Chapter 2 Solutions — Human Reproduction

Functions of Testis:

1. Spermatogenesis — the testis produces male gametes (sperms) in the seminiferous tubules by the process of spermatogenesis. The spermatogonia undergo meiotic divisions leading to the formation of spermatozoa.

2. Androgen secretion — the interstitial cells (Leydig cells) present in the spaces outside the seminiferous tubules synthesise and secrete male sex hormones called androgens (e.g., testosterone). Androgens regulate spermatogenesis and the development of male secondary sexual characteristics.

Functions of Ovary:

1. Oogenesis — the ovary produces female gametes (ova) by the process of oogenesis. Primary oocytes develop through follicular stages and ultimately a mature secondary oocyte (ovum) is released at ovulation.

2. Ovarian hormone secretion — the ovary secretes steroid hormones (ovarian hormones): estrogens (secreted by developing follicles) and progesterone (secreted by the corpus luteum). Estrogens regulate the follicular phase and female secondary sexual characteristics; progesterone maintains the endometrium for implantation and supports pregnancy.

The following hormones regulate spermatogenesis:

1. GnRH (Gonadotropin Releasing Hormone) — secreted by the hypothalamus at puberty. It acts on the anterior pituitary to stimulate release of LH and FSH.

2. LH (Luteinising Hormone) — secreted by the anterior pituitary. It acts on the Leydig cells (interstitial cells) of the testis, stimulating them to synthesise and secrete androgens.

3. Androgens (primarily Testosterone) — secreted by the Leydig cells. They stimulate the process of spermatogenesis within the seminiferous tubules.

4. FSH (Follicle Stimulating Hormone) — secreted by the anterior pituitary. It acts on the Sertoli cells and stimulates secretion of factors (such as androgen-binding protein) that are essential for spermiogenesis — the differentiation of spermatids into spermatozoa.

Spermiogenesis:

Spermiogenesis is the process by which haploid spermatids (produced after the second meiotic division during spermatogenesis) are transformed into mature, motile spermatozoa (sperms). During spermiogenesis, the round spermatid undergoes extensive morphological changes: the nucleus becomes elongated and condensed, a cap-like acrosome (filled with hydrolytic enzymes) develops over the anterior portion of the nucleus, the middle piece develops with numerous mitochondria (which provide energy), and the tail (flagellum) grows. The excess cytoplasm is shed as a residual body.

Spermiation:

Spermiation is the process by which mature spermatozoa are released from the Sertoli cells (in which the sperm heads had become embedded after spermiogenesis) into the lumen of the seminiferous tubules. After spermiation, sperms are transported by the accessory ducts (rete testis → vasa efferentia → epididymis → vas deferens) to the outside.