Alveoli Capillaries

Alveoli Capillary Alveoli HIGH O2 Capillary LOW O2 Capillary HIGH O2 Alveoli LOW O2

O2 Capillary HIGH O2 Body cells LOW O2

CO2 Body Cells HIGH CO2 Capillary LOW CO2

POINT: 1.Diffusion is the key to many processes in your body. 2.Concentration Gradients needed for diffusion.

The Importance of Oxygen A.) ALL the cells in your body need a steady supply of oxygen. How is this supply delivered? B.) When you inhale, air containing oxygen moves down your trachea. 1.) Your trachea splits into 2 tubes that lead into your 2 lungs. 2.) Once inside the lungs, the tubes branch off into smaller and smaller tubes that eventually end in air sacs called alveoli. Note: Technically O2 is still outside the body…

The Importance of Oxygen C.) The alveoli are COVERED with tiny blood vessels called capillaries.

2.) The concentration of oxygen in the blood within these capillaries is LOW while the concentration of oxygen in the alveoli is HIGH. 3.) Oxygen molecules DIFFUSE out of the alveoli and into the blood in the capillaries.

D.) ALL the capillaries around the alveoli in the lungs empty into a large blood vessel that empties into the heart. 1.) The heart contracts, pushing the oxygen- containing blood out into arteries which branch into smaller & smaller vessels throughout the ENTIRE body.

E.) Once the blood is in vessels that are small enough (capillaries) to be surrounding cells, oxygen diffuses OUT of the blood and INTO the surrounding cells.

The Importance of Oxygen 1.) WHY? Because the cells in your body are constantly using up oxygen in the process of cellular respiration! Therefore, by the time blood containing oxygen comes around again, they have a LOW oxygen concentration and are ready for more!

Gas Exchange A.) But wait! At the same time that oxygen diffuses into the cells, a waste product of cellular respiration needs to diffuse out or it will kill the cell. This waste product is carbon dioxide!

1.) Since carbon dioxide is being produced inside the cell as a waste, its concentration is HIGH in the cell. It diffuses OUT of the cell and into the blood which has a LOW carbon dioxide concentration.

Gas Exchange B.) The blood that has undergone “gas exchange” (oxygen & carbon dioxide are “trading places”) moves through vessels and is returned to the lungs (through the action of our contracting heart). This blood ends up back in the capillaries around the alveoli of the lungs. 1.) This blood has a HIGH concentration of carbon dioxide and a LOW concentration of oxygen.

2.) Therefore, carbon dioxide diffuses out of the blood and into the alveoli at the same time that oxygen moves out of the alveoli and into the lungs.

Gas Exchange 3.) You then exhale, breathing out the carbon dioxide….and then you inhale to get more oxygen for the next round of oxygen depleted blood that will be coming through your lungs…and then you exhale the carbon dioxide that diffuses out of the blood…and then you inhale…you get the idea.

Gas Exchange C.) The entire process that was just described RELIES ON DIFFUSION. You depend on differences in concentration inside and outside your cells and body surfaces move the molecules you need in and the wastes you don’t need out.

SA SA