Systemic Circulation - Veins

Portal Circulation The hepatic portal system is designed to take nutrient- rich venous blood from the digestive tract capillaries, and transport it to the sinusoidal capillaries of the liver. As it percolates through the liver sinusoids, the hepatocytes of the liver, acting as the chemical factories of the body, extract and add what they wish to maintain homeostasis (extracting sugars, fats, proteins when appropriate and then dumping them back into the circulation when necessary).

Portal Circulation

Fetal Circulation The fetus has special circulatory requirements because their lungs, kidneys and GI tract are non-functional. The fetus derives its oxygen and nutrients and eliminates wastes through the maternal blood supply by way of the placenta. Normally, there is no maternal/fetal mixing; the fetus is totally dependant on capillary exchange.

Fetal Circulation Oxygenated blood leaves the placenta through the umbilical vein. It then bypasses the liver via the ductus venosus and dumps into the inferior vena cava en route to the right heart. This oxygen-rich blood then bypasses the lungs by traveling to the left heart through the foramen ovale.

Fetal Circulation Blood remaining in the right heart that manages to flow through the right ventricle meets with very high resistance from the closed and soggy lungs. This blood is diverted into the left-sided circulation by passing through the ductus arteriosus before returning to the placenta via the umbilical arteries.

Fetal circulation (before birth)

Neonatal Circulation After Birth At birth, the neonate’s lungs open and in just a few seconds, there is a massive drop in pulmonary vascular resistance. Blood now entering the right heart now sees lower pressure looking into the lungs and has no “incentive” to flow through the foremen ovale or the ductus arteriosus. Another change also occurs very rapidly - the umbilical cord is severed. And so begins the adult pattern of blood flow.

Neonatal Circulation After Birth Within hours, days, or weeks after birth, the umbilical vein atrophies to become the ligamentum teres. The ductus venosus atrophies to become the ligamentum venosum. The foramen ovale becomes the closed fossa ovale. The ductus arteriosus atrophies to become the ligamentum arteriosum. Umbilical arteries atrophy to become the medial umbilical ligaments.

Neonatal Circulation After Birth

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