GLOSSARY

Alveolus (pl. alveoli): Small saclike structure. In the lungs, the alveolus is one of millions of tiny balloon-like structures located at the ends of the bronchioles where oxygen is exchanged for carbon dioxide. Air enters through the nose or mouth, down the trachea, through the bronchi, further into the bronchioles, and finally into the alveoli.

Capillary: The smallest type of blood vessel in the body, connecting the arterioles and venules. Different types of capillaries vary by location in the body; continuous are found in the muscle, lung and central nervous system; sinusoid are found in the liver, spleen and bone marrow; fenestrated are located in the endocrine glands, the intestine, gallbladder and the kidneys.

Erythrocyte (red blood cell, RBC): The major cellular element of the circulating blood, reddish in color and biconcave (indented on both sides) in shape, approximately seven micrometers in diameter, and responsible for oxygen delivery to the body's cells.