Question

Why must the pH values of the mouth, stomach, and small intestine be different?

Answer 1

Hint: Digestion is the mechanical and enzymatic breakdown of food into molecules that can be absorbed into the bloodstream. Fats, carbs, and proteins are three macronutrients that must be digested before they can be absorbed. So they require different acidic medium or basic medium to digest food.

Complete answer:
In the absence of enzymes, food macromolecules are stable and unlikely to be digested into simple chemicals. Enzymes function best at a specific pH, which varies depending on the enzyme.

Salivary amylase, for example, performs best in a slightly acidic solution, while the pH of saliva is typically between 6.5 and 6.8, slightly acidic.

Pepsin, a protein-digesting enzyme found in the stomach, works best in an acidic environment, which is given by the hydrochloric acid released by the stomach's digestive glands.

The intraluminal pH changes quickly in the duodenum, from very acidic in the stomach to roughly pH 6. The pH of the small intestine gradually rises from pH 6 to around pH 7.4 in the terminal ileum. In the caecum, the pH lowers to 5.7, then progressively rises again, reaching pH 6.7 in the rectum.

The stomach, the second section, has to produce enough acid to break down the food into its constituent components. When food enters the intestines, however, it no longer requires acid. The substance is brought closer to the body's pH through both intestines.

The enzymes that "operate" in the small intestine require an alkaline pH in order to function optimally. As a result, the pH must be decreased to avoid harm. Finally, bile, an alkaline material produced by the liver, is used to modify the pH of the small intestine.

Note:
Bile is not an acidic substance. Bile salts, bile pigments, cholesterol, and lecithin make up this alkaline fluid. It is created by the liver, stored in the gallbladder, and released intermittently into the duodenum, which is the upper part of the small intestine, when it is required for digestion.