The Pathway Of Digestion
- After food is taken into the mouth, mastication and the beginning stages of enzymatic chemical digestion occurs. It is then swallowed, entering the esophagus.
- Once the swallowed food has entered the gastrointestinal tract, it is called a bolus. The esophagus’s job is to transport the bolus to the stomach. The bolus travels through the esophagus and enters the stomach, where the second stage of chemical (enzymatic) digestion happens.
- In the stomach, hydrochloric acid is secreted by parietal cells in the stomach lining. Other digestive enzymes are secreted from the stomach lining and also dumped into the stomach. At this point the bonds that form the proteins, carbohydrates, and fats begin to break down. This forms a semi-fluid that can now enter the small intestine.
- Next, the bolus travels in to the upper part of the small intestine called the duodenum. Here the liver secretes enzymes, the gall bladder secretes bile to break down fats, and the pancreas secretes a variety of pancreatic enzymes to further break down (primarily) proteins and fats.
- The bolus continues to travel through the small intestine. Movement through the small intestine allows nutrients to be absorbed through the small intestine wall into the blood stream.
- What is not assimilated into the bloodstream through the small intestine moves into the large intestine. Waste material is processed into stool (feces), while water and usable chemicals are absorbed into the bloodstream to preserve the body's fluid balance.
- Waste material (feces) is excreted through the anus after being prepared for excretion in the rectum.