Cardiovascular System


Blood circulation, large body circulation, small body circulation Medical: Cardio-pulmonary circulation


The cardiovascular system can be imagined as a composition of two individual sections (the small and large body circulation), which are connected in series. They are connected by the heart. The large circulatory system supplies the body with nutrients and starts on the left side of the heart with its outlet in the right atrium. The small circulation goes from the right heart through the lungs for gas exchange and flows into the left atrium.

Structure of the cardiovascular system

The cardiovascular system roughly consists of the blood vessels and the heart as a muscle pump (the task of the heart), which allows the blood to circulate through the body and supply the tissues with oxygen and nutrients. The organs and body tissues consume oxygen. Accordingly, new, oxygen-rich blood must be constantly supplied.

For this purpose, the “used” blood is transported through the veins back to the heart. The many smaller veins from the extremities and organs unite in the abdomen and upper thorax in the great vena cava (vena cava superior and inferior). This opens from above and below into the right atrium of the heart.

From there, the blood passes through a valve into the right ventricle and is then ejected through another valve into the right and left lungs. There the blood is enriched with oxygen again. The blood then passes from the lungs to the left atrium of the heart, through a valve into the left ventricle and then through the large main artery (aorta) back into the large circulation.

From there, it is distributed throughout the body via the arteries and delivers oxygen and nutrients to all organs and extremities. Depending on the environmental conditions (heat, cold, exertion, rest) the heart changes its beat frequency. The blood vessels can expand or contract.

If it is cold outside, the blood vessels in the extremities contract, so that less blood flows there and the body does not cool down as quickly (centralization). In contrast, when it is hot, the vessels dilate as the body tries to release the excess heat and keep the core body temperature constant. Sweating also serves this purpose.

During physical exertion, the vessels also dilate, especially the vessels in the muscles, as these require more oxygen during exertion. Accordingly, the blood volume is distributed over a larger cross-sectional area. The heart must now beat faster in order to circulate sufficient volume in the vascular system.

In athletes, the heart increases in size over time as a result of training. As a result, it can eject more volume per beat, so that it requires a lower beat frequency both at rest and under stress. This explains the often significantly lower resting heart rate of athletes.

All in all, the cardiovascular system is very complex and consists of the smallest vessels (capillaries) to large arteries and veins that lead the blood to and from the heart. The regulation of the cardiovascular system is also very complex and can adapt very flexibly to different conditions in healthy people. Arteries are the vessels that lead away from the heart, veins are vessels that flow towards the heart.

If the veins – especially those on the surface of the leg – are no longer able to transport the blood back to the heart quickly enough, varicose veins (varices) develop. By slowing down the blood flow in a deep vein, a blood clot (thrombus) can form, which causes the clinical picture of thrombosis. If such a blood clot breaks loose and is carried into the lung with the bloodstream, a life-threatening pulmonary embolism can develop.