Lungs

The lungs are a paired respiratory organ that occupies most of the chest cavity. The right lung consists of three lobes, the left - of two (smaller due to the heart). The mass of both lungs is about 1 kg, but when inhaling they can hold up to 6 liters of air.

Bronchial tree

Air enters through the trachea, which at the level of the IV–V thoracic vertebrae is divided into two main bronchi. What follows is a series of dichotomous divisions:

• Main bronchi → lobar → segmental → lobular → terminal bronchioles
• Total 23 generations of branching from trachea to alveoli

With each division, the diameter decreases, but the total cross-sectional area increases, and the air flow speed decreases.

Alveoli - place of gas exchange

Terminal bronchioles end in alveoli - thin-walled vesicles with a diameter of 0.2–0.3 mm. In both lungs there are about 300 million alveoli, the total surface area of ​​which reaches 70 m² - the size of a one-room apartment.

The alveolar wall consists of a single layer of cells (type I alveocytes) and is closely adjacent to the capillary wall. The total thickness of the airborne barrier is only 0.5 microns. Oxygen diffuses from the alveoli into the blood, and carbon dioxide diffuses in the opposite direction.

Surfactant is a special substance secreted by type II alveocytes. It reduces surface tension and prevents the alveoli from collapsing during exhalation. In premature infants, surfactant deficiency leads to respiratory distress syndrome.

Blood supply

The lungs have dual blood supply:

• Pulmonary arteries (small circle) - carry venous blood for gas exchange
• Bronchial arteries (large circle) - nourish the tissue of the lungs themselves

Pleura

Each lung is covered with pleura - a two-layer serous membrane. Between the visceral and parietal layers there is a pleural cavity with a small amount of fluid. The negative pressure in this cavity keeps the lungs expanded.

With a penetrating wound to the chest, air enters the pleural cavity - pneumothorax develops, the lung collapses and ceases to participate in breathing. This is an emergency condition that requires immediate drainage.

You can see the lobes, segments and bronchial tree of the lungs in three-dimensional space in 3D atlas Humio - rotate the model and zoom in on any area.