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biology 0610printed 218 · PDF 218
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progesterone.
● It helps to maintain the thick uterus lining so that the embryo can implant into
it. Once the placenta develops, it takes over the role of secreting
progesterone which it does throughout pregnancy.
● The high levels of progesterone inhibit the secretion of FSH so no more
follicles develop in the ovary.
Sexually Transmitted Infections
● Sexually transmitted infections or STIs for short are infections caused by
bacteria or viruses that can be passed from one person to the other during
sexual contact.
● One of the most important infections is HIV/AIDS.
● HIV stands for Human Immunodeficiency Virus.
● HIV affects white blood cells and in particular a type called T cells.
● Over a long period of time HIV destroys T cells. Their number drops so low
that they become unable to fight against pathogens.
● After several years of infection, a person is likely to develop symptoms of
AIDS.
● They become very vulnerable to infections. They may develop cancer as well.
Brain cells can also be damaged. Normally a person suffering with HIV dies
from a collection of illnesses.
● However there are drugs to control HIV called antiretrovirals. They stop the
virus from multiplying.
Preventing HIV Transmission
● A person can catch HIV through a number of ways.
● One way is through sexual contact. During sexual intercourse fluids from one
partners come in contact with the fluids of the other.
● The best way to avoid it is to have only one sexual partner. Using a condom
is another way.