Pulmonary alveolus thin fluid coating within all alveoli. The fluid coating is produced by the body in order to facilitate the transfer of gases between blood and alveolar air. The surfactant is produced by the type II cells which are the most numerous cells in the alveoli, yet do not cover as much surface area as the squamous alveolar cells (a squamous epithelium). Type II cells also repair the endothelium of the alveolus when it becomes damaged. Insufficient surfactant in the alveoli can contribute to atelectasis (collapse of part or all of the lung). Without pulmonary surfactant, atelectasis is a certainty; however,
Cold and heat adaptations in humans air temperature from reaching the skin. There has been very little research done in the genetics behind adaptations to heat and cold stress. Data suggests that certain parts of the human genome have only been selected for recently. Research on gene-culture interaction has been successful in linking agriculture and lactose tolerance. However, most evidence of links between culture and selection has not been proven. Cold and heat adaptations in humans Cold and heat adaptations in humans are a part of the broad adaptability of "Homo sapiens". Adaptations in humans can be physiological, genetic, or cultural, which allow people to live