(4)	+Breathing+&+gas+exchange

====**Breathing** is the movement through inhalation and exhalation. The respiratory system moves air to nose, pharynx, larynx, trachea, and bronchus to the Alveoli where gas exchange is occurred. **Gas exchange** is the primary function of the lungs that includes the process of transferring the oxygen from the air that is inhaled onto the blood and the transfer of carbon dioxide from the blood into the exhaled air. This process mostly takes place in Thoracic Cavity (chest). ====

[[image:http://concept2.co.uk/assets/images/breathing1.jpg width="400" height="343" align="right"]]
====During this process, there are two muscles that are associated. The Intercostal muscles and the diaphragm. **Intercostal muscles** are the groups of muscles that are located between the ribs, to which two of the layers present are the external intercostal muscle(inhalation) and external intercostal muscle(exhalation). **The diaphragm** is located between the lungs and stomach. It separates the thoracic cavity from the abdominal cavity. ====

====During **inhalation**, the diaphragm and Intercostal muscles **contracts **(shrinks), therefore enlarging the external intercostal muscles. This enlargement causes to gather more oxygen. When these muscles contracts, the diaphragm pulls itself down and the intercostal muscles will affect to raise the ribs and elevate the sternum(series of bones connected with the ribs).The contraction of the diaphragm will lower the bottom border of the thorax(part of the humans between neck and abdomen contain the heart,lungs, etc.), and the intercostal muscles will raise the top border of the thorax, both resulting to increase the thoarcic volume but decreasing its pressure. ==== ====During **exhalation**, the diaphragm and intercostal muscles will **relax ** in oppose to inhalation. This movement will increase the pressure in the thorax by reducing the volume of the thorax which then causes the expiration. ====


 * Process of Gas Exchange **

Oxygenated air goes from the nose to the **pharynx, larynx, trachea, bronchus and alveoli.**
====**The PO2(partial pressure of oxygen)** in the alveloar space around the lungs is greater than the PO2 in the blood. Therefore by the process of diffusion, oxygen diffuses into red blood cells from air in the lungs. The bronchi carrying air subdivide into smaller branches called bronchiole, containing alveolar sacs. Through the alveolar sacs is the alveoli, where the gas exchange takes place. ==== ====**The PCO2(partial pressure of carbon dioxide)** in the lungs is less than the PCO2 in the blood, making CO2 diffusing out of the red blood cell into the air of lungs. The carbon dioxide moves into the alveolies, 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. ====

= = The Respiratory System media type="youtube" key="hc1YtXc_84A" height="315" width="560"