I. Essay pp. 3-5
II. References p. 6
The diaphragm is a muscle in the chest cavity that contracts and relaxes according to signals received by the respiratory center in the brain. In doing so, the diaphragm changes the pressure in the cavity. When the diaphragm contracts, it increases the volume of the chest cavity and lowers the air pressure, thus, air rushes in. This is called inhalation. Exhalation is caused by the relaxation of the diaphragm, which decreases the volume in the chest cavity and increases the air pressure. This causes air to rush out.
Air passes the nostrils and enters the nasal passages where it is warmed, moistened and filtered, by the hairs, mucous, and blood vessels, which line the passages. Hairs collect dust and germs, mucous moistens the air, and the blood vessels warm the air.
The pharynx is the next structure the air comes in contact with, then larynx (voice box). Air passes the vocal chords and the epiglottis. From there its to the trachea, which branches out into the left and right bronchial tubes, which each branch out and become smaller and smaller. At the end, there is a tiny group of tubes called bronchioles.
Each bronchiole ends in a cluster of sacs called the alveoli. The alveoli contain respiratory surfaces (thin, moist, and loaded with blood vessels). Gas exchange occurs between the blood cells and the alveoli. Smoking brings in particles to the alveoli. These particles get in the way of gas exchange and reduce the amount of oxygen that the cells get.
There are actually four stages of gas exchange:
l.Breathing - air in and out of lungs
2.External respiration gas exchange between blood and air from environment in the alveoli
3.Transport of oxygen to cells and carbon dioxide away from the cells 4.Internal respiration gas exchange between blood and internal cells The point of breathing is to get rid of carbon dioxide and to...