at the end of the bronchi tree, there are alveoli, right?

Question

When arteries and veins come together, in between comes capillaries. The capillaries give the oxygen to the body tissues. When the pulmonary vein and the pulmonary artery come together they form on the alveoli. So are there capillaries on the alveoli too? Since I thought that the capillaries was thin enough so that it could take oxygen from the lungs all by itself. But instead the alveoli does that job. Is the alveoli some sort of super capillarie?

Answer 1

Yes - the alveoli are at the end of the branching tree of bronchi/bronchioles.

They are essentially a sac. The air can come from the bronchi, via bronchioles, into the sac and be exposed to the capillaries.

As the capillaries surround the alveoli and bring blood from the pulmonary arterioles the exchange of gas occurs.

The blood leaves in the venules (which become veins) and bring the (now oxygenated) blood back to the heart in the pulmonary veins.

See the wikipedia

Answer 2

Yes, at the end of bronchi tree are Alveoli. Alveoli are the site of gas exchange.

Alveoli are NOT some sort of super capillaries. Alveoli are envelope by networks of capillaries. Gas exchange occurs because of Partial pressure and Diffusion. The very thin membrane between alveoli and capillaries make the oxygen and carbon dioxide pass easily.

"The alveoli are the final branchings of the respiratory tree and act as the primary gas exchange units of the lung. The gas-blood barrier between the alveolar space and the pulmonary capillaries is extremely thin, allowing for rapid gas exchange. To reach the blood, oxygen must diffuse through the alveolar epithelium, a thin interstitial space, and the capillary endothelium; CO2 follows the reverse course to reach the alveoli."

See the drawing:
http://www.phschool.com/atschool/science_activity_library/images/respiratory_system_alveoli.jpg

http://www.phschool.com/atschool/science_activity_library/images/respiratory_system_gas.jpg

http://www.besthealth.com/besthealth/bodyguide/reftext/images/Alveoli_Capillaries.jpg

http://www.fm120.com/english/photo/alveoli2.jpg


Check these sites if you want to know more:
http://science.nhmccd.edu/biol/respiratory/alveoli2.htm

http://people.eku.edu/ritchisong/301notes6.htm

http://oac.med.jhmi.edu/res_phys/Encyclopedia/Alveoli/Alveoli.HTML

http://www.msu.edu/user/terbrack/817Redesign/frames/capillariesFrame.htm

http://ithacasciencezone.com/biozone/lessons/05human/alveoli.htm