Reproductive System

Without the reproductive system, new members of a species could not be produced and the species would become extinct. Although the foundation of reproductive organs exist at birth, it is not until about ten years later that the full functioning of the system is spurred by the endocrine system, and its sudden change in hormone production to begin puberty. These same hormones are responsible for sex drive and secondary sex characteristics, including facial and genital hair, distribution of body fat and breast development. The hormones also affect emotions in both sexes. They are produced in the sexual organs themselves and in endocrine glands outside the reproductive system.

In men, the main reproductive organs include the penis, the testes, ducts and the accessory sex glands (the seminal vesicles, bulbourethal glands and the prostate). The testes (or testicles) are oval glands where sperm is produced and hormones are secreted. The testes are contained in a pouch called the scrotum. The muscle fibers in the scrotum regulate the temperature of the testes which is important to the survival of the sperm-they must be kept 5.4°F (3°C) lower than the core body temperature or else they will die.

Sperm mature in ten to fourteen days at a rate of three hundred million per day. When a sperm matures, it begins to move through a series of ducts in the reproductive system, mixing with different fluids to become semen. Sperm are eventually ejaculated from the body. Once sperm have been ejaculated by the penis into the vagina, they have a life expectancy of forty-eight hours.

Semen gives sperm a medium of transportation, as well as providing the sperm with nutrients. Accessory sex glands secrete most of the liquid portion of semen. Pouch-like structures called seminal vesicles, and the bulbourethral glands, release substances which give semen its alkaline nature and mucus-like consistency. It is necessary to neutralize the acidic environment of the female reproductive tract or else the sperm would be inactivated and killed, thwarting conception. The mucus lubricates the urethra to prevent injury to the sperm as it leaves the penis. The prostate gland contributes to the composition of semen by releasing a slightly acidic fluid with enzymes which gives semen its milky appearance, and aids in sperm motility and viability. Healthy men can retain their reproductive capacity for seventy or eighty years. After the age of fifty-five, fewer sperm are viable for insemination.

In women, the ovaries, uterus and vagina are the major reproductive organs. Once a month, the ovaries will produce an egg, which will be released into one of two Fallopian tubes at midcycle. This process is called ovulation. While the egg is in the Fallopian tube, it may or may not be fertilized by sperm. The uterus prepares for possible fertilization by building up its walls to protect the fertilized egg when it arrives from the Fallopian tube, and provide it with nutrients until the placenta takes over.

The vagina is a muscular organ that can stretch considerably to receive the penis during sexual intercourse. After sperm is ejaculated into the vagina, if fertilization is to occur, it will usually happen within the twenty-four hours after ovulation. If conception between the egg and sperm is successful, the cells will divide for a week and then move into the uterus. The embryo will attach itself to the uterine wall, where it will gestate for nine months. If the egg is unfertilized, it will disintegrate, and the uterus will discharge blood, tissue fluid and mucus through the vagina in a process called menstruation.

When a pregnancy goes to full-term and labor begins, the baby is pushed out of the uterus and through the vagina. After a few weeks, the female reproductive organs will go back to their pre-pregnancy state, and the cycle will continue. The female reproductive system has a limited fertility period of only thirty to forty years.

Overview of Hormone Effects

Although the effects of hormones are many and varied, their actions can be categorized into seven broad areas.

1. Regulate the chemical composition and volume of the internal environment (extracellular fluid).
2. Help regulate metabolism and energy balance.
3. Help regulate contraction of smooth and cardiac muscle fibers and secretion by glands.
4. Help maintain homeostasis despite emergency environmental disruptions such as infection, trauma, emotional stress, dehydration, starvation, hemorrhage and temperature extremes.
5. Regulate certain activities of the immune system.
6. Play a role in the smooth, sequential integration of growth and development.
7. Contribute to the basic processes of reproduction, including gamete (egg and sperm) production, fertilization, nourishment of the embryo and fetus, delivery and nourishment.

PDF Diagram of the Male (l) and Female (r) Reproductive System