The fetal circulation.
The placenta is the source of oxygenation, nutrition and elimination of waste for the fetus . There are several temporary structures in addition to the placenta and the umbilical cord that enable the fetal circulation to occur. These are:
* The ductus venous which connects the umbilical vein to the inferior vena cava .
* The foramen ovale is an opening between the right and left atria.
* The ductus arteriosus which leads from the bifurcation of the pulmonary artery to the descending aorta.
* The hypogastric arteries which branch off from the internal iliac arteries and become the umbilical arteries when they enter the umbilical cord.
*The fetal circulation takes the following course.
Oxygenated blood from the placenta travels to the fetus in the umbilical vein. The umbilical vein divide into two branches, one supplies the Portal vein in the liver, the other the ductus venous joining the inferior vena cava. Most of the oxygenated blood that enters the right atrium passes across the foramen ovale to the left atrium and from here into the left ventricle and then the aorta. The head and upper extremities received approximately 50% of the blood via the coronary and carotid arteries and then the subclavian arteries respectively. The rest of the blood travels down the descending aorta mixing with deoxygenated from the right ventricle.
Deoxygenated blood collected from the upper part of the body return to the right atrium in the superior vena cava. Blood that has entered the right atrium from the superior and inferior vena cava passes into the right ventricle. A little blood travels to the lung in the pulmonary artery, for their development . most blood passes through the ductus arteriosus into the descending aorta. This blood although low in oxygen and nutrients is sufficient to supply the lower body . It is also by this means that deoxygenated blood travels back to the placenta via the internal iliac arteries, which leads into the hypogastric arteries, which leads into the umbilical arteries.
At birth, there is a dramatic alteration to the fetal circulation and an almost immediate change occurs . The cessation of the umbilical blood flow causes a cessation in the flow of ductus venous, a fall in pressure in the right atrium and the closure of the foramen ovale. As the birthday takes the first breath, the lungs inflate, There is a rapid fall in the pulmonary vascular resistance. The ductus arteriosus constricts due to bradykinin released from the lungs on initial inflation. The effect of the bradykinin is dependants on the increase in arterial oxygen. In the term baby, the ductus arteriosus closes within the first few days of birth
These structural changes become permanent and become as follows.
• The umbilical vein becomes the ligamentum teres
• the ductus venous becomes the ligamentum venosum
• the ductus arteriosus becomes the ligamentum arteriosum
• the foramen ovale becomes the fossa ovale
• the hypogastric arteries are known as the obliterated arteries except for the first few centimetres, which remain open as the superior vesical arteries.
Sen. Umaru Isah
Department of Nursing sciences.
AAU Ekpoma, Edo- Nigeria