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 to having more cells, and have a smaller surface area compared to smaller individuals, which reduces heat loss. A study by Frederick Foster and Mark Collard found that Bergmann’s rule can be applied to humans when the latitude and temperature between groups differ widely. Allen’s rule is a biological rule that says the limbs of an endotherm is either shorter in cold climates or longer in hot climates. Limb length affects the body’s surface area, which helps with thermoregulation. Shorter limbs help to conserve heat, while longer limbs help to dissipate heat. Marshall T. Newman argues that this can be