Alveoli

Anatomy of the bronchus , details of the alveoli and pulmonary circulation

The alveoli or alveoli (from latin alveolus ) set as extensions of the alveolar ducts and the Alveolarsäcke the blind end of the respiratory tract , and are the structural elements of the lung , where, when the respiratory gas exchange between blood occurs and alveolar air.

histology

The alveoli are in the form of small vesicles. They are grouped like grapes around an alveolar duct ( ductus alveolaris ) to form alveolar sacs ( sacculi alveolares ) that attach to the ends of the bronchioles . A single alveolus has a rounded to polyhedral basic shape. The diameter of the alveoli depends on the state of development and fluctuates between 50 and 250 μm in inhalation and exhalation. The alveoli in the supply area of a terminal bronchiolus form the smallest unit of the lung, the acinar . About 12 acini form the basic units for a lung lobe ( lobule , 2 × 1 cm).

Adjacent alveolar alveoli are separated from one another by narrow alveolar septa, which are lined on the lumen side with a specialized cell type, the alveolar epithelial cells (pneumocytes). In the septa there are very fine pores that connect neighboring alveoli with one another (Kohn pores). One differentiates:

Flat alveolar epithelial cells, called type I pneumocytes , which are sometimes less than 0.1 μm thick and are attached to the basement membrane .

cubic alveolar epithelial cells, called pneumocytes type II , the producers of the surfactant , an anti-atelectasis factor.

In addition, there are alveolar macrophages in the alveolar lungs, which come from the blood and phagocytize dust (dust cells) or absorb blood pigment after bleeding ("heart defect cells"). Below the alveolar epithelium, in the alveolar septa, there is subepithelial connective tissue called the interstitium of the lungs. It contains abundant blood capillaries, as well as fibroblasts , collagen fibers , elastic fibers and proteoglycans .

physiology

The exchange of breathing gases between the filled cavities and the blood in the pulmonary capillaries takes place in the alveoli. The number of alveoli is estimated to be around 300 million and their total surface area to be 80–120 m ² . 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 breathing gases carbon dioxide and oxygen can diffuse through it. Since the intercellular contacts of the capillary endothelium are more permeable to fluid than those of the pulmonary alveoli cells, fluid can escape into the connective tissue in heart failure and lead to interstitial edema .

literature

Ernst Mutschler , Hans-Georg Schaible, Peter Vaupel : Thews. Mutschler. Vaupel. Human anatomy, physiology, pathophysiology. 6th, completely revised and expanded edition. Knowledge Verlag-Ges., Stuttgart 2007, ISBN 978-3-8047-2342-9 .
Peter Lotz: Anatomy and Physiology of the Respiratory Tract. In: J. Kilian, H. Benzer, FW Ahnefeld (ed.): Basic principles of ventilation. Springer, Berlin et al. 1991, ISBN 3-540-53078-9 , pp. 3-45. (2nd, unchanged edition, ibid 1994, ISBN 3-540-57904-4 )

Web links

Wikibooks: Alveoli - learning and teaching materials

Wiktionary: alveoli - explanations of meanings, word origins, synonyms, translations

Individual evidence

^ Christopher B. Daniels, Sandra Orgeig: Pulmonary Surfactant: The Key to the Evolution of Air Breathing. In: News in Physiological Sciences . Volume 18, No. 1, 2003, pp. 151-157, doi: 10.1152 / nips.01438.2003 .

This text is based in whole or in part on the Alveole entry in Flexikon , a wiki from DocCheck . The takeover took place on October 14, 2007 under the then valid GNU license for free documentation .

[1] Christopher B. Daniels, Sandra Orgeig: Pulmonary Surfactant: The Key to the Evolution of Air Breathing. In: News in Physiological Sciences . Volume 18, No. 1, 2003, pp. 151-157, doi: 10.1152 / nips.01438.2003 .