L11 fetal circulation


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L11 fetal circulation

  1. 1. INTERNATIONAL UNIVERSITY Fetal circulation Dr. Sam Nang
  2. 2. • All of the respiratory, excretory, and nutritional needs of the fetus are provided for by diffusion across the placenta instead of by the fetal lungs, kidneys, and gastrointestinal tract. • Fetal circulation is adaptive to these conditions.
  3. 3. Objective : • Describe the fetal circulation to and from the placenta. • Describe the structure and function of the foramen ovale, ductus venosus, and ductus arteriosus.
  4. 4. • The circulation of blood through a fetus is by necessity different from blood circulation in a newborn . • Respiration, the procurement of nutrients, and the elimination of metabolic wastes occur through the maternal blood instead of through the organs of the fetus.
  5. 5. • The capillary exchange between the maternal and fetal circulation occurs within the placenta . • This remarkable structure, which includes maternal and fetal capillary beds, is discharged following delivery as the afterbirth.
  6. 6. • The umbilical cord is the connection between the placenta and the fetal umbilicus. • It includes one umbilical vein and two umbilical arteries, surrounded by a gelatinous substance.
  7. 7. • Oxygenated and nutrient rich blood flows through the umbilical vein toward the inferior surface of the liver. • At this point, the umbilical vein divides into two branches.
  8. 8. • One branch merges with the portal vein, while the other branch, called the ductus venosus , enters the inferior vena cava.
  9. 9. • Thus, oxygenated blood is mixed with venous blood returning from the lower extremities of the fetus before it enters the heart. • The umbilical vein is the only vessel of the fetus that carries fully oxygenated blood.
  10. 10. • The inferior vena cava empties into the right atrium of the fetal heart. • Most of the blood passes from the right atrium into the left atrium through the foramen ovale, an opening between the two atria.
  11. 11. • Here, it mixes with a small quantity of blood returning through the pulmonary circulation. • The blood then passes in to the left ventricle, from which it is pumped into the aorta and through the body of the fetus.
  12. 12. • Some blood entering the right atrium passes into the right ventricle and out of the heart via the pulmonary trunk. • Since the lungs of the fetus are not functional, only a small portion of blood continues through the pulmonary circulation (the resistance to blood flow is very high in the collapsed fetal lungs).
  13. 13. • Most of the blood in the pulmonary trunk passes through the ductus arteriosus into the aortic arch, where it mixes with blood coming from the left ventricle. • Blood is returned to the placenta by the two umbilical arteries that arise from the internal iliac arteries.
  14. 14. • Notice that, in the fetus, oxygen-rich blood is transported by the inferior vena cava to the heart, and via the foramen ovale and ductus arteriosus to the systemic circulation.
  15. 15. • Important changes occur in the cardiovascular system at birth. • The foramen ovale, ductus arteriosus, ductus venosus, and the umbilical vessels are no longer necessary.
  16. 16. • The foramen ovale abruptly close with the first breath of air because the reduced pressure in the right side of the heart causes a flap to cover the opening.
  17. 17. • This reduction in pressure occurs because the vascular resistance to blood flow in the pulmonary circulation falls far below that of the systemic circulation when the lungs fill with air. • The pressure in the inferior vena cava and right atrium falls as a result of the loss of the placental circulation.
  18. 18. • The constriction of the ductus arteriosus occurs gradually over a period of about 6 weeks after birth as the vascular smooth muscle fibers constrict in response to the higher oxygen concentration in the postnatal blood.
  19. 19. • The remaining structure of the ductus arteriosus gradually atrophies and becomes nonfunctional as a blood vessel. • Transformation of the unique fetal cardiovascular system is summarized in table 16.6.
  20. 20. THE END