Why do scientist consider it to be accurate that nutrients are not really inside the body until they have passed through wall of small intestine?

Scientists consider nutrients to be truly inside the body only after passing through the wall of the small intestine because of the process called digestion. Digestion involves the physical and chemical breakdown of food into smaller components, which can then be absorbed and utilized by the body. Here are the reasons why nutrients are not considered to be truly inside the body until this occurs:

1. Physical Barrier: The wall of the small intestine, also known as the intestinal epithelium, acts as a physical barrier between the intestinal lumen (where the food is present) and the bloodstream. Nutrients cannot directly enter the bloodstream without crossing this barrier.

2. Chemical Breakdown: Digestion involves the chemical breakdown of complex food components into simpler forms. Enzymes produced by the pancreas and the cells lining the small intestine help to break down proteins, carbohydrates, and fats into smaller molecules, such as amino acids, simple sugars, and fatty acids.

3. Absorption: Once the nutrients are broken down into smaller molecules, they can be absorbed through the villi and microvilli, which are small finger-like projections lining the small intestine. These structures increase the surface area of the intestine, facilitating the absorption of nutrients into the bloodstream.

4. Transport: After absorption, nutrients are transported through the bloodstream to various cells and tissues in the body, where they are used for energy, growth, repair, and other essential functions.

Therefore, nutrients are not truly considered to be inside the body until they have been properly digested, broken down, and absorbed through the wall of the small intestine, and transported throughout the body via the bloodstream. This process ensures that the body receives the necessary nutrients in a usable form and supports overall health and function.