 Hey everybody, Dr. Rowe here, this is where we're going to talk about the uterus. So here you see the uterus in all of its glory, fully stretched out, 500 times larger potentially than it is pre-pregnancy. The uterus provides mechanical protection, nutritional support and then waste removal for the developing embryo in weeks one through eight and the developing fetus from weeks nine until delivery. Obviously the uterus is primarily a large muscle and when that muscle contracts, it can help eject and deliver the baby as well. Let's go and take a look at the three parts of the uterus here. We have the part of the uterus that's above or superior to the openings from the uterine tubes. It's called the fundus. The largest portion of the uterus is called the body and then we have the cervix. So the cervix is the part of the uterus that projects into the vagina. The cervix produces this mucus secretions that gets real thin and stringy under the influence of estrogen, which means that it's going to facilitate the transitive sperm through the cervix into the uterus. So that's going to be one of the functions there of the cervix. The layers of the uterus, we have the outer layer. The most superficial layer is called the perimetrium or the cirrus membrane. It's going to be the connective tissue layer on the outside. The most important layer is the myometrium or the muscular layer. So the huge majority of the uterus is the muscle and that's responsible for the uterine contractions, the powerful contractions that can deliver a baby, but it also contractions that help expel blood during the menstrual cycle. And then we have the innermost layer, the endometrium and that's going to be what we'll talk about here now. So the endometrium is the part that changes depending on which part of the uterine cycle you're in. There are two distinct portions of the endometrium. We have the basal layer often called the stratum basalis and that's the permanent part that's never slept off. And then we have the functional layer or the stratum functionalis. That's the part that actually during the proliferative phase here will get thicker. During the secretory phase will get even thicker still, but that's also the portion that is slept off during menstruation if there's not a baby. So the functional layer is the part that grows and then is removed with a normal uterine cycle. So if an egg is fertilized, so once the egg is released from a follicle, remember that the leftover becomes the corpus luteum that's going to produce a progesterone for 10 to 12 days. So if there is a fertilized egg, the signals are going to be sent to that corpus luteum to keep those progesterone levels elevated. So if there's not, the corpus luteum will slowly break down and the egg will just pass through. But if there is a fertilized egg, the corpus luteum will continue to produce progesterone until the mom's body can finish taking over for that job and will allow for implantation and for the development of the baby. All right, if that doesn't happen, that's when you see, so let's talk about each phase here. We'll come back to the menstruation. But the proliferative phase, you see under the influence of estrogen, the functional layer of the uterine lining or the endometrium does start to thicken. During the secretory phase, we really see these branches of the uterine arteries called spiral arteries are going to allow the uterine lining to get thicker and thicker and also produce a bunch of mucus to allow for implantation and the feeding of the fertilized egg, whatever it is at that stage. But if there is no fertilized egg and progesterone levels are allowed to drop, these spiral arteries are going to break down and they're going to stop carrying oxygen to this tissue and this extra layer of tissue is going to die and slough off and be lost and that's what we have for menstruation. So menstruation is the beginning of the uterine cycle. It's the sloughing off of last month's functional layer so you can produce a new functional layer, produce all the secretions it needs to, the glycogen and the mucus and everything to wait for implantation. If that doesn't happen, this functional layer will be sloughed off next month and the cycle will continue. All right, so that's the parts of the uterus you have to know. I hope this helps. Have a wonderful day. Be blessed.