Food digestion is a process regulated by several different organs. The word "digestion" refers to the chemical and mechanical breakdown of food into smaller molecules that can be used to fuel your body's metabolic processes. Digestion begins as soon as food enters the mouth. From the mouth, food enters the esophagus and continues to the stomach where it proceeds to the intestines. Chemical digestion involves the breakdown of food macromolecules by enzymes that are produced by the salivary glands, stomach, pancreas and small intestine.
Mouth and Esophagus
Your mouth is where digestion of food begins. Mechanical digestion occurs as your teeth are used for mastication, the act of chewing food and breaking it into smaller pieces. The saliva in your mouth also contains enzymes that begin to break the chemical bonds in food particles, making them more usable to your body. From your mouth, food proceeds into a straight muscular tube known as the esophagus. The esophagus regulates food entry into your stomach.
Stomach
The stomach is a muscular organ that functions mainly as a place for food storage in your body. Your stomach contributes to both the mechanical and chemical digestion of food. Your stomach relaxes to allow food to enter shortly after swallowing. Upon receiving food, your stomach begins to contract rhythmically, helping to mechanically digest food. During these peristaltic contractions, the food in your stomach is mixed with a variety of enzymes and acids to aid in chemical digestion. The mixture of food and gastric juice is called chyme.
Liver, Gallbladder and Pancreas
Your liver and pancreas secrete enzymes and hormones that are important in digestion. The liver receives blood directly from the stomach and intestines. Cells of the liver absorb sugars, amino acids and vitamins after a meal. Your liver also secretes bile, a yellow-green fluid rich in minerals, acids, fats and cholesterol. Bile is important in the digestion and absorption of fat. Bile is stored and concentrated in the gallbladder. The pancreas secretes hormones that regulate your blood sugar levels and enzymes that are secreted into the intestines to aid in chemical digestion of food molecules.
Intestines
The small intestine is the site of almost all chemical digestion and nutrient absorption. The small intestine is so named because of it's diameter, as it is the longest part of the digestive tract. The small intestine has a large surface area to aid in nutrient absorption. The small intestine is the site of starch digestion and carbohydrate absorption. Additionally, amino acids, lipids, nucleic acids, vitamins, minerals and water are absorbed through the small intestine. From the small intestine, indigestible material moves on to the large intestine, which helps to reduce the amount of food waste produced by absorbing water and salts. Waste, known as feces, is then eliminated by defecation.
References
- "Anatomy and Physiology: The Unity of Form and Function (5th Edition)"; Ken Saladin; 2010
- National Digestive Diseases Information Clearinghouse; Your Digestive System and How it Works; April 2008
