Pulmonary alveolus

The air sacs ( alveoli medically, from Latin alveolus, english pulmonary alveolus, air vesicles ) are the structural elements of the lungs in which takes place at the breathing gas exchange between blood and alveolar air.

Histology

The alveoli are in the form of small bubbles. They are wine grapes like an alveolar duct ( alveolar duct ) around to alveolar sacs ( alveolar sacs ) summarized that attach at the ends of the bronchioles. A single alveolus is a round to polygonal base shape. The diameter of the alveoli is dependent on the development of state and varies in inspiration and expiration between 50 and 250 microns. The alveoli in the coverage area of ​​a terminal bronchiole are the smallest lung unit, the acinus. About 12 acini form the basic units of a pulmonary lobules ( lobular, 2 × 1 cm).

Adjacent alveoli are separated by narrow alveolar another which are luminal side with a specialized cell type, the alveolar epithelial cells ( pneumocytes ), lined. In the septa to find the finest pores adjacent alveoli with each other ( Kohnsche pores). We distinguish:

• Flat alveolar epithelial cells, type I pneumocytes called that are in parts less than 0.1 microns thick and mount the basement membrane
• Cubic alveolar epithelial cells, pneumocytes called type II, the producers of the surfactant, a Atelektasefaktors.

In addition, can be found in the alveoli alveolar macrophages derived from the blood and dust phagocytose (dust cells) or after bleeding blood pigment record ( "heart failure cells"). Below the alveolar epithelium is found in the alveolar subepithelial connective tissue, which is called the interstitium of the lung. It contains abundant blood capillaries, along with fibroblasts, collagen fibers, elastic fibers and proteoglycans.

Physiology

In the alveoli, the exchange of respiratory gases between the filled cavities and the blood takes place in the pulmonary capillaries. The number of the alveoli are estimated to be about 300 million, and their total surface area of 80-120 m2. The alveoli are closely connected to the capillary system of the lungs. Both basement membranes are largely fused together. The alveolar epithelium is so thin that the respiratory gases oxygen and carbon dioxide to diffuse therethrough. Since the Interzellularkontakte the capillary endothelium of liquid are more permeable than those of the lung alveoli cells in heart failure may leak fluid into the connective tissue and lead to interstitial edema.