Gametogenesis in Human

The process of formation of male and female gametes in all sexually reproducing organisms is called gametogenesis.

In today’s post we will understand about Gametogenesis, Spermatogenesis and Oogenesis.

We shall also try to understand how oogenesis differs from spermatogenesis.

What is Gametogenesis?

The process in which haploid male & female gametes are formed is called gametogenesis.

However, sperm formation in the male takes place till old age. But the process of oogenesis (ovum or egg formation) takes place only till the age of 45 to 50 years in females.

There are two types of gametes, the first is the male gametes, called the sperm or spermatozoa and the second is the female gametes, called the ovum or egg.

Both the gametes are always haploid in nature that is contain only one complete set or half set of chromosomes.

The formation of sperm takes place in the male gonad called testis. The formation of the ovum takes place in the female gonad called ovary.

Both gametes are haploid, in which the sperm is motile and small, while the ovum is large and non-motile cells.

Both cells are also called germ or sex cells, and further fertilization takes place

After fertilization (fusion of male and female gametes), the zygote is formed, and this zygote later produces a body by embryogenesis.

The process of formation of sperm is called spermatogenesis, while the process of formation of ovum is called oogenesis.

The process of Gametogenesis can be divided into three parts.

• First multiplication phase
• Second growth phase
• Third maturation phase

Multiplication phase

In the multiplication phase, gametes divide by the mother cell mitosis cell division, and form multiple cells, all of which are diploid.

Growth phase

In the same growth phase, there is no division and cell growth takes place. they gets bigger in size by absorbing of nutrients.

Maturation phase

In the maturation phase, meiosis cell division occurs, leading to the formation of haploid cells. These cells are called gametes.

Hormones in Gametogenesis

Hormones play a major role in the entire process of gametogenesis, and different hormones exert their effects at different stages.

For example, the male hormone testosterone hormone in the male and estrogen in the female hormone regulate gametogenesis.

Apart from this, hormones released from the pituitary gland such as follicular stimulating hormone (FSH-follicular stimulating hormone & LH-luteinizing hormone) and luteinizing hormone.

Along with this, GnRH- Gonadotropin releasing hormone released from the hypothalamus of the brain also has a big role.

Let us now understand spermatogenesis and oogenesis separately.

What is Spermatogenesis?

The process of spermatogenesis begins at the stage of puberty or puberty, which is between 13 and 16 years of age in the male.

In male sperm formation occurs till old age. But in the female, process of oogenesis takes place only at the age of 45 to 50 years in the female.

The process of spermatogenesis is divided into 3 phases.

Multiplication phase

In this phase the cells of the germinal epithelium of the seminiferous tubule divide, and form the sperm mother cell.

The sperm mother cell is called spermatogonia.

Spermatogonia are diploid-2N cells, meaning they have 2 sets of chromosomes.

The number of spermatogonia increases in the multiplication face, but there is no change in the number of chromosomes of any kind.

Growth phase

Spermatogonia increase in size in this phase.

But no type of cell division takes place, their size increases as nutrients accumulate in the cytoplasm.

And at the end of the growth phase, they are now called primary spermatocytes.

The point to be noted here is that the number of chromosomes will be diploid, it means there is no change takes place in the chromosomes.

Maturation phase

In this phase, the primary spermatocytes undergo meiosis cell division, leading to the formation of secondary spermatocytes.

Secondary spermatocytes are haploid cells as they have completed meiosis first.

Now secondary spermatocytes complete meiosis 2nd and haploid spermatids are formed.

These spermatids later transform into sperm or spermatozoa.

What is Spermiogenesis?

The transformation of spermatids into sperm is called spermiogenesis.

After spermiogenesis, the sperm attaches to their head region in the Sertoli cell or nurse cell, and takes up nutrients from the Sertoli (nurse cell or subtentacular cell) cell.

What is Spermiation?

The process of release of sperm from the somniferous tubules is called spermiation.

Points to remember

Each spermatogonium produces single primary spermatocytes.

Two secondary spermatocytes are formed from each primary spermatocyte.

Four spermatids or sperm are formed from each primary spermatocyte.

In this way, two spermatids or two sperm are formed from each secondary spermatocyte.

What is Oogenesis?

The process of oogenesis is quite different from that of spermatogenesis, although only haploid cells are formed in both the process.

But the process of oogenesis starts before birth.

This process begins in the ovary of the female embryo during embryogenesis or during embryonic development.

 

The germinal epithelium cells in each ovary begin to divide, forming a million of oogonia or egg mother cell.

No new oogonia is formed and added after birth.

These oogonia enter the growth phase, and go into prophase first of meiosis first and stay temporarily till the stage of puberty.

During this, the oogonium turns into primary oocytes and a layer of Granulosa cells forms around it.

Now these are called primary follicles, after the formation of multiple layers of granulosa again, it gets transformed to secondary & tertiary follicles.

It is in the tertiary follicles that the primary oocytes complete meiosis-II, and transform into haploid secondary oocytes.

Tertiary follicles have a fluid field cavity called the Antrum.

Secondary oocytes form a new layer around them, which is called Zona pellucida.

By the time the puberty is reached, a large number of primary follicles are destroyed (degenerates). And only 60000 to 80000 primary follicles remain inside the ovary.

Upon reaching puberty (which occurs between 10 and 13 years of age in females), secondary oocytes release in ovulation from the ovary (one of the each ovary, not from both the ovary simultaneously) on the 14th day of the menstrual cycle.

The process of oogenesis is also divided into 3 phases.

Multiplication phase

In this phase the cells of the germinal epithelium of the ovary divide, and form the ovum mother cell.

Ovum mother cell is called oogonia. These are diploid cells, that is to say, 2 sets of chromosomes are present in them.

In the multiplication phase, the number of oogonia increases, but there is no change in the number of chromosomes.

Growth phase

In this phase, oogonia increase in size. The growth phase has a period of several years in females.

There is no cell division in the growth phase, as the nutrients accumulate in the cytoplasm of the oogonia, they increase in size.

And at the end of the growth phase, these are now called primary oocytes.

It is to be noted here that the number of chromosomes will be diploid.

no change in the number of chromosomes in the primary oocytes.

Maturation phase

In this phase, the primary oocytes undergo meiosis cell division, leading to the formation of secondary oocytes and a very small first polar body, or polocytes.

The first polar body or polocytes are subsequently destroyed.

Secondary oocytes are haploid cells as they have already completed meiosis first.

Now secondary oocytes complete meiosis second and the formation of haploid ootid and second polar body or polocytes takes place.

The second polar body or polocytes are also later destroyed.

This ootid later transform into haploid ovum.

Points to remember

One primary oocyte is formed from each oogonium.

Secondary oocytes are formed from each of the primary oocytes.

One ovum is formed from each of the primary oocytes.

In this way an ovum is formed from each of the secondary oocytes.

Conclusion

What did we learn?

In today’s post we understood about Gametogenesis, Spermatogenesis and Oogenesis.

In addition, we also learnt how Oogenesis differs from spermatogenesis.

Hope you have understood today’s post, if there is any kind of suggestion or any mistake, then tell us by commenting, we will try to correct it and add it to the post.

Thank you so much for taking the time and reading this post.

Good luck with your online journey.