Gametogenesis

Gametogenesis, the process of forming mature gametes, is an integral part of the health and well-being of both individuals and species. It specialises in the important male and female genetic and epigenetic processes that underlie ordinary gametogenesis through  differentiation up to fertilisation.

In animals and higher plants, different differentiation programs result in the formation of two morphologically different types of gametes (males and females). Gametogenesis occurs during the formation of haploid cells from diploid cells by meiosis. We call gametogenesis in male spermatogenesis, which produces sperm. In women this is called oogenesis. It acts in the formation of ovules.

Males and females of a sexually reproducing species  have different forms of gametogenesis

1. Spermatogenesis (males) 

2. Oogenesis (female)

Spermatogenesis

Beginning

Men begin sperm production when they reach puberty. Puberty is usually around 10-16 years old. Biological men constantly produce large amounts of sperm (about 200 million per day). This maximises the chance that sperm will reach the egg after ejaculation. 

 Sperm production takes place in the male testicles, especially the seminiferous tubules. The blood-testis barrier forms in the testicles and separates the tubules  from the systemic circulation.

Sperm protection

Sertoli cells form the blood-testis barrier. This is important to prevent substances in the blood from affecting  developing sperm. These products may contain hormones and waste products. 

 It is likewise critical as it prevents the male immune system  from spotting sperm as overseas bodies-sperm are genetically unique from men and  specific exceptional floor antigens.

Formation of functional sperms

Sperm cells are the initial pool of diploid cells that divide by mitosis to form two identical cells. One of these cells is used to replenish the sperm pool. These are A1 sperm cells. This recruitment of sperm means that the male is fertile during adulthood. Another cell, type B sperm, eventually produces mature sperm. 

Type B sperm replicate multiple times via mitosis 

To form the same diploid cells linked by cytoplasmic bridges. These cells are now called primary sperm cells. The primary spermatocytes then undergo meiosis. 

Maturation

The cytoplasmic bridge breaks and sperm cells are released into the lumen of the seminiferous tubule. This is a process known as spermatogenesis. Sperm cells undergo spermatogenesis (remodelling and differentiation into mature sperm) as they travel along the seminiferous tubules until they reach the epididymis. 

The cells then migrate to the epididymis, where  sperm are stored and go through the final stages of maturation.

Ejaculation

When the sperm leaves the male body and enters the female reproductive system, the sperm conditionally acquires capacity. This removes cholesterol and glycoproteins from the sperm head, allowing the sperm  to bind to the zona pellucida.

Oogenesis

Oogenesis differs from spermatogenesis in that it begins in the foetus before birth. Primordial germ cells (which rise up from the yolk sac of the embryo) migrate to localization withinside the cortex of the number one gonads. Mitotic replication peaks at about 7 million pups in mid-pregnancy (~20 weeks).

Meiosis I begins before birth to form primary oocytes. Therefore, the number of eggs is limited. Primary oocytes are located in clusters in the gonads. 

Primary oocytes go through three stages:

1. Pre-antral

2. Antral

3. Pre-ovulatory

Pre-Antral

Primary oocytes are still in meiosis I, but  grow dramatically at this stage. Follicular cells grow and proliferate to form  stratified squamous epithelium. These are called granulosa cells, and secrete glycoproteins. 

Antral

Fluid crammed areas shape among granulosa cells, those sooner or later integrate collectively to shape a important fluid stuffed area referred to as the antrum. We now call the follicles secondary follicles. In every month-to-month cycle this kind of secondary follicles turns dominant and develops in addition beneath the effect of FSH, LH and oestrogen.

Pre-ovulatory

The LH surge triggers this stage and meiosis I is now complete. Two haploid cells of different sizes are formed in the hair follicle. One of the daughter cells receives much less cytoplasm than the other cells and forms the first polar body. It does not later form ovules. Another haploid cell  known as the secondary oocyte is also formed. Both daughter cells then undergo meiosis II. A preliminary polar frame will reflect to present  polar our bodies however the secondary oocyte arrests in metaphase of meiosis II. This occurs three hours previous to ovulation.

Ovulation

LH surge occurs and  collagenase activity increases. This is an enzyme that destroys collagen. As a result, the follicle wall weakens. This, coupled with the contraction of the muscles of the ovarian wall, results in the release of eggs from the ovaries. The egg cells are then absorbed into the fallopian tubes through the cilia .

The final stage – Fertilisation

The secondary oocyte will most effectively complete meiosis II following fertilisation. Here, it offers off a 3rd polar body. Following meiosis II, a fertilised egg results. If fertilisation doesn’t occur, the oocyte degenerates 24 hours after ovulation, ultimately arrested in meiosis II.

Conclusion

Gametogenesis is an important part of mammalian reproduction, with germ cell lines going through a series of complex developmental processes to produce fully mature gametes, sperm and  oocytes. Several conditions, including infertility, result from  abnormal conditions in gametogenesis.