Why alveoli surrounded by capillaries

Inside the body cells the chemical reaction gives off heat and other forms of energy. This energy provides the power we need to talk and move and think. When a fire burns, carbon dioxide is formed. When a body cell combines sugar with oxygen to get energy, carbon dioxide is formed there, too.

But too much carbon dioxide could poison a cell. They need some way to get rid of carbon dioxide. The blood brings oxygen to the body cells and takes away their carbon dioxide. The blood that travels back to the heart and lungs is dark red. It has picked up carbon dioxide from the body cells, and it has left most of its oxygen with the cells.

This is the blood that the heart pumps into the lungs. The carbon dioxide in the blood is exchanged for oxygen in the alveoli. These tiny air sacs in the lungs are only one cell thick and they are surrounded by capillaries that are also only one cell thick. Blood from the heart flows through these capillaries and collects oxygen from the alveoli. At the same time, carbon dioxide passes out of the capillaries and into the alveoli. When you breathe out, you get rid of this carbon dioxide.

The bright red, oxygen-rich blood is returned to the heart and pumped out to the body. There is an exchange of gases between the alveoli and their surrounding capillary blood vessels. Oxygen diffuses from the alveoli into the blood.

Carbon dioxide diffuses from the blood into the alveoli. These three features are particularly important to our lungs for efficient gas exchange. Most of them also apply to other exchange surfaces such as the small intestine, body tissues and placenta. Gas exchange in the lungs The cells in the body need oxygen to release energy from food efficiently by carrying out aerobic respiration.

The lungs Air gets from the mouth and nose to the lungs through the windpipe trachea. Thin lining: the lining of the alveoli is very thin so that gases can quickly diffuse through it. In addition, a small fraction of the blood pumped from the heart Function of the Heart The heart and blood vessels constitute the cardiovascular circulatory system. Merck and Co. From developing new therapies that treat and prevent disease to helping people in need, we are committed to improving health and well-being around the world.

The Manual was first published in as a service to the community. Learn more about our commitment to Global Medical Knowledge.

This site complies with the HONcode standard for trustworthy health information: verify here. Common Health Topics. Biology of the Lungs and Airways. Test your knowledge. Coughing up blood from the respiratory tract is called hemoptysis. Which of the following is the most likely cause of hemoptysis in adults?

More Content. Gas Exchange Between Alveolar Spaces and Capillaries The function of the respiratory system is to move two gases: oxygen and carbon dioxide. Ventilation is the process by which air moves in and out of the lungs.