Question

1) discuss the origin of sperm and testosterone.

2) discuss the origin of the ovum and both estrogen and progesterone.

Answer 1

First question:

Spermatogenesis:

Spermatogenesis is the process by which the male gametes called spermatozoa (sperms) are formed from the primitive spermatogenic cells (spermatogonia) in the testis. It takes 74 days for the formation of sperm from a primitive germ cell.

Stages of spermatogenesis:

• Stage of Proliferation:

Each spermatogonium contains a diploid number (23 pairs) of chromosomes. During the proliferative stage, spermatogonia divide by mitosis, without any change in chromosomal number. This results in the formation of primary spermatocyte.

• Stage of Growth:

In this stage, the primary spermatocyte grows into a large cell. Apart from growth, there is no other change in spermatocyte during this stage.

• Stage of Maturation:

After reaching the full size, each primary spermatocyte undergoes meiotic division, which occurs in two phases:

First phase: In the first phase, each primary spermatocyte divides into two secondary spermatocytes. Each secondary spermatocyte receives only the haploid or half the number of chromosomes (23 chromosomes include 22 autosomes and a X or a Y chromosome).

Second phase: Each secondary spermatocyte undergoes the second meiotic division, resulting in the formation of spermatids. Each spermatid has a haploid number of chromosomes.

• Stage of Transformation:

There is no further division. Spermatids are transformed into mature spermatozoa (sperms), by means of spermiogenesis and released by spermination.

Spermiogenesis:

Spermiogenesis is the process by which spermatids become mature spermatozoa.

Changes taking place during spermiogenesis: Condensation of nuclear material, Formation of the acrosome, mitochondrial spiral filament and tail structures, Removal of extraneous (extra volume of nonessential) cytoplasm.

Spermination:

Spermination is the process by which the matured sperms are released from Sertoli cells into the lumen of seminiferous tubules.

Synthesis if testosterone:

Adrenal sex hormones are secreted mainly by zona reticularis. Zona fasciculata secretes small quantities of sex hormones. The adrenal cortex secretes mainly the male sex hormones, which are called androgens. But, a small quantity of estrogen and progesterone are also secreted by the adrenal cortex.

Androgens secreted by the adrenal cortex are Dehydroepiandrosterone, Androstenedione, and Testosterone.

Second question:

Oogenesis:

• The process of formation of a mature female gamete is called oogenesis.
• An ovarian follicle consists of an oocyte surrounded by one or more layers of follicular cells, granulosa cells, which are derived from the germinal epithelium lining the ovary.
• The oogonial cells start division and enter into Prophase 1 of meiotic division, and get temporary arrested at this stage called a primary oocyte. The primary oocyte gets surrounded by a layer of granulosa cells and are called primary follicles.
• With the onset of puberty, a primary follicle begins to mature with each ovarian cycle. The primary follicles get surrounded by more layers of granulosa cells, and a new theca called secondary follicle.
• The secondary follicle son transforms into tertiary follicle which is characterized by a fluid-filled cavity called the antrum.
• The primary oocyte within the tertiary follicle grows in size and completes its first meiotic division at puberty. It is an unequal division resulting in the formation of large haploid secondary oocyte and the tiny first polar body.
• The secondary oocyte retains the bulk of the nutrient-rich cytoplasm of the primary oocyte. The tertiary follicle change into mature Graafian follicle.
• In the presence of the LH hormone, the Graafian follicle ruptures to release the secondary oocyte developing from the ovary by the process called ovulation.
• After ovulation, the ruptured follicle left in the ovary is converted into a structure called corpus luteum which secretes mainly progesterone.

Synthesis of estrogen and progesterone:

Starting from cholesterol, the ovary synthesizes estradiol, the major estrogen, and progesterone, the major progestin.

Estrogen biosynthesis requires two ovarian cells (theca and granulosa cells) and two gonadotropins (LH and FSH), whereas progestin synthesis requires only a single cell.