Your respiratory system enables you to breathe. It is divided between the upper and lower respiratory tracts. The upper respiratory tract includes the structures outside of your chest cavity--the nose, pharynx and larynx or voice box. The lower respiratory tract includes the trachea or windpipe, bronchi, alveoli and lungs.
Inspiration
Contraction of your diaphragm increases the volume of your chest cavity. It changes the air pressure between your chest cavity and the air outside your body; air flows through your upper respiratory tract and into your lungs. When you inhale air through your nose, your nose performs several functions. Tiny hairs in your nose filter out impurities. Tubular shaped structures in your nasal cavity warm and moisten the air you breathe. Nasal fluid and mucous trap particles, preventing them from going into your lungs. When you inhale air through your mouth, the air passes through your larynx, which also serves to remove debris, warm and humidify air. Your larynx prevents solids and liquids from going into your trachea.
Gas Exchange
The air you inhale through your mouth and nose flow to your left and right bronchi, serving your right and left lung. Each bronchi further divides into microscopic tubes delivering air to the alveolar sacs. The alveolar sacs are made of numerous alveoli, air filled structures where the exchange of carbon dioxide and oxygen take place. The oxygen in the air you breathe flows across the very thin membranes of the alveoli and the capillaries in your lungs. Oxygen is necessary to complete cellular respiration, or the conversion of your food into energy the cells can use. Oxygen binds with hydrogen to form water, which is then expelled from your body. Carbon dioxide is the waste product of cellular functions. It enters your blood and is transported into your lungs. Carbon dioxide in the capillaries of your lungs crosses the capillary and alveolar membranes, passing into your alveoli to be exhaled. Your lungs have about 300 million alveoli, which if opened up, cover nearly the size of a tennis court. This large surface area permits the fast exchange of oxygen and carbon dioxide in your lungs.
Expiration
When your diaphragm relaxes, it decreases the volume of your chest cavity and increases the pressure in your lungs. This causes air to flow out. Airflow stops when your diaphragm is completely relaxed; you are ready for another inhalation of air. Exercise increases the concentration of carbon dioxide in your blood. Chemical receptors sense this rise in carbon dioxide, relaying this information to your brain. Your brain signals your diaphragm and the muscles between your ribs to contract faster and with greater force, increasing your depth and rate of breathing. You will inhale and exhale more air at a faster rate to breathe in more oxygen and get rid of more carbon dioxide.
References
- “Anatomy & Physiology”; Gary Thibodeau, Ph.D. and Kevin Patton, Ph.D.; 2007
- “Exercise Physiology, Energy, Nutrition & Human Performance”; William McArdle, Frank Katch and Victor Katch; 2007
