fetal circulation.pptx

Fetal circulation

1. FETAL CIRCULATION

2. The circulatory system of a fetus is called fetal circulation. It exists only in fetus and contains special structures that allow the developing fetus to exchange materials with its mother. It differs from the postnatal (after birth) circulation because the lungs, kidneys and GIT do not begin to function until birth. The fetus obtains O 2 and nutrients from the maternal blood and eliminates CO 2 and other wastes into it.

3. The exchange of materials btw fetal and maternal circulation occurs through placenta. Maternal blood Placenta umbilical cord fetal circulatory system

4. Pattern of fetal circulation Umbilical vein Brings oxygenated blood from the placenta, which act as the lungs for the fetus. This blood is 80% saturated with O 2 (compared with 98% saturation in arterial blood in adults) The umbilical vein, before supplying blood to liver, bypasses most of the blood to the inferior vena cava through ductus venosus .

5. IVC thus receives some blood (80% saturated O 2 ) from the umbilical vein through ductus venosus , and other blood from the hepatic veins and systemic veins draining from the trunk and inferior extremities (26% saturated with O 2 ) The mixed blood from the IVC (with approximate 67% saturation) then enters the right atrium.

6. Right atrium receives blood from the IVC (67% saturation) and from SVC (26% saturation) The fate of blood entering the right atrium → From RA, majority of blood coming from IVC passes to the left atrium directly through the foramen ovale (an opening in the interatrial septum) and joins the blood coming from the pulmonary vein (42% saturation). The mixed blood from left atrium (62% saturation) passes on to the left ventricle

7. Eustachian valve

8. From the right atrium, most of the blood coming from the superior vena cava (26% saturation) and small amount of blood from IVC (67%), passes into right ventricle. This mixed blood (52% saturation) is pumped into the pulmonary artery. But, since the fetal lungs are collapsed, their vascular resistance is very high.

9. Hence only a small amount of blood passes through the lungs to reach the left atrium via pulmonary veins. Majority of the pulmonary artery blood enters the descending aorta directly by a vascular connection called ductus arteriosus .

10. Left ventricle pumps the blood (62% sat) into the ascending aorta, from where the most of the blood goes into the vessels of head and neck and upper limbs and only small amount of blood goes to the descending aorta. Descending aorta, thus receives blood mainly from the pulmonary artery through ductus arteriosus (52% sat) and only a small amount from the left ventricle (62% sat). T he descending aorta then supplies the blood (58% sat) to the whole body (except head, neck and upper limbs)

11. 2 Umbilical arteries , which are the branches of anterior division of internal iliac artery brings the blood (58% sat) back to the placenta for another exchange of materials.

12. Changes after birth After birth, when lungs, kidneys and GIT begin to function, the following changes occur: When the umbilical cord is tied off, blood no longer flows through the umbilical arteries, they fill with connective tissue, and the distal portion of UA become fibrous cords called medial umbilical ligament. (Although the arteries are closed functionally only a few minutes after birth, complete obliteration of the lumens may take 2- 3 months)

13. 2. The umbilical vein collapses but remains as the ligamentum teres , a structure that attaches the umbilicus to the liver. 3. The ductus venosus collapses but remains as the ligamentum venosum , a fibrous cord on the inferior surface of the liver. 4. Placenta is expelled as the ‘afterbirth’

14. 5. The foramen ovale normally closes shortly after birth to become the fossa ovalis , a depression in the inter atrial septum. ( When an infant takes its first breath, the lungs expand and blood flow to the lungs increases. Blood returning from the lungs to heart through pulmonary veins increases pressure in the left atrium. This closes the foramen ovale by pushing the valve that guards it against the interatrial septum. Permanent closure occurs in about a year )

15. 6. The ductus arteriosus close by vasoconstriction almost immediately after birth and becomes the ligamentum arteriosum . ( Complete anatomical obliteration of the lumen takes 1-3 months. )

16. Changes in short Placenta expelled – lungs, kidneys, GIT functions Umbilical arteries → medial umbilical ligaments Umbilical vein → ligamentum teres Ductus venosus → ligamentum venosum Ductus arteriosus → ligamentum arteriosum Foramen ovale → fossa ovalis

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