The small intestine is where approximately 95% of digestion and nutrient absorption takes place.
The Role of the Small Intestine in Digestion
The small intestine is the primary site for both the chemical digestion and absorption of nutrients. Its structure, including the villi and microvilli, significantly increases the surface area available for these processes.
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Surface Area: The inner lining of the small intestine is highly folded and contains finger-like projections called villi. Each villus is covered in even smaller projections called microvilli. This intricate structure greatly increases the surface area available for absorption.
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Enzymatic Digestion: Enzymes from the pancreas and the small intestine itself break down carbohydrates, proteins, and fats into smaller molecules that can be absorbed.
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Nutrient Absorption: Once nutrients are broken down, they are absorbed through the walls of the small intestine into the bloodstream.
What Happens in the Large Intestine?
While the small intestine handles the bulk of digestion and nutrient absorption, the large intestine (colon) plays a crucial role in:
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Water Absorption: The large intestine reabsorbs water and electrolytes from the remaining undigested material.
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Formation of Feces: The undigested material is compacted into feces.
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Gut Microbiome: The large intestine harbors a vast community of bacteria (the gut microbiome) that ferment undigested material, producing vitamins and short-chain fatty acids that can be absorbed. The pH in the colon is slightly acidic, typically between 5.6 and 6.9.
Other Organs Involved in Digestion
It is important to note that other organs, like the stomach and mouth, also play important roles in digestion but not to the same extent as the small intestine.
- Mouth: Mechanical digestion (chewing) and initial enzymatic digestion of carbohydrates by salivary amylase.
- Stomach: Mechanical churning and initial enzymatic digestion of proteins by pepsin.
