The first trimester of pregnancy is a miraculous time, as a single cell develops into an embryo and...
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The first trimester of pregnancy is a miraculous time, as a single cell develops into an embryo and then a fetus. After conception occurs, a single cell divides to form a cluster of cells that travels to the uterus and implants itself in the lining. This marks the beginning of what is called the embryonic stage, which lasts through the eighth week after conception, or tenth week of pregnancy. The astonishing process of human development continues as the rapidly dividing cells within the sphere organize into a disc, which folds into three layers. Simultaneously, each layer will develop into many tissues, organs, and structures, while the surrounding environment will also change to nourish, protect, and support this development. A groove forms down the center of the disk, which now has a top and bottom, front and back, and left and right side. This neural groove deepens and then forms a tube, which develops into the brain and spinal cord. An early circulatory system develops from tubes on the left and right side of the groove. The tubes merge, kink, and fuse together to form the chambers of the heart, which will begin to beat and pump blood. The central nervous system is also developing. The neural groove closes like a zipper, forming a tube that becomes the spinal cord and brain. The closing is faster toward the head end, as the different parts of the brain develop. The ends of the groove then close. Other organs such as the liver begin to develop. Arm and leg buds appear. To support this growth, nutrients come from the mother through the placenta via the umbilical cord. The arms and legs continue to grow, with paddle-like shapes where the hands and feet will be. The hands and feet continue to develop, and soon the arm can bend at the elbows. Fingers and toes appear. Facial features start to appear as the brain grows to support the senses, such as vision and hearing. The intestines also develop, first projecting into the umbilical cord outside the body and then inside the abdomen. Muscles and bones begin to develop. The position of the limbs moves from the center to the side, and the knees take shape in the legs. As development continues, facial features become more refined. All the organs are developing. Some, such as the liver and thyroid, are already functioning. By the end of the first trimester, the developing baby is a miniature person.

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