Blood pressure in the vessels
A very important indicator of the state of the human body is blood pressure.
Blood pressure is created by the force of contraction of the ventricles of the heart and the resistance of the vessel wall.
It is not the same in different vessels. The pressure difference in different parts of the circulatory system ensures a continuous blood flow through the vessels from the area of higher pressure to the area of lower pressure.
The highest blood pressure in the aorta (120 mm Hg). As the blood moves through the vessels, it gradually decreases, reaching the smallest value in the superior and inferior vena cava. In large veins of the chest cavity, the pressure is almost equal to atmospheric pressure. The blood pressure in the capillaries is reduced to 15 mm Hg. Art.
If the blood pressure drops sharply (for example, with large blood loss), then the organs do not receive the required amount of nutrients and oxygen. A person’s condition worsens: weakness, drowsiness appears, attention and memory are impaired. With low pressure, a person can lose consciousness, and without timely medical assistance, even die.
If blood pressure rises, then this is also very dangerous. With a sharp increase in pressure, the thin walls of blood vessels can collapse, and then hemorrhage occurs.
Measurement of pressure
Blood pressure is usually measured in the brachial artery with a manometer.
In healthy people at rest, the average pressure is 120 mm Hg. Art. at the moment of contraction of the heart (maximum pressure), and at the moment of relaxation – 70–80 mm Hg. Art. with a relaxed heart (minimal pressure).
Persistent increase in blood pressure in humans is called hypertension.
Persistent lowering of blood pressure in humans is called hypotension.
Blood flow rate
Blood flow rate is an important characteristic of blood circulation. In different parts of the blood circulation, the speed of blood movement differs. It depends on the total lumen of the vessels and on the resistance that the walls of these vessels have.
The highest speed of movement of blood in the aorta is approximately 0.5 m / s.
The cross section of the capillaries is much larger than the cross section of the aorta, so the blood flow rate in them is the lowest – only 0.5–1.2 mm / s. The low speed of blood flow through the capillaries ensures the exchange of gases and substances between blood and tissues: oxygen and nutrients have time to penetrate into the cells, and their waste products and carbon dioxide enter the blood.
Redistribution of blood in the body
The supply of blood to various organs depends on the intensity of their work. More blood flows to a working organ that needs oxygen and nutrients than to an organ at rest. So, when doing physical work, a large amount of blood flows to the muscles. At the same time, its flow to the digestive organs decreases. That is, blood is redistributed all the time in the body: more of it flows through some organs, and less through others.
A change in the blood supply to an organ is associated with a change in the lumens of its vessels. The lumen of blood vessels is regulated by both the nervous system (contraction of the muscular walls of the vessels under the influence of impulses coming along the sympathetic nerves from the central nervous system – these changes occur reflexively) and biologically active substances (humoral regulation).