In point form:

• oxygen is inhaled into the body through the nose, rib muscles push up and out and diaphram moves down to create lower pressure in the lungs, air flows in
• air is warmed in the nose pushed back to the pharynx (throat)
• air then skips past the eppiglottis and the larynx, down the trachea, into one of the the bronchi, to the bronchial tubes, in the bronchiols, in the air sacs, and to the alveoli
• When oxygen reaches the alveoli it diffuses through the one cell thick wall and attaches itself to a molecule of hemoglobin which is carried on the red blood cells
• the red blood cell travels in the pulmonary vein to the left atrium and to the left ventricle where it is pumped out through the aorta to the body cells
• the red blood cell travels through arteries until it reaches smaller arteries called capillaries
• at the capillaries the the oxygen diffuses out of the hemoglobin through the intercellular fluid and into the body cell so aerobic cellular respiration can take place
• carbon dioxide is a product of cellular respiration
• it diffuses out of the cell through the intercellular fluid and into the plasma of the blood, but it travels as a bicarbonate ion
• it travels through veins to get back to the heart
• it enters the right atrium then the right ventricle and is pumped through the pulmonary artery to the lungs
• when it reaches the lungs carbon dioxide comes out of the bicarbonate ion and diffuses back into the alveoli and is forced out by the relaxing of the diaphram and rib muscles
• the carbon dioxide travels from the alveoli to the air sacs to the bronchiols to the bronial tubes to the connecting bronchi to the trachea past the larynx and eppiglottis and past the pharynx and out the nose

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