Development of Birth
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2. The three stages of development are: 1st trimester, 2nd trimester and 3rd trimester. In the 1st trimester, its deals with the fertilization and the development of the embryo. This trimester is dealing with the first 12 weeks after conception. Fertilization, the joining of the sperm and the egg in the fallopian tube to form a unique human being, occurs. Forty-six chromosomes provide the blueprint for the embryos physical characteristics. At this point, the blastocyst, or developing embryo, is looking for a spot to implant in the uterus. Early formation of the central nervous system, backbone, and spinal column has begun. The gastrointestinal system has also begun to develop with the kidneys, liver, and intestines forming. The heart has begun to form. Hormones produced by the embryo stop the mothers menstrual cycle. The embryos tiny heart begins to beat by day twenty-one. The brain has developed into 5 areas and some cranial nerves are visible. Arm and leg buds are visible and the formation of the eyes, lips, and nose has begun. The spinal cord grows faster than the rest of the body giving a tail like appearance which disappears as the embryo continues to grow. The placenta begins to provide nourishment for the embryo. Major organs have all begun to form. The embryo has developed its own blood type, unique from the mothers. Hair follicles and nipples form and knees and elbows are visible. Facial features are also observable. The eyes have a retina and lens. The major muscle system is developed and the embryo is able to move. The embryo is reactive to its environment inside the amniotic sac where it swims and moves. Hands and feet can be seen. At the end of week 8, the embryonic period is over and the fetal stage begins. The heart is almost completely developed and the heart rate can be heard on a Doppler machine at the doctors office. Most major organs and tissues have developed and red blood cells are now produced in the liver. The face is well formed and the eyes are almost fully developed. The eyelids will close and not reopen until the 28th week. Arms, hands, fingers, legs, feet, and toes are fully formed. Nails and earlobes start to form and tooth buds develop in the gums. Fetus can make a fist with its finger. Testosterone (male sex hormone) is produced by the testes in male fetus.
In the 2nd trimester the fetus starts the development of movement, hearing and pain. The brain is fully developed and the fetus can suck, swallow, and make irregular breathing sounds. Fetus can feel pain. Fetal skin is almost transparent. Muscles tissue is lengthening and bones are becoming harder. Liver and organs produce appropriate fluids. Eyebrows and eyelashes appear and the fetus makes active movements including kicks and even somersaults. “Quickening” (when the mother can feel the fetus moving) usually occurs around this time. Finger and toenails appear. Lanugo, a fine hair now covers the entire body. The fetus can hear and recognize the mothers voice. Sex organs are visible on ultrasound devices.
In the 3rd trimester is the total development of the nervous system. A protective waxy substance called Vernix covers the skin. By birth, most of the vernix will be gone but any that is left is quickly absorbed. Fetus has a hand and startle reflex. Footprints and fingerprints are forming. Fetus practices breathing by inhaling amniotic fluid into its developing lungs. Rapid brain development occurs during this period and the nervous system is able to control some bodily functions. The fetus eyelids now open and close. At 25 weeks there is a 60% chance of survival if born. The fetus is considered legally viable at 28 weeks and there is a 90% chance of survival if born at this point. There is a rapid increase in the amount of body fat the fetus has. Rhythmic breathing occurs, but the lungs are not yet mature. The fetus sleeps 90-95% of the day. At this point there the survival rate is above 95% if the baby is born. The fetus is considered full-term. Lanugo is gone except on upper arms and shoulders. Hair on the babys head is now coarser and thicker. The lungs are mature. The average weight of the baby at this point is seven and a half pounds. At birth the placenta detaches from the uterus and the umbilical cord will be cut as the baby takes his first breaths of air. Breathing will trigger changes in the heart and bypass arteries forcing all blood to now travel through the lungs.
. The hazards to Prenatal Development are present during the entire pregnancy. The fetus is not immune from the outside world. In fact, some things can be damaging to the unborn child. These are called teratogens, and often result in birth defects. They include such things as maternal disease, poor nutrition, stress, pollutants, and cigarette smoking. In many respects, the first three months of pregnancy are the most crucial of all the nine months. Nine times out of ten when an infant is born addicted to any substance it is because the mother is not aware that she is pregnant until after most of the damage has been done. Some of the major birth defects