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Spermatogenesis Definition
Spermatogenesis is the production of sperm from the primordial germ cells. The term spermatogenesis is derived from the Greek words sperma, which means “seed,” and genesis, which means “birth,” “origin,” and “creation.”
What is Spermatogenesis?
Spermatogenesis is the biological process of generating mature sperm cells in a sexually reproducing organism’s male gonad. A series of events occurs in this process, in which undifferentiated male germ cells transform into spermatozoa. (1) spermatocytogenesis, (2) spermatidogenesis, and (3) spermiogenesis and spermiation are the phases.
Except for spermiation, which takes place in the epididymis, all phases take place in the seminiferous tubules of the testis. Spermatogenesis in humans begins at puberty and lasts for the rest of one’s life. The complete procedure might take up to 64 days. Male spermatogenesis is the male equivalent of female oogenesis. The two types of gametogenesis are spermatogenesis and oogenesis.
Spermatogenesis and Germ Cells
The male gonad of animals, including humans, is the testis (plural: testes). It is here where mature sperm cells are generated, as well as androgen hormones (most notably testosterone). It is made up of testicular septa, lobules, efferent ductules, rete testis, and seminiferous tubules in humans.
Convoluted or straight seminiferous tubules are also possible. The twisted or curved tubules that serve as the location of spermatozoa production are known as convoluted seminiferous tubules. The short straight tubules between the convoluted seminiferous tubules and the rete testis are known as straight seminiferous tubules.
As a result, they act as a conduit for spermatozoa from the convoluted seminiferous tubules to reach the rete testis. The germ cells and the epithelial cell lining are the primary cellular components of the seminiferous tubules.
The cells that develop into sex cells are known as germ cells (gametes). Spermatogonia (singular: spermatogonium), spermatocytes, and spermatids are the germ cells in spermatogenesis. Spermatogonia are germ cells that divide to create additional spermatogonia by mitotic division. Some of them will go on to become spermatocytes. Spermatocytes are the germ cells that go through the meiosis process.
Primary and secondary spermatocytes are the two kinds of spermatocytes. The main spermatocyte is the germ cell that splits into two secondary spermatocytes after the first meiotic division. The second meiotic division occurs in each secondary spermatocyte, resulting in the formation of two spermatids. To become a spermatozoon, the spermatid goes through spermiogenesis (plural: spermatozoa).
Apart from germ cells, the Sertoli cell is another important cell type in the tubular lining. The Sertoli cells are seminiferous tubule epithelial cells. Nurse cells are so named because they nurture the germ cells that are connected to them while they grow.
They also produce testis-determining factor, a protein that concentrates testosterone near the germ cells in the developing testis. They are also the cells that phagocytose the spermatid’s remaining cytoplasm during spermiogenesis. Leydig cells are found between the seminiferous tubules.
The gonadal cells are the cells that generate and release androgen hormones, such as testosterone. The epididymis is a convoluted tube that acts as a storage and development location for sperm.
Hormonal Regulation of Spermatogenesis
The pituitary gland in the brain controls sperm cell and testosterone synthesis in the testes. The anterior pituitary, in particular, secretes luteinizing hormone (LH), which regulates testosterone production. It’s also where the follicle-stimulating hormone is produced (FSH). Spermatogenesis is controlled by pituitary hormones and testosterone from the testes. The major male sex hormone, testosterone, is responsible for the activation of genes involved in spermatogenesis.
Spermatogenesis Stages
Spermatogenesis is divided into three stages: (1) spermatocytogenesis, (2) spermatidogenesis, and (3) spermiogenesis and spermiation. A spermatogenic cycle is one that starts at one stage and ends at the same stage on a specific segment of the seminiferous tubule over a certain period of time. The number of steps in the spermatogenic cycle varies by species.
i. Spermatocytogenesis
The initial step of spermatogenesis is spermatocytogenesis. The spermatogonia in the convoluted seminiferous tubule’s basal lamina divide repeatedly during mitosis, generating identical spermatogonia. Others enter the first meiotic division as primary spermatocytes in the adluminal compartment of the convoluted seminiferous tubule. Diploid spermatogonia and main spermatocytes are also present.
ii. Spermatidogenesis
Spermatidogenesis is the following stage after spermatocytogenesis. As a result, it is the spermatogenesis stage in between. Meiosis, a form of cell division that consists of two divisions: the first meiotic division (meiosis I) and the second meiotic division (meiosis II), is the highlight of this stage (meiosis II).
The seminiferous tubule is the sole location in a male’s body where meiosis occurs in humans and other animals. The primary spermatocyte begins meiosis I at this point, with its DNA replicated, to produce two haploid secondary spermatocytes. Each of the secondary spermatocytes will start meiosis II right away, resulting in four genetically distinct haploid spermatids.
iii. Spermiogenesis and Spermiation
Spermatidogenesis is followed by spermiogenesis. The spermatids develop into mature spermatozoa at this stage of spermatogenesis. The Golgi phase, Cap phase, Tail phase, and Maturation phase are the four stages of spermiogenesis. Nuclear condensation, acrosome formation, mid piece formation, and tail creation will all occur in the spermatids.
The spermatozoa, on the other hand, are not completely functioning at this stage. They are not yet motile, despite having acquired characteristics necessary for fertilising an ovum (e.g., becoming compressed and streamlined rather than the original spherical form with leftover cytoplasm). When they reach the epididymis, they will become motile.
Non-motile spermatozoa exit the seminiferous tubules after spermiogenesis and go to the rete testis in the mediastinum testis, the efferent ducts, and eventually the epididymis. Spermiation is the process of spermatozoa migrating to the epididymis. Because the spermatozoa aren’t yet motile, the Sertoli cells produce testicular fluid to help them along their journey.
Post-Spermatogenesis Events
The head, the midpiece, and the tail are three separate components of a motile and differentiated spermatozoon (sperm cell). An acrosome adorns the top of the head. Following fertilisation, the acrosome contains enzymes that can break down the ovum’s wall. The middle section contains many mitochondria, which are the organelles that produce ATP.
As the sperm cell prods its tail in pursuit of the ovum, this chemical energy is required. The tail is a flagellum with a 9 + 2 axoneme arrangement. The motile spermatozoa are kept in the epididymis until they are ready to be released (ejaculation). Spermatozoa migrate out of the epididymis, through the vas deferens, into the urethra, and out of the urethral aperture during ejaculation.
Biological Importance of Spermatogenesis
The biological process of spermatogenesis is crucial. It is the process of producing male gametes. Meiosis allows for genetic recombination, which increases genetic diversity and hence improves the gene pool. Any disruption or intervention in this process might result in male fertility being decreased. Temperature and diet are two elements that may have an impact on efficiency.
The typical scrotal temperature in humans is around 34 degrees Celsius, which is lower than the core body temperature of 37 degrees Celsius. Vitamin B, E, and A should all be present in appropriate amounts. To ensure that sperm cells are free of defects and abnormalities, spermatogenesis must be well-controlled and kept within ideal circumstances.
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