Stages

=The Stages of Embryology=

Human development from conception to birth is divided into three trimesters.

First Trimester


The first trimester is the time of most radical change for both mother and embryo. Before the development of a human begins, a cell undergoes a series of cell divisions that results in the formation of a new human being. When the cell is still a single cell, it is called a zygote, after this is goes through the two cell stage, four cell stage, the morula, and the blastocyst. Once the zygote has formed into a blastocyst, it then connects to the uterine lining and the baby formation begins. Within the first trimester, the baby begins to form many of its body parts and organs. In this time period the baby's brain and spinal cord have begun to take shape. The embryo has also started to form four stumpy limb buds, a short tail, and elements of a gill pouch. After 9 weeks of fertilization, the embryo is now called a fetus. At this time, the fetus now has a planceta, hands with finger, feet with toes, and the formation of many organs. At this time, the baby may also begin to move its arms and legs, turn its head, and smile. Also, the sex of the baby can be detected at this time.

Second Trimester


In the second trimester, the main developmental changes are an increase in size and refinement of the human body parts and features. During this time the fetus's has formed eyebrows and eyelashes. All of the fetus's limbs have grown in size and its fingernails and toenails are covered in small hair. During this trimester the fetus has become more active and the mothers abdomen has increased in size. At the end of this trimester, the fetus's eyes have begun to open, and teeth are forming.

Third Trimester


The third trimester is time meant for growth and gaining strength it will need after birth. The fetus's circulatory and respiratory systems are changing that will switch to air breathing. The fetus can now maintain its own temperature and its bones and muscles harden, and thicken. The fetus then loses all of its fine hair, becomes less active, and fills space in the uterus. From this point the baby is ready to be born.

Click [|here] to see many videos of the embryo taking shape into a new born.

Click [|here] to see an animation of the skeletal formation of a fetus.