Complex sentence: Found in the lung parenchyma, the pulmonary alveoli are the dead ends of the respiratory tree, which outcrop from either alveolar sacs or alveolar ducts, which are both sites of gas exchange with the blood as well.
Split into simpler sentences: Found in the lung parenchyma, the pulmonary alveoli are the dead ends of the respiratory tree. They outcrop from either alveolar sacs or alveolar ducts, which are both sites of gas exchange with the blood as well.