In human body, the blood flows in two closed systems of vessels connected to the heart, - pulmonary and systemic circulation. Pulmonary circulation

Pulmonary and systemic circulation

In human body, the blood flows in two closed systems of vessels connected to the heart, — pulmonary and systemic circulation.

Pulmonary circulation

Pulmonary circulation — is the way the blood flows from the right ventricle to the left atrium.

Venous, low-oxygen blood enters the right side of the heart. Contracting, the right ventricle ejects it into the pulmonary artery. By two branches, the pulmonary artery is divided, this blood flows to the lungs. There branches of the pulmonary artery, dividing into smaller and smaller arteries, transform into capillaries that thickly braid multiple lung bubbles that contain air. Passing through the capillaries, the blood is enriched with oxygen. Simultaneously, carbon dioxide passes from the blood into the air, which fills the lungs. Thus in the capillaries of the lungs venous blood turns to the arterial. It gets into the veins which, interconnecting, form four pulmonary veins that drain into the left atrium (diagram 57, 58).

Time of blood flow in the pulmonary circulation is 7-11 seconds.

Systemic circulation

Systemic circulation — is the way the blood flows from the left ventricle through the arteries, capillaries and veins to the right atrium. Taken from http://worldofschool.org

Diagram 57. Scheme of a pulmonary (a) and systemic (b) circulations: 1 — pulmonary veins; 2 — pulmonary artery; 3 — upper and lower vena cava; 4 — the right atrium; 5 — left atrium; 6 — right ventricle; 7 — left ventricle; 8 — aorta; 9 — the capillaries of the systemic circulation; 10 — the capillaries of pulmonary circulation
Diagram 58. Blood circulation: 1 — the temporal artery; 2 — temporal vein; 3 — front vein; 4 — jugular vein; 5 — carotid artery; 6 — upper hollow vein; 7 — aorta; 8 — pulmonary artery; 9 — pulmonary veins; 10 — shoulder veins; 11 — the heart; 12 — lower hollow vein; 13 — gastric artery; 14 — renal artery; 15 — ulnar artery; 16 — digital arteries; 17 — cubital vein; 18 — finger vein; 19 — femoral artery; 20 — femoral vein; 21, 22 — large tibial artery; 23, 24 — the tibia veins; 25 — plantar artery; 26 — plantar veins

The left ventricle, contracting, pushes the arterial blood into the aorta — the largest artery of human. Arteries that supply all organs with blood, particularly the heart, branch from aorta. Arteries in each organ gradually branch out, forming a dense grid of smaller arteries and capillaries. Oxygen and nutrients proceed to all tissues of the body from the capillaries of the systemic circulation, and carbon dioxide goes out of the cells into the capillaries. Wherein, the blood transforms from the arterial to venous. The capillaries merge into veins, first in small and then in larger. From them, the whole blood is collected in two large vena cava. The upper hollow vein carries blood from the heart to the head, neck, arms, but lower hollow vein — from all other parts of the body. Both hollow veins fall into the right atrium (diagram 57, 58).

Time of blood flow in the systemic circulation is 20-25 seconds.

Semilunar valves

Venous blood from the right atrium enters the right ventricle, from which flows a pulmonary circulation way. Semilunar valves (diagram 58) are located at the exit of the aorta and pulmonary artery out of the heart ventricles. They are pocket-like and placed on the inner walls of blood vessels. When the blood is pushed into the aorta and pulmonary artery, semilunar valves are pressed against the vessel wall. When the ventricles relax, blood cannot get back to the heart because, flowing in the pocket, it stretches them and they close tightly. Therefore, the semilunar valves allow blood flow only in one direction — from the ventricles into the arteries.

Questions:
  • Explain the advantage of two circulation types in comparison with one.