This lesson will explain the process involved in the implantation of a zygote in the uterus.

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Source: Video and Images Created by Amanda Soderlind

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Welcome to this lesson on implantation. In this lesson today, we will be discussing the process involved in the implementation of a zygote into the uterus. So implantation occurs when a blastocyst attaches to the endometrium of the uterus. And this will usually occur about one week-- between five days and one week after fertilization.

So basically what occurs is that the zona pellucida, which was previously enclosing the blastocyst, will break open. And then the cells of the blastocyst's outer layer will attach to this connective tissue of the endometrium. And the endometrium is that tissue within the uterus. So this is occurring inside the uterus, right in here.

So once it has attached-- once this blastocyst has attached to the endometrium here, it will start secreting human chorionic gonadotropin, which is abbreviated HCG. So once it has attached and implanted onto the endometrium of the uterus, it releases this hormone HCG.

And what this does is it stimulates the corpus luteum to secrete estrogen and progesterone to prevent menstruation. So if it's attached here inside the uterus, we don't want menstruation to occur because then this would be menstruated along with the lining of the uterus. So menstruation has to be stopped. And that's done by progesterone and estrogen being secreted by the corpus luteum.

So remember that is formed from remnants of the ruptured follicle when it was released from the ovary. So it's released from the ovary. These remnants of this follicle will then release hormones to stop menstruation if the oocyte has been fertilized. So generally we have fertilization that occurs in the Fallopian tubes. And then the fertilized egg will move into the uterus, attach onto the endometrium, and then began its development there.

But sometimes pregnancy can occur somewhere else in the oviduct. So rather than the egg moving into the uterus and developing there, the pregnancy can actually occur in the oviduct or in this Fallopian tube. And we call that ectopic or tubal pregnancy. So when the embryo actually starts to develop here in the Fallopian tube or the oviduct, we call that ectopic or a tubal pregnancy. So generally, those type of pregnancies, the embryo will not survive. They can only survive if they are developing here in the uterus. So this lesson has been an overview on implantation.

  • Implantation

    A term used to describe when the blastocyst attaches to the endometrium of the uterus.

  • Endometrium

    The inner layer of tissue within the uterus; the deepest tissue layer of the uterus where the blastocyst implants itself.

  • Ectopic Pregnancy

    Also called tubal pregnancy, an ectopic pregnancy occurs when implantation occurs in the oviduct instead of the uterus. Ectopic pregnancies result in abdominal pain that will eventually cause the oviduct to rupture if the pregnancy isn’t terminated.

  • Human Chorionic Gonadotropin (HCG)

    A hormone secreted from the developing placenta(blastocyst) that prevents the destruction of the corpus luteum; the corpus luteum secretes estrogen and progesterone which prepares the female’s body for pregnancy.