First, let’s set the record straight: The only thing large about this intestine is its width — it needs a spacious interior, to accommodate the slowly desiccating remains of your meal. By far the longest part of your intestines is the small intestine — the site where the great preponderance of digestion and nutrient absorption occur in the body.
What’s passed on to the large intestine is a soggy slurry of undigestible food bits — especially the undigestible long-chain carbohydrates known as “fiber”. What remains of value in this mix is water and electrolytes (such as sodium and potassium), which the large intestine absorbs.
Don’t be misled, though — the large intestine is vital for your survival. All the organs of the digestive system from the mouth to the small intestine secrete large amounts of fluid. These secretions add digestive enzymes and other additives to process the food. Enough fluid is released in this way, that you’d quickly dehydrate, without the large intestine’s help. Indeed, the inability to absorb fluids in the large intestine, resulting in watery feces, or diarrhea, is a deadly condition that kills millions every year.
Incidentally, the mouth of our thirsty friend is accurately placed — it represents the opening where the small intestine attaches, and thus, releases its slushy contents into the large intestine. At that junction, an ileocecal valve prevents backflow of feces into the small intestine. Other parts are (more or less) anatomically correct as well — from the portly cecum (shown as the “body” of our absorptive acquaintance), and a tail-like vermiform appendix, through the ascending colon, transverse colon, descending colon, sigmoid colon (the S-shaped “zigzag” near the end), rectum, and anal canal. The end!