Definition
The blood circulation consists of the heart and the blood vessels. The heart serves as a pump to pump the blood in the vessels through the body. For this purpose, the human body has a vascular system that branches out from the large vessels that originate directly from the heart to reach every part of the body. When the blood has reached the “end”, for example at the fingertips, toes or organs, it flows back to the heart to close the circulation, to be “recycled” again and to be distributed again in the body.
Functions of the blood circulation
The task of the bloodstream is to supply the organs with all the nutrients they need to perform their respective functions. This nutrient transport is performed by the blood. The blood transports oxygen through the body to all the organs, because they cannot work without oxygen and would die.
In addition, the carbon dioxide produced in the organs is absorbed by the blood and transported away. The oxygen does not simply “float” around freely in the blood, but is bound to a transport medium called haemoglobin during transport. One molecule of haemoglobin (imaginable as a large ball) can bind four molecules of oxygen (imaginable as small balls) to itself and release it again at another location, absorbing carbon dioxide in return.
It could be compared to a beverage supplier who brings four crates of water (oxygen for survival) to a household (organ) in a car (haemoglobin) and takes four empty crates of water (carbon dioxide that was used up) to make room for the new, full ones. The beverage supplier takes them to his company (lungs) to refill them there. Other nutrients, such as fats, sugars or proteins from food are also transported by the blood and each is absorbed by its target organ from the blood.
Waste products produced in the organs, such as urea, are absorbed by the blood and transported to their excretory organ. In addition, messenger substances (hormones) are also distributed in the bloodstream, which ensure that signals (for example hunger) can be passed on within the body. A further task of the blood circulation is the regulation of the temperature in the body. Heat can be absorbed and released through the blood, so that a constant state can be achieved. The cells that are responsible for causing our blood to clot when we have injured ourselves are also transported in the bloodstream.
Vascular system
You can imagine the beginning of the vascular system like a tree. Starting with the thick aorta (diameter: 2.5 – 3.5 cm), the vessels branch out further and further and become thinner the further away they are from the heart. The vessels can be divided into arteries that carry the oxygen-rich blood from the heart to the whole body.
In this way, the blood is increasingly deprived of nutrients and oxygen, so that the oxygen-rich blood becomes oxygen-depleted blood. This oxygen-poor blood is then returned to the heart via the veins. The capillaries form the transition between arteries and veins.
These are the smallest vessels with a diameter of 5-10 μm, through which just one red blood cell (erythrocyte) can pass. Because these vessels are so narrow, the blood flows through them very slowly. So there is a lot of time for the organs to take up oxygen from the blood and at the same time release produced carbon dioxide into the blood.
The capillaries are followed by the veins. Here the size is the exact opposite of the arteries. Starting with small veins that connect to the capillaries, these become thicker and thicker until finally the largest veins open into the heart.
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