Lecture 13 objectives.doc

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Lecture 13 objectives 1. From memory , draw a diagram of the fetal circulatory system, how the blood flows through it, and the degree of oxygenation at various points in the system.. Page 277 2. Now describe the major features of the fetal circulatory system Respiratory and digestive systems? Describe the 3 major bypasses (shunts) and their functions Explain how the fetus acquires oxygen and nutrients, eliminates carbon dioxide and wastes such as urea. Don’t forget about IgG. The three major bypasses are the foramen ovale, ductus venosus, and ductus arteriosus. The foramen ovale allows blood to bypass the lungs. Deoxy blood from the lower part of the fetus’ body enter the inferior vena cava and mixes with well-oxy blood from the ductus venosus. Most blood that enter R atrium jets through foramen ovale into L atrium. From L atrium it passes into L ventricle and is pumped out through the ascending aorta, which supplies heart, head, neck and upper limbs. Ductus venosus allows blood to bypass the liver. It can regulate amount of blood passing into liver by using a sphincter. This prevents overloading the heart when umbilical venous blood flow is suddenly increased as uterine contractions squeeze the placenta. Ductus arteriosus is used when the small amount of blood goes through R atrium without jetting through Foramen Ovale. The leftover mixes with deoxy blood from superior vena cava and coronary sinus. It is directed downward through the tricuspid valve into the right ventricle. It then gets pumped into the aorta. Only 5% of blood passes into the lungs in the fetus. The fetus uses the placenta to circulate oxygen and nutrients. Blood passes through the placenta and to the organs and tissues. This blood delivers the right nutrients and oxygen, and once it delivers it, it picks up waste and carbon dioxide. This then returns to the placenta where it is expelled from the fetus into the mother’s body via the placenta.
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3. Describe in detail with diagrams the changes that occur in the fetal circulatory system at birth, and how the adult pattern of blood flow is established.
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