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Oxygenated blood leaves the lungs through pulmonary veins, which return it to the left part of the heart, completing the pulmonary cycle. [3] [6] This blood then enters the left atrium, which pumps it through the mitral valve into the left ventricle. [3] [6] From the left ventricle, the blood passes through the aortic valve to the aorta.
Blood flows through the heart in one direction, from the atria to the ventricles, and out through the pulmonary artery into the pulmonary circulation, and the aorta into the systemic circulation. The pulmonary artery (also trunk) branches into the left and right pulmonary arteries to supply each lung.
It is responsible for directing blood to the skin and lungs. Blood flows from the ventricle into an artery called the conus arteriosus and from there into either the left or right truncus arteriosus. They in turn each split the ventricle's output into the pulmocutaneous circuit and the systemic circuit. [1]
Flow here is sometimes compared to a starling resistor or waterfall effect. Zone 3 comprises the majority of the lungs in health. There is no external resistance to blood flow and blood flow is continuous throughout the cardiac cycle. Flow is determined by the Ppa-Ppv difference (Ppa - Ppv), which is constant down this portion of the lung.
The blood flow through the bird lung is at right angles to the flow of air through the parabronchi, forming a cross-current flow exchange system (Fig. 19). [ 44 ] [ 46 ] [ 49 ] The partial pressure of oxygen in the parabronchi declines along their lengths as O 2 diffuses into the blood.
The pulmonary and the systemic circulations are the two parts of the vasculature. The pulmonary circulation system consists of the network of blood vessels from the right heart to the lungs and back to the left heart. The rest of the blood flow loop is called systemic circulation system.
Venous return (VR) is the flow of blood back to the heart. Under steady-state conditions, venous return must equal cardiac output (Q), when averaged over time because the cardiovascular system is essentially a closed loop. Otherwise, blood would accumulate in either the systemic or pulmonary circulations.
Blood enters the upper right atrium, is pumped down to the right ventricle and from there to the lungs via the pulmonary artery. [3] Blood going to the lungs is called the pulmonary circulation. [4] When the blood returns to the heart from the lungs via the pulmonary vein, it goes to the left side of the heart, entering the upper left atrium.