Special Circulations

Circle of Willis Circulatory System

Special Circulations

Arterial anastomosis Base of brain--surrounding pituitary gland and optic chiasma Formed by internal carotids, anterior communicating artery, and posterior communicating artery Insures blood supply to brain

Pulmonary Circulation Does not serve metabolic needs of tissue Brings blood into close contact with alveoli of lungs Permits gas exchange to occur

Hepatic Portal Circulation Blood from digestive organs delivered to liver for processing Arteries feed digestive organs Blood collected in veins of hepatic portal system and sent to liver Hepatic veins return blood to general circulation

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Hepatic veins Hepatic portal vein

Fetal Circulation Gastric vein Splenic vein Inferior mesenteric vein Superior mesenteric vein

In fetus lungs and digestive organs not functional Nutrient and gas exchange through placenta Umbilical vein carries nutrient and oxygen rich blood to fetus Umbilical arteries carry waste from fetus to placenta

Most blood from umbilical vein travels directly to right atrium in ductus venosus Much of blood entering right atrium shunted to left atrium through foramen ovale Blood entering pulmonary trunk shunted to aorta through ductus arteriosus

Changes in Fetal Circulation at Birth Foramen ovale closes--fossa ovalis Ductus arteriosus closes and converts to fibrous ligamentum arteriosum

Changes in Fetal Circulation at Birth Ductus venosus becomes fibrous band on liver--ligamentum venosum Remnants of umbilical arteries and veins become ligaments of liver ligamentum teres and medial umbilical ligaments

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