File Name: stages of spermatogenesis and oogenesis .zip
Gametogenesis is the process of formation and differentiation of haploid gametes sperms and ova from the diploid primary germ cells, gametogonia spermatogonia and oogonia present in primary sex organs called gonads testes in male and ovaries in female respectively. It is the formation of haploid, microscopic and functional male gametes, spermatozoa from the diploid reproductive cells, spermatogonia, present in the testes of male organism. In the seasonally breeding animals, the testes undergo testicular cycle in which the testes and their spermatogenic tissue become functional only in the specific breeding season. So in some seasonally breeding mammals like bat, otter and llama, testes enlarge, become functional and descend into the scrotum in the breeding season as become heavier due to accumulation of sperms, while become reduced, non-functional and ascend into the abdomen in other seasons. But in human male, lion, bull, horse etc.
Spermatogenesis is the process by which haploid spermatozoa develop from germ cells in the seminiferous tubules of the testis. This process starts with the mitotic division of the stem cells located close to the basement membrane of the tubules. The mitotic division of these produces two types of cells. Type A cells replenish the stem cells, and type B cells differentiate into primary spermatocytes.
The primary spermatocyte divides meiotically Meiosis I into two secondary spermatocytes; each secondary spermatocyte divides into two equal haploid spermatids by Meiosis II. The spermatids are transformed into spermatozoa sperm by the process of spermiogenesis. These develop into mature spermatozoa, also known as sperm cells. Spermatozoa are the mature male gametes in many sexually reproducing organisms. Thus, spermatogenesis is the male version of gametogenesis , of which the female equivalent is oogenesis.
In mammals it occurs in the seminiferous tubules of the male testes in a stepwise fashion. Spermatogenesis is highly dependent upon optimal conditions for the process to occur correctly, and is essential for sexual reproduction. DNA methylation and histone modification have been implicated in the regulation of this process.
Spermatogenesis starts in the bottom part of seminiferous tubes and, progressively, cells go deeper into tubes and moving along it until mature spermatozoa reaches the lumen, where mature spermatozoa are deposited. The division happens asynchronically; if the tube is cut transversally one could observe different maturation states. A group of cells with different maturation states that are being generated at the same time is called a spermatogenic wave.
Spermatogenesis produces mature male gametes, commonly called sperm but more specifically known as spermatozoa , which are able to fertilize the counterpart female gamete, the oocyte , during conception to produce a single-celled individual known as a zygote.
This is the cornerstone of sexual reproduction and involves the two gametes both contributing half the normal set of chromosomes haploid to result in a chromosomally normal diploid zygote.
To preserve the number of chromosomes in the offspring — which differs between species — one of each gamete must have half the usual number of chromosomes present in other body cells. Otherwise, the offspring will have twice the normal number of chromosomes, and serious abnormalities may result. In humans, chromosomal abnormalities arising from incorrect spermatogenesis results in congenital defects and abnormal birth defects Down syndrome , Klinefelter syndrome and in most cases, spontaneous abortion of the developing foetus.
Spermatogenesis takes place within several structures of the male reproductive system. The initial stages occur within the testes and progress to the epididymis where the developing gametes mature and are stored until ejaculation.
The seminiferous tubules of the testes are the starting point for the process, where spermatogonial stem cells adjacent to the inner tubule wall divide in a centripetal direction—beginning at the walls and proceeding into the innermost part, or lumen —to produce immature sperm. For humans, the entire process of spermatogenesis is variously estimated as taking 74 days   according to tritium-labelled biopsies and approximately days  according to DNA clock measurements.
Including the transport on ductal system, it takes 3 months. Testes produce to million spermatozoa daily. 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.
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. 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.
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. 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.
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.
One important mechanism is a thermal exchange between testicular arterial and venous blood streams. Specialized anatomic arrangements consist of two zones of coiling along the internal spermatic artery. This anatomic arrangement prolongs the time of contact and the thermal exchange between the testicular arterial and venous blood streams and may, in part, explain the temperature gradient between aortic and testicular arterial blood reported in dogs and rams.
Moreover, reduction in pulse pressure, occurring in the proximal one third of the coiled length of the internal spermatic artery. 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. Human Reproduction. Journal of Molecular Histology. Retrieved Acta Histochemica et Cytochemica. Recent Prog Horm Res. J Androl. Proc R Soc B.
The Anatomical Record. Fishman and Kyoung H. Jo Curr Biol. Epub Oct Human Reproduction Update. The Journal of Experimental Biology. Fertility and Sterility. Experimental Cell Research.
Spermatogenesis and oogenesis are both forms of gametogenesis, in which a diploid gamete cell produces haploid sperm and egg cells, respectively. Gametogenesis, the production of sperm and eggs, takes place through the process of meiosis. The production of sperm is called spermatogenesis and the production of eggs is called oogenesis. Oogenesis occurs in the outermost layers of the ovaries. As with sperm production, oogenesis starts with a germ cell, called an oogonium plural: oogonia , but this cell undergoes mitosis to increase in number, eventually resulting in up to one to two million cells in the embryo.
Spermatogenesis is the process by which haploid spermatozoa develop from germ cells in the seminiferous tubules of the testis. This process starts with the mitotic division of the stem cells located close to the basement membrane of the tubules. The mitotic division of these produces two types of cells. Type A cells replenish the stem cells, and type B cells differentiate into primary spermatocytes. The primary spermatocyte divides meiotically Meiosis I into two secondary spermatocytes; each secondary spermatocyte divides into two equal haploid spermatids by Meiosis II. The spermatids are transformed into spermatozoa sperm by the process of spermiogenesis.
Gametogenesis occurs when a haploid cell n is formed from a diploid cell 2n through meiosis. We call gametogenesis in the male spermatogenesis and it produces spermatozoa. In the female, we call it oogenesis. It results in the formation of ova. This article covers both oogenesis and spermatogenesis.
These cell multiplies repeatedly by mitosis to produce large number of spermatogonia. It is a diploid cell. After maturation spermatogonia is known as Sperm mother cell because it will eventually develop into the mature sperm. First meiotic division produce two Primary spermatocyte with haploid number of chromosome. The first meiotic division separates the homologous chromosomes from each parent.
Clinical Reproductive Medicine and Surgery pp Cite as. The physiology of gamete development is at the core of understanding reproductive medicine. In humans, oogenesis begins approximately 3 weeks after fertilization. Primordial germ cells PGCs , arising from the yolk sac, migrate to the genital ridge. PGCs undergo rapid mitotic division and give rise to oogonia.
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