What is necessary for pregnancy formation?
For pregnancy to occur, the following are necessary:
*Normal production of sperm with the correct characteristics in men
*Open and sufficient function of the sperm ducts
*Production of egg cells in women
*Open fallopian tubes in women
*Sexual intercourse on ovulation days
*The meeting of sperm and egg and fertilization
*Suitable uterine function for the implantation of the fertilized egg
*The fertilized egg settling in the uterus and taking the form of an embryo and fetus (fetus)
*Birth of the fully developed baby
Sperm Production
The male reproductive cell, sperm, is produced in the testes. Unlike in females, production starts at puberty in males and continues until the end of life. The main sperm cells (spermatogonia) that will produce sperm are present in the male testes at birth. Until adolescence, these cells remain dormant. With the increase in hormones (FSH, LH) secreted by the brain at puberty, division of the main sperm cells inside the testes begins. The newly formed cells go through various division, development, and differentiation stages to become sperm.
Approximately 50,000 to 200,000 sperm are produced per minute in the testes. The sperms formed in the channels of the testes enter a canal system called the epididymis. Here, the sperms continue to mature, and when they reach the tail of the epididymis, they gain the ability to move independently. The complete development of a sperm cell from start to maturity takes about 70 days.
A sperm is about 5-7 microns long, 3-4 microns wide, with a pear-shaped head, a neck about 2-3 microns long, and a tail about 40-45 microns long.
Ejaculation of Sperm
When sexual arousal occurs, sperm cells accumulate in the secretions of the seminal vesicles and prostate, as well as in the posterior urethra and ejaculatory ducts. For accumulation, the upper part of the urethral canal in the prostate and the lower part of the prostate are kept closed by the sphincter mechanism, preventing the accumulated fluids from escaping into the bladder and urethra. The accumulated fluid is called semen.
When sexual arousal reaches its peak, the ejaculation reflex begins. While the inner sphincter of the urethra remains closed, the outer sphincter opens. At the same time, the muscles in the urethra and ejaculatory ducts contract rapidly and rhythmically. With these contractions, semen is expelled through the urinary opening in spurts.
Production of Egg Cells
The tissues on both sides of the lower back of the fetus in the mother's womb begin to differentiate into either testes or ovaries based on the chromosomal structure of the fetus. The main egg cells (oogonia) become apparent in the ovaries around the 6th week of pregnancy. These main egg cells multiply by division until the 20th week. After that, these cells, which have 46 chromosomes, enter a division stage that reduces the number of chromosomes by half. This division, which occurs between the 7th and 9th months of pregnancy, is not completed. The cells that remain in the division stage are called oocytes. Surrounded by a layer of cells, the oocytes start waiting silently in the ovary. Their number is determined and remains unchanged. Unlike in men, the female ovary has a specific number of reproductive cells.
From birth to adolescence, the oocytes wait unchanged in the ovary, and after adolescence, they develop into mature egg cells. However, while 99% of them are lost for various reasons, only about 1% of them develop into egg cells.
Ovulation
Around the 14th day of a woman's menstrual cycle, the amount of the hormone LH secreted by the pituitary gland (the region of the brain that secretes hormones) suddenly increases. Subsequently, the membrane of the mature follicle ruptures, releasing the egg cell. This event is called ovulation.
During the development of the egg cell in the ovary, hormones called estrogen and progesterone are produced. In the first period of the cycle before ovulation, estrogen, and in the second period after ovulation, progesterone, make the tissues inside the uterus suitable for the implantation of the fertilized egg. Otherwise, if the fertilized egg does not implant in the uterus, a miscarriage will occur.
Fertilization
Fertilization is the union of the male reproductive cell, sperm, with the female reproductive cell, egg, resulting in the sperm entering the egg. This event takes place inside one of the woman's fallopian tubes.
During sexual intercourse, after ejaculation, the sperm in the semen rapidly enter the uterus through the cervix, the neck of the womb. From there, the sperms move upwards inside the uterus and then enter the fallopian tubes.
After the egg cell is released from the woman's ovary, it falls into the lower part of the abdominal cavity. The place where it falls is close to the free end of the fallopian tube, which has extensions like the fingers of a glove. The egg cell is taken into the tube by the extensions. As the egg cell is slowly conveyed towards the uterus inside the tube, if there is a sperm cell that has reached the tube, the meeting required for fertilization takes place.
After the sperm and egg cell meet, the sperm enters the egg by breaking through its membranes using enzymes in the head. Once a sperm enters the egg, it changes the properties of the egg's membrane, preventing other sperm from entering.
Pregnancy
After fertilization, the fertilized egg (zygote) remains silent for about 30 hours without any visible change. At this time, the chromosomes from the male and female have combined to form the chromosomes of the new organism. After fertilization inside the fallopian tubes, the zygote moves towards the uterus. It takes 3-5 days to reach the uterus. During this time, the zygote divides and multiplies. The number of cells increases to 2, 4, 8, 16, and so on. At the implantation stage, the zygote is composed of cells arranged in a single layer surrounding a cavity. The cells in one part of this cell group develop more in number and in layers. This region is the attachment area to the uterus. At this stage, the new organism is called an embryo.
Implantation begins between the 5th and 8th days after fertilization and is completed by the 9th or 10th day. Therefore, the process of fertilization and implantation is completed about 4-5 days before a woman's period. When the woman realizes she is not having her period, the embryo is about 15-20 days old.
After implantation in the uterus, the embryo continues to develop rapidly. The period from fertilization to the end of the second month is called the embryonic period. The new organism, now called a fetus, continues its development until birth.
Most abnormalities in the developing fetus occur in the first 12 weeks. Therefore, the mother should avoid drugs, vaccines, harmful chemicals, viruses, and certain infections, as well as radiation and similar harmful factors.
The fetus in the mother's womb is attached to the placenta (the baby's companion) through the umbilical cord. The placenta is also attached to the uterus. The placenta allows the exchange of nutrients and various substances between the mother's blood and the baby's blood without mixing them. This way, the fetus receives nutrients from the mother and gives back waste products. The placenta is permeable to certain hormones, chemical substances, microorganisms, and small molecules. Therefore, some harmful factors affecting the mother also affect the child. For example, a mother's smoking and alcohol consumption directly affect the child. Similarly, the hormones released in the mother's stress affect the fetus through the placenta.
