blood circulation

Eva Rudolf-Müller is a freelance writer in the medical team. She studied human medicine and newspaper sciences and has repeatedly worked in both areas - as a doctor in the clinic, as a reviewer, and as a medical journalist for various specialist journals. She is currently working in online journalism, where a wide range of medicine is offered to everyone.

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The bloodstream is the closed vascular system in which the heart pumps blood around the body. The blood brings oxygen and nutrients to the body cells and removes waste products such as carbon dioxide. There are two circuits connected in series, the large blood circulation (body circulation) and the small blood circulation (pulmonary circulation). Read everything you need to know about blood circulation!

What is the bloodstream?

The blood circulation is a self-contained vascular system with a supply and disposal function. All body cells must be supplied with vital substances such as oxygen (bound to the red blood pigment hemoglobin), nutrients, vitamins and minerals. By contrast, waste products (such as carbon dioxide) are carried away from the tissue 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 strong hollow muscle pumps blood through the vessels day and night and thus keeps the blood circulation going. The heart and vascular system together form the cardiovascular system.

Low pressure system and high pressure system

A distinction is made between a low-pressure system and a high-pressure system in the human blood circulation. In the low-pressure system, the average blood pressure is no more than 20 millimeters of mercury (mmHg). This section of the circulatory system includes all veins and capillaries, the pulmonary vessels, the right atrium and the right ventricle, the left atrium and, during diastole, also the left ventricle. About 85 percent of the total blood volume is in the low pressure system.

The high pressure system - consisting of the left ventricle during systole and all arteries (including aorta and arterioles) - has a much higher blood pressure: it fluctuates between about 80 mmHg (during diastole) and 120 mmHg (during systole). The high pressure system houses about 15 percent of the total blood volume.

Small and large blood circulation

The bloodstream is made up of two interconnected circuits: the large bloodstream or body circulation and the small bloodstream or pulmonary circulation.

The great blood circulation or body circulation begins in the left heart chamber (ventricle), which pumps the oxygen-rich blood at high pressure into the aorta (main artery). Via the aorta and its branches (arteries, arterioles), the blood reaches the finest vessels, which at the same time represent the transition to the venous system - the capillaries. The exchange of substances (oxygen, nutrients, waste products such as carbon dioxide, etc.) between the tissue and the bloodstream takes place via its thin wall. The blood, which is now depleted in oxygen and loaded with carbon dioxide, then returns to the heart via the veins, namely to the right half of the heart. This is where the small bloodstream, or pulmonary circulation, begins.

What is the job of the bloodstream?

The most important task of the blood circulation is the distribution and removal of nutrients, messenger substances and gases. For more information, see the following texts:

Pulmonary circulation

You can read everything you need to know about the small bloodstream in the pulmonary circulation article.

Portal vein circulation

A special section of the circulatory system is the venous circulation, which transports the 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 blood circulation or blood pressure is regulated by different mechanisms in which the vegetative nervous system and hormones are involved.

Short-term regulation is possible via circulatory reflexes, for example. Various sensors are involved in this, such as pressure receptors (baroreceptors) in the vessel walls that measure the prevailing blood pressure. The most important baroreceptors are located in the wall of the aortic arch and carotid sinus. When the blood pressure rises, the vessel walls are stretched, which excites the baroreceptors. They pass the information on to the brain via nerves, which can then counter-regulate by activating the parasympathetic nervous system: This part of the autonomic nervous system ensures, among other things, that the heart beats more slowly and the blood vessels widen. As a result, blood pressure drops.

Conversely, a drop in blood pressure is also registered by sensors and reported to the brain. When the sympathetic system is activated, the heart rate increases and the vessels constrict - blood pressure rises again.

Important sensors for regulating blood pressure are also located in the kidneys. They register it when the blood flow to the kidneys decreases. As a result, the neurotransmitter renin is released, which in turn ensures the release of angiotensin II. This hormone causes the blood vessels to constrict, which increases blood pressure.

In the long term, the blood circulation or blood pressure can be controlled via the water and electrolyte balance. With increased blood pressure, the body can excrete more water via the kidneys and thus reduce the blood volume - blood pressure drops. If the blood pressure is too low, the kidneys can retain more water in the body in order to increase the blood volume and thus the blood pressure again.

What problems can the bloodstream cause?

High blood pressure (arterial hypertension) is a major burden for the heart and circulation: those affected have a long-term blood pressure of 140/90 mmHg or more. Without treatment, this damages the heart and blood vessels.

If the first (systolic) blood pressure value is below 100 mmHg, there is hypotension (low blood pressure). This is only relevant if the person concerned shows symptoms such as reduced performance, impaired ability to concentrate or cold hands and feet.

In some people, getting up quickly from a lying or sitting position leads to a sudden drop in blood pressure (orthostatic hypotension): The affected person feels dizzy, their ears ring and their eyes flicker. Other symptoms such as palpitations, sweating and paleness up to a circulatory collapse and fainting (syncope) are possible.

Another circulatory health problem is shock. This is understood to mean a circulatory failure with a critical reduction in blood flow to organs. The cause can be, for example, a large loss of blood (hypovolemic shock) or a failure of the heart to pump (cardiogenic shock). Another possibility is a violent allergic reaction of the immediate type, which leads to a failure of the blood circulation regulation (anaphylactic shock).

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