Short notes on the process of spermatogenesis

Short notes on the process of spermatogenesis

The process of spermatogenesis takes place in the male gonads called the testis. In most of the vertebrates the testis consists of many fine tubules called seminiferous tubules. These tubules have a wall lined by the cells of the germinal epithelium. The sperms are formed by these cells of the ger­minal epithelium. The seminiferous tubules also have certain cells called the nurse cells or Sertoli. These are actually sematic cells which do not undergo reduction division. There function is to provide nourishment to the developing sperms.

The development of the sperms from the germinal epithelium, although is a continuous process may be divided into two stages. These are

1. Formation of spermatids and

2. Maturation of spermatids into sperms (spermiogenesis).

Formation of spermatids:

The germinal cells of the seminiferous tubules produce the spermatids. The germinal cells are also referred as primordial cells or primary germi­nal cells. To begin with, the germ cells are diploid and they give rise to the spermatids. This process is believed to take place in three phases – multi­plication phase, growth phase and the maturation phase. Multiplication phase.

At this stage the testis consists of numerous semin­iferous tubules made up of un differentiated germinal epithelium cells. These cells have large deeply staining nuclei. The primordial germ cells increase their number by undergoing repeated mitotic divisions. As a result of this a large number of cells called sperm mother cells (spermatogonia) are formed. Each sperm mother cell is diploid and is like any other body cell in its chromosome constitution.

Growth phase:

This follows the multiplication phase. In this phase there is no multiplication in the number of the cells. But the cells which are al­ready formed absorb nutrition from the surrounding cells of germinal epithelium and grow in size. These cells have a large am of food materials and are also rich in chromatin. These enlarged cells are called spermato­cytes. It has been observed that during the growth period the pairing or synapse of the chromatids becomes visible. Hence it may be said that meiosis (reduction division) is initiated in this stage.

Maturation phase:

During this phase the process of reduction division or meiosis which has been initiated will be completed. Meiosis involves two successive cell divisions – meiosis I and meiosis II. During meiosis I there is reduction division so that the two daughter cells are formed after divi­sion will have exactly half of the number of chromosomes than present in the original cell. Meiosis II is an equational division. At the end of the division four cells are formed.

The two haploid cells that are formed after meiosis I are called secondary spermatocytes. The two secondary spermatocytes undergo meiosis II to produce four cells which are called spermatids. The spermatids do not undergo any further division but simply undergo metamorphosis to pro­duce the sperms. Thus at the end of maturation phase each germinal cell would have produced four spermatids.