Function: Gas exchange between living organisms and the environment.
       Deliver air to the lungs:
  O2 from lungs to blood
  CO2 from blood to lungs

Structure:
 Nose: Nasal Cavity- main use for breathing in and out. Nasal cavity is   cleaned, moistened and warmed to prevent injury to membranes in   the lungs.
  *Mouth breathing brings cold and unfiltered air to lungs and   creates a dry lining of the mouth and throat.

 Pharynx: throat- incoming air. adenoids & tonsils (lymphatic tissue)
  where nasal cavity and mouth meet.
 
 Larynx: voice box- guards entrance for the trachea.
  *contains vocal cords. (boys grow longer to 1 1/4inches for    deeper  voice)(girls is 3/4) adamís apple (lump of      cartilage) also grows.
  * adamís apple in frontof trachea, also grows for men.
  *glottis- opening to windpipe, slit in larynx.
  *epiglottis- flap to cover glottis, stops food from entering into the    trachea.
 
 Trachea: windpipe- flexible tube with u-shaped rings of cartilage.
  Back tube is the esophagus- leading to the stomach: which is    why the trachea is flexible, it collapses for food to pass by.
 
 Bronchi: two tubes branch from the trachea to the lungs
  singular- bronchus
 
 Lungs: cone shaped soft bags. has blood vessels, lymphatic vessels    and nerves.
  *pleura- thin membrane covering lungs.
  *pneumonia- infection caused by infection or bacteria in the     lungs.
 
 

 Bronchioles:  smaller branches of bronchi within the lungs.
  *bronchitis- inflamation of bronchial tubes.
  *asthma- bronchial spasms, decr5ease air movement & air    trapped in alveoli.
 
 Alveoli: tiny air sacs exchange gases between air and blood.
  300 million in lungs. fill up like balloons when breath in.
  capillaries- blood vessels
 
 Diaphragm: Flat sheet of muscle that seperates the chest and     abdominal cavities.
  *contracts and increases size in chest cavity and air gets     vacuumed in; hi - lo pressure.
  * hiccup- sudden contraction of diaphragm and vocal cords    snap shut.
 

Breathing: contraction and relaxation of muscles.
  pressure and volume of air moves from high concentration to    low.
 inspiration- diaphragm contracts
 expiration- diaphragm relaxes

 *Oxygen attatches to hemoglobin and then spreads out throughout   the body.

 *rate of breathing is controlled by the medulla oblongata. decided by   CO2 in the blood ( increase of CO2 levels increases breathing)