Biology 12

196 MHR • Unit 2 Homeostasis

The Female Reproductive System

The female reproductive system (illustrated in

Figure 6.26 on page 198) performs many functions

— it produces the female reproductive cell (the

ovum), maintains a fertilized egg through its

development as an embryo and fetus, and allows

for the birth of the baby.

The vagina acts as an entrance for the erect penis

to deposit sperm during sexual reproduction and

an exit for the fetus during childbirth. The cervix

forms the opening/exit to the uterus, a thick-walled

muscular organ about the size and shape of an

inverted pear. Although the uterus is usually the

size of a fist, it must be capable of expanding to six

times its usual size to accommodate a fetus. The

lining of the uterus, called the endometrium, is

richly supplied with blood vessels to provide

nutrients to a developing fetus. The endometrium

is affected by the changing hormone levels of the

menstrual cycle.

The two ovariesproduce the ova and are

suspended in the abdominal cavity. They are each

held in place by two ligaments; one extends from

the ovary to the abdominal wall while the other

Biology Magazine TECHNOLOGY • SOCIETY • ENVIRONMENT

Steroid Use

Would you want to take a drug that builds your muscle

mass, increases your strength, reduces your body fat,

improves your endurance, and makes you feel powerful?

All these effects are produced by the male sex hormone

testosterone, and by synthetic versions of the hormone

called anabolic steroids (“anabolic” means growing or

building). Many people, especially athletes of both sexes,

find the positive effects of steroids appealing. But adding

more hormones to the body’s normal level unbalances

hormonal regulating cycles and may lead to health

problems. Typically, abusers of steroids use levels that

are 10 to 10 000 times higher than those prescribed by

doctors for therapeutic purposes. Would you still want to

take steroids if you knew they can also result in shrunken

testes, reduced sperm count, breast enlargement, and

impotence in males, and menstrual irregularities, breast

reduction, masculine features, and sterility in females? In

addition, steroids can lead to acne, mood disturbances,

and increased risk of diseases of the heart, liver, and

kidneys in both sexes. If taken by teenagers and young

adults, steroids can also stunt growth.

What Are Steroids?

Steroids form a class of about 30 hormones normally

secreted by the adrenal cortex, testes, ovaries, placenta,

and corpus luteum (a group of cells that produces

progesterone). Testosterone is a steroid hormone

produced by the testes from puberty throughout adult

life, in quantities of 4 mg to 10 mg per day. Testosterone

has three main functions:

1.It stimulates the development of male secondary sex

characteristics such as beard growth, deep voice,

and the maturation of sperm. These are called

androgenic functions.

2.It helps the body retain dietary protein, which

accelerates muscle growth, increases the formation

of red blood cells, and speeds up regeneration and

recovery time after injuries or illness. These are called

anabolic functions.

3.It provides feedback for the sex hormone regulating

cycle. Excessive levels of testosterone in the blood

signal the hypothalamus to release less LH-releasing

hormone (also known as GnRH or gonadotropin-

releasing hormone). GnRH stimulates secretion of LH

(leutenizing hormone) from the anterior pituitary,

which in turn stimulates the testes to produce

testosterone. In other words, a negative feedback

loop ensures that if you have high levels of

testosterone, your body will reduce or even stop

production of this hormone until levels subside to

normal. This regulating cycle produces pulses in the

levels of testosterone circulating in the bloodstream

throughout the day.

The feedback function of testosterone explains many of

the negative side effects experienced by steroid users.