Where do the lungs get oxygenated blood from?

Large & small blood circulation

How does the blood circulation work now? First of all, you need to know that there is not just one, but 2 blood circuits that are connected in series. The great circulatory system begins with the relaxation and expansion phase of the heart muscle, the diastole. The left ventricle relaxes and expands, allowing it to take in oxygen-rich blood from the left atrium. At the same time, in the right heart, the oxygen-poor blood flows from the right atrium into the right ventricle. During diastole, blood flows from the two atria into the two heart chambers. The atria help by contracting and "pushing" the blood into the chambers. In the subsequent tension and expectoration phase, the systole, the left ventricle pumps the blood into the main artery (aorta) and the right ventricle pumps the blood into the Pulmonary artery (pulmonary artery). The heart chambers contract strongly, the technical term for this is "contraction".

Let us first follow the path of the oxygen-rich blood from the left ventricle of the heart: From the aorta, the blood passes into larger and smaller arteries, arterioles and capillaries, to the individual body cells. There the blood releases oxygen, nutrients and other important substances and takes carbon dioxide (CO2) and "waste materials". The now oxygen-poor blood is collected via venules, smaller and larger veins and reaches the right atrium from the upper half of the body via the upper and from the lower half of the body via the lower vena cava into the right atrium. From there it reaches the above relaxation and expansion phase (diastole) described in the right ventricle the small pulmonary circulation: The right ventricle pumps the oxygen-poor blood in the systole into the pulmonary artery (arteria pulmonalis) - at the same time as the left ventricle drives the oxygen-rich blood into the aorta. The pulmonary artery branches out into capillaries via smaller arteries and arterioles, which span the alveoli like a fine network. Gas exchange takes place in the alveoli: the blood releases carbon dioxide and absorbs fresh oxygen. The oxygen-rich blood now flows through the pulmonary veins into the left atrium. Now the two bloodstreams can start all over again.