Fetal circulation

Discussion of the basics of fetal circulation

1. Fetal Circulation Dr. Komal Parmar

2. Embryonic circulation Figure 6.15 Extraembryonic blood vessel formation in the villi, chorion, connecting stalk, and wall of the yolk sac in a presomite embryo of approximately 19 days. Langman’s Embryology, 12 th ed.

3. Embryonic circulation Hill, M.A. 2017  Embryology   Embryonic Circulations.jpg . Retrieved November 24, 2017, from  https://embryology.med.unsw.edu.au/embryology/index.php/File:Embryonic_Circulations.jpg

4. Placental Circulation Organ facilitating gaseous and nutrient exchange between the fetal and maternal compartment Fetal Part- Develops from trophoblast and chorionic plate. Maternal Part- Develops from decidua basalis. Begins around the 8 th week of Gestation.

5. Implantation and Invasion of Uterine Tissue

6. Growth of Placenta

7. Difference between fetal and neonatal/adult circulation Fetal Neonatal Gas exchange Placenta Lungs RV, LV circuit Parallel Series Pulmonary circulation High resistance Low reistance Fetal heart contractility weak strong Dominant ventricle right left

8. Course of Fetal Circulation

9. 1. Placenta

10. Transport across placenta: 2 types Uteroplacental flow Blood circulation, ions and gases: 500ml/min Lipids Antibodies Endocrine functions: various oestrogens, β- endorphins, progesterone, hCG and human chorionic somatomammotropin ( hCS ), which is also known as placental lactogen ( hPL ) 11beta-HSD2 Drugs Microbes

11. 2. Fetoplacental Circulation

12. 2. Umbilical Vein F orm by the convergence of venules that drain the splanchnopleure of the extraembryonic allantois. The peripheral venules drain the mesenchymal cores of the chorionic villous stems and terminal villi. V ena umbilicalis impar Right and Left Umbilical Vein Enter their corresponding cardiac sinual horns lateral to the terminations of the vitelline veins . Hill, MA 2017   Embryology  Kollmann512 . jpg  . Retrieved December 22, 2017, from  https ://embryology.med.unsw.edu.au/embryology/index.php/File:Kollmann512.jpg

13. Around 5 th week of development the right umbilical vein retrogresses completely. The left umbilical vein retains some vessels discharging directly into the sinusoids, but new enlarging connections with the left half of the subhepatic intervitelline anastomosis emerge. The latter is the start of a bypass channel for the majority of the placental blood , which continues through the median ductus venosus F inally the right half of the subdiaphragmatic anastomosis, to reach the termination of the inferior vena cava.

14. 3. Ductus V enosus D irect continuation of the umbilical vein and arises from the left branch of the portal vein, directly opposite the termination of the umbilical vein . Connects the midpoints of the subdiaphragmatic and subhepatic anastomoses between the right and left vitelline veins. Axial vessel during the early symmetric phase of liver development. Sphincter mechanism It passes for 2–3 cm within the layers of the lesser omentum , in a groove between the left lobe and caudate lobe of the liver, before terminating in either the inferior vena cava, or in the left hepatic vein immediately before it joins the inferior vena cava.

15. 4. IVC Right half of the Subdiaphragmatic anastomoses. Parts of the left branch of the umbilical vein, proximal and distal to their junctions, function as branches of the portal vein, carrying oxygenated blood to the right and left parts of the liver. Blood in the left umbilical vein therefore reaches the inferior vena cava by three routes: via the hepatic veins; circulates through the liver with portal venous blood ductus venosus (80%)

16. 5. Right Atrium R ight atrial pressure is much greater than left atrial pressure, it forces the flap-like valve of the septum primum to the left, which permits passage of blood from the right to the left atrium. The valve of the inferior vena cava is so placed as to direct 75% of the richly oxygenated blood from the umbilical vein to the foramen ovale and left atrium , where it mingles with the limited venous return from the pulmonary veins .

17. 6. Left Atrium 7. Left Ventricle 8. Aorta

18. 9. Umbilical Arteries In direct continuation with the internal iliac arteries. Thickening of the tunica media Before birth there is a proliferation of connective tissue within the vessel wall. The umbilical vessels constrict in response to handling, stretching, cooling and altered tensions of oxygen and carbon dioxide. Umbilical vessels are muscular, but devoid of a nerve supply in their extra-abdominal course.

19. Right Ventricular Circulation Blood from the head and upper limbs returns to the right atrium via the superior vena cava, flows through the right atrioventricular orifice into the right ventricle. Pulmonary Trunk D uctus arteriosus directly to the aorta The mixture descends in the aorta and most is returned via the umbilical arteries to the placenta: some is distributed to the lower limbs and the organs of the abdomen and pelvis.

20. Ductus Arteriosus It is 8–12 mm long, and joins the aorta at an angle of 30–35º on the left side, anterolaterally , below the origin of the left subclavian artery . In the neonate , the ductus arteriosus is closely related to the left primary bronchus inferiorly and the thymus gland anteriorly . Histology similar to Muscular Artery (relation to RLN) Contraction prevented by Prostaglandins E2, I2 and F2a.

21. Transition From Extra-Uterine Life To Intrauterine Life Essential components for a normal neonatal transition • Clearance of fetal lung fluid • Surfactant secretion, and breathing • Transition of fetal to neonatal circulation • Decrease in pulmonary vascular resistance and increased pulmonary blood flow • Endocrine support of the transition

22. Mechanical compression of the chest during the vaginal birth forces approximately 1/3 of the fluid out of the fetal lungs. As the chest is delivered, it re-expands, generating a negative pressure and drawing air into the lungs. Passive inspiration of air replaces fluid. As the infant cries , a positive intrathoracic pressure is established which keeps the alveoli open, forcing the remaining fetal lung fluid into the lymphatic circulation. Pulmonary Adaptations

23. Changes with the first breath With the infant’s first breath and exposure to increased oxygen levels, there is an increased blood flow to the lungs. Umbilical cord clamping decreases oxygen concentration, increases carbon dioxide concentration, and decreases the blood pH. This stimulates the fetal aortic and carotid chemoreceptors, activating the respiratory centre in the medulla to initiate respiration.

24. Removal of Placental source The clamping of the umbilical cord eliminates the placenta as a reservoir for blood, triggering an increase in systemic vascular resistance (SVR), an increase in blood pressure, and increased pressures in the left side of the heart. The removal of the placenta also eliminates the need for blood flow through the ductus venosus , causing functional elimination of this fetal shunt. Systemic venous blood flow is then directed through the portal system for hepatic circulation. Umbilical vessels constrict , with functional closure occurring immediately. Fibrous infiltration leads to anatomic closure in the first week of life. Temperature change and Bradykinins.

25. Umbilical Arteries After the cord is severed the umbilical arteries contract, preventing significant blood loss; thrombi often form in the distal ends of the arteries. The arteries obliterate from their distal ends until, by the end of the second or third postnatal month, involution has occurred at the level of the superior vesical arteries. The proximal parts of the obliterated vessels remain as the medial umbilical ligaments.

26. Umbilical Vein and Ductus Venosus

27. Closure of Foramen Ovale D ecrease in pressure also occurs in the inferior vena cava Atrial pressures become equal and the valvular foramen ovale is closed by apposition, and subsequent fusion, of the septum primum to the rims of the foramen . Contraction of the atrial septal muscle, synchronized with that in the superior vena cava, Although the foramen ovale closes functionally after pulmonary respiration is established, It is obliterated in fewer than 3% of infants 2 weeks after birth,and in 87% by 4 months after birth.

28. Closure of Ductus Arteriosus starts to close immediately after birth attributed to increased oxygen tension. A neural factor may also be involved: the muscular wall has afferent and efferent nerve endings and responds to adrenaline and noradrenaline. Removal of Placenta and Prostaglandins. The first stage of ductal closure is completed within 10–15 hours and the second stage takes 2–3 weeks. Stage 1 (10-15 hrs ) Functional Stage 2 (2-3 weeks) Anatomical contraction of the smooth muscle cells and development of subendothelial oedema. Destruction of the endothelium and proliferation of the intima

29. Fetal and Neonatal heart S ituated midway between the crown of the head and the lower level of the buttocks. Fetal : foramen ovale lies at the level of the third intercostal space It is almost exactly in the coronal plane of the body At birth, the average thicknesses of the lateral walls of both the ventricles are approximately equal (5 mm ).

30. Summary

31. Clinical Correlations

32. Patent Foramen Ovale

33. Persistent Pulmonary Hypertension Of The Newborn

34. Umbilical Artery Cateterization In order to keep the catheter patent, a small volume of fluid is continuously infused through it . the tip of the catheter should be located well away from arteries branching from the aorta. ‘ high’ position ’, above the coeliac artery but well below the ductus arteriosus ‘ low’ position , below the renal and inferior mesenteric arteries but above the point where the aorta bifurcates into the two common iliac arteries.