Reproductive Systems

Lesson Objectives

• State the functions of the male reproductive system.
• Identify and describe the male reproductive organs.
• State the functions of the female reproductive system.
• Identify and describe the female reproductive organs.

Introduction

Dogs have puppies. Cats have kittens. All organisms reproduce, including humans. Like other mammals, humans have a body system that controls reproduction. It is called the reproductive system. It is the only human body system that is very different in males and females. The male and female reproductive systems have different organs and different functions.

Functions of the Male Reproductive System

The male reproductive system has two main functions: producing sperm and secreting testosterone. Sperm are male gametes. Gametes are sex cells that may unite to form a new organism. Sperm form when certain cells in the male reproductive system divide by meiosis. Mature males produce millions of sperm each day.

Testosterone is the main sex hormone in males. You read about hormones in the Controlling the Body chapter. Hormones are chemicals that control many body processes. Testosterone has two major roles.

• During the teen years, testosterone causes the reproductive organs to mature. It also causes other male traits to develop. For example, it causes hair to grow on the face.
• During adulthood, testosterone is needed for a man to produce sperm.

Testosterone is not the only sex hormone that males secrete. Males also secrete small amounts of estrogen, the main female sex hormone. Scientists think that estrogen is needed for normal sperm production in males.

Male Reproductive Organs

The male reproductive organs include the penis, testes, and epididymis. These organs are shown in Figure below. The figure also shows other parts of the male reproductive system.

The penis is a cylinder-shaped organ. It contains the urethra. The urethra is a tube that carries urine out of the body. The role of the urethra in reproduction is to carry sperm out of the body.

The two testes (singular, testis) are egg-shaped organs. They produce sperm and secrete testosterone. The testes are contained in the scrotum. As you can see from Figure above, the scrotum is a sac that hangs down outside the body. The scrotum also contains the epididymis.

The epididymis is a tube that is about 6 meters (20 feet) long in adults. It is tightly coiled, so it fits inside the scrotum. It rests on top of the testes. The epididymis is where sperm mature. The epididymis also stores sperm until they leave the body.

Other parts of the male reproductive system include the vas deferens and prostate gland. Both of these structures are shown in Figure above. The vas deferens is a tube that carries sperm from the epididymis to the urethra. The prostate gland secretes a fluid that mixes with sperm to help form semen. Semen is a milky liquid that passes through the urethra and out of the body.

Female Reproductive System

Most of the male reproductive organs are outside the body. In contrast, most of the female reproductive organs are inside the body. The male and female organs also look very different. They have different functions, as well. However, two of the functions of the female reproductive system parallel the functions of the male reproductive system. Like the male system, the female system produces gametes and a major sex hormone.

Functions of the Female Reproductive System

One function of the female reproductive system is to produce eggs. Eggs are female gametes, and they are produced in the ovaries. Mature females release only one egg at a time. Eggs actually form before birth. However, they do not fully develop until later in life. This will be discussed later in this lesson.

Another function of the female system is to secrete estrogen. Estrogen is the main sex hormone in females. Estrogen has two major roles.

• During the teen years, estrogen causes the reproductive organs to mature. It also causes other female traits to develop. For example, it causes the breasts to grow.
• During adulthood, estrogen is needed for a woman to release eggs.

The female reproductive system has another important function. It supports a baby as it develops before birth. It also gives birth to the baby at the end of pregnancy.

Female Reproductive Organs

The female reproductive organs include the vagina, uterus, Fallopian tubes, and ovaries. These organs are shown in Figure below. The breasts are not shown in this figure. They are not considered reproductive organs. However, they are involved in reproduction. They contain mammary glands that secrete milk to feed a baby. The milk leaves the breast through the nipple when the baby sucks on it.

The vagina is a cylinder-shaped organ. One end of the vagina opens at the surface of the body. The other end joins with the uterus. During sexual intercourse, sperm may be deposited in the vagina. The sperm move through the vagina and into the uterus. During birth, a baby passes from the uterus through the vagina to leave the body.

The uterus is a hollow organ with muscular walls. The narrow part of the uterus where it connects with the vagina is called the cervix. The uterus is where a baby develops until birth. The walls of the uterus expand as the baby grows. The muscular walls of the uterus push the baby out during birth.

The two ovaries are small, oval organs on opposite sides of the uterus. Each ovary contains thousands of eggs. The eggs do not fully develop until a female has gone through puberty. About once a month, an egg completes its development and is released by the ovary. The ovaries also secrete estrogen.

The two Fallopian tubes are narrow passages that open off the uterus. Each tube reaches one of the ovaries. However, the tubes are not attached to the ovaries. Notice in Figure above that the end of each Fallopian tube by the ovary has “fingers.” They sweep an egg into the Fallopian tube. Then the egg passes through the Fallopian tube to the uterus.

CK-12 Foundation, Biology. http://creativecommons.org/licenses/by-nc-sa/3.0/