system
Given the following post, respond as if you're commenting on Reddit:
human
Is the amount of caffeine absorbed into the bloodstream dependant on the same variations that alcohol absorption is based upon?
gpt
Well, it's dependent on the same mechanisms in your GI tract. So all chemicals from food and drink end up in your blood stream the same way. There are a few differences specifically between caffeine and alcohol that I'll mention, but everything is a little different.

What you are ultimately talking about is something called bioavailability. That is the measure of something you put in your body that actually reaches where it has to go. So, alcohol and caffeine have to get to your brain, but not 100% of what you eat or drink of them makes it there. The amount that does, that bioavailability in percentage. 

All the blood from your stomach and intestines flows out and immediately goes into your liver. This is a great setup because your liver is like a chemical processing plant. If you eat something toxic, it ends up in your liver and the liver might be able to break it down before it makes it to the rest of your body. Alcohol is heavily broken down by the liver so only a small portion of what you drink ends up available to make you "drunk."

About caffeine:

>Caffeine absorption is rapid and complete in humans, with 99% of orally ingested caffeine absorbed from the digestive tract within 45 minutes.2 Absorption is not modified by gender, genetics, liver disease, or the ingestion of drugs or alcohol.3 Caffeine crosses all biological membranes and is distributed in all body fluids.

And Alcohol:
>Orally ingested alcohol is rapidly absorbed into the human bloodstream from the stomach and small intestine and distributes into total body water. On an empty stomach, peak blood alcohol levels occur about 30 minutes following the oral ingestion of alcohol.7 For ingested liquids, the principal determinant of the gastric emptying rate is volume; large volumes empty at an exponentially faster rate than small volumes.8 Because alcohol absorption occurs more rapidly in the small intestine, delays in gastric emptying decrease the rate of alcohol absorption. Food in the gastrointestinal tract slows alcohol absorption; the higher the dietary fat content of a meal, the longer the absorption process takes.7 A small amount of alcohol is metabolized in the stomach by the enzyme alcohol dehydrogenase (ADH). Compared with men, women have lower activity of ADH in their stomachs, causing a larger proportion of ingested alcohol to reach the bloodstream.

Obviously that a little dense for ELIM but let me know if you have any questions.