- Outer layer of cells embedded with keratin – Nucleus of an epithelial cell - Basement membrane -Connective tissue Epidermal layer of the skin - Mucus - Cilia (only some mucous membranes have cilia) - Mucus- producing cell Mucous membrane FIGURE 14.3 Epithellal Barriers Cells of these barriers are tightly packed together and rest on a layer of thin fibrous material, the basement membrane.

Where are exchange epithelial cells found? What did the alveoli look like on the slide, and why is their structure important? Do these cells have tight junctions? Explain why.

The structure in the lungs known as the respiratory membrane is where gases are exchanged- oxygen leaves the lungs and enters the blood, and carbon dioxide leaves the blood and enters the lungs. The respiratory membrane is composed of two extremely thin layers of simple squamous epithelium. Explain how the structure of the respiratory membrane follows its function.

what is the oxygen pressure in alveoli, arterial blood and tissue? what is the direction of oxygen diffusion in lugs and tissue?

Certain medical conditions cause the simple squamous epithelium in the lung to thicken. Predict the consequences of this thickening?