Small and Large intestine
Final Digestion of Food
The small intestine is the site of final food digestion. This process takes place with the help of various enzymes that are present in the small intestine. These enzymes break down most food molecules into absorbable units.
Most enzymes in the small intestine are produced in the pancreas. These enzymes are then delivered into the small intestine through a duct that connects the pancreas to the intestine.
Common Mistake
Some students think digestion ends in the stomach, but most digestion and nutrient absorption actually occur in the small intestine.
Nutrients Are Absorbed
We learned how food is digested into absorbable molecules. The nutrient molecules in the small intestine are so small that they can pass through the lining of the intestinal wall.
The small intestine is the only part of the digestive system where all nutrients are absorbed and enter the bloodstream.
Important Concept
Absorption is the process by which digested molecules move through the intestinal wall and into the blood so they can be transported to cells throughout the body.
Question
Considering the function of the small intestine, why are these folds important?
Show Answer
These folds increase the surface area of the small intestine, allowing more digested nutrients to be absorbed efficiently. Without them, the absorption area would be too small to meet the body’s needs.
What Remains
Substances that are not digested in the small intestine leave it and enter the large intestine. For example, parts of vegetables like lettuce that pass through with bread are not digested in the small intestine.
Have you thought about this?
Some of the substances that reach the large intestine still contain water and minerals. Some of these are absorbed in the large intestine. If the large intestine didn’t do this job, we’d lose a lot of water and minerals like sodium and potassium with waste.
In the large intestine, certain types of bacteria also help with digestion. These bacteria break down undigested substances and even produce useful materials such as vitamin K and some B vitamins, which are absorbed into the bloodstream.
The material left in the large intestine becomes more solid. The accumulation of this waste in the large intestine causes the urge to defecate and triggers movement toward the rectum.
Quick Fact
The bacteria in the large intestine are part of the body’s natural microbiome. They help digest fiber and also produce essential vitamins that we cannot synthesize ourselves.
Question
Show Answer
The large intestine reabsorbs water and minerals like sodium and potassium to prevent dehydration and nutrient loss. Without this function, the body would lose too much fluid and essential ions with the waste.