RESPIRATORY SYSTEM OF HUMANS:

In humans and other animals, the anatomical features of the respiratory system include airways, lungs, and the respiratory muscles. Molecules of oxygen and carbon dioxide are passively exchanged, by diffusion, between the gaseous external environment and the blood. This exchange process occurs in the alveolar region of the lungs.

The primary function of the respiratory system is to supply the blood with oxygen in order for the blood to deliver oxygen to all parts of the body. The respiratory system does this through breathing. When we breathe, we inhale oxygen and exhale carbon dioxide. This exchange of gases is the respiratory system's means of getting oxygen to the blood.

The Pathway

• Air enters the nostrils
• passes through the nasopharynx,
• the oral pharynx
• through the glottis
• into the trachea
• into the right and left bronchi, which branches and rebranches into
• bronchioles, each of which terminates in a cluster of
• alveoli

Only in the alveoli does actual gas exchange takes place. There are some 300 million alveoli in two adult lungs. These provide a surface area of some 160 m² (almost equal to the singles area of a tennis court and 80 times the area of our skin!). 

Parts of the respiratory system

Lung

 The lungs are the main organs of the respiratory system. In the lungs oxygen is taken into the body and carbon dioxide is breathed out. The red blood cells are responsible for picking up the oxygen in the lungs and carrying the oxygen to all the body cells that need it. The red blood cells drop off the oxygen to the body cells, then pick up the carbon dioxide which is a waste gas product produced by our cells. The red blood cells transport the carbon dioxide back to the lungs and we breathe it out when we exhale.

Trachea
 The trachea (TRAY-kee-uh} is sometimes called the windpipe. The trachea filters the air we breathe and branches into the bronchi.

Bronchi     

The bronchi (BRAHN-ky) are two air tubes that branch off of the trachea and carry air directly into the lungs.

Diaphragm 

Breathing starts with a dome-shaped muscle at the bottom of the lungs called the diaphragm (DY-uh-fram). When you breathe in, the diaphragm contracts. When it contracts it flattens out and pulls downward. This movement enlarges the space that the lungs are in. This larger space pulls air into the lungs. When you breathe out, the diaphragm expands reducing the amount of space for the lungs and forcing air out. The diaphragm is the main muscle used in breathing.