Lungs - are a paired organ (diagram 73.). They are placed in the thoracic cavity on both sides of the heart, adjacent at the bottom with diaphragm,

Lungs structure

Lungs — are a paired organ (diagram 73.). They are placed in the thoracic cavity on both sides of the heart, adjacent at the bottom with diaphragm, have a conical shape and consist of particles, which are three in the right lung and two in the left. Each lung is covered with two sheets of membrane — the pleura, forming a sealed sac — the pleural cavity. It has no air, and a negative pressure relative to atmospheric. Due to this, the venous blood in systemic circulation is returned to the right atrium and the lungs can expand during inhalation.

Normally, the pleura are wet and during breathing easily slide over one another without creating any sensation. If there is inflammation, pleura sheets get thickened, dried, rub against each other, and cause the strong chest pain during inhalation.

On the inner side of each lung there is a gate that is entered by the main bronchus, pulmonary artery and exited by pulmonary veins. The left lung has a cardiac notch, where lies the heart.

Diagram 73. The structure of the lung: 1 — right main bronchus; 2 — ribs; 3 — particles of lungs; 4 — the diaphragm; 5 — cardiac notch; 6 — pleura; 7 — the trachea; 8 — left main bronchus; 9 — alveoli
Diagram 74. Alveoli structure: 1 — blood, saturated with carbon dioxide; 2 — blood, oxygen-rich; 3 — pulmonary capillaries; 4 — capillary; 5 — erythrocytes; 6 — air


The basic structural and functional unit of the lungs are the alveoli. Taken from

Each lung has 300-350 million alveoli (fig. 74), which total area (respiratory surface of the lungs) is 90-100 m2; that is 50 times more than the area of ​​the body surface. The alveoli are the part of the lungs where gas exchange occurs between the atmospheric air and the air of the cavity, that is — pulmonary ventilation. Alveoli diameter is 150-300 microns, wall thickness — 0.4-1.5 microns. The walls of the alveoli are made of a single layer of cells and elastic fibers, which give the opportunity to expand the alveoli during inspiration and contract during exhalation. The walls of the alveoli densely braided with network of capillaries. Venous blood flows through the capillaries to the lungs from the pulmonary artery branches. It is saturated with carbon dioxide and poor in oxygen. Through a thin alveolar-capillary membrane, carbon dioxide goes into the cavity to the alveoli via diffusion, and excretes from the body during exhalation. At the same time, oxygen from the alveoli air enters the blood, turning it in into the arterial, which flows off into the left atrium.

  • What is structure the structure of the lungs?

  • How the gas exchanges in the alveoli?