|MadSci Network: Anatomy|
This is a very good question. Most people now know (or should learn) that AIDS is spread to adults in three main ways - having sex, high-risk drug use (like needle-sharing), and blood transfusions. All of these are ways that the HIV virus can get from one personís blood to another personís blood. But obviously babies donít do any of these things, except maybe for a small number of blood transfusions. And yet AIDS is definitely a problem in pediatrics as well as adult medicine. So how do babies and little kids get it? Almost all babies with AIDS got it from their HIV-infected mother while they were inside the uterus (also known as the womb). In other words, the HIV virus was spread from the motherís blood to the babyís blood before the baby was born. Even if they donít get AIDS until years later, little kids were still almost always infected with HIV when they were inside their mother. The thing is, only about one-third of babies born from mothers who have AIDS will actually get infected with HIV themselves (and treatment of the mother with AZT can drop this down even farther). This is because there is actually an inherent resistance to transmitting viruses from mother to baby, but this resistance is just not perfect. We can understand how all of this works by considering the special anatomy of the pregnant woman. The mother "feeds" the baby, i.e. nutrients pass from the motherís blood to the babyís blood, through a special organ called the placenta (also known as the afterbirth). In the placenta, blood from the mother washes over small blood vessels from the baby, allowing sugar, oxygen and other good things to diffuse across. But the blood never actually mixes, it is separated by a blood vessel wall, and so big things like viruses canít get into the babyís blood. As an aside, the babyís blood vessels get to the placenta through the umbilical cord, which was attached to your body where your belly button is now. The problem is that the placenta has SO MANY of these little blood vessels that sometimes they get damaged and torn. This rarely causes a major bleeding problem, but it does allow the motherís blood and the babyís blood to mix just a little bit. We call this a "maternal-fetal transfusion", which literally means passing of blood between mother and baby. The more virus there is in the motherís blood, the more likely it is that these small blood exchanges will infect the baby. Hope this helps you understand. And remember, please, talk to your parents or teachers about how to PROTECT YOURSELF FROM AIDS!!! Tom Wilson, MD PhD
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