You will prepare and submit a term paper on Human Reproduction and Development. Your paper should be a minimum of 1250 words in length. After fertilization, the zygote/ new embryo travels down the oviduct to the uterus in a process that takes about 24 hours in which the embryo simultaneously matures and sticks itself to the uterine wall. Implantation takes place when the embryo attaches itself to the wall of the uterus about 7 to 9 days after fertilization The development phases of pregnancy are called trimesters (three-month periods) because of the distinct transformations that take place during each phase The diagram displayed below shows a blastocyst that has burrowed itself into the uterine membrane between the 7th and the 9th days.
Implantation occurs during the second week of pregnancy and during this period, structures that feed and protect the developing fetus start to form. These include the amnion, yolk sac, chorion, placenta, and umbilical cord. After four weeks, the spinal cord and the primitive brain start to appear in the embryo. Heart, ribs, backbone, muscles, and the digestive tract begin to form. The embryo is about 6mm tall (1/4 inch). Many external features like the face, arms, and legs of the body begin to develop within 5 to 8 weeks of pregnancy when the embryo is 25cm tall (1 inch) and weighs 4 grams (1/7 ounce). The embryo begins to develop a sense of touch, and it can now move. The fast increase in body size begins between the 9th and 12th weeks of pregnancy. Organs, muscles, and nervous system become structured and connected. New behavioral abilities such as kicking, mouth opening, thumb sucking, and rehearsal of breathing begin to appear. External genitalia becomes well developed, and the sex of the fetus can be identified. The fetus now weighs about 28 grams (less than an ounce) and is about 7.6 cm tall (3 inches).
Between the 13th and the 24th weeks (second trimester), the developing organism continues to grow fast, and the baby’s movements can be felt by the mother. Most of the brain’s neurons have been formed by week 24.