Male Speaker: Presented here is a microanatomy of the lungs and its components alveolar sacs are the terminal portions of the breathing tube system composed of up to 30 tiny air patches or alveoli they provide it along a total surface area of about 850 sq feet for the exchange of gases. Alveoli walls composed of a single layer of cells and the thin boundaries of capillaries a barrier only 125,000 of an inch thick are all the separate blood and air, exchange of carbon dioxide and oxygen across this barrier is completed in only a fraction of a second terminal bronicles that carry air to and from alveolar sacs cells lining bronchiole walls bears sillier my -- hairs whose beating action prevents large dust particles from entering the alveolar sacs.

Macrophages cells on the inner alveolar surface ingest and destroy dust so it another foreign particles, these cells are the body's main lined of defense against the air borne bacteria drawn into the lungs. Connective tissue fibers form a frame around the alveoli and support the delicate walls. Lymph vessels carry excess tissue fluid away from the alveoli. Pulmonary venous take oxygen rich blood back to the heart pulmonary arterioles conduct carbon dioxide rich oxygen depleted blood to the alveoli.

Blood capillaries from a mesh work around the alveoli as blood flows through the capillaries it loses carbon dioxide and takes up oxygen and changes from dark to bright red in color.