Breathing is a process that is taking oxygen in (inhalation) and release the carbon dioxide out (expiration) of the body. The gas exchange is the movement of respiratory gases (oxygen and carbon dioxide) across the respiratory membranes; oxygen and carbon dioxide move in opposite direction (Breathing).

external image muscles.jpg
The two muscles that participate in breathing process are the intercostal muscle and the diaphragm. Intercostal muscle located between ribs, and the diaphragm muscles located between lungs and stomach ("Swallowing").

What occurs when you breath?

When you breath in, the intercostal muscle and the diaphragm muscle contract. The diaphragm stretches downwards, while the intercostal muscles expands outward with elevating ribs. Through this muscle movement, the volume of the thorax (part of body between neck and waist, where lungs located) increases. As the volume increases, the pressure inside decreases lower than the atmosphere which forces the inhalation.
When you breath out, the diaphragm and intercostal muscles relax. This movement increase the pressure in the thorax by reducing the volume of the thorax which causes the expiration ("The Breathing").
external image breathing.jpg

The diagram above shows how both inhalation and exhalation occurs.

Gas Exchange
During the gas exchange, oxygen and carbon dioxide are exchanged. As the pressure of oxygen in the air in the lung is higher than the pressure of oxygen in the blood cell, the oxygen diffuses into alveolies(tiny sacs), where the oxygen will travel on onto other parts of the body that require oxygen, through the blood stream. On the contrary, the pressure of carbon dioxide in the blood cell is higher than the pressure of the carbon dioxide in the air. Therefore the carbon dioxide diffuse out from the blood cell (Gas Exchange). The carbon dioxide moves into the aveolies, as an exchange with the oxygen that leaves the alveoli. Then, the carbon dioxide travels back out of the body out our noses and mouth.
When we breath in air, the air contains about 21% of oxygen. And when we breath there is about 17% of oxygen remaining. This means we use about 20% of oxygen that inhaled with the air (Gaseous Exchange).

Gas move from high pressured-areas to low pressured-areas. The pressure of oxygen is represented as PO2; the pressure of carbon dioxide is represented as PCO2.
The CO2 molecules move to the lungs through the capillary and into in the alveoli.
(mm Hg = the measurement of pressure)


At the same time, oxygen also moves into the alveoli of the lungs through capillary. However, as an exchange to carbon dioxide moving into the alveoli, the oxygen molecules move out from the alveoli to the capillary. This exchange keeps the blood oxygenated.


The oxygenated blood, created through the gas exchange of carbon dioxide and oxygen, now moves to the tissues around the body to remove carbon dioxide that is produced in the cellular metabolism.


Animation and explanation of the Respiratory System:

Work cited:

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"Chemical Burn or Reaction." University of Pennsylvania Health System. Web. 21 Feb. 2012. <>.

Diaphragm Movement
. N.d.
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Muscles of Inspiration
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