Renal circulation, this phase is where the kidneys filter waste from the blood. Portal circulation, this phase is where blood from the small intestine collects in the portal vein which passes through the liver. The liver filters sugars from the blood, storing them for later.
Blood enters the right atrium through two large veins called vena cavae.
The right atrium contracts, pushing blood into the right ventricle via a one-way valve. The right ventricle then contracts, pushing waste-rich blood into the pulmonary artery. The pulmonary artery leads to the lungs. Red cells in the blood offload carbon dioxide and take on oxygen from the air that has just been inhaled into lungs, the carbon dioxide is expelled when you exhale. The fresh, oxygen rich blood enters the pulmonary veins and returns to the heart, this time entering through the left atrium.