How does the digestive system absorb nutrients?

The digestive system absorbs nutrients through various processes that break down food and extract essential components. Here are the main steps of nutrient absorption:

1. Mechanical Digestion:

- The process begins in the mouth, where teeth break down food into smaller pieces, increasing the surface area for enzymes to work.

- Further mechanical digestion occurs in the stomach as muscles contract and churn the food, mixing it with digestive juices.

2. Chemical Digestion:

- In the stomach, hydrochloric acid and the enzyme pepsin break down proteins into smaller peptides.

- In the small intestine, the pancreas secretes enzymes such as amylase, protease, and lipase that break down carbohydrates, proteins, and fats, respectively.

- Bile produced by the liver helps emulsify fats, making them easier for lipase to digest.

3. Nutrient Absorption in the Small Intestine:

- The small intestine is the primary site for nutrient absorption. It has a large surface area due to the presence of finger-like projections called villi and even smaller microvilli on the intestinal cells.

- The epithelial cells of the small intestine have specialised transport proteins that facilitate the absorption of different nutrients:

- Carbohydrates: Broken down into simple sugars (glucose, galactose, fructose) and absorbed by active and facilitated transport.

- Proteins: Peptides are further broken down into amino acids, which are absorbed by active transport.

- Fats: Fats are broken down into fatty acids and glycerol. Fatty acids are absorbed by passive diffusion, while glycerol is absorbed by facilitated transport.

- Vitamins: Most vitamins are absorbed in the small intestine, either through passive diffusion, active transport, or facilitated diffusion.

- Minerals: Minerals such as iron, calcium, and magnesium are absorbed by active transport or facilitated diffusion.

4. Absorption in the Large Intestine (Colon):

- The colon absorbs water, electrolytes (such as sodium and chloride ions), and some vitamins synthesized by gut bacteria.

- While most nutrient absorption occurs in the small intestine, the large intestine plays a role in water balance and the absorption of certain vitamins and minerals.

Throughout the digestive process, nutrients are transported through the intestinal wall and into the bloodstream, where they can be distributed to various tissues and organs in the body.