Human digestion, or the change that food undergoes in the digestive system, takes place in a long tube like canal called the alimentary canal, or the digestive tract. There is good reason why the passageway used by food to travel through the body is called the alimentary canal. Just as canals are constructed to guide ships through waterways to their destinations, the alimentary canal guides food as it travels through the human body. The whole canal is lined with a mucous membrane.

Ingestion, which occurs in the mouth, is the first step of the digestive process. After food enters the mouth,

The ileum is the last portion of the small intestine, and it is responsible for absorption of fats, and bile salts, which are a component of bile. The pores in the ileum are slightly bigger than those in the jejunum and allow vitamin B12, vitamins dissolved in fatty liquids, electrolytes, bile salts and water to soak through the walls and into the blood stream. The lining of the small intestine contains many folds. These folds increase the surface area that can be in contact with the food products. Where the ileum joins the large intestine is a valve, called the ileocecal valve, which prevents the back flow of materials into the small intestine. By the time material reaches this point, it has a rather pasty consistency.

The main parts of the small intestine are the duodenum, jejunum, and ileum. Two large glands, the liver and the pancreas, connect with the small intestine by ducts, or tubes. Through these ducts the liver and pancreas pour secretions which further aid digestion and absorption.

In the stomach, a mixture of hydrochloric acid and Pepsin, which is secreted by the stomach wall, liquefies the food. At the same time, a substance called intrinsic factor binds Vitamin B in food and various gastric enzymes, such as Pepsin which begins protein digestion, which are secreted by the stomach wall. Secretions of mucus protect the stomach from its digestive enzymes. The food is then mixed in the stomach, turning it into chyme(digested food). Then is passed on by peristalsis into the small intestine.

The parts of the food that can’t be digested get pushed into the large intestine, also called the colon. It is about 5 feet long. Its function is to move the waste from the small intestine on to the rectum. The material first passes through the ascending colon and then through the transverse colon. Throughout this process, it absorbs more water. By the time the waste reaches the segment called the sigmoid, it is quite firm. The sigmoid colon is designed to slow down this movement of the waste until it is ready to be eliminated.

Some topics in this essay:
Digestion Introduction, Key Hypothesis, active site, digestive process, substrate molecules, active site substrate, substrate molecules fit, active site region, hydrogen ion concentration, site substrate molecules, digestive system, blood stream, hydrogen ion, bile salts, site substrate, food swallowed, pancreatic juice,