Why doesn't food and oxygen pass through arteries and veins?

Well wouldn't that be a mess, a wee bit of steak stuck in a vein between your fingers of your left hand and no way to get it out. Truth of the matter is this, food and oxygen do pass through the veins however not the way you may think. See the body is a complex machine, with various departments handling specific jobs but all relying on each other.

Air is inhaled into the lungs, this as you know contains all sorts of gases, some the body can use some it can't (what it can't use it gets rid of on the exhale breath) the lungs take the air, and from it, they take what they need in this case oxygen. Which is absorbed by the blood in the air sacs of the lungs as the carbon dioxide is expelled out of the air sacs to be exhaled.

The newly recharged blood is pumped out of the lungs by the heart and off to resupply the bodies muscles and other organs with freshly oxygenated blood by means of the *Arteries under pressure (*Systole = contraction of the heart). The blood flows by the two sets of lines through out the body, Arteries (under pressure) to the organs, limbs, brain etc. and returns by the *Veins ( *Diastole = relaxation of the heart) under low pressure from the organs, limbs, brain etc. back to the heart and through the lungs to start the cycle again.

Now blood contains several components that allow it to carry a host of needed materials to various organs in the body, sugars, minerals, proteins, antibodies and oxygen. Because blood is a universal component it can do this for every organ and system in the body. Every organ in the body adds to the blood what ever the body or other organs need at any given time and with very short notice.

The Kidneys filter out the blood and remove toxins and components the body doesn't want, the Liver and Spleen do the same sort of thing adding what ever the body needs to operate.

The blood runs it's form of courier service so to speak, carrying needed components from one place to another in a specific order, then back to the lungs to vent gases and refresh it's self before doing it all again.

The digestive system processes the foods we eat and converts it to sugars, minerals and fats, some to be used right away like the minerals and sugars and some to squirrel away for times when we may need it later that would be the various types of fat. The rest of the material that the body can't use is discarded by the body as waste materials and liquids.

So in a very simplistic way the food we eat and the air we breath does pass through the veins and arteries, but in a form that all the organs of the body can work with and add to. So don't worry about that wee bit of steak getting stuck in a vein, it just won't happen (not without potatoes and gravy).