The large and |small intestine| comprise the lower alimentary (digestive) tract. The |small intestine| is responsible for completing digestion and for absorbing the usable food products into the lymphatic system and bloodstream. The |small intestine| itself consists of a coiled, narrow tube (1-2 inches in diameter), between 19 and 22 feet (about 6-7 meters) long, in the lower abdomen, below the |stomach|. The |small intestine| extends from the |duodenum| (where it accepts the ~chyme~, or predigested food), to the iliocecal orifice (where it passes semifluid food by-products to the |large intestine|). The food is passed through the intestinal tract by wave-like |contractions|, called peristalytic waves, in the intestinal wall. The food is further digested by ~bile~ and other digestive juices deposited into the |duodenum| from the gallbladder, |pancreas|, and |liver|. The digesting food passes by the millions of villi (projections) on the inside wall of the intestines, which absorb |proteins| and |carbohydrates| into their |capillaries|, and lymphatic nodules, which absorb |fats|. The villi pass the |proteins| and |carbohydrates| to the |liver| for metabolic processing, and the lymphatic nodules pass the |fats| through the lymphatic system into the bloodstream. The |small intestine| is anchored to the spinal column by a vascular membrane called the mesentary.
The |large intestine| is a broad, corrugated tube which accepts the by-products of digestion from the |small intestine| and passes it along to be excreted, continuing to ~process~ the material on the way. Any unabsorbed materials are stored in the |large intestine| where water used in processing the food is partially reabsorbed back into the body. The remaining wastes are passed along to the |anus| for elimination. The reabsorption of too much water may lead to hard, relatively dry ~feces~ which can become impacted, making elimination difficult. This condition is known as ~constipation~. If not enough liquid is reabsorbed, as often caused by some viral ~infections~ or malnutrition, the |large intestine| passes on a fluid to the |anus|, making control of elimination difficult. This condition, and the fluid (which is often painful to the anal tissues) is known as ~diarrhea~. The |large intestine| is divided into eight sections: the |cecum|, the |appendix|, the |ascending colon|, the |transverse colon|, the |descending colon|, the |sigmoid colon|, the |rectum|, and the |anus|.
