Spermatogenesis & Mature Sperm: Insights on Structure | Biology Blog

                                     Spermatogenesis

                                 
                                                 

Spermatogenesis is the process of formation of sperms from the germinal epithelium of the seminiferous tubules of the testes. The germinal epithelium contains cuboidal primordial germ cells and tall somatic cells called Sertoli cells or nurse cells. Thesertoli cells anchor the differentiating cells and provide nourishment to the developing sperms.

Phases of spermatogenesis - It involves the following two phases -

A. Formation of spermatids - It includes the following phases -

• Multiplication phase - The sperm mother cells or spermatogonia mitotically divides to form new sex cells. Some of these cells move towards the lumen of the seminiferous tubules and enter the growth phase known as Primary spermatocyte. Some cells produced this way remain in their original position and continue to divide giving rise to primary spermatocyte. Such cells are known as stem cells.
• The phase of growth - In this phase, spermatocyte and nuclei enlarge in size.
• The phase of maturation - Each primary spermatocyte undergoes the first maturation division which is educational division and two daughter cells are formed with the haploid number of chromosomes. These daughter cells are called secondary spermatocyte. Secondary spermatocyte undergoes second maturation division which is simple mitotic division and this way four daughter cells are formed which are known as Spermatocyte. Thus, from each primary spermatocyte, four spermatids are formed. 

B. Formation of Spermatozoa - The transformation of spermatids into spermatozoa are known as spermatogenesis. The spermatozoa are known as Sperm. Spermatids formed as a result of maturation division are like typical haploid animal cells and in this form can not function as a male gamete. During this process of metamorphosis, a non-motile spermatid is converted into motile sperm by following changes -

• Sperm increases lengthwise in size.
• The nucleus shrinks by losing water from the nuclear sap and assumes various shapes in different animals. The shape of the nucleus determines the shape of the head of the sperm.
• The cell membrane of the spermatid remains as an envelope over the entire mature sperm including its tail.
• The two centrioles of the spermatid get arranged one after the other behind the nucleus. The anterior one is called Proximal Centriole and the posterior as Distal centriole. The distal one changes into the basal body and gives rise to the axial filament of the sperm.

Structure of motile sperm -

 The mature sperm consists of four parts -

•    Head part 
•    Neck
•   Middle 
•   Tail Part

                               

• The Head part consists of a dense nucleus in which cell organelles are present. On the tip of the nucleus, a small cap-like structure is presently known as Acrosome which is formed from the Golgi complex. It helps in penetration of Egg membrane during fertilization by dissolving enzymes called hyaluronidase.
  
  
• The Neck part is a short segment of sperm that contains two centrioles, proximal and distal centriole. These are introduced at the time of fertilization along with the sperm nucleus to initiate cleavage in the zygote.
  
  
• The middle part, Which is also known as the body of the sperm that contains mitochondria is present which function as to provide energy for the movement of sperm during copulation.
• The last one is the Tail part which is the longest segment of sperm, consisting of central axial filament, the thin layer of cytoplasm, and an outer smooth plasma membrane. They have flagellar movement during copulation. 

Check - Male reproductive system in Hindi 

Difference between spermatogenesis and oogenesis - 

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