Functions of the Digestive System
There are four main functions of the digestive system:
- Ingestion: taking in of food
- Digestion: breaking down the food
- Absorption: movement of nutrients into the bloodstream
- Defecation: elimination of indigestible waste
Ingestion simply refers to placing food in the mouth. There are a number of other movements that must happen in order to get the food from one part of the digestive system to the next. Smooth muscles lining the digestive tract propel the food along its journey. Peristalsis is the alternating waves of contractions and relaxations that squeeze food along the GI tract. |
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Digestion is the breaking down of food. There are two types of digestion: mechanical and chemical.
Mechanical digestion happens in the mouth when food is broken down by teeth and is mixed around with the tongue. It also happens when food gets churned in the stomach. Segmentation in the small intestines is another example of mechanical digestion. All mechanical digestion prepares the food for further breakdown by enzymes during chemical digestion.
Chemical digestion occurs when enzymes chemically break down large molecules into their building blocks for use by the body. Each major food group uses different enzymes.
Mechanical digestion happens in the mouth when food is broken down by teeth and is mixed around with the tongue. It also happens when food gets churned in the stomach. Segmentation in the small intestines is another example of mechanical digestion. All mechanical digestion prepares the food for further breakdown by enzymes during chemical digestion.
Chemical digestion occurs when enzymes chemically break down large molecules into their building blocks for use by the body. Each major food group uses different enzymes.
- Carbohydrates are broken down into monosaccharides (simple sugars)
- Proteins are broken down into amino acids
- Fats are broken down into fatty acids and glycerol
After digestion is complete, the products must be absorbed by the body. The digested food product must enter mucosal cells, then pass into either the blood or lymph capillaries. Most absorption happens in the small intestines.