Human Reproductive System

The human reproductive system and the ability to reproduce make life possible. In sexual reproduction, two individuals produce offspring that have some of the genetic characteristics of both parents. The primary function of the human reproductive system is to produce sex cells. When a male and female sex cell unite, an offspring grows and develops.

The reproductive system is usually comprised of either male or female reproductive organs and structures. The growth and activity of these parts are regulated by hormones. The reproductive system is closely associated with other organ systems, particularly the endocrine system and urinary system. 

Gamete Production

Gametes are produced by a two-part cell division process called meiosis. Through a sequence of steps, replicated DNA in a parent cell is distributed among four daughter cells. Meiosis produces gametes that are considered haploid because they have half the number of chromosomes as the parent cell. Human sex cells contain one complete set of 23 chromosomes. When sex cells unite during fertilization, the two haploid sex cells become one diploid cell that contains all 46 chromosomes.

Spermatogenesis

The production of sperm cells is known as spermatogenesis. Stem cells develop into mature sperm cells by first dividing mitotically to produce identical copies of themselves and then meiotically to create unique daughter cells called spermatids. Spermatids then transform into mature spermatozoa through spermiogenesis. This process occurs continuously and takes place within the male testes. Hundreds of millions of sperm must be released in order for fertilization to take place.

Oogenesis

Oogenesis (ovum development) occurs in the female ovaries. In meiosis I of oogenesis, daughter cells divide asymmetrically. This asymmetrical cytokinesis results in one large egg cell (oocyte) and smaller cells called polar bodies. The polar bodies degrade and are not fertilized. After meiosis I is complete, the egg cell is called a secondary oocyte. The haploid secondary oocyte will only complete the second meiotic stage if it encounters a sperm cell. Once fertilization is initiated, the secondary oocyte completes meiosis II and becomes an ovum. The ovum fuses with the sperm cell and fertilization completes while embryonic development begins. A fertilized ovum is called a zygote.

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An Introduction to Male and Female Gonads

By Regina Bailey

Reproductive System Disease

The reproductive system is susceptible to a number of diseases and disorders. These are of varying degrees of detriment to the body. This includes cancer that can develop in reproductive organs such as the uterus, ovaries, testicles, and prostate.

Disorders of the female reproductive system include endometriosis—a painful condition in which endometrial tissue develops outside of the uterus—ovarian cysts, uterine polyps, and uterine prolapse.

Disorders of the male reproductive system include testicular torsion—twisting of the testes—testicular under-activity resulting in low testosterone production called hypogonadism, enlarged prostate gland, swelling of the scrotum called hydrocele, and inflammation of the epididymis.

Reproductive Organs

Both male and female reproductive systems have internal and external structures. Reproductive organs are considered to be either primary or secondary organs based on their role. The primary reproductive organs of either system are called gonads (ovaries and testes) and these are responsible for gamete (sperm and egg cell) and hormone production. Other reproductive structures and organs are considered secondary reproductive structures and they aid in the growth and maturation of gametes and offspring.