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We appreciate your support of the preservation process, and thank you for being an important part of keeping this knowledge alive and relevant. Read more Read less. No customer reviews. The entire process of spermatogenesis can be broken up into several distinct stages, each corresponding to a particular type of cell in humans. The primary spermatocyte is arrested after DNA synthesis and prior to division. Spermatocytogenesis is the male form of gametocytogenesis and results in the formation of spermatocytes possessing half the normal complement of genetic material.
In spermatocytogenesis, a diploid spermatogonium , which resides in the basal compartment of the seminiferous tubules, divides mitotically, producing two diploid intermediate cells called primary spermatocytes. Each primary spermatocyte then moves into the adluminal compartment of the seminiferous tubules and duplicates its DNA and subsequently undergoes meiosis I to produce two haploid secondary spermatocytes , which will later divide once more into haploid spermatids.
This division implicates sources of genetic variation, such as random inclusion of either parental chromosomes, and chromosomal crossover that increases the genetic variability of the gamete.
Use of confocal microscopy for the study of spermatogenesis
Each cell division from a spermatogonium to a spermatid is incomplete; the cells remain connected to one another by bridges of cytoplasm to allow synchronous development. Not all spermatogonia divide to produce spermatocytes; otherwise, the supply of spermatogonia would run out. Instead, spermatogonial stem cells divide mitotically to produce copies of themselves, ensuring a constant supply of spermatogonia to fuel spermatogenesis.
Spermatidogenesis is the creation of spermatids from secondary spermatocytes. Secondary spermatocytes produced earlier rapidly enter meiosis II and divide to produce haploid spermatids. The brevity of this stage means that secondary spermatocytes are rarely seen in histological studies. During spermiogenesis, the spermatids begin to form a tail by growing microtubules on one of the centrioles, which turns into basal body. These microtubules form an axoneme. Later the centriole is modified in the process of centrosome reduction.
Integrated transcriptome analysis of mouse spermatogenesis
Spermatid DNA also undergoes packaging, becoming highly condensed. The DNA is packaged firstly with specific nuclear basic proteins, which are subsequently replaced with protamines during spermatid elongation. The resultant tightly packed chromatin is transcriptionally inactive. The Golgi apparatus surrounds the now condensed nucleus, becoming the acrosome.
Maturation then takes place under the influence of testosterone, which removes the remaining unnecessary cytoplasm and organelles. The excess cytoplasm, known as residual bodies , is phagocytosed by surrounding Sertoli cells in the testes. The resulting spermatozoa are now mature but lack motility, rendering them sterile.
The mature spermatozoa are released from the protective Sertoli cells into the lumen of the seminiferous tubule in a process called spermiation. The non-motile spermatozoa are transported to the epididymis in testicular fluid secreted by the Sertoli cells with the aid of peristaltic contraction. While in the epididymis the spermatozoa gain motility and become capable of fertilization. However, transport of the mature spermatozoa through the remainder of the male reproductive system is achieved via muscle contraction rather than the spermatozoon's recently acquired motility.
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At all stages of differentiation, the spermatogenic cells are in close contact with Sertoli cells which are thought to provide structural and metabolic support to the developing sperm cells. A single Sertoli cell extends from the basement membrane to the lumen of the seminiferous tubule, although the cytoplasmic processes are difficult to distinguish at the light microscopic level. Sertoli cells serve a number of functions during spermatogenesis, they support the developing gametes in the following ways:.
The process of spermatogenesis is highly sensitive to fluctuations in the environment, particularly hormones and temperature. Testosterone is required in large local concentrations to maintain the process, which is achieved via the binding of testosterone by androgen binding protein present in the seminiferous tubules. Testosterone is produced by interstitial cells, also known as Leydig cells , which reside adjacent to the seminiferous tubules.
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Seminiferous epithelium is sensitive to elevated temperature in humans and some other species, and will be adversely affected by temperatures as high as normal body temperature. Consequently, the testes are located outside the body in a sack of skin called the scrotum. This is achieved by regulation of blood flow  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 is 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 FSH and testosterone. FSH stimulates both the production of androgen binding protein ABP by Sertoli cells , and the formation of the blood-testis barrier. ABP is essential to concentrating testosterone in levels high enough to initiate and maintain spermatogenesis.
Intratesticular testosterone levels are 20— or 50— times higher than the concentration found in blood, although there is variation over a 5- to fold range amongst healthy men. The hormone inhibin acts to decrease the levels of FSH. Studies from rodent models suggest that gonadotropins both LH and FSH support the process of spermatogenesis by suppressing the proapoptotic signals and therefore promote spermatogenic cell survival. The Sertoli cells themselves mediate parts of spermatogenesis through 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. Estrogen has been found to be essential for spermatogenesis in animals. From Wikipedia, the free encyclopedia. Spermatogenesis Seminiferous tubule with maturing sperm. Main article: Spermatocytogenesis. Main article: Spermatidogenesis. Main article: Spermiogenesis. Main article: Sertoli cell.
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