Digestion and Absorption
Digestion and absorption are important physiological processes through which the food we eat is broken down into simpler substances and then taken into the bloodstream for use by the body.
1. Digestion
Digestion is the mechanical and chemical breakdown of complex food substances into simpler, smaller molecules that can be absorbed by the body.
The major nutrients undergo digestion as follows:
- Carbohydrates → Monosaccharides mainly glucose
- Proteins → Amino acids
- Fats → Fatty acids + Monoglycerides
- Nucleic acids → Nucleotides and smaller components
Digestion occurs mainly in the mouth, stomach and small intestine.
2. Absorption
Absorption is the process by which digested nutrients pass from the gastrointestinal tract into the blood or lymph.
The small intestine is the principal site of absorption because it has numerous villi and microvilli, which greatly increase the surface area available for absorption.
Major Sites of Digestion and Absorption
| Organ | Major function |
|---|---|
| Mouth | Chewing; salivary amylase begins carbohydrate digestion |
| Stomach | Protein digestion begins; gastric acid helps denature proteins |
| Small intestine | Major site of digestion and absorption |
| Large intestine | Mainly absorbs water and electrolytes; some vitamins are produced/absorbed through gut microbiota |
Important Point
Digestion = Breaking down food
Absorption = Taking the digested nutrients into the body
Example:
Starch → glucose (digestion) → glucose enters blood (absorption).