The pulmonary circulation, also called the small circulation, is part of the human cardiovascular system. It regulates the transport of blood between the heart and the lungs and is used for gas exchange, i.e., the absorption of oxygen into the blood and the release of carbon dioxide into the air we breathe.
What is the pulmonary circulation?
The pulmonary circulation, also called the small circulation, is part of the human cardiovascular system. It regulates the transport of blood between the heart and the lungs. The heart is the driving pump for the transport system of the human organism, the so-called blood circulation. Its function is to supply the organs and tissues with oxygen and nutrients and to remove metabolic products. This transport system, also known as the cardiovascular system, is made up of two sub-circuits: the large systemic circulation and the small pulmonary circulation. Both circuits are functionally coordinated in such a way that the used blood is first transported through the lungs to oxygenate it before it reaches the various regions of the body again. The blood that feeds the pulmonary circulation comes from the right side of the heart. It is pumped through an arterial vascular system to the capillaries of the lungs, where oxygen is absorbed into the blood from the air we breathe and carbon monoxide is simultaneously released from the blood into the air we breathe. This exchange of oxygen and carbon dioxide is called gas exchange. The return transport of the now oxygenated blood occurs via the pulmonary veins and ends in the left side of the heart, where the systemic circulation begins.
Function and task
The depleted, or deoxygenated, blood is returned to the right side of the heart via the two great vena cavae. From the atrium, it flows into the right main chamber. This forms the starting point of the pulmonary circulation. The contraction of the heart muscle during the expulsion phase causes the blood to be pumped, through the opening pulmonary valve, into the large pulmonary trunk, which splits into the left and right pulmonary arteries. These lead to the right and left lungs, respectively. There, in accordance with the anatomical structure of the lungs, they branch into the so-called pulmonary lobes and pulmonary segments to form ever finer arteries, culminating in arterioles, and finally end in the capillary vessels. Like a dense network, the capillaries surround the alveoli, which are filled with respiratory air and attach to the ends of the bronchioles. During the process of respiration, gas exchange takes place between the alveolar air and the blood in the capillaries. The alveoli and capillaries are separated only by a thin, selectively permeable wall. By means of diffusion, therefore, carbon dioxide can be released from the blood into the alveoli and exhaled on the one hand. On the other hand, inhaled oxygen can be absorbed from the alveoli into the blood. The oxygen-rich blood is transported back to the heart via a venous vascular system that runs between the individual lung segments. So-called venules, i.e. the smallest veins, first collect the blood from the capillaries and then join together to form ever larger veins, which ultimately flow into the great pulmonary vein. This vein carries the blood to the left atrium, from where it enters the left ventricle and is drained to the periphery of the body via the systemic circulation. The vascular system of the pulmonary circulation is called the vasa publica. This is because, compared with the vessels that supply oxygen to the lungs themselves, known as vasa privata, it serves the entire organism by allowing gas exchange, i.e., the intake of oxygen and the release of carbon dioxide.
Diseases and ailments
The vital exchange of gases during the pulmonary circulation can be disturbed by various medical conditions that cause decreased oxygen saturation and excess carbon dioxide in the blood. The undersupply of oxygen is usually manifested by rapid fatigue, shortness of breath and shortness of breath, dizziness and a bluish discoloration of the skin and lips. Even organ damage can be the result. The body therefore tries to counteract the acute deficiency with an increased respiratory and heart rate. Pulmonary emphysema, a chronic disease of the lungs, is responsible for such a disturbance in gas exchange. The flow of breath is impeded because the inhaled air is, as it were, dammed up in the alveoli.It is caused by irreversible enlargement of the alveoli due to enzymatic destruction of the partition walls that serve for gas exchange. Pulmonary edema describes a condition in which water accumulates in the lungs. More specifically, fluid leaks from the capillary vessels into the alveoli, severely impairing gas exchange. Causes of pulmonary edema can include acute pump failure in the left side of the heart, renal insufficiency, and severe allergic reactions, as well as dangerously low oxygen partial pressure of the ambient air at altitudes above about 3,000 meters. Other serious conditions affecting the vessels around the lungs include pulmonary hypertension and pulmonary embolism. Pulmonary hypertension, also called pulmonary arterial hypertension, is characterized by chronically elevated pulmonary arterial pressure. This high blood pressure in the pulmonary artery can be attributed to a narrowing of the blood vessels and an associated increase in vascular resistance. The consequence is poor oxygen supply and increased compensatory pumping by the heart. Especially of the right side of the heart, which is why right heart failure can occur. Pulmonary embolism refers to the occlusion of a pulmonary artery by endogenous or exogenous objects, causing pulmonary infarction with tissue damage. The extent of the damage depends on the size of the affected artery and can be life-threatening. The vascular blockage is usually causally related to thrombi, small blood clots, from the veins of the legs or pelvis.
