Today we're going to journey down the respiratory tract.  First, though, we need to shrink you down a bit...

There!  You're now the size of an oxygen molecule, and feel a warm, humid draft as you're inhaled.  The following is what you'll see along the way (click links for pictures and videos):

Nares (nostrils): You waft through the nasal openings, barely inching between  hairs meant to keep particles out. This begins the upper airway.

Nose: It's not just an organ of smell, it also aids in phonation and easily lets air in.  It's also the first line of defense against inhaled particles.   

Epithelial cells: You'll see these cells lining the air passages from the oropharynx to the respiratory bronchioles. Their main function is protection of underlying tissue and secretion.  Note the wavelike movement of  hair-like structures on the surfaces.

Goblet cells: These are specialized epithelial cells that are randomly scattered along the way. Their job is to secrete mucin, which dissolves in water to form mucus.

Mucus:  This is formed by goblet cells and traps particles in inspired air to prevent them from getting to the lungs.  It then rides up on those fine hair-like structures to the mouth.  Once in the mouth it's called sputum.

Cilia:  These are those fine hair-like structures referred to above.  They wave in rhythmic fashion and act as an escalator to move mucus to the mouth. Each ciliated cell has 200 cilia, and there are 1 to 2 billion cilia per square centimeter.

Nasal septum: This is what divides the two nasal passages from the nare to the nasopharynx.

Vestibule: This is the main cavity of the nose. Air is warmed to 98.6° Fahrenheit and humidified.

Turbinates: These are three bone-like shelves that project into the nasal cavity from the lateral wall.  They help with the sense of smell and warm and humidify inspired air.    

Pharynx: This is a funnel shaped passage where are travels from the nasal cavity to the larynx. It too aids in phonation. Both food and air travel this way.

Nasal pharynx: This is the upper portion of the pharynx. 

Oropharynx: This is the middle portion of the pharynx, and from here you travel to the larynx.  Look down!  That dark opening is called the glottis, and those white objects on either side are the vocal cords. 

Vocal cords: These are only open when you inhale. This is another means to keep particles out of the lungs. As air brushes past them when you breathe out they vibrate, creating sound. 

Epiglottis: This is the object projecting upward and guarding the opening to the

glottis.  When you swallow it lies down to keep food out of the lungs.