You are viewing an organ of the respiratory system and note the following tissues: folded mucosal layer containing simple cuboidal epithelium and smooth muscle, shifting into simple squamous epithelia. Identify the organ.

Respiratory bronchiole  

Explanation:

The respiratory bronchioles represent the narrowest airways within the lung, being continuations of terminal bronchioles that have approx. 0.5 mm in size. The epithelium of the respiratory bronchiole is composed of cuboidal ciliated cells and a small number of non-ciliated (secretory) Clara cells. The respiratory bronchioles lead into alveolar ducts composed of smooth muscle and connective tissue (i.e., elastin and collagen), connecting the respiratory bronchioles to the alveolar sacs.

when you breathe in, or inhale, your diaphragm contracts (tightens) and moves downward. this increases the space in your chest cavity, into which your lungs expand. the intercostal muscles between your ribs also enlarge the chest cavity. they contract to pull your rib cage both upward and outward when you inhale.