Ethanol must first enter the bloodstream
Ethanol is a water soluble compound—it dissolves readily in water-based solutions and once it is swallowed, it moves into water spaces throughout the body, including the bloodstream. Here is a brief review of what happens:
- Molecules of ethanol travel across the membranes made of epithelial cells that line the stomach and small intestine.
- Ethanol molecules move across the membrane via passive diffusion.
- Once on the other side of the gut cells, these small ethanol molecules then easily pass through the walls of the tiny capillaries that line the gut.
To review the details about ethanol absorption go to Module 1B.
Learn more about diffusion across a biological membrane.
Figure 4.1 Absorption of ethanol from the gut into the bloodstream. Ethanol molecules in the gut diffuse passively across epithelial cells, through the interstitial space, and then into nearby capillaries.
Ethanol travels through the bloodstream to the lungs
Ethanol, in its liquid form, travels in the capillaries to the veins, and then heads up to the lungs. It takes the same route that deoxygenated blood takes to become oxygenated. Refer to Figure 4.2 to follow the route that the ethanol takes to the lungs.
- Ethanol is carried by the venous circulation to the right side of the heart.
- Ethanol enters the right atrium (like a foyer), and then moves into the right ventricle (a pump).
- The right ventricle pumps the venous blood to the lungs.
- In the lungs, red blood cells unload carbon dioxide and pick up oxygen brought in by respiration (breathing).
- Some of the ethanol dissolved in the blood gets eliminated as a gas by the lungs during exhalation.
- Ethanol that remains in the blood returns to the left side of the heart (the atrium).
- The left atrium supplies blood to the left ventricle of the heart, which pumps the blood to the rest of the water-containing compartments and tissues of the body via the arteries.
- The branch of the circulatory system that moves blood between the heart and the lungs is called the pulmonary circulation, while the branch that moves blood throughout the rest of the body is called the systemic circulation.
Figure 4.2 Ingested ethanol travels from the gut to the liver before reaching the heart and lungs. Inhaled ethanol travels to the brain before it goes to the liver. Ethanol in the veins travels to the heart, then the lungs, where a portion is exhaled. The arterial side is red, the venous side is blue. Adapted from www.thepepproject.net.