Respiratory System

Cells continually use oxygen (O₂) for the metabolic reaction that release energy from nutrient molecules and produce ATP (Adenosine triphosphate). At the same time, these reaction releases carbondiaxide (CO₂). Because an excessive amount of CO₂ produces acidity that can be toxic to cell, excess CO₂ must be eliminated quickly and efficiently. The two systems that cooperate to supply O₂ and eliminate CO₂are the Cardiovascular System and Respiratory System. The Respiratory System provides for gas exchange -- intake of O₂ and elimination of CO₂-- whereas the cardiovascular system transport blood containg the gases between the lungs and blood cells and both the systems regulate the blood pH.

Structurally, the respiratory system consists of the nose, pharynx (throat) are in the upper part and larynx (voice box), trachia (windpipe), bronchi, lungs are in the lower part. Functionally, it consists two parts: (a) The conducting portion consists of a series of interconnecting cavities and tubes both out side and within the lungs -- the nose pharynx, larynx, trachea, bronchi, bronchioles and terminal bronchioles -- that filter, warm and moisten air and conduct it into the lungs. (b) The respiratory portion consistsof tissues within the lungs where gas exchange occures -- the respiratory bronchioles, alveolar ducts, alveolar sacs and alveoli, the main sites of gas exchange between air and blood. The volume of the conducting portion in the adult is about 150 mL; that of the respiratory portion is 5 to 6 liters.