What is the blood circulation?
The circulatory system is a self-contained vascular system with supply and disposal functions. It supplies all the body’s cells with vital substances such as oxygen (bound to the red blood pigment hemoglobin), nutrients, vitamins and minerals. Waste products (such as carbon dioxide), on the other hand, are transported away from the tissues by the blood. In addition, messenger substances (such as hormones) and defense cells of the immune system circulate in the blood.
The blood is driven by the heart. The powerful hollow muscle pumps blood through the vessels day and night, thus keeping the blood circulation going. The heart and vascular system together form the cardiovascular system.
Low pressure system and high pressure system
In the high-pressure system – consisting of the left ventricle during systole and all arteries (including the aorta and arterioles) – blood pressure is much higher: it varies here between about 80 mmHg (during diastole) and 120 mmHg (during systole). The high-pressure system accommodates about 15 percent of the total blood volume.
Small and large blood circulation
The circulatory system is composed of two interconnected circuits: the great circulation or systemic circulation and the small circulation or pulmonary circulation.
What is the function of the circulatory system?
The most important task of the blood circulation is the distribution and removal of nutrients, messenger substances and gases. For more details, see the following texts:
Pulmonary circulation
You can read everything important about the small blood circulation in the article Pulmonary circulation.
Portal circulation
A special section of the circulatory system is the venous circulation, which transports blood from the digestive tract via the liver to the inferior vena cava. You can read more about this in the article Portal vein circulation.
How is the blood circulation regulated?
The circulatory system, or blood pressure, is regulated by various mechanisms involving, among others, the autonomic nervous system and hormones.
Conversely, a drop in blood pressure is also registered by sensors and reported to the brain. Activation of the sympathetic nervous system increases the heart rate, and the vessels constrict – blood pressure rises again.
Important sensors for blood pressure regulation are also located in the kidneys. They register when blood flow to the kidneys decreases. As a result, the messenger substance renin is increasingly released, which in turn causes angiotensin II to be released. This hormone causes the vessels to constrict, which drives up blood pressure.
In the long term, blood circulation or blood pressure can be controlled by the water and electrolyte balance. If blood pressure is elevated, the body can excrete more water via the kidneys and thus reduce the blood volume – the blood pressure drops. If blood pressure is too low, the kidneys can retain more water in the body to increase blood volume and thus blood pressure again.
High blood pressure (arterial hypertension) is a major burden on the heart and circulation: Sufferers have blood pressure of 140/90 mmHg or more over a long period of time. Without treatment, this damages the heart and blood vessels.
If the first (systolic) blood pressure value is below 100 mmHg, hypotension is present (low blood pressure). This is only of medical significance if the person affected shows symptoms such as reduced performance, impaired ability to concentrate, or cold hands and feet.
In some people, rising quickly from a lying or sitting position causes a sudden drop in blood pressure (orthostatic hypotension): Sufferers feel dizzy, have ringing in the ears and a flickering before the eyes. Other symptoms such as palpitations, sweating and pallor, and even circulatory collapse and fainting (syncope) are also possible.
