Pregnancy and Birth: Stages in the Life Cycle
There are three general stages in the process of prenatal development in human beings. The first two weeks are collectively known as the germinal stage. The third week through the 8th week is the embryonic period. The rest of the time past the ninth week is generally known as the fetal period of development.
The fertilized egg is known as a zygote and moves toward the uterus. This journey can take up to a week. About 24 to 36 hours after conception cell division begins to take place. If the implantation is a success, then the hormonal changes in the woman will stop her menstrual cycle and will cause a myriad of changes in her. Some women are less palatable to some activities that they previously enjoyed such as smoking or drinking coffee and alcohol.
Cells are then known as an embryo. The beginning of the third week after conception is the beginning of this stage of development. The embryo will divide into three layers which eventually become the parts of the young and developing human body. About 22 days after conception, neural tube begins to form. This will become the central nervous system and will eventually form the spinal cord and the brain of the baby. During the 4th week the baby will begin to form the head and the eyes, nose, mouth, and ears. The last thing to develop is the cardiovascular system which will eventually form the blood vessel that leads to the heart. The fifth week is when the buds that form the legs and arms appear.
One the cell differentiates, the embryo enters the stage where it will start to be known as a fetus. This period will begin during the ninth week of development and will last until the baby is born. Early body systems and structures that are first being established in the second stage will continue to develop in this stage. The brain forms from the neural tube and so do the spinal cord and the neurons. Sex organs will begin to be created during the third month. The fetus continues this growth in both size and weight.
This stage lasts the longest and is characterized by a huge amount of change and growth in the baby. Sometime during the third month the sex organs will form and by the end of that month all of the general parts of the body exist. The weight of the fetus at this point is around three ounces. Also during this month is the end of the first trimester of the pregnancy. Following that is the second trimester when the heartbeat will get stronger and the body systems will develop. This is also when the baby will grow in size by a great deal. The third trimester is when the lungs begin to expand the muscles will start to prepare the baby for life outside of the womb.
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