Cells begin to specialize to form body systems, starting with the nervous system. ![]() TIM: Things happen really fast in the 1st trimester! After about 2 weeks, the blast o c y st becomes an embryo. The 1st 3 months are labeled ‘1st semester,’ the next 3 ‘and semester’ and the last 3 ‘3rd semester.’ The fetus starts from a small dot in the 1st box and ends with the silhouette of a curled-up baby in the last box. Pregnancy is usually divided up into 3 trimesters, each about 3 months long.Ī timeline shows 9 months, each represented by a box containing the silhouette of a growing fetus. TIM: Yep, the pregnancy has begun! Over about 9 months, that clump of cells will grow into a baby. Onscreen, a blast o c y st moves through the fall op i an tube and into the uterus, attaching to its wall. It attaches to the lining about a week after fertilization. TIM: The blast o c y st travels through the fall op i an tubes and into the uterus. Once the sperm cell and the nucleus of the egg cell become one, the egg cell divides into two cells, then four, then eight, then many. It splits about once every 20 hours until it’s a hollow ball called a blast o c y st.Ī sperm cell is shown entering the outer portion of the egg cell and moving towards the center. The zygote divides into two cells, then four cells, then eight, and so on. TIM: The egg cell and sperm cell join together to make a whole new cell called a zygote, a fertilized egg cell. Onscreen, many sperm cells surround an egg cell, and one merges into it. Out of the hundreds of millions of sperm cells released, it only takes one to fertilize the egg. TIM: During sexual intercourse, sperm cells are released from the penis, a male reproductive organ. The ovary releases an egg into the fall op i an tube, and it is fertilized by a sperm cell. A cross section of one ovary is magnified to show the egg cells. While the egg is moving through the tubes, it can be fertilized by a sperm cell.Ī woman’s silhouette shows ovaries and a uterus in the lower part of her torso. At puberty, ovaries begin to release one egg into the fall op i an tubes each month. They’re contained in the ovaries, the two small organs on either side of the uterus. ![]() TIM: Others are born with a female reproductive system, complete with about 100,000 egg cells, or ova. Onscreen, animation shows the silhouette of male reproductive organs, then a sperm cell. TIM: Some babies are born with a male reproductive system, which can produce sperm cells. One of the sperm cells penetrates the egg cell. Onscreen, several sperm cells move towards a female egg cell. The human development process starts when an egg cell is fertilized by a sperm cell. TIM: Dear Tim and Moby, How does a baby grow? From Eric. Tim, with the egg broken over his head and running down his face shows him holding a letter. Moby drops the egg and throws it back to Tim. ![]() Text reads: The Mysteries of Life with Tim and Moby.Ī boy, Tim and a robot, Moby, throws the egg back and forth to each other.
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