The Endocrine and Reproductive Systems

This section is about reproduction and is intended for older students. Please preview the material before presenting to your children. Remember, you are in charge of your children’s education and are totally empowered to skip over any material that you deem unsuitable.

For you created my inmost being;

you knit me together in my mother’s womb.

Psalm 139:13, New International Version

Adolescence is a time of great changes for mammals. An adolescent dog becomes clumsy and trips easily over its quickly growing legs. Young male elephants can go rampaging around in an apparent rage of destruction. Human teenagers start to plan for their future, take risks, and begin thinking about they person who they would like to marry. Not to mention all of the physical changes that they undergo – growth spurts, body hair, deeper voices for boys and curvier bodies for girls.

What causes all of those changes? Why do they start and stop so suddenly? We have the endocrine system to thank for that. This is a relatively small system in our bodies (a system is a group of organs that work together, as I’m sure you remember), but it has dramatic effects on our bodies for our entire lives. It is made up of several types of glands, organs that make a type of protein called hormones. Hormones are like messengers carrying orders around your body.

Different glands boss around different parts of your body. The butterfly-shaped thyroid gland in your neck tells your cells how quickly to use up their fuel. The tiny pine-cone shaped pineal [pie-nee-ul] gland in your brain controls your sleep. Your corncob of a pancreas in your abdomen controls the amount of sugar in your blood (this is the organ that malfunctions in Type 1 diabetes). Many parts of your digestive system (stomach, small intestines, etc.) also produce hormones that can affect your mood, which is what we can thank for the word “hangry.”

For puberty, the body’s time of maturing, the most important gland is the pituitary gland. This guy is like the master commander than tells all the other glands what’s what, as well as releasing the growth hormone at the right time. I’m sure you’ve guessed that the growth hormone makes you grow, increasing the size of your bones, muscles, and organs. Your brain also produces hormones that cause the development of the reproductive system – the organs used for producing offspring.

The reproductive system is the only system that is dramatically different between males and females. Hormones from the brain stimulate the development of the ovaries (which produce eggs in women as well as the hormone estrogen) and the testes (which are responsible for making sperm and the hormone testosterone in men). Estrogen and testosterone are responsible for many of the other sexual differences, such as deeper voices and greater aggression in men and the growth of breasts in women.

In addition to ovaries, women have other parts in their reproductive system. The uterus, or womb, takes center stage as the potential home for developing baby. About once a month, an egg travels there from one of the two ovaries through the Fallopian tube. If the eggs is not fertilized, it passes out the opening in the uterus called the cervix as the woman’s menstrual cycle (also known as a period). If the egg is fertilized, it will attach itself to the uterus and begin to develop.

Like all mammals, babies have a special organ called a placenta while they are growing in the womb. This absolute powerhouse of an organ provides all the oxygen and nutrients the young one needs, delivered from the mother’s blood directly to the baby’s through the umbilical cord (you can see the remnants of your umbilical cord in your belly button). While growing, the baby is bathed in amniotic fluid, something like saltwater that also has antibodies to keep the baby healthy.Nine months later (give or take), the baby will exit the uterus through the cervix and out the birth canal (also known as the vagina), into the world of light and sound.

Of course a baby cannot come into the world at all without a father as well. A man’s reproductive system is centered around the testes, which make about 100 million sperm every day after puberty (that comes out to over 2 trillion sperm in a lifetime). The sperm reaches the egg during sexual intercourse when the man and woman join together their penis (yes, sperm comes out of the same place as urine!) and vagina. During intercourse, the sperm go on a bit of a roller coaster ride, going through the vas deferens way up to near the small intestines until looping back down through the prostate gland. Here the sperm get special fluid that protect them before traveling through the urethra and out the penis. Sperm then have to try to reach the egg, starting from around 200 million sperm to just a handful ending up anywhere near an egg. If one lucky sperm reaches the egg, it will burrow into it and fertilize it. The egg can then implant in the uterus, allowing the zygote to develop into a newborn baby.