How to Compare Mechanical & Chemical Digestion

Digestion is the process our bodies use to obtain nutrients from food. Each step in the process facilitates the next. Digestion begins in the mouth, where mechanical processes start to break down food into smaller pieces. It continues through the digestive tract, where both mechanical and chemical functions continue to process the food, extract nutrients, and send them to awaiting cells. Although the mechanical and chemical functions of digestion are quite different, they must work together to get the job done.

Instructions

• 1

  Understand that digestion begins in the mouth as a mechanical action. Your teeth tear and crush the food, while your tongue moves the food around to mix it with saliva. Chemicals in saliva, known as enzymes, begin to digest the starches in food. Infant saliva also has the capacity to begin fat digestion, which diminishes with age. The last mechanical action that occurs in the mouth is when the tongue pushes the food back to the throat to be swallowed.

• 2

  Know that each swallow triggers a peristaltic wave in the esophagus. Peristalsis is the mechanical process by which muscles of the esophagus expand and contract in a wavelike motion to push the food down the esophagus to the stomach.

• 3

  Learn that food is held in the upper area of the stomach, where saliva continues to break down starches. Small amounts of food are sent to the lower part of the stomach, where gastric juices halt the chemical breakdown of starch. The gastric juices go to work on proteins next. The enzymes in the gastric juice unwind the proteins into strands, then clip the strands into smaller pieces. Mechanically, the stomach churns and grinds the food into smaller and smaller pieces, turning it into a substance of nutrients and gastric juices known as chyme.

• 4

  Understand that the stomach periodically squirts small amounts of chyme into the small intestine. The gallbladder sends an enzyme called bile to break down fats. The pancreas also sends an enzyme to break down proteins and carbohydrates. These chemical reactions break down the chyme into very basic molecular units of nutrients, which are then absorbed through the intestinal lining and carried away by blood or lymph. The mechanical action of the small intestine is another peristaltic wave that pushes the broken-down nutrient chemical soup along its length to the large intestine.

• 5

  Know that most nutrients are already absorbed before the chyme reaches the large intestine. The large intestine absorbs some of the water used by digestion. The large intestine also absorbs small amounts of fiber and minerals. Peristalsis is again employed to push the waste products of digestion down to the anus to be excreted.