* Carbohydrates: These are broken down into simple sugars like glucose, fructose, and galactose.
* Proteins: These are broken down into amino acids.
* Fats (lipids): These are broken down into fatty acids and glycerol.
Why do these need to be digested?
* Size: The molecules of these food classes are too large to be absorbed directly into the bloodstream. Digestion breaks them down into smaller units that can be easily absorbed.
* Solubility: Some nutrients, like fats, are not soluble in water. Digestion makes them more soluble so they can be transported through the bloodstream.
What doesn't need digestion?
* Water: Water is already in a form that can be absorbed directly.
* Vitamins and Minerals: These are already in small enough units to be absorbed.
The digestive process:
The digestive process involves both mechanical and chemical breakdown of food:
* Mechanical digestion: This is the physical breakdown of food, like chewing, churning in the stomach, and segmentation in the small intestine.
* Chemical digestion: This is the breakdown of food molecules by enzymes.
The small intestine is the primary site of absorption:
Once food is digested, the small intestine absorbs nutrients into the bloodstream. This is facilitated by the large surface area provided by the villi and microvilli lining the small intestine.
