Figure 7 Control group of bronchial asthma model (hematoxylin and eosin, 400). Light microscopic study showed the normal histological picture of lung tissues. It consisted of respiratory bronchioles, alveolar ducts, sacs, and thin-walled alveoli. The alveoli were composed of a single layer of squamous epithelium. A thin layer of connective tissue and capillaries were present between alveoli.