Chapter 2 – Digestion
What You Should Know About Your Body
Your body is approximately fifty-five percent (55%) water, twenty percent (20%) protein, fifteen percent (15%) fat, nine percent (9%) minerals, and one percent (1%) carbohydrates and vitamins.
These basic components must constantly be replenished through the foods we eat. But, not necessarily in the same proportions for each of us. Some foods enter our bodies as fuel and are burned on consumption to meet energy needs. Others become the basic building blocks of tissues and fluids. Still, others are vital to the delicate interactions required by the body’s many functions.
You Are a “One-of-a-Kind”
Throughout your personalized program you will continually hear how each of us is unique. We are all different. This holds true for our digestive process as well. The metabolic process begins with digestion. The digestion tract involves the mouth, esophagus, stomach, small intestine and the large intestine. The mechanical and chemical phase of digestion occurs in these organs.
Your Body is a Sophisticated Food Processor
The mechanical phase of digestion is responsible for sub dividing, mixing and propelling of food along the digestive tract. It includes chewing, swallowing, and the muscular activity of the walls of the? digestive tract itself. The chemical phase of digestion is responsible for the final breakdown of food particles. It is brought about by digestive enzymes. Enzymes act as catalysts in the body. They increase the rate of a reaction without becoming part of the final reaction product. Digestive enzymes aid in the breakdown of large nutrient molecules into smaller molecules. For example, carbohydrates are changed into simple sugar, fats into glycerol, and fatty acids and? proteins into amino acids.
The Digestive Process
The process of digestion starts when food enters the body through the mouth where it is chewed, broken into small pieces, and mixed with saliva. The fluid secreted by the salivary glands contains digestive enzymes that act upon carbohydrates. From the mouth, food passes to the stomach by way of the esophagus.
The digestion of certain foods continues in the stomach under the influence of the secretions and churning action of the stomach wall. Ordinarily, a mixed meal leaves the stomach in three to four hours. Carbohydrates leave the stomach most rapidly, followed by protein. Fats remain in the stomach for a longer period.
Thus, the sensation of hunger will occur sooner after a meal that is high in carbohydrate than after a meal containing adequate amounts of proteins or fat.
Beyond the Stomach
After leaving the stomach, the liquefied mass, called chyme, passes into the small intestine for further absorption into the body. The small intestine is affected by secretion from its walls and from the liver and pancreas. The undigested food residues pass from the small intestine to the large intestine or colon. This material also contains some of the end products of digestion such as water, as well as waste materials. These waste products travel through the large intestine where they await periodic excretion from the body.
How Your Body Absorbs Nutrients
Absorption follows digestion. The function of digestion is to prepare the nutrients for absorption through the walls of the digestive tract. Most of this absorption takes place in the small intestine. However, water and small amounts of simple sugars and alcohol pass through the mucosa of the stomach into the bloodstream. And, various minerals and water are absorbed in the large intestine.
Located on the wall of the intestines and into the food canal are finger-like projections called villi. They increase the absorption surface area about 600-fold. Each villus contains a network of tiny vessels that drink up the nutrients as they pass along the food canal.
There are two kinds of tiny vessels in each villus. One contains lymph and accepts digested fats (lymphatic vessels). The other contains blood and accepts all other digested nutrients (capillaries). These little vessels are the means by which the absorbed nutrients are circulated to every cell throughout the body. Nutrients then circulate throughout the body in a manner analogous to diners at a cafeteria. As the blood flows by cells take what they need.
Excess nutrients may be stored, converted to more complex compounds, or excreted.