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Blood flows through our body in a closed system - it is always the same blood circulating. The role of the blood vessels is to provide the body cells with oxygen and nutrients and at the same time dispose of the end products of cell metabolism. In this way circulation is a supply and waste management system with the heart as central pumping and distribution station. The "conduits" of this system consist of three types of blood vessels - each with a different assignment:
- Arteries: These are blood vessels in which the blood flows away from the heart.
- Capillaries: These vessels are responsible for the exchange of oxygen, nutrients and metabolic waste products. They are the link between the arteries and veins.
- Veins: These are the blood vessels in which the blood flows to the heart.
Systemic (body) circulation
The starting point for the systemic or greater circulation is the left ventricle. From there blood is pumped into the aorta through the aortic valve, into the main body artery. Two smaller arteries branch off directly behind the aortic valve, these are the left and right coronary arteries. Their job is to supply the heart with blood. The aorta itself initially follows an upward path (the aorta ascendens) and then, at the point where the windpipe divides (truncus pulmonalis), it forms a curve and runs downwards (aorta descendens) along the backbone. Its shape is therefore more or less comparable with that of a walking stick.
The place where the aorta forms the curve is called the aortic arch. This arch is important in the sense that several main arteries branch off from the aorta at this point. The first of these is the brachiocephalic trunk (truncus brachiocephalicus). After a few centimeters it further divides into the right collarbone artery (art. subclavia dextra), and the right common carotid artery (art. carotis communis dextra). Dextra is the medical term for right, sinistra for left. These make up the communal artery for the right arm and the right side of the head and neck. After the truncus brachiocephalicus, two more arteries branch off from the aorta in the aortic arch – the left common carotid artery (art. carotiscommunis sinistra) and the left collarbone artery (art. subclavia sinistra). These perform the same functions on the left side.
Pulmonary (lung) circulation
Pulmonary circulation is also sometimes called "the lesser circulation". It begins in the right ventricle and ends in the left atrium. The right ventricle ejects the de-oxygenated blood through the large pulmonary vein (truncus pulmonalis). This moves away from the heart and is therefore, strictly speaking, an artery. But it is still used to transport de-oxygenated blood.
The truncus pulmonalis divides in the right and left lung arteries (art. pulmonalis). Each artery leads to the relevant left and right lobe of the lung. There the blood vessels keep branching out - as in the greater circulation - until they are just as thin as the capillaries. In the capillary network of the lungs, which surrounds the fine alveoli like a net, an exchange of materials takes place. The blood, which is low in oxygen, gives off carbon dioxide into the alveoli. At the same time oxygen from inhaled air in the alveoli is absorbed into the blood vessels. Carbon dioxide is exhaled with the breath.
After this material exchange the blood which is now rich in oxygen again, flows back to the heart. The small venules and veins of the lung converge to form the four large pulmonary veins (venae pulmonales), which transport the blood into the left atrium.
