Heredity

Every human life begins from a single cell, which is formed when a sperm fertilizes an egg. In normal fertilization occurs in the fallopian tube, which connects the ovary to the uterus. At this time, the uterus is the size and shape resembles a large pear; it consists of the muscles to be stretched as the size of the fetus.

Human cells contain deoxyribonucleic acid (DNA) - a substance that allows the cells to reproduce and pass on their characteristics from generation to generation .  When cells divide, DNA takes the form of chromosomes, which carry the genetic information is passed from parent to offspring .  Different species of animals number of chromosomes different: for example, mice of 40 and 38 in cats .  Human cells normally have 46 chromosomes .  However, in each sperm and egg of only 23, so that during fertilization, they complement each other .  These reproductive cells called gametes (from the Greek word meaning "husband" or "wife") .  When they "get married", a new cell - a human embryo having 46 chromosomes and a unique combination of genes .  At this point begins the development of the fetus and the future of man, as long as it is called an embryo, and its diameter is about 0 . 1 mm .  Features such as reduced and the structure of the hair, skin, eye shape and color, sex, height, constitution, determined at the time of fertilization of the information obtained from the DNA of mother and father .

Implantation

After fertilization, the cell divides into two, then each of these cells is also divided into two, forming four, four cells obtained from eight of eight - sixteen and so on. At this stage, the embryo is called a morula development - from the Latin word meaning berries Mulberry as he looks more like them.

For about four days, the embryo in the uterus down the fallopian tube. By the time he is in the womb, a cluster of cells becomes hollow and filled with fluid - now called a blastocyst. At this stage of development is already determined what organs and body parts will be certain groups of cells. At the same time the inner membrane of the uterus prepares for implantation of the embryo. Embryo "climbs" in this shell and gradually closes it. Typically, the process begins at the sixth day after fertilization and ends after seven days. When completed the implantation, the embryo gives the body a hormonal signal, and the mother does not begin menstruating.

At about 25 days of gestation have different body and the rudiments of small arms and, later, the legs. At such a young embryo still has a process similar to the tail - in fact, it's protective shell spine. Around the same time, the heart begins to beat the fetus. There are the beginnings of other internal organs and facial features.

Second month

During the second month of fetal body length is increased from 5 mm at the fourth week up to 40 mm at the end of the eighth week. The length of the body of the fetus is usually measured from the top to the end of the spine.

• On the sixth week after fertilization there fingers, and a few weeks later - toes. In the seventh week the baby already has a unique fingerprint.
• Also on the sixth week of the eyes begin to develop - there are lens and retina; eyelids gradually take the correct form.
• In the seventh week, already have external ears, but the inner ear is already quite well developed.
• At about 45 weeks, almost fully formed the skeleton of a child, though it is composed of cartilage, not from the bones. Then the fruit is starting to make the first movement, though it will take about 12 weeks before they are strong enough to be felt mother.
• On the fortieth day of fetal ECG detects impulses of his brain.

Signs of fetal maturity

A full-term fetus under unfavorable conditions of fetal development may have signs of immaturity, and vice versa, aborted fetus may be born mature, so the concept of term and maturity do not always coincide.

An important feature of fetal maturity are its length (at least 47 cm) and weight (at least 2, 5 kg). The signs of maturity are also included the position of the navel: it should be positioned midway between the sternum and pubis. What matters as the state of the skin (pink), the lack of "senile" wrinkling, the development of the subcutaneous tissue, the presence of vellus hair only on the shoulders and upper back, the condition of hair, nails, and other signs.

With a weight of 4 to 5 kg of fruit is a large, more than 5 kg - a giant. Weight gain may be due to the peculiarities of maternal nutrition, hereditary factors, the number of births, various diseases of the mother (such as diabetes mellitus Diabetes - threatening and incurable disease   fruit often large), etc. The newborn, which has a large weight should be carefully examined in order to avoid possible diseases.

The last days before the birth and the beginning of an independent life

In recent days and weeks before the birth the baby is in the normal head down. In some cases, it does not turn, and it can cause difficulty during childbirth, though modern medicine is - familiar and completely solvable problem.

The probability of survival of children born much earlier period, in recent decades, is constantly increasing. So, now it survives more than 70% of infants born between 22 and 27 weeks after conception Conception, ovarian cycle, fertilization and genetics of a child . However, it should be borne in mind that not all hospitals and even not all countries have the conditions necessary for the care of these children, so the probability of survival to a large extent depends on exactly where the child was born.

The uterus begins to decline, the cervix gradually opens. Amnion or amniotic sac ruptures, releasing the amniotic fluid. Uterine contractions become more frequent as the baby passes the birth canal, and feelings become more painful. Although it is impossible to tell exactly what the child feels during labor may be more likely to assume that his labors are also not very pleasant process.

Typically, labor lasted several hours, but in some cases they may last at least an hour, and more than a day. When a child is born, the umbilical cord is cut, and for him, in a sense, to begin their life - now he can live outside the mother's body, breathe the air, and falls under the protection of the existing legislation, as well as any other person. Furthermore, it is the moment of birth, he is not officially called a fetus, and child.