The blood moves through the arteries with a certain pressure , which is very important for the exchange of substances between it, cells and tissues.

Blood pressure and its regulation mechanism [Arterial]

The blood moves through the arteries with a certain pressure, which is very important for the exchange of substances between it, cells and tissues. The blood flows under high pressure (in normal — 130 mmHg) from the left ventricle to the main artery — the aorta. Right ventricle pumps blood in the pulmonary artery at a much lower pressure — 25 mmHg (this is the maximum or systolic pressure). During relaxation of the heart the blood pressure is reduced (minimum, or diastolic), but never drops to zero, and equals 70-80 mmHg in the aorta and large arteries of the systemic circulation, and lung — 10 mmHg.

The blood pressure in the arteries decreases as their distance from the heart. Where arteries transform into the capillaries, it drops to 20-30 mmHg. The difference (differential) of blood pressure in different parts of the arterial system provides normal blood flow. Blood pressure is measured at the brachial artery by a special device — a tonometer (diagram 65). There a normal arterial pressure is 110/70 — 120/80 mmHg.

Stimulation of the sympathetic nervous system (that is accompanied by an increase in blood adrenaline concentration) increases blood pressure, and the excitation of the parasympathetic — reduces it. In a healthy person the blood pressure is constant. It can be increased with a significant physical or emotional stress. However, sometimes excessive, even positive emotions can cause a sudden decrease in blood pressure. Then the person loses consciousness. To keep blood pressure at a constant level, in healthy humans there are special adaptive mechanisms. Superior centers of such regulation are the hypothalamus and vaso-motor center of the medulla oblongata, whose one part is responsible for the increase in blood pressure, and the other — for his reduction. Taken from http://worldofschool.org

Diagram 65. Blood pressure measurement at the brachial artery

It is known that only half of the circulating blood is in the blood vessels, the rest is in the blood depots: in the liver (20% of blood), spleen (16%), skin (10%). If necessary (for example, when performing physical work, loss of blood) blood ejected from the depot into the blood vessels.

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Questions:
  • What determines the level of blood pressure?

  • Why is the blood pressure in a healthy human constant?

  • What are the factors that disrupt blood pressure?

  • Explain the adaptive significance of the relative constancy of the blood pressure.

  • What are the factors that contribute to the normalization of blood pressure?