 When you take your first sip of, say, beer, it of course ends up in your stomach. What happens next depends a lot on whether you've eaten or not. If you have eaten, the alcohol is effectively trapped in your stomach while it works to break up the solid food. Alcohol can be absorbed into the bloodstream through your stomach, but this happens relatively slowly. So your blood alcohol concentration, or BAC, also goes up relatively slowly while it's trapped in there. But if you haven't eaten, well, then alcohol passes quickly into the small intestine. And here it's absorbed into your bloodstream a lot faster, mainly because the small intestine has a much larger surface area. The layer of cells that line the inside of your small intestine is called the epithelium. The epithelium is composed of several different cell types, and together they're organised into little finger-like protrusions called villi, and they're covered by even smaller protrusions called microvilli. The particular cells that absorb nutrients and alcohol are called enterocytes. The presence of villi and microvilli massively increase the surface area to help absorb water and nutrients such as amino acids, sugars, fats, and alcohol out of the small intestine and into blood vessels. Because ethanol is only a small molecule, roughly three times as big as a water molecule, it can easily pass through the same channels and pores that water uses to enter the bloodstream. Everything you eat or drink that's absorbed through the digestive tract into the bloodstream goes to your liver first via a special system of veins called the portal system. Within the liver, the portal veins enter into a series of small channels that act like an exchange network, and some ethanol will be metabolised or broken down on the first pass through the liver. The rest is carried with the rest of the blood to the heart, through to the lungs for oxygenation, before being taken back to the heart and then pumped out through the arterial system to all organs in the body, including the brain, which is where the effects we generally associate with drinking happen.