trachea and lungs

trachea

framework of smooth muscle about 16 - 20 rings of cartilage and ensures trachea remains open

epiglottis (2)

prevents food from entering trachea

lower trachea

branches into bronchi that leads to lungs and terminates alveoli

lungs

composed of abt 200 million alveoli

RBC pass through capillaries > oxygen enters RBC > binds to hemoglobin

CO2 leaves capillaries > enters alveoli when breath taken

CO2 reaches alveoli as bicarbonate ions

inhalation

ribs / diaphragm contract and increases volume of chest cavity

when increased, it reduces air pressure > air rush into alveoli > force to expand

exhalation

ribs / diaphragm relax > chest cavity diminish > internal air pressure increases
compressed air force alveoli to close and air flows out