Alveolar surface

If particles reach and become deposited in the alveoli, they tend to stay imbedded in the fluid on the alveolar surface or move into the lymph nodes. The one mechanism by which particles are physically resuspended and removed from the AI region is coughing. For modeling purposes, the AI region is divided into three subcompartments to represent different clearance rates, all of which are slow. 

The collapsing pressure (P) is proportional to the alveolar surface tension (ST) and inversely proportional to the radius (r) of the alveolus. In other words, the greater the surface tension and the smaller the radius, the greater the collapsing pressure. 

Pulmonary i Respiratory muscle strength i Chest wall compliance i Total alveolar surface i Vital capacity i Maximal breathing capacity... 

Species Body Weight (kg) Lung Volume (ml) Minute Volume (ml min-1) Alveolar Surface Area (m2) Lung Volume % Surface Area Minute Volume % Lung Volume Minute Volume % Surface area... 

Vitamin C (VC, L-ascorbic acid) is known to be essential for many enzymatic reactions. Sodium-dependent VC transporters (SVCT), SVCT1 and SVCT2, were recently identified and reported to be localised in the apical cell membrane of AECs in the lung of adult rats. These results suggest that SVCT proteins could transport the reduced form of VC from the airway/alveolar surface liquid into respiratory epithelial cells [106],... 

The situation is, however, different in the alveolar region of the lung where the respiratory gas exchange takes place. Its thin squamous epithelium is covered by the so-called alveolar surface liquid (ASL). Its outermost surface is covered by a mixture of phospholipids and proteins with a low surface tension, also often referred to as lung surfactant. For this surfactant layer only, Scarpelli et al. [74] reported a thickness between 7 and 70 nm in the human lung. For the thickness of an additional water layer in between the apical surface of alveolar epithelial cells and the surfactant film no conclusive data are available. Hence, the total thickness of the complete ASL layer is actually unknown, but is certainly thinner than 1 gm. 

Scarpelli EM (2003) Physiology of the alveolar surface network. Comp Biochem Physiol A Mol Integr Physiol 135 39-104... 

The alveolar epithelium consists of so-called Type I and Type II cells. Type I cells cover over 90% of the alveolar surface, have a large surface, and are thin. Type II cells are larger in numbers but are small. Therefore, they cover only about 7% of the surface of the alveoli. Type II cells produce the phospholipids that make up the surfactant layer. 

Ideally, toxicology studies should mimic, as near as possible, human exposure. Thus, both the route of administration and the exposure should, where possible, be similar to that in man. The classic route of administration in man is oral and thus most toxicology studies are conducted by the oral route. Elowever, parenteral routes may be used either to mimic the clinical route or to ensure exposure. The administration of some medicines is directly on to highly differentiated surfaces such as the alveolar surface of the lungs or the skin. It is, therefore, important to assess the topical irritancy, absorption and subsequent systemic toxicity following such applications. It should be remembered that some compounds, for example, chlorinated hydrocarbons, may be more toxic when given by the inhalation route than when given orally or may directly affect... 

The lower respiratory tract (pulmonary region or alveolar ducts and sacs) is the area where gas exchange occurs. Alveolar sacs, clusters of two or more alveoli, branch from alveolar ducts. It is generally considered that there is a total of approximately 300 million alveoli in the lungs of adult humans. The total alveolar surface area in the lungs of adult humans is... 

T e II cells (granular pneumonocytes) are distributed throughout the alveoli between T e I cells. Although they are more numerous than T e I cells, they are cuboidal in shape and occupy far less of the alveolar surface area. The prime function of this cell is the production of pulmonary surfactant, and it is generally less susceptible to injury than the Type I cell. 

Respiration into the lung alveoli is the most important hazard for plant workers. The average lung has 300 million alveoli with a surface area of about 70 m, which is designed for rapid gas exchange. This alveolar surface area is about 40 times larger than the external skin area of a person. There has been a systematic study of the major air pollutants associated with the protection of industrial workers, as monitored by the OSHA and the ACGIH, and there are three well-documented measurements and databases ... 

Despite the fact that most of the alveolar surface is composited of alveolar epithelium, three primary types of cells are present in the alveoli type I alveolar cells, type II alveolar cells, and alveolar macrophages. Type I alveolar cells are also referred to as squamous pulmonary epithelial cells and are the continuous lining of the alveolar sac. Type II alveolar cells are also referred to as septal cells. Type II alveolar cells secrete the alveolar fluid that is necessary to keep the surface moist and to maintain surface tension of the alveolar fluid surface tension is necessary to keep the alveoli from collapsing. Alveolar fluid is a suitable environment for proteins when compared to the low pH and high protease levels associated with the intestine... 

For the analysis of extracellular glycolipids of respiratory tract, we have chosen the acellular material lining the alveoli of mammalian lungs. This unique lipid-protein mixture, responsible for the reduction of alveolar surface forces during respiration,... 

The pulmonary alveolar epithelium is comprised of two morphologically distinct cells, type I and type II cells. Type I cells are extremely large, squamous cells that make up 95% of the alveolar surface. Type II cells are smaller cuboidal cells that secrete and recycle surfactant and cover the remaining 5% of the alveolar surface. Mechanical distention of fetal lung tissue has been shown to stimulate expression of the type I cell phenotype and inhibit expression of the type II phenotype. Lumenal mechanical stim-... 

Costa DL, Kutzman RS. 1985. Compensatory increase in diffusing capacity and alveolar surface area in the rat as a response to acrolein injury. Am Rev Respir Dis 131(4 Suppl.) A200. 

Type I cells comprise 8-11% of the structural cells found in the alveolar region and yet cover 90-95% of the alveolar surface. Their major function is to allow gases to equilibrate across the air-blood barrier and to prevent leakage of fluids across the alveolar wall into the lumen. The type I epithelium is particularly sensitive to damage from a variety of inhaled toxicants due to their large surface area. Moreover, their repair capacity is limited because they have few organelles associated with energy production and macromolecular synthesis. 

The alveolar surface represents a thin liquid film formed at the interface between the alveolar gas phase and a liquid hypophase covering the epithelium. This film is stabilised by the alveolar surfactant (AS), consisting mainly of phospholipids and proteins. AS plays an important role in alveolar stabilisation in the process of breathing. It is known that AS components exist as individual molecules and as various lipid and protein/lipid micellar structures present in the so-called hypophase and, according to some researchers, form a continuous lipid monolayer at the water/air interface [e.g. 1-4]. 

The microscopic foam bilayer proved to be an appropriate model for investigation of alveolar surface and alveolar stability as well [21]. This approach is in agreement with the findings of Scarpelli that at birth the lung surfactant takes the form of intraalveolar bubbles with formation of foam films [e.g. 2,22,23],... 

These studies of AS multilayer films as well as of lipid bilayers give reason to propose a new hypothesis of the structure of the alveolar surface. According to it the continuous lipid monolayer of the alveolar surface is in contact with the multilayer or with the membrane of epithelial cells situated under it, i.e. at the contact sites as well as between the individual... 

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