What are the two functions of blood
Structure & function of the blood circulation
Heart & blood vessels
The bloodstream is a network of blood vessels. The heart pumps blood steadily and regularly through the blood vessels. Via this supply and disposal network, the blood reaches every area of the body and back again: in organs such as the heart, lungs, liver, stomach, intestines, brain, kidneys or spleen, in skin and muscles and other tissues. Blood consists of a liquid part, the blood serum, and solid parts, the blood cells. Certain blood cells called red blood cells (erythrocytes) contain the blood pigment hemoglobin. Hemoglobin binds oxygen. With the help of hemoglobin, the red blood cells transport the oxygen to the body cells and release it there. The cells need the oxygen (O2) for their metabolism. Carbon dioxide (CO2). This is transported back to the lungs in the red blood cells and released there via the exhaled air. The blood cells are then "loaded" with fresh oxygen and the cycle starts all over again.
The "motor" of the blood circulation is the heart. With its pumping capacity, it ensures that all organs, tissues and even the smallest cell in our body are constantly supplied with sufficient oxygen, nutrients, vitamins, minerals, messenger substances and other important substances. It beats steadily and without a break - about 100,000 times every day. The heart muscle pumps up to 10,000 liters of blood through the blood vessels every day.
Which organ or tissue receives how much blood is precisely regulated in the body. The brain is best perfused with blood: About 13% of the amount of blood that the heart pumps into the body in one minute (= cardiac output) reaches the brain. In some situations - for example when reading, writing or arithmetic, the brain is supplied with more blood than, for example, during sleep. The brain reacts particularly sensitively to a lack of oxygen: without oxygen, nerve cells in the brain die quickly and cannot be replaced by new cells. Overall, however, the blood flow to the brain is kept relatively constant.
Different organs receive different amounts of blood
The coronary arteries are also always supplied with blood as evenly as possible - with around 4% of the cardiac output (CO). Because the coronary vessels are important so that the heart itself is supplied with oxygen. The kidneys are supplied with blood with around 20 to 25% of the cardiac output. Compared to their weight (only 0.5% of body weight), the kidneys receive quite a bit of blood. So much blood must flow through them that they cleanse the blood of harmful substances and excrete them in the urine.
The other organs get sometimes more, sometimes less blood, depending on how "active" they are. After eating, for example, the gastrointestinal tract receives a lot of blood, around 24% of the CO physical work, the blood supply to the skeletal muscles is stronger than at rest.The heart then pumps more blood into the body per minute, around three quarters of which reaches the skeletal muscles during physical exertion.
Syncope: fainting due to circulatory collapse
With these percentages it is clear that the gastrointestinal tract and skeletal muscles cannot, of course, have maximum blood flow at the same time. That is why you should wait 1-2 hours after eating before doing sports. During physical exertion, the skin is also supplied with blood. This causes the body to give off heat.
In emergency situations, the body can reduce the blood flow to the organs that are "not so important" in this case: the gastrointestinal tract, kidneys, skeletal muscles and skin are no longer supplied with blood as much. People in or shortly before a shock therefore see pale If the brain is no longer adequately supplied with blood, those affected faint - this is called a "syncope".
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