The portal vein system is mainly used to collect the digestive tubes in the abdominal cavity,pancreasandspleenThe portal vein enters the liver and divides into a capillary network in the liver (which, together with the hepatic artery blood, is injected into the hepatic blood sinus), and then flows back from the hepatic vein to the heart through the inferior vena cava.
The pulmonary artery originates from the right ventricle and enters the left and right lungs through the left and right pulmonary hilum respectively.The blood in the pulmonary artery is venous blood.Two pulmonary veins, one on the left and the other on the right, exit the lung from the left and right pulmonary hilus and flow into the left atrium.The blood in the pulmonary vein is arterial blood.
The blood vessels of systemic circulation include the aorta from the heart and its branches at all levels, as well as those returning to the heartSuperior vena cava、Inferior vena cava、coronary sinusAnd its subordinate branches at all levels.
The systemic circulation arteries originate from the left ventricle and distribute throughout the body.The systemic circulation veins start from the capillary network of each part, gradually converge into larger veins, and finally converge into superior vena cava, inferior vena cava, and coronary sinus, and flow into the right atrium.
The systemic circulation veins can be divided into three major systems: superior vena cava system, inferior vena cava system (including portal vein system) and cardiac vein system.The superior vena cava system is a conduit that collects venous blood from the head and neck, upper limbs, chest and back to return to the heart.The inferior vena cava system is a series of tubes that collect venous blood from the abdomen, pelvis and lower limbs to return to the heart.The cardiac vein system is the venous blood pipeline that collects the heart.
Systemic circulation
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Systemic circulation
Systemic circulationIt refers to the circulation in which the blood flows from the left ventricle into the aorta, flows through all levels of arteries, capillary networks, and veins of the whole body, and finally gathers into the superior and inferior vena cava, and flows back to the right atrium.While the systemic circulation is going on,Pulmonary circulationIt is also in progress.The venous blood flows back to the right atrium and then into the right ventricle.Starting from the right ventricle, venous blood is injected into the pulmonary artery and then flows into the pulmonary capillary network.Here, the venous blood in the alveoli and capillaries is gas exchanged:carbon dioxideFrom the blood into the alveoli, oxygen from the alveoli into the blood capillary.In this way, venous blood with less oxygen and more carbon dioxide will become arterial blood with more oxygen.Arterial blood flows back to the left atrium through the pulmonary vein;Complete pulmonary circulation.
Pulmonary circulation
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Pulmonary circulation
Pulmonary circulationStart from the right ventricle.The venous blood is pumped out by the right ventricle, and then flows through the pulmonary artery to the capillary network around the alveoli, where carbon dioxide is discharged, fresh oxygen is absorbed, and the venous blood becomes arterial blood, and then flows back to the left atrium through the pulmonary vein.The blood from the left atrium reenters the left ventricle and circulates throughout the body.In this way, the blood circulates continuously through the systemic circulation and pulmonary circulation, completing the important task of blood circulation.
In vertebrates, the double cycle of amphibians and reptiles is not perfect.Among them, Reptilia has made some progress compared with amphibians.From the bird class,Thermostatic animal(and birds and mammals) have perfect double circulation.
