperm cells differentiate in distinctive associations.
Each spermatogenic association has been classified as a stage of the seminiferous epithelial cycle. A spermatogenic cycle is defined as the time it takes for the reappearance of the same stage within a given segment of the tubule.
Each stage of the cycle follows in an orderly sequence along the length of the tubule. The distance between the same stage is called the spermatogenic wave. One tubule can contain numerous complete waves. Adjacent segments of the tubule evidently communicate in some unknown manner. The number of stages within a spermatogenic cycle and the number of cycles required for the completion of spermatogenesis varies between species.
There are 12 different stages of the cycle in the bull of about 14 days each; approximately four cycles within a given region of the tubule occur before an A1 spermatogonia is transformed into a spermatozoa. Six stages have been noted in man; four day cycles are needed to complete spermatogenesis.
The linear pattern of the spermatogenic cycle is less ordered in man than in farm animals or rodents. Hormonal regulation. Spermatogonia continue to divide, but in reduced numbers, after hypophysectomy.
Spermatocytogenesis is completely arrested at the primary spermatocyte stage in hypophysectomized animals; this step is restored by testosterone. Androgen-binding protein the testicular counterpart of SHBG sequesters testosterone within the seminiferous tubule and caput epididymis.
Meiosis II is hormonally-independent. Metabolism 2. Cell Respiration 3. Photosynthesis 9: Plant Biology 1. Xylem Transport 2. Phloem Transport 3. Plant Growth 4. Plant Reproduction Genetics 1. Meiosis 2. Inheritance 3. Speciation Animal Physiology 1. Antibody Production 2. Movement 3. The Kidney 4. Sidebar [Skip]. This is achieved by begulation of blood flow [2] and positioning towards and away from the heat of the body by the cremasteric muscle and the dartos smooth muscle in the scrotum.
Dietary deficiencies such as vitamins B, E and A , anabolic steroids , metals cadmium and lead , x-ray exposure, dioxin, alcohol, and infectious diseases will also adversely affect the rate of spermatogenesis. Hormonal control of spermatogenesis varies among species. In humans the mechanism are not completely understood, however it is known that initiation of spermatogenesis occurs at puberty due to the interaction of the hypothalamus , pituitary gland and Leydig cells. If the pituitary gland is removed, spermatogenesis can still be initiated by follicle stimulating hormone and testosterone.
Follicle stimulating hormone stimulates both the production of androgen binding protein by Sertoli cells, and the formation of the blood-testis barrier. Androgen binding protein is essential to concentrating testosterone in levels high enough to initiate and maintain spermatogenesis, which can be times higher than the concentration found in blood.
Follicle stimulating hormone may initiate the sequestering of testosterone in the testes, but once developed only testosterone is required to maintain spermatogenesis. However, increasing the levels of follicle stimulating hormone will increase the production of spermatozoa by preventing the apoptosis of type A spermatogonia.
The hormone inhibin acts to decrease the levels of follicle stimulating hormone. The Sertoli cells themselves mediate parts of spermatogenesis though hormone production. They are capable of producing the hormones estradiol and inhibin. The Leydig cells are also capable of producing estradiol in addition to their main product testosterone. Categories: Developmental biology Animal physiology Male reproductive system. Read what you need to know about our industry portal bionity.
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