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Biology Chapter 43-2 Human Development VOCAB Cleavages- mitotic cell divisions of the zygote Morula- four days after fertilization the embryo is a solid ball of about 50 cells Blastocyst – a fluid filled cavity forms in the center of the embryo transforming it into a hollow structure Implantation- when the blastocyst attaches itself to the wall of the uterus and beings to grow inward Gastrulation- a cluster of cells that sorts into two layers, which then produce a third layer by process of cell migration Ectoderm- one of the three cell layers formed by gastrulation Develops into: epidermis of skin: hair and nails, nervous system, tooth enamel, lining of mouth and nose Mesoderm -one of the three cell layers formed by gastrulation Develops into: skeleton, muscles, excretory system, circulatory system, gonards Endoderm -one of the three cell layers formed by gastrulation Develops into: digestive tract, respiratory system, liver, and pancreas Amnion- one of the membranes that surround, protects, and nourishes the developing embryo Chorion- one of the membranes that surround, protects, and nourishes the developing embryo Placenta- the connection between mother and the developing embryo. It provide nutrients and oxygen and eliminates carbon dioxide and metabolic wastes. Fetus- the embryo after 8 weeks of development Umbilical Cord- contains two arteries and one vein that contains the fetus to the placenta Amniotic Sac- fluid filled sac that cushions and protects the developing fetus Labor- a series of rhythmic contractions that expand the cervix so that it will be large enough to allow the baby to pass through it Early Development The first few mitotic cells divisions of the zygote take place while the zygote is still in the fallopian tube. Four days after fertilization the embryo is a solid ball of about 50 cells called morula. As the embryo grows, a fluid-filled cavity form in the center called the blastocyst. After 6 to 7 days of fertilization the blastocyst attaches itself to the wall of the uterus and begins to grow inward in a process called implantation A cluster of cells gradually forms in the cavity of the blastocyst. The cluster forms into two lays which then produce a third, by gastrulation: Ectoderm- one of the three cell layers formed by gastrulation Develops into: epidermis of skin: hair and nails, nervous system, tooth enamel, lining of mouth and nose Mesoderm -one of the three cell layers formed by gastrulation Develops into: skeleton, muscles, excretory system, circulatory system, gonards Endoderm -one of the three cell layers formed by gastrulation Develops into: digestive tract, respiratory system, liver, and pancreas These are known as the primary germ layers. During implantation the outer layer of cells of the blastocyst produces the amnion and chorion membrane. At the end of the third week, the nervous system had begun to form and so has the tube that will start the digestive system. The chorion had grown into the uterine layer to form the placenta. The placenta is the embryo’s organ of respiration, nourishment, and excretion. After 8 weeks the embryo is know as a fetus. By the end of 3 weeks development, most major organs and tissues are fully formed and the umbilical cord is formed The muscular system is developed and fetus may show signs of reflexes The fetus is about 9cm and 15grams. The amnion has developed into the fluid-filled amniotic sac. Later Development During the 4th, 5th, and 6th months, the tissues of fetus continue to become more complex and specialized. A skeleton begins to form and a fetal heartbeat become strong enough to be heard with stethoscope. A layer of soft hair grows over the fetus’s skin. The developing fetus will be about 35 cm in length and have a mass of about 700gramds by the end of the 6th month. The last 3 month the fetus doubles in mass and the lungs and other organs undergo changes that help them for life outside the mother. Childbirth About 9 months after fertilization, at the end of full pregnancy, the fetus is ready for birth. When the time comes oxytocin is released from the Pituary gland. When the muscles around the uterus are stimulated, they begin rhythmic contractions that expand the opening of the cervix so that it will be large enough for the baby to pass though. As the contractions continue, they get more powerful and more frequent, occurring every minute or two. In a process that last 2 to 16 hours, the baby is force toward the vagina as labor continues. The amniotic sac breaks releasing the fluid. As the baby meets the outside world, it may cough or cry to rid its lungs of the fluid. The umbilical cord is clamped and cut, leaving a small piece attached to the baby that will dry and fall off leaving the navel. In a final series of uterine contractions, the placenta itself and the empty amniotic sac are expelled from the uterus as the after birth. After Childbirth Within a few hours, the Pituary hormone prolactin stimulates the production of milk in the breast tissues of the mother. If the mother breastfeeds the baby regularly, the milk is always ready then needed and seldom runs dry, yet stops when the mother ends breastfeeding. Upon stimulation, the nerve cells in the breast transmit nerve impulses to the hypothalamus. This cause the Pituary gland to release nearly 10 times the amount of prolactin. The increased levels of prolactin enable milk production to keep up with demand.