10.4. Respiration. The lungs.

10.4.2. Working with texts.

In humans the circulatory system transports gases between the lungs and other parts of the body.

The lungs are located in the chest cavity, which is bounded at the bottom by the diaphragm. Air enters the body through the nostrils. From the nostrils, air passes through the nasal cavity and then the pharynx. From the pharynx air moves into the larynx (voicebox). From the larynx, air moves to the lungs through the trachea (windpipe). The trachea branches into 2 bronchi, one leading to each lung. Within the lung the bronchus separates into bronchioles. The bronchioles end in the alveoli. The alveoli are tiny air sacs, their shape resembles that of a grape.  

A thin layer of epithelial cells covers the inner surface of the alveoli. That is the surface where gases are exchanged. The O2 is diffused into the capillaries that cover the alveoli. CO2 travels in the opposite direction, from the capillaries to the alveoli, bronchiole, bronchus, and finally out of the body.  

10.4.3. Words with Latin and Greek origin