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 warm them during the colder nights . The only mechanism the human body has to cool itself is by sweat evaporation. Sweating occurs when the ambient air temperatures is above 28 °C (82 °F) and the body fails to return to the normal internal temperature. The evaporation of the sweat helps cool the blood beneath the skin. It is limited by the amount of water available in the body, which can cause dehydration. Humans adapted to heat early on. In Africa, the climate selected for traits that helped us stay cool. Also, we had physiological mechanisms that reduced the