The Anatomy of the Pulmonary System
Just like people, an equine athlete is only as good as his ability to breathe. Breathing is actually a very simple term for a rather complex act. The equine athlete must be able  to inspire enough air so that sufficient amounts of oxygen can be delivered  to his lungs. When the horse inhales, his diaphragm, a large muscle that separates the abdomen from the chest, contracts. This creates a vacuum, much like drawing back the plunger in a syringe. The vacuum, or negative pressure, causes air to flow into the lungs. (For a demonstration, use a turkey baster and place it under water. When you squeeze the bulb of the turkey baster, you cause  a negative pressure, or vacuum in the body of the turkey baster. Since nature abhors a vacuum, water rushes in to fill the empty space. In both the equine and human (and most mammels), the negative pressure in the chest generated by the contraction of the diaphragm causes air to passively flow into the lungs via the trachea, or breathing tube. The trachea  branches off into the right and left main bronchus, which then go to their respective lung. When the bronchi reach the lung, they branch off into smaller and smaller tubes calles bronchioles. (Think of the trachea being the trunk of a tree, with 2 main branches {the bronchi}, and tons of tiny twigs {the bronchioles}). The bronchioles continue to branch off and get tinier and tinier until they terminate into tiny little sacs, called alveoli. Surrounding each alveoli are tiny tiny blood vessels called capillaries. Oxygen diffuses or crosses from the alveoli into teh capillary, and in exchange the capillaries release carbon dioxide, which diffuses or crosses into the alveoli. This part of breathing is called exchange. Exhaling causes the process to be reversed. The diaphragm relaxes, causing the chest cavity to "shrink." This causes carbon dioxide to be pushed out from the alveoli, to the bronchioles, through the bronchi and the trachea and out the nose and/or mouth. Exhaling, or getting rid of carbon dioxide is called ventilation. The process of getting oxygen to body tissues is called oxygenation. So next time you and your horse take a deep breath, remember it's not as easy as it looks!
1. bucchal cavity
2. nasal cavity
3. inferior maxillary sinus
4. superior maxillary sinus
5. frontal sinus
6. guttural pouch
7. pharanyx
8. trachea
9. bronchus
10. alveolus
11. lungs
12. larynx
a. trachea
b. cartiledge
c. vocal cords
d. epiglotis sinus