Tags: Anatomical Structure.
Type I pneumocyte cells (also called type I alveolar cells or squamous alveolar cells) are extremely attenuated cells that line the alveolar surfaces of the lungs. They cover 97% of the alveolar surface with type II pneumocytes covering the remainder. These cells are so thin (sometimes only 25 nm) that the electron microscope was needed to prove that all alveoli are covered with an epithelial lining.