Fertilization general description
Fertilization – is a process of union of human egg and sperm, haploid reproductive cells or gametes which lead to a formation of a diploid cell zygote. The most common procedure begins with ejaculation during copulation, follows with ovulation, and finishes with fertilization. It is the process that exists in a life cycle of all organisms which have meiosis. Meiosis is a type of cell separation which reduces the number of chromosomes by half.
Fertilization is the first stage of creating a new life. As it was mentioned it begins from meetings and connection of two sex cells: male and female – sperm and egg. In place of their connection is forming zygote – the cell, which combines the full set of 46 chromosomes with genetic information obtained from the parental cells. At this stage of fertilization the sex of a person is already determined. It’s selected randomly as a lottery. It is known that ovum and sperm contain 23 chromosomes, one of which –sex one. And an ovum may contain only X- sex chromosome and sperm – both X and Y- sex chromosomes. When an ovum fuses with a sperm with X-sex chromosome, a child will be female, if with a Y-chromosome – male. The sexually reproduced cell which fuses with another cell during fertilization is called gamete.
There are few forms of fertilization:
- isogamy – gametes don’t differ from each other on size, active and amoeboid;
- anisogamy – gametes differ in size, but both types of gametes (microgamete and macrogamete) are mobile and have flagella;
- oogamy – one of the gametes (ovum) is much larger than other, motionless and meiotic division which leads to its formation is sharply asymmetrical (instead of four cells there are formed one ovum and two abortive «polar bodies»); another gamete (sperm) is mobile, have flagella or amoeboid.
The process of fertilization
In the middle of woman’s menstrual period ovulation occurs when from the follicle, located in the ovary, leaves the mature egg, capable for fertilization and goes to abdominal cavity. Then it’s immediately picked-up by the cilia of the fallopian tubes which shrink and push the egg inside. From this moment woman’s body is ready for fertilization and viable egg will wait for the sperm in the fallopian tubes for around twenty-four hours. For realizing this meeting, the sperm will do a long and challengeable way. Nearly half of a billion of it come inside during the sexual act, wagging the tails and moving up. Before meeting the sperms will need to overcome the distance in 20 cm which takes several hours. During the way a lot of its will die because of faced obstacles.
For the making the fertilization successful the 10 millions of sperms must penetrate to uterus. Only few thousands will reach the finish and one of them gets inside. As soon as sperm is inside of egg, they fuse and this is actually the process of fertilization. Now it is not sperm and egg separately, and single cell – a zygote. Soon it will start its first division, forming two cells. Then there will be their further division into four, eight cells, etc. After that dividing, cells become an embryo, which will be pushed by fallopian tubes in the direction of uterus. It needs to leave this place as soon as possible, because if it will be some delay, it might be the implantation in the oviduct and as a result – ectopic pregnancy.
In around five or six days, the embryo will reach the goal and it gets into the uterus, where a couple of days will be in the free swimming, looking for a place where to attach. Implantation period happens on seventh-tenth day after conception. When the embryo finds a comfortable place, it will cling to the endometrium. When it’s plunging deep it touches blood vessels located in the wall of the uterus, therefore it might be small hemorrhages in the place of implantation. At this time, a woman may notice spotting, called implantation bleeding and it is an early symptom of pregnancy.
Implanted embryo starts to excrete pregnancy hormone to woman’s blood and so the pregnancy tests can react on it. In ten days after ovulation, you can try the first test. In case of confirmation of a successful pregnancy, the embryo will continue to grow, and after 9 months the world will have a new human.
Artificial insemination – is an introduction of sperm into female’s uterus by artificial method in which the male’s sperm is prepared in advance. This kind of insemination helps couples to conceive a baby in case of male or female infertility. A particular method of artificial insemination is prescribed depending on the cause of infertility. Pregnancy occurred as a result of any of this methods are completely natural and do not require further special observation.
There are three basic ways of artificial insemination:
- AI (artificial insemination)
- IVF (in vitro fertilization)
- ICSI (intracytoplasmic sperm injection)
The easiest and most affordable is artificial insemination. In this procedure, male’s seminal fluid is injected through a catheter directly into the woman's uterus; sperm continues to move by its own into the fallopian tube to meet the egg, where fertilization takes place naturally.
Before this, the sperm goes throught special preparation: the weak sperm is culled and the most active and mobile, capable for fertilization are left.
Artificial insemination is mostly prescribed in case of absence of evaluation, vaginismus, cervical factor infertility, partner's sexual dysfunction and inability to conduct a full sexual intercourse, bad semen analysis, infertility. The effectiveness of this method is around 20-25%.
IVF – in vitro fertilization procedure is combining eggs and sperm outside the body in a laboratory. It is prescribed when all methods of infertility treatment are tried already, and there are no results. Also IVF may be an option if one partner is diagnosed with endometriosis, problems with ovulation, low sperm counts, antibody problems that harm sperm or eggs, problems with the uterus or fallopian tubes, an unexplained fertility problem. IVF consists with several stages. First of all, woman has to go through ovarian hyperstimulation when in an organism is injected certain hormones for getting ready the eggs to the fertilization. Then the eggs are taken out under general anesthesia. After this, the most active and full sperms are mixed with eggs. A day after it can be seen, whether fertilization has occurred. If it is done, then the most viable zygotes are selected for growing embryos. The probability of pregnancy by IVF is 20-30%.
ICSI – is a sperm injection, prescribed in case of male’s infertility when the sperm by any reasons cannot penetrate into the egg. Most often this occurs because of the small number of mobile sperm, lack of sperm in the semen, and other pathologies of sperm. In this procedure, the sperm, using the thinnest needle, is injected into the egg. The selection of sperm takes place under a very powerful microscope.
Diseases and disorders that affect on fertilization
Males and females reproductive system can be affected by various diseases that cause some problem during fertilization or even make it impossible.
The woman’s reproductive organs can be affected by cancer. It can attack the uterus, ovaries, breast and cervix and other organs. Another common disorder of the female reproductive system is a vaginal yeast infection, which is caused by a yeast fungus in the vagina.
The most common male’s disease of the reproductive system is prostate cancer. Also, men can experience testicular and penile cancer. Erectile dysfunction is very common trouble that affects about one in 10 males in the world.
Preparation to the fertilization
There are some factors you should pay attention in before you decide to have a baby: the age of future parents, blood group and Rh factor, presence/absence of hereditary and acquired diseases, lifestyle and the presence/absence of bad habits, nutrition, methods of contraception used before the fertilization.
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