This one has me stumped. An inquisitive 2nd cousin of mine asked what seemed simple first.
Water and food go in the mouth, down the throat and into the stomach. Food has a direct connection into the small intestine, large intestine and out the colon/anus.
How does water or beer get from the stomach into the kidney?
Am I recalling correctly that theres a direct pathway from the kidney to the bladder?
Urine is produced by your kidneys from your blood. Water and some substances like urea are filtered out of your blood. Kidneys have a direct path to the bladder through tubes called ureters. Kidneys serve other functions like regulating blood pressure.
Where did those two tall cans of Budweiser go then? 
thats a quart of fluid.
Yep- basically your blood goes through little tiny things called nephrons contained within the kidney, where water and other substances are separated from your blood and carried to the bladder.
It’s quite interesting that urine comes from blood, if you consider that some things you eat change your urine - like one of the B vitamins, asparagus, and some mushrooms - that means they’ve been in your blood. So does asparagus make your blood smell too?
Rather than thinking of blood as a substance in itself, think of blood as water that circulates round the body that various parts of the body find a convenient way of transporting stuff around in.
In addition the the red blood cells needed to move oxygen, and the platelets needed to stop up leaks, the blood is used for all sorts of things.
The digestive system cuts up your food into tiny pieces that can migrate into the blood stream. Not all that much happens to complex compounds here, they pretty much just get dumped into the blood. They get transported to parts of the body where they can be used - with a lot of processing occurring in the liver, as well as being directly used by cell mechanisms.
The liver’s job is to process the blood in many ways, it breaks down stuff with a whole raft of mechanisms, it also dumps stuff into the blood, for use by the body. The liver will also dump some junk into the bile (bile is mostly needed for digestion) but some junk will be eliminated in the faeces by this route, or reprocessed usefully, and digested as if it were food. Dead blood cell bits especially go this way.
The kidney’s job is to regulate the composition of the blood and to filter out a whole raft of junk dumped in there by the liver and the rest of the body as it operates. The kidneys can’t do this with perfect efficiency, so along with the junk, the kidneys do pass useful stuff as well. So you need to replenish them - which includes water, electrolytes, and quite a other of other compounds.
Other bits of the body find the bloodstream a convenient way of communicating with the body as a whole, so they dump various hormones and the like in there on the basis that some will eventually find its way to the think it wants to control. So pituitary, pineal, adrenals etc don’t do much other than this, whilst kidneys, testes/ovaries and the like have multiple roles but also use the bloodstream as a way communicating their desires. This is how the kidneys are involved in the control of blood pressure.
In addition, the immune system finds the blood a useful way of transporting its agents to where they are needed, and finding out what it needs to be working on.
Rather ignored, the lymph system is a second system that has a lot of parallel roles to the bloodstream, but it doesn’t circulate in the same manner, rather being more of a drainage system, but a critical role in the immune system.
So as noted above, urine doesn’t really travel anywhere except from the kidneys out. Rather it is the mix of stuff the kidneys have extracted from the blood. Most of which is usefully extracted as waste.
And here’s another interesting item I learned in Junior College Biology class about how the kidneys work:
You blood might contain any number of different kinds of toxins or waste products, depending on what you’ve been eating lately, and your kidneys can’t be “smart” enough to recognize any old arbitrary junk that might show up in your blood.
Rather, the kidneys can recognize and filter the stuff that DOES belong in your blood.
So it works backwards: It starts with whole blood. Instead of filtering out the bad stuff and sending what remains back into your bloodstream, it does the opposite: Filter out the good stuff and dump that back into your bloodstream, and dump whatever is left over into the ureters, which carry it to the bladder.
You also exhale and sweat some of it out.
I see now why a blood test is accurate for determining alcohol intoxication. Somehow whatever beverage you drink gets in the blood before reaching the kidneys.
I had a bad infection one time and the hospital was doing daily blood work monitoring the antibiotic’s effect on my kidney function. They had to reduce my IV dose for a day or two when the blood test showed a problem with my kidney function.
Like the canals in Venice!
I knew the basic answer to OP’s question, but clicked the thread anyway expecting to learn something. I was not disappointed.
BTW, it’s claimed that the similarity in shapes of kidneys and airports is not a coincidence.
Most things you eat and drink are primarily absorbed by your small intestine- little finger-ish projections called villi do the actual absorbing of nutrient molecules and water for your body. Each villus connects to the bloodstream, so in a sense, it’s kind of like a reverse nephron.
Solids go into the large intestine, which acts sort of like a compactor in the sense that it removes most of the water from the remaining intestinal contents and solidifies them before they go out your anus.
So if you drink an alcoholic beverage, about 20% is absorbed directly by your stomach, and the remaining 80% is absorbed by the small intestine.
Once it’s in the bloodstream, it’s pretty evenly distributed throughout your body- that’s why they can find it in the exhaled air from your lungs- it’s leaving through the blood vessels in your lungs. It’s also going out in sweat, in urine, and being metabolized by your liver simultaneously.
The reason we get drunk however, is because each of those mechanisms only removes a tiny fraction of alcohol per unit time, with the liver being far and away the biggest blood alcohol remover. So basically if you have a single beer, it takes roughly an hour for it to leave your body through the combined efforts of all the mechanisms because none of them eliminate alcohol very fast.
And yes, they can do a urine test for alcohol- either directly or by testing for alcohol’s metabolites in the body (for example, if you’re court-ordered not to drink, they can test for metabolites that stay in your body up to 80 days)
Water can also be expelled through the anus, though usually when it does so it’s mixed with feces and called diarrhea. (Unless you’re cleaning yourself out for a colonoscopy prep. By the end it should be clear water being expelled.) That’s why diseases that produce heavy diarrhea can be dangerous as well as uncomfortable. Dehydration is a serious consequence and can be fatal.
Lactose intolerance is an interesting example. Normally, as bump said, water is absorbed through the villi. However undigested lactose causes the osmolality in the chyme (the slurry that moves through the intestines) to increase which actually draws water into the intestines from the surrounding tissues, creating the diarrhea.
On that topic… its dangerous to drink too much water because it dilutes the blood.
Some people have slower kidneys than others, and may be at risk of suffering this.
A radio station unwisely had a water drinking competition a few years ago and one contestant died from diluting her blood too much. Guinness book of records won’t take entries for gluttonous consumption for this reason among other reasons.
Competitions may be safer if they are merely consuming a regular amount in the Fastest time.
Kind of. Too much water causes an electrolyte imbalance, which causes cell swelling to rebalance, which can in turn cause swelling of the brain or all kinds of other problems. It’s more complicated than merely having diluted blood, although that’s where it starts.
By and large, we can safely and pretty easily pee out up to about 12 L/day of excess water. The reason for the 12 L limit (which, of course, is an approximate figure with lots of individual variation) is interesting - we run out of solute (with key solutes being urea - from protein metabolism, and various ions - Na and Cl esp. In other words, to pee out water, the kidney needs a solute to accompany the water. Simply put, you can’t pee out pure water; there must be solute in it. Turns out that the minimum solute required is about 50 mOsm per L of water, and we have, on average, about 600 mOsm of solute available to us each day mostly from diet and metabolism. So, we only have enough solute to excrete around 12 L of water per day.
ETA: phrased differently, for the average person, his/her blood will not even start to become pathologically diluted by drinking water until they’ve consumed over 12L in a day (and remember, not all water is lost through the kidneys thus providing even more of a cushion, e.g. breathing, sweating lose water too)