Diagram of the alveoli with both cross-section and external view

An alveolus (plural: alveoli, from Latin alveus, "little cavity"), is an anatomical structure that has the form of a hollow cavity. Mainly found in the lung, the pulmonary alveoli are spherical outcroppings of the respiratory bronchioles and are the primary sites of gas exchange with the blood. Alveoli are particular to mammalian lungs;common in humans. Different structures are involved in gas exchange in other vertebrates.^[1] Look up alveolus, alveolar in Wiktionary, the free dictionary. ... A diagram of the alveoli, both in cross section and externally. ... A diagram of the alveoli, both in cross section and externally. ... Gas exchange or respiration takes place at a respiratory surface - a boundary between the external environment and the interior of the body. ... Human blood smear: a - erythrocytes; b - neutrophil; c - eosinophil; d - lymphocyte. ...

Location

The alveoli are found in the respiratory zone of the gasbags.

Anatomy

The lungs contain about 300 million alveoli, representing a total surface area of 70-90 square metres, each wrapped in a fine mesh of capillaries.

The alveoli have radii of about 0.05 mm but increase to around 0.1 mm during inhalation.

The alveoli consist of an epithelial layer and extracellular matrix surrounded by capillaries. In some alveolar walls there are pores between alveoli.

There are three major alveolar cell types in the alveolar wall (pneumocytes): The alveoli are lined with two types of cell, the Type I and Type II pneumocytes. ...

• Type I cells that form the structure of an alveolar wall
• Type II cells that secrete surfactant to lower the surface tension of water and allows the membrane to separate thereby increasing the capability to exchange gases.
• Type III cells that destroy foreign material, such as bacteria.

The alveoli have an innate tendency to collapse (atelectasis) because of their spherical shape, small size, and surface tension due to water vapor. Phospholipids, which are called surfactants, and pores help to equalize pressures and prevent collapse. Surfactants, also known as tensides, are wetting agents that lower the surface tension of a liquid, allowing easier spreading, and lower the interfacial tension between two liquids. ... Atelectasis is defined as a state in which the lung, in whole or in part, is collapsed or without air. ... Two schematic representations of a phospholipid. ... Surfactants, also known as tensides, are wetting agents that lower the surface tension of a liquid, allowing easier spreading, and lower the interfacial tension between two liquids. ...

Diseases

• Acute respiratory distress syndrome (ARDS) is a severe inflammatory disease of the lung. Usually triggered by other pulmonary pathology, the uncontrolled inflammation leads to impaired gas exchange, alveolar flooding and/or collapse, and systemic inflammatory response syndrome. It usually requires mechanical ventilation in an intensive care unit setting.

• Infant respiratory distress syndrome (IRDS) is a syndrome caused by lack of surfactant in the lungs of premature infants.

• In asthma, the bronchioles, or the "bottle-necks" into the sac are restricted causing the amount of air flow into the lungs to be greatly reduced. It can be triggered by irritants in the air, photochemical smog for example, as well as substances that a person is allergic to.

• Emphysema is another disease of the lungs, whereby the elastin in the walls of the alveoli is broken down by an imbalance between the production of neutrophil elastase (elevated by cigarette smoke) and alpha-1-antitrypsin (the activity varies due to genetics or reaction of a critical methionine residue with toxins including cigarette smoke). The resulting loss of elasticity in the lungs leads to prolonged times for exhalation, which occurs through passive recoil of the expanded lung. This leads to a smaller volume of gas exchanged per breath.

• Chronic bronchitis occurs when an abundance of mucus is produced by the lungs. The production of this substance occurs naturally when the lung tissue is exposed to irritants. In chronic bronchitis, the air passages into the alveoli, the broncholiotes, become clogged with mucus. This causes increased coughing in order to remove the mucus, and is often a result of extended periods of exposure to cigarette smoke.

• Cystic fibrosis is a genetic condition caused by the dysfunction of a transmembrane protein responsible for the transport of chloride ions. This causes huge amounts of mucus to clog the bronchiolites, similar to chronic bronchitis. The result is a persistent cough and reduced lung capacity.

• Diffuse interstitial fibrosis

• Lung cancer is a common form of cancer causing the uncontrolled growth of cells in the lung tissue. Due to the sensitivity of lung tissue, such malignant growth is often hard to treat effectively.

• Pneumonia is an infection of the alveoli, which can be caused by both viruses and bacteria. Toxins and fluids are released from the virus causing the effective surface area of the lungs to be greatly reduced. If this happens to such a degree that the patient cannot draw enough oxygen from his environment, then the victim may need supplemental oxygen.

• Cavitary pneumonia is a process in which the alveoli are destroyed and produce a cavity. As the alveoli are destroyed, the surface area for gas exchange to occur becomes reduced. Further changes in blood flow can lead to decline in lung function.

Acute respiratory distress syndrome (ARDS), also known as respiratory distress syndrome (RDS) or adult respiratory distress syndrome (in contrast with IRDS) is a serious reaction to various forms of injuries to the lung. ... Gas exchange or respiration takes place at a respiratory surface - a boundary between the external environment and the interior of the body. ... In medicine, systemic inflammatory response syndrome (SIRS) is an inflammatory state of the whole body (the system) without a proven source of infection. ... mechanical or forced ventilation is the use of powered equipment, e. ... Intensive care medicine or critical care medicine is concerned with providing greater than ordinary medical care and observation to people in a critical or unstable condition. ... Infant respiratory distress syndrome (RDS, also called Respiratory distress syndrome of newborn, previously called hyaline membrane disease), is a syndrome caused by developmental lack of surfactant and structural immaturity in the lungs of premature infants. ... The bronchioles are the first airway branches that no longer contain cartilage. ... Photochemical smog is the term to represent a multitude of chemical agents which are considered to be detrimental to the environment and health. ... Elastin is a protein in connective tissue that is elastic and allows many tissues in the body to resume their shape after stretching or contracting. ... Bronchitis is an inflammation of the bronchi (medium-size airways) in the lungs. ... A transmembrane protein is a protein that spans the entire biological membrane. ... Diffuse parenchymal lung disease (DPLD), also known as interstitial lung disease, refers to a group of lung diseases, affecting the alveolar epithelium, pulmonary capillary endothelium, basement membrane, perivascular and perilymphatic tissues. ... Lung cancer is a disease of uncontrolled cell growth in tissues of the lung. ... This article is about human pneumonia. ... This article is about biological infectious particles. ... Phyla/Divisions Actinobacteria Aquificae Bacteroidetes/Chlorobi Chlamydiae/Verrucomicrobia Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Nitrospirae Omnibacteria Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Bacteria (singular, bacterium) are a major group of living organisms. ... Cavitary Pneumonia is a disease in which the normal lung architecture is replaced by a cavity. ...

Additional images

Bronchial anatomy Image File history File linksMetadata Size of this preview: 775 × 600 pixel Image in higher resolution (2646 × 2048 pixel, file size: 1. ...

References

External links

• MeSH Pulmonary+Alveoli