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,
Body language of dogs tail, the ears, and the head/body. Tail-wagging is a common tail movement used by dogs to communicate. Additionally, ear flattening or heightening are typical movements made using the ears. In terms of the head/body, it is of interest to study turning of the head, as well as the overall posture of the dog. Because dogs communicate differently than humans, it is more difficult for humans to interpret their emotional states. By focusing on the combinations of motions made by dogs, and studying the aftermath of such sequences, humans are able to attribute different emotional states (i.e., contentment, fear, or aggression)