Embryonic Development in Humans
Other People Are Reading
-
Variation
-
Text books and professionals often vary in small degrees to the exact weeks differentiating each period of embryonic development in humans, but the process does not change. The journey from separate egg and sperm cells to a fetal human is universal, barring chemical or biological abnormality.
Beginnings
-
For the first eight to 10 days after conception, the fertilized egg cell is splitting and multiplying. The egg cell travels to the uterus to implant and receive nourishment. By the third week, the cells are officially called an embryo. Some professionals term this first 10 to 14 days the gestational period. During this time, the embryo will develop a beating heart, vertebrae and the beginnings of eyes, nose, mouth and brain, but it still does not look like a human. The title "embryo" will remain until eight to 10 weeks after conception.
-
Early Development
-
From around eight to 10 weeks until birth, the developing embryo is termed "fetus." This time period can be broken down further into trimesters. The first trimester lasts from conception until 12 to 14 weeks. The developing fetus begins to move frequently, though the mother will not feel it until around 24 to 26 weeks. Between six to eight weeks, all of the internal organs are present and begin to function.
Middle Development
-
During second trimester, the fetus continues growing, and other complex body systems begin to develop, such as the digestive and excretory systems. The fetus develops fingernails and teeth during the second trimester, as well as hair. The reproductive system of each fetus is developed and begins to be discernible; females have immature eggs within their ovaries, and male testicles are producing testosterone. Brain development during the second semester is rapid. By 22 to 25 weeks, the fetus's brain can sustain life outside of the womb by controlling breathing and heartbeat, but before the brain is developed enough, a fetus will not survive outside the womb. A fetus in the second trimester can sense light, even though its eyes remain closed until the third trimester.
Final Stages
-
In the third trimester, major systems of the fetus continue to develop, and the bones strengthen. Heart and lung tissue gets stronger and better equipped to survive outside of the womb. The fetal brain during this trimester becomes distinctly formed with typical wrinkles and convolutions, and the number of brain cells increase dramatically. The body weight of the fetus increases three to five pounds during this time for a delivery weight typically between seven and nine pounds. The fetus is covered in fine, downy hair called lanugo and a protective, waxy substance called vernix.
-
References
- Photo Credit Priests for Life
