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Organ system development
Development of the cardiovascular system
Development of the ear
Development of the eye
Development of the face and palate
Pharyngeal arches, pouches, and clefts
Development of the digestive system and body cavities
Development of the gastrointestinal system
Development of the teeth
Development of the tongue
Development of the integumentary system
Development of the axial skeleton
Development of the limbs
Development of the muscular system
Development of the nervous system
Development of the renal system
Development of the reproductive system
Development of the respiratory system
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In the adult, oxygenated blood is sent from the left atrium to the left ventricle and then out the aorta to arteries in the rest of the body. Blood then returns through veins to the right atrium and goes into the right ventricle, which pumps it to the lungs in order to drop off carbon dioxide and pick up oxygen.
In the fetus, the lungs are not mature enough to do that, so oxygenation happens in the placenta, and four key adaptations or structures make this possible.
These are the umbilical veins and arteries in the umbilical cord, the ductus venosus, the foramen ovale, and the ductus arteriosus.
So imagine you’re an oxygen rich red blood cell that has to get from the placenta to the fetal tissues. Blood from the placenta is highly oxygenated blood, so let’s color that red.
From the placenta, blood heads through the umbilical vein, the first adaptation of fetal circulation, that carries oxygenated blood toward the liver.
When the umbilical vein reaches the liver, it dumps blood into the portal vein. The blood in the portal vein goes out to every lobule of the liver, and becomes deoxygenated so we’ll color it blue, although in reality it’s more of a dark, dark red color.
This deoxygenated blood enters the hepatic vein, which then drains into the inferior vena cava, which is one of two enormous veins that carries deoxygenated blood from the lower half of the body to the right atrium.
Fetal circulation is different from adult circulation because the fetus' blood doesn't mix with the mother's blood. The placenta acts as a filter, so the baby receives nutrients and oxygen from the mother, and sends its metabolic wastes into the mother's circulation for elimination.
The fetal circulatory system has some special adaptations, such as the foramen ovale, an opening between fetal heart atria; the ductus arteriosus, a small vessels that shunts blood from the pulmonary artery to the aorta; the ductus venosus which shunts blood from the umbilical vein to the inferior vena cava; the umbilical arteries which carry deoxygenated blood from fetal circulation to the placenta; and the umbilical vein, which returns oxygenated blood from the placenta to the fetus , and the ductus venosus.
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