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Studying for a test? Prepare with these 14 lessons on Human anatomy and physiology.
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- Let's talk about one of the major female sex hormones, Estrogen. And before we officially start, I should mention that even though I said estrogen is one of the major female sex hormones, I just want to be clear here that males also produce and need a bit of estrogen as well, but we just produce sort of a small fraction of what female's need and produce. So let's take a look. Estrogen is produced in females primarily by the ovaries, and as sort of a bonus, when she's pregnant, her placenta also produces some estrogen as well. There's also a little bit made by the adrenal glands that sit on top of the kidneys, the breasts, and by fat cells in general, but we'll sort of keep our focus on the ovaries as the primary source for now. So, the Anterior Pituitary hormone called follicle stimulating hormone, or FSH, causes follicles in the ovaries to develop, and when follicles in the ovaries develop, two groups of cells within them called Theca cells and Granulosa cells start to sort of team up and release estrogen into the bloodstream, and the amount sort of goes up and down throughout each month and that's because of signals from the Hypothalamus and the Anterior Pituitary. So, now we know where we get most of the estrogen in the body, and we know that its levels are regulated by interactions between the brain and the ovaries, but before we talk about what it does from a biological standpoint, I want to go over how estrogen actually works. So after estrogen is made in the ovaries by these Granulosa cells, it's transported to other places in the body by the bloodstream. And so I'll just draw little red blood cells here, and then I'll draw estrogen in light purple here. And these blood vessels take the estrogen all over the body so it can carry out all of its biological functions, but once it gets to its target, what exactly happens? How exactly does it work? So to show you this, I'll blow up a cell here in the thigh, and let's say that this here is the cell membrane, and this purply-blue thing here is the blood vessel that's sort of lining or running beside that cell. So we'll draw in our red blood cells and our estrogen. So when estrogen sees a cell that it wants to enter, it crosses the cell membrane, where it's picked up by a carrier protein, and I'll draw that as a taxi because all it's really doing it picking up estrogen and transporting it to its next destination in the cell, which is the nucleus, and the nucleus is where our DNA is. And so estrogen works by binding near to certain genes to change their expression, and so that'll ultimately change the behavior of that target cell. So that's how it works, but what exactly does it do in the body? What sort of effect does it have on a person's body? And I purposely say a person's body here to remind you that males and females sort of depend on estrogen to do different things in our respective bodies. So, for example, in males specifically, estrogen has a role in the maturation of sperm, and is stored to sorta pair up with testosterone to increase libido, also known as the sex drive. But estrogen does a lot of female-specific stuff. It actually has a lot to do with the growth and the development of the female reproductive tract. So for one, we know that it stimulates the growth of the ovaries and the follicles inside the ovaries as part of the reproductive cycle. It also causes growth of the smooth muscle components of the female reproductive tract. For example, the smooth muscle in the uterus and the uterine tubes after puberty. It also stimulates the growth of the female's external genitalia and breasts during puberty as well, and the way it sort of manages breast growth is by primarily increasing the fat that gets deposited in the breasts. And speaking of fat deposition, estrogen's also responsible for the so-called female fat distribution pattern, which is deposition on the hips as well as the breasts, in contrast to the male pattern, which is fat distribution around the tummy. So those are the major effects that estrogen has on the reproductive tract and on that fat distribution role. There are some other really important non-reproductive roles that estrogen has as well, and we'll touch on two of those. So number one, estrogen does some really good things for your blood cholesterol levels, and for you to really appreciate this point, I kind of have to tell you a bit about cholesterol first. So, bear with me for a minute, and let's have a quick chat about cholesterol. So cholesterol is a lipid molecule that, despite all the negative press it receives, it's kind of essential for life. It's required to make nice, healthy cell membranes, and, maybe a bit ironically, we make a lot of our hormones out of cholesterol, and in fact our testosterone and estrogen themselves are made from cholesterol. Our cholesterol has to be carried around our bodies in the bloodstream, and essentially, we have a couple types of molecules that carry the cholesterol around. So we have one molecule called HDL, or high-density lipoprotein, and we have another molecule called LDL, or low-density lipoprotein. And all that density business in their names just refers to the ratio of protein to cholesterol that these molecules have in them. So, for example, HDL has lots of protein and a little bit of cholesterol. So it's high-density in terms of its protein content, but for simplicity sake, we'll just call them good cholesterol, being the HDL, and bad cholesterol, being the LDL, and the reason they're differentiated as being "good and bad" is because high levels of the bad kind, LDL, is implicated in causing problems with your blood vessels, which can lead to things like heart attacks or strokes, and optimum levels of the good kind, HDL, is correlated with reduced risk of having these bad things happen. So, back to estrogen. Estrogen actually reduces the bad cholesterol, LDL, and increases the good cholesterol, HDL. So that's pretty great. Kind of a lot of cholesterol background to make that point, but it's physiologically a really important role of estrogen and, in fact, after a female slows her production of estrogen in her fifties, her level of HDL can actually start to go down. So that's estrogen and cholesterol. Another really important estrogen role is one that has to do with preserving the strength of our bones in our skeletal system. So, throughout our lives, bones are constantly undergoing renovations, and that sounds a bit weird, right, because we always tend to think of bones as being these static unchanging things, but actually on a microscopic level, they're constantly being broken down and built back up, and estrogen actually affects part of that process. So estrogen slows down the cells that are involved with the breakdown portion of your bone renovations. So as a result of that, your skeleton stays more dense for a longer period of time, and that means that as estrogen levels get lower when a female gets older, she's more at risk for developing a bone condition where the bones get brittle and weak, and that's called osteoporosis. So that's a little overview of the importance of estrogen and a few of its biological roles within the body.