Sexual activity can cause the brain to release the hormone oxytocin 1,6 , which causes the innermost layer of the uterus to contract and push the sperm onwards 1,5,6. The uterus also has little finger like structures called cilia that help move the sperm, hopefully, towards the egg 1.
Sperm triggers an immune response when it enters the uterus 5. Also, sperm may end up going up the wrong fallopian tube. The vast majority of the time, a person only releases one egg from one ovary. That means that only one of the two fallopian tubes will have eggs, and some sperm will have gotten it wrong. Only a tiny fraction of the sperm that entered the vagina make it to the fallopian tube 5.
As the fallopian tube pushes the egg towards the uterus, cilia push the sperm towards the egg. Progesterone and estrogen influence this process by increasing the number of cilia and how fast they move 1. The egg and surrounding cells produce a chemical that attracts sperm 1,7. Sperm may be attracted to the temperature at the ovarian-end of the fallopian tube, which tends to be warmer 1,5. As they travel through the fallopian tubes, sperm gain the ability to fertilize an egg 1.
Break through a group of cells known as the cumulus oophorus that surround the egg. The sperm dissolves these cells using an enzyme 1,7. Break through the outer membrane of the egg. The sperm essentially fuses to and digests this membrane using an enzyme 1,7. Once a sperm has penetrated an egg, this membrane changes, and becomes impenetrable to other sperm 1,7.
Once it meets the egg, the nuclei from the egg and sperm merge and share their genetic material 1,7. If all this goes well, what fertilized egg becomes a zygote 1,7. The egg now contains all the genetic material it will need to become a person. It takes about days for the fertilized egg to travel to the uterus and attach to the uterus in a process known as implantation 1,8.
The egg is pushed back towards the uterus by the cilia 1. The egg must attach to the uterus to become a viable pregnancy. While traveling to the uterus, the egg has been dividing and forming a few different structures 7. Once that barrier is broken down, the blastocyst can attach to the endometrium 1. Sometimes, though, a fertilized eggs can't make it to implantation.
These losses generally aren't considered miscarriages, as most healthcare professionals consider a pregnancy to have begun at implantation. The magic of conception can happen any time in the week after sexual intercourse has taken place.
Research has shown that visible zinc sparks are released along with calcium levels at the time of fertilization. As she grows and ages, the eggs start to die and a mature egg is set free from the ovaries approximately every 28 days. This egg travels to the fallopian tubes and rests there for 24 hours. Unless the egg is fertilized by a sperm, this mature egg will end up in the uterus and break down.
Without conception, the ovary will stop synthesizing the hormones progesterone and estrogen along with the thick uterine lining. It takes about months for the body to create a sperm cell and the typical lifespan of sperm is a few weeks. Adhesive sites on the cilia, which are located on the surface of the fimbriae, are responsible for egg pickup and movement into the tube.
The cilia within the tube, and muscular contractions resulting from the movement of the egg, create a forward motion. Transport through the tube takes about 30 hours. Conditions such as pelvic infections and endometriosis can permanently impair the function of the fallopian tubes, due to scarring or damage to the fimbriae. Following ovulation, the egg is capable of fertilization for only 12 to 24 hours. Contact between the egg and sperm is random. Once the egg arrives at a specific portion of the tube, called the ampullar-isthmic junction, it rests for another 30 hours.
Fertilization — sperm union with the egg — occurs in this portion of the tube. The fertilized egg then begins a rapid descent to the uterus. The period of rest in the tube appears to be necessary for full development of the fertilized egg and for the uterus to prepare to receive the egg.
Defects in the fallopian tube may impair transport and increase the risk of a tubal pregnancy, also called ectopic pregnancy. A membrane surrounding the egg, called the zona pellucida, has two major functions in fertilization. First, the zona pellucida contains sperm receptors that are specific for human sperm.
Second, once penetrated by the sperm, the membrane becomes impermeable to penetration by other sperm. Following penetration, a series of events set the stage for the first cell division. The single-cell embryo is called a zygote. Over the course of the next seven days, the human embryo undergoes multiple cell divisions in a process called mitosis. At the end of this transition period, the embryo becomes a mass of very organized cells, called a blastocyst.
It's now believed that as women get older, this process of early embryo development is increasingly impaired due to diminishing egg quality.
Once the embryo reaches the blastocyst stage, approximately five to six days after fertilization, it hatches out of its zona pellucida and begins the process of implantation in the uterus. In nature, 50 percent of all fertilized eggs are lost before a woman's missed menses. In the in vitro fertilization IVF process as well, an embryo may begin to develop but not make it to the blastocyst stage — the first stage at which those cells destined to become the fetus separate from those that will become the placenta.
The blastocyst may implant but not grow, or the blastocyst may grow but stop developing before the two week time at which a pregnancy can be detected. The receptivity of the uterus and the health of the embryo are important for the implantation process. UCSF Health medical specialists have reviewed this information. It is for educational purposes only and is not intended to replace the advice of your doctor or other health care provider.
We encourage you to discuss any questions or concerns you may have with your provider.
0コメント