Conception step by step
Conception occurs when two cells fuse together to begin a new life. To understand how it starts, we need to begin with ovulation. Each month, in one of woman’s ovaries, a group of immature eggs start to develop in small fluid-filled cysts called follicles. One of the follicles is selected to complete development which is called maturation. This “dominant follicle” suppresses the growth of all of the other follicles, which cease growing. The mature follicle ruptures and releases the egg from the ovary. This is a process called ovulation, and it happens about two weeks before a woman gets her period.
Conception and the cervical mucus
The cervix is located at the top of the vagina. It begins to secrete a type of mucus when the ovulation period is getting close. For conception to be possible, the sperm needs to go through the cervical mucus, so it can meet the ovule. Here are five important roles the cervical mucos plays:
Roles of cervical mucus
The cervical mucus plays an important role in the conception process: During the menstrual cycle, the cervical mucus changes its viscosity. For several days around the time of ovulation, “fertile” types of mucus are produced.
The cervical mucus gives clues about a woman’s fertility: During a woman’s fertile days, cervical mucus has a higher water content, and is less acidic and higher in electrolytes.
The cervical mucus protects the sperm from the acidity of the vagina: The vaginal environment is biologically very hostile to sperm. After ejaculation, the sperm is transferred in the cervical mucus where it is protected from the acidity of the vagina. When the mucus has a low water content it acts as a barrier to the uterus. When it has a high water content, it acts as a transport medium for the spermatozoa to enter the uterus and fertilize an ovule.
The cervical mucus is an environment that mobilizes the sperm: When the ovulation occurs, a single mature egg is released into the uterus. This ovule can be fertilized about 12 hours after its release. If it does not happen, it will begin to disintegrate. During the ovulation, the cervical mucus gets thinner, becomes clearer and more abundant. For some women, the cervical mucus becomes thinner two days before ovulation so that after intercourse, the sperm are carried through the uterus, and are already near the uterus or fallopian tube when she ovulates.
The cervical mucus is a barrier to abnormal sperm: Abnormally shaped sperm swim more slowly in cervical mucus. This process of natural selection that occurs in the cervical mucus is an effective way to facilitate fecundation.
A mature egg is ready for conception, but this will only occur only if a spermatozoon penetrates it. This process is called fertilization or fecundation. The mother provides only X chromosomes (she’s XX). If a Y sperm fertilizes the egg, your baby will be a boy (XY); if an X sperm fertilizes the egg, your baby will be a girl (XX). After the fertilization of an ovule by the spermatozoon, the new entity is called a zygote.
Main fertilization stages
- The coupling reaction: The semen contact with the ovule is done by the nearest spermatozoon, which will penetrate the ovule. The coupling reaction is done by the ovule receptors but there is also a chemical attraction.
- The attachment of the spermatozoon: After about 3 hours from ejaculation, there are many spermatozoon near the ovule (an average human ejaculate contains about 180 million sperm) but only one will come to penetrate the ovule.
- The release of enzymes: For the spermatozoon to be able to penetrate the ovule, special enzymes are released in order to facilitate its entrance inside the ovule.
- The penetration phases: Once the attachment is completed and the penetration of the ovule’s membrane begins, the spermatozoon will move forward until it is incorporated into the ovule.
- The cortical reaction: After the spermatozoon is completely incorporated into the ovule, it will not allow another penetration.
- The actual conception: The cell membrane that surrounds the egg will fuse with the sperm and the two cells will become one. The chromosomal chain, consisting of 23 chromosomes, which are located in the egg, will unite with those of sperm. They will grow and move toward one another, until they meet in the center of the egg. The two membranes that surround them will unite and the two groups of 23 chromosomes will fuse in pairs. The two #1 chromosomes–one from the paternal set and one from the maternal set–wrap tightly about each other in a process called synapsis. A single perfectly defined cell will be formed. The cell contains all the genetic information necessary for future development of the baby.
- Cellular division: Now that conception is complete, the growth process begins. The cells start to multiply.
The implantation stage refers to the adhesion of the egg to the uterus. Before it reaches the uterus, the egg is continuously dividing. After 3 days, it becomes a morula (Latin, morus: mulberry) and has between 8 -16 cells, and it resembles a mulberry plant though not in size. Further it goes through the fallopian tubes and then it enters the uterus. Once there, the egg is not implanted immediately. After 6 to 7 days, it becomes a blastocyst.
Main implantation stages
- The penetration: At one week after conception, the blastocyst is ready for implantation in the endometrium which is the inner layer of the uterus’s lining and it will remain there to feed during the 9 months of pregnancy. The exact mechanism for implantation is still not completely scientifically understood. The blastocyst adheres to the uterine wall and it makes vascular connections which build the placenta.
- The implantation: After implantation, the blastocyst becomes an embryo, a more advanced stage of egg development. The process is complete when the amniotic sac and placenta are formed. The baby will develop inside the amniotic sac, floating in the amniotic fluid. The placenta is attached to the uterine wall and its functions are to feed and oxygenate the newly conceived fetus until birth.
Conception is the root of all human life. It is one of the most scientifically complex processes, and yet streamlined and simple – egg meets sperm. Within three weeks, the blastocyst cells begin to grow as clumps of cells within that little ball, and the baby’s first nerve cells have already formed. Your developing baby is called an embryo from the moment of conception to the eighth week of pregnancy. After the eighth week and until the moment of birth, your developing baby is called a fetus. Thus a new baby develops from humble beginnings – when two cells fuse to form new life.
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