As we know, an organism undergoes a series of transformations during its entire life cycle. Similarly, Reproduction is an important step for the origination of a new life cycle. Further, gametogenesis plays a significant role in humans to support the continuation of generations.
Author – Kshitij Dwivedi
What is gametogenesis ?
“Gametogenesis is the process of production and development of haploid gametes by the primary sex organs.”
In simpler terms, gametogenesis means the genesis of gametes. It is called spermatogenesis in males, likewise, it is called oogenesis in females.
Furthermore, spermatogenesis leads to the formation of a male gamete called the sperm. Whereas, oogenesis leads to the formation of a female gamete known as the ovum.
Spermatogenesis Definition :
“The process by which new spermatozoa or sperms are created from spermatogonia is called spermatogenesis.“
Furthermore, it occurs in the testis which is the primary sexual organ of males. In humans, it takes an average of 74 days.
Phases of Spermatogenesis :
The process of spermatogenesis takes place in phases, such as:
1. Phase of mitotic division of spermatogonia:
Firstly, spermatogonia divide mitotically 7 times to form 128 spermatogonia.
2. Phase of formation of primary spermatocyte by maturation:
Then, 128 spermatogonia undergo maturation to form 128 primary spermatocytes. Further, these are large cells with a diploid number of chromosomes.
3. Phase of formation of secondary spermatocyte by 1st meiotic division:
During 1st meiotic (reductional division),128 primary spermatocytes convert into 256 secondary spermatocytes with a haploid number of chromosomes.
4. Phase of formation of spermatid:
Further, each secondary spermatocyte undergoes 2nd meiotic division(similar to mitosis) to give rise to 2 spermatids. Thus, a total of 512 spermatids form, having a haploid number of chromosomes.
5. Phase of formation of spermatozoan:
Finally, spermatids stop dividing further but undergo morphological changes to form sperms or spermatozoa.
Factors influencing Spermatogenesis :
Spermatogenesis is regulated by certain important factors, such as:
- Testosterone: It is essential in high concentration for growth and division of testicular germinal cells, which is the first stage in forming sperm.
- Luteinizing Hormone: It is secreted by anterior pituitary gland and helps by stimulating the Leydig cells to produce testosterone which is essential for spermatogenesis.
- Follicle Stimulating Hormone: It is the key gonadotropin for spermatogenesis, secreted by anterior pituitary. In addition, it helps in the conversion of spermatid to sperm by stimulating the Sertoli cells to produce some local factors.
Spermatozoan (The sperm):
The sperm about 60 mm long is a single cell that has a ‘head’ and a ‘tail’. Moreover, the head is the nucleus of the cell containing the DNA material. Also, the head is capped by an acrosome made up of mucopolysaccharide and acid phosphatase enzymes.
Furthermore, in the fallopian tube, the acrosomal membrane is removed so as to expose the acrosomal enzymes. These enzymes are digestive in nature that facilitate their activity by enabling the sperm to penetrate the ovum to cause fertilization. Thus, the removal of the acrosomal membrane is called sperm capacitation.
Sertoli cells are large, complex glycogen-containing cells that stretch from the basal lamina of the tubule to the lumen.
- Sertoli cells: secrete androgen binding factors (ABP), inhibin, MIS (mullerian inhibiting substance).
- They have receptors for FSH and testosterone. After combining with FSH, Sertoli cells stimulates the first half of spermatogenesis. Subsequently, testosterone-Sertoli cells binding causes development of last half of spermatogenesis.
Important Points for NEET-UG Exam:
- Capacitation occurs inside the female genital tract.
- The extremely long length of the epididymis helps in the maturation of the sperms.
- Spermiation is the process by which, Sertoli cells release the mature sperms the into the lumen of seminiferous tubules.
- Ejaculation is the process by which the male releases semen from the urethra into the female genital tract.
- Spermiogenesis is the process of conversion of spermatids into spermatozoan.
- Cryptorchidism is a condition in which the testes do not descent into the scrotum leading to infertility.
Click here to read Gametogenesis (Part II), which has a detailed discussion on gametogenesis in females, i.e., oogenesis.
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