字幕表 動画を再生する 英語字幕をプリント - Welcome to the reproductive system. So, let's start by asking, "What is the reproductive system?" It's basically a system in our bodies that includes our sex organs and certain parts of our brain. You can see the sex organs here on the male, and here in two places on the female. So, this system within our bodies allows us to reproduce, it allows us to make babies. And to make babies what we're doing is combining genetic material from a biological mother's egg and a biological father's sperm to make our offspring. And we typically do this by sexual intercourse. So, let's first take a brief look at a couple of the most important sex organs that make males and females have in their reproductive systems. So, the males have the testes. And these are the most important structures. Sort of the structures that everything else is built around in a male. And that's because the testes produce his contribution to a baby. They make these small mobile cells that carry his genetic material into a female to fuse with her genetic material to cause a pregnancy. And these small mobile cells are his sperm. Another important male organ is the penis. And the penis is used to deliver his sperm inside the female mate to increase the chance that it meets her egg. So, those are really the major male organs. Now on the female side, one of her major organs is the ovary and she has two just like how males have two testes. And in fact the ovaries and testes are homologous, they came from the same precursor in development. Now the ovaries are responsible for producing the female's genetic contribution to a baby, that is the egg. The ovaries, though, are a lot different to the testes, in that the testes are constantly producing lots and lots of sperm. To the tune of of millions per day. Where as the ovaries only release one egg per month. So, the next really important female organ is called the uterus. And the uterus is basically a really thick muscular organ that's capable of stretching out and it's actually where the baby's actually developing during pregnancy until birth. The next really important female structures are the breasts. And the breasts are important because they produce milk during the pregnancy and afterwords via a process called lactation. And lactation happens due to a series of hormones that generally get released around pregnancy. So, this breast milk that gets produced can feed and nourish the growing baby and it actually plays a roll in creating a stronger immune system for the baby. So, we've seen some of the major structures of both male and female reproductive systems. But is that all the reproductive systems are? Actually, no. Besides producing the sperm and egg, the reproductive systems produce chemicals whose signals have a really strong influence over activities in our bodies. We call these chemicals, hormones and because they come from our reproductive systems we refer to them as our sex hormones. For example, the male's major sex hormone, testosterone, which is actually produced in the testes, is responsible for many masculine traits. Such as body hair, the deepening of your voice, muscle growth, and there's possibly even a link to levels of aggression in males. On the female side of things, the ovary is the primary producer of some major female hormones, like estrogen and progesterone. Estrogen and progesterone play a major roll in the timing of egg release from the ovaries. Estrogen is also responsible for the development of a lot of feminine traits. For example, breast development. So, there's the making of the sperm and the egg, there's the production of the major sex hormones. What else does the reproductive system do? Well it does one more really important thing. And that's coordinate the meeting of the sperm and the egg. And it does that by the males penis and the females vagina. These two organs are used to ensure that the sperm and the egg meet each other. So, the penis actually deposits sperm within the vagina, so that sperm has a better chance of reaching and fertilizing the egg released inside her reproductive tract. So, you might be thinking, "Does the reproductive system "do all this stuff on it's own?" I mean what tells it what to do? And that's a good question. The reproductive system is actually controlled by the brain. There's an area in the brain called the hypothalamus that sits just about there on the inside of the brain, just about in the middle. And the hypothalamus actually releases a hormone called gonadotropin releasing hormone or GNRH. GNRH effects another part of the brain called, anteriorpituitary which sits right about there just under the hypothalamus. And anteriorpituitary in response to GNRH releases two hormones lutenizing hormone or LH and follicle stimulating hormone or FSH. And its the lutenizing hormone and the follicle stimulating hormone that primarily effect the male and female sex organs. So, the male's testes and the female's ovaries to control their functions. Finally, a word on pregnancy, as pregnancy is a huge part of reproduction and certainly the most long lasting part. So, pregnancy results when a sperm successfully fertilizes an egg to create a zygote. A zygote is a first cell in a new organism that has genetic material from both mom and dad. And that genetic material has come from the sperm and the egg that have fused. The zygote goes through a series of developments and eventually implants itself within the inner wall of a woman's uterus to grow. So, that's in here, remember that thick muscular organ we talked about? The third step is what we'll really broadly call gestation. Gestation is basically the development of the fetus into a baby. So, the development of all the fetus's organ systems including their brains, spinal cord, lungs, cardiovascular system, their reproductive system, all the systems in their body. Gestation readies the developing infant to be born. And it takes about nine months. When the babies ready to come out of the uterus and into the world a number of hormonal changes take place in the mother's body. This signals her to start getting ready to push the baby out of her body, in other words, give birth to the baby. She then goes through a process called labor, also known as parturition, to give birth to the baby. After the baby's born, the last step is to give him or her a name.