Small intestine

Definition

The small intestine is a long, coiled tube in the digestive system where most of the digestion and absorption of nutrients occurs. It consists of three main parts: the duodenum, jejunum, and ileum, each playing a crucial role in breaking down food and absorbing essential nutrients, including proteins and lipids.

5 Must Know Facts For Your Next Test

1. The small intestine is about 20 feet long in adults, making it crucial for maximizing nutrient absorption due to its extensive surface area.
2. Enzymes produced by the pancreas and bile from the liver are secreted into the duodenum to aid in lipid and protein digestion.
3. Absorption in the small intestine occurs primarily in the jejunum and ileum, where nutrients enter the bloodstream through capillaries in the villi.
4. The pH in the small intestine is slightly alkaline (around 7-8), which helps activate digestive enzymes and facilitates nutrient absorption.
5. The small intestine plays a vital role not just in digestion but also in immune function, as it contains lymphoid tissue that helps protect against pathogens.

Review Questions

• How does the structure of the small intestine facilitate nutrient absorption?
  • The structure of the small intestine is optimized for nutrient absorption through its length and presence of villi. These tiny, finger-like projections significantly increase the surface area available for absorption. This means that as chyme moves through, more nutrients can be absorbed into the bloodstream efficiently, particularly in the jejunum and ileum sections.
• Discuss the role of digestive enzymes and bile in protein and lipid digestion within the small intestine.
  • Digestive enzymes from the pancreas, including proteases for protein digestion and lipases for lipid digestion, are released into the duodenum. Bile, produced by the liver and stored in the gallbladder, emulsifies fats to increase their surface area for lipase action. This combined action ensures that proteins are broken down into amino acids while lipids are emulsified and further digested into fatty acids and glycerol, allowing for effective nutrient absorption.
• Evaluate how disorders affecting the small intestine can impact overall health, particularly regarding protein and lipid metabolism.
  • Disorders like celiac disease or Crohn's disease can severely affect nutrient absorption in the small intestine. In celiac disease, exposure to gluten leads to damage to intestinal villi, reducing surface area for absorption. This impairment can result in malnutrition due to poor uptake of essential amino acids from proteins and fatty acids from lipids. Consequently, individuals may face a range of health issues such as weight loss, fatigue, and deficiencies in essential vitamins and minerals.

Related terms

Duodenum: The first part of the small intestine where the majority of chemical digestion occurs, aided by enzymes from the pancreas and bile from the liver.

Villi: Small, finger-like projections lining the walls of the small intestine that increase surface area for absorption of nutrients.

Chyme: The semi-fluid mass of partially digested food that moves from the stomach into the small intestine for further digestion and absorption.