Lifetime Nutrition and Wellness TEKS: 2ABC

Digestion  Before your body can use the nutrients in the food you eat, it must go through digestion.  Then nutrients must go through absorption.  Digestion-the bodily process of breaking food down into simpler compounds the body can use  Absorption-the process of taking in nutrients and making them part of the body

The Digestive Tract  The digestive or gastrointestinal tract is a tube about 30 feet long.  It extends from the mouth to the anus.  Contains the esophagus, stomach, small intestine, and large intestine  They work together to both mechanically and chemically help the body use food.

The Digestion Process  The body breaks down complex molecules from the food into simple, soluble materials.  They pass through the digestive tract into the blood and lymph systems.  Vitamins and minerals undergo very little chemical change during digestion.  Fats, proteins, and carbs undergo many changes.

The Mechanical Phase  Begins in the mouth, the teeth chew the food and break it down into small pieces  Contractions of the muscular walls of the digestive tract carry on the mechanical action. The contractions mix food particles and break them into smaller pieces  Waves of contractions knows as peristalsis, the muscles push food through the digestive tract  Emotions can slow down or speed up the process

The Chemical Phase  Begins in the mouth  As you chew, food is mixed with saliva. (mucus and enzyme containing liquid)  It moistens food particles, helping them move down the esophagus into the stomach.  Saliva also begins to break down starches.

The Chemical Phase  In the stomach, gastric juices containing hydrochloric acid and several enzymes are secreted.  These juices break down the food more.  Ordinary meal usually leaves the stomach in about 2 to 3 hours  Carbs leave the stomach first, proteins second, fats last  You will feel hungry sooner after a meal high in carbs

Chemical continued…  Then the semi-liquid food leaves the stomach and enters the small intestine  Intestinal juices, pancreatic juices, and bile act on the food  Digestive enzymes help break down the carbs, proteins, and fats into simple substances the body can absorb and use.  Once digestion is complete absorption can take place.

Large Intestines  Indigestible residues, bile pigments, other wastes, and water travel from the small intestine to the large intestine.  The large intestine acts as a reservoir, or storage area.  Eventually the body will excrete these materials.

Absorption Process  The body can absorb water, ethyl alcohol and simple sugars directly from the stomach.  They pass through the stomach walls into the bloodstream.  However, most absorption takes place in the small intestines.

Absorption Process  Millions of hair like fingers called villi line the small intestines.  The villi increase the absorptive surface of the small intestine by more than 600%.  Each villus contains a lymph vessel surrounded by a network of capillaries.  Nutrients absorbed by the capillaries pass into the portal vein and travel directly to the liver.

Metabolism  The chemical processes that take place in the cells after the body absorbs nutrients  Enzymes cause nearly all metabolic reactions.  The body uses nutrients to replace substances used for growth and to carry out body processes.

Metabolism  The body breaks down some nutrients into simpler substances to release energy.  The body uses part of this energy to carry out metabolic reactions.  It converts the rest into heat.  The body converts all carbs into glucose for use as an energy source.  If they are not needed for immediate energy, they can be converted to glycogen or in the body as fat tissue.

Metabolism  During fat metabolism, fatty acid chains are shortened. The body uses most fat for fuel.  The body can use amino acids from protein metabolism for cell maintenance or cell growth.  It can also use amino acids to make enzymes, antibodies, nonessential amino acids, and as an energy source.

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