6. - Begins to develop toward the end of the third week. - Heart starts to beat at the beginning of the fourth week. - The critical period of heart development is from 20 day to 50 day after fertilization. - Many critical events occur during cardiac development, and any deviation from this normal pattern can cause congenital heart defects, if development of heart doesn't occur properly.
7. -The fetus is connected by the umbilical cord to the placenta, the organ that develops and implants in the mother's uterus during pregnancy. -Through the blood vessels in the umbilical cord, the fetus receives all the necessary nutrition, oxygen, and life support from the mother through the placenta. -Waste products and carbon dioxide from the fetus are sent back through the umbilical cord and placenta to the mother's circulation to be eliminated. The fetal circulatory system works differently than after birth
8.
9. Inside the fetal heart: -Blood enters the right atrium, the chamber on the upper right side of the heart. Most of the blood flows to the left side through a special fetal opening between the left and right atria, called the foramen ovale . -Blood then passes into the left ventricle (lower chamber of the heart) and then to the aorta, (the large artery coming from the heart). -From the aorta, blood is sent to the head and upper extremities. After circulating there, the blood returns to the right atrium of the heart through the superior vena cava. -About one-third of the blood entering the right atrium does not flow through the foramen ovale, but, instead, stays in the right side of the heart, eventually flowing into the pulmonary artery.
10. Inside the fetal lung: Because the placenta does the work of exchanging oxygen (O2) and carbon dioxide (CO2) through the mother's circulation, the fetal lungs are not used for breathing. Instead of blood flowing to the lungs to pick up oxygen and then flowing to the rest of the body, the fetal circulation shunts (bypasses) most of the blood away from the lungs.
11. Three shunts in the fetal circulation 1. Ductus arteriosus - In the fetus, blood is shunted from the pulmonary artery to the aorta through a connecting blood vessel “ ductus arteriosus”. - Protects lungs against circulatory overload. - Allows the right ventricle to strengthen. - High pulmonary vascular resistance, low pulmonary blood flow. - Carries mostly med oxygen saturated blood.
12. 2. Ductus venosus - Fetal blood vessel connecting the umbilical vein to the IVC - Blood flow regulated via sphincter.( The sphincter in the ductus venosus constricts, so that all blood entering the liver passes through the hepatic sinusoids) - Carries mostly hi oxygenated blood 3. Foramen ovale shunts highly oxygenated blood from right atrium to left atrium
16. 1- With the first breaths of air the baby takes at birth, the lungs are filled with air instead of fluid. 2- Alveoli filled with air instead of fluid allows for vascular resistance to decrease. 3- Increase in pulmonary blood flow. 4- Higher concentration of oxygen in the blood. 5- Placenta is removed from circulation. 6- Decreased prostaglandin levels. 7- When the umbilical cord is clamped, the umbilical vein closes, Systemic vascular resistance is increased . 8- Decreased pulmonary vascular resistance closes the ductus arteriosus . (The normal connection between the aorta and the pulmonary valve).
39. Summary: **There is 3 major shunts exist in the fetal circulation: “ Ductus arteriosus, ductus venosus & foramen ovale”. -Blood is shifting from the Rt atrium to the Lt atrium through the foramen ovale. -The ductus venosus allow blood to bypass the fetal liver partially. -The ductus arteriosus allow blood to bypass the lung & enter the descending aorta “these structures functionally close shortly after birth”. ** Rh incompatibility is a condition which develops when there is a difference in Rh blood type between that of the pregnant mother (Rh negative) and that of the fetus (Rh positive).
![Outline: ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)