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. This critical organ connects the stomach to the large intestine and is divided into three parts: the duodenum, jejunum, and ileum. It plays a vital role in breaking down food, absorbing nutrients, and ensuring that the body receives the essential elements it needs for energy and growth.

5 Must Know Facts For Your Next Test

1. The small intestine is approximately 20 feet long in adults, making it a crucial area for nutrient absorption due to its extensive surface area.
2. The process of digestion in the small intestine involves both mechanical and chemical breakdown of food with help from bile and pancreatic juices.
3. Absorption in the small intestine occurs mainly in the jejunum and ileum, where nutrients like amino acids, fatty acids, vitamins, and minerals enter the bloodstream.
4. The presence of villi and microvilli greatly enhances the absorptive capacity of the small intestine, allowing for efficient nutrient uptake.
5. Certain disorders affecting the small intestine, like celiac disease or Crohn's disease, can lead to malabsorption and nutritional deficiencies.

Review Questions

• How does the structure of the small intestine facilitate its primary functions of digestion and absorption?
  • The structure of the small intestine, with its long length and numerous folds, allows for an extensive surface area to optimize digestion and nutrient absorption. The presence of villi and microvilli further increases this surface area, enhancing absorption efficiency. Additionally, its three distinct sections—duodenum, jejunum, and ileum—play specific roles in breaking down food and absorbing different nutrients, ensuring that essential elements are efficiently processed.
• Discuss the roles of bile and pancreatic enzymes in the functioning of the small intestine.
  • Bile and pancreatic enzymes are crucial for digestion in the small intestine. Bile, produced by the liver and stored in the gallbladder, emulsifies fats to facilitate their breakdown. Pancreatic enzymes, secreted by the pancreas into the duodenum, help digest carbohydrates, proteins, and fats. Together, they ensure that food is adequately broken down into its constituent nutrients before absorption takes place in the latter sections of the small intestine.
• Evaluate how conditions like celiac disease can impact nutrient absorption in the small intestine.
  • Celiac disease is an autoimmune disorder that leads to damage in the lining of the small intestine when gluten is ingested. This damage results in flattened villi and reduced surface area, severely impairing nutrient absorption. Individuals with celiac disease may experience malnutrition despite adequate food intake because essential nutrients like vitamins, minerals, and macronutrients are not effectively absorbed. Managing this condition requires a strict gluten-free diet to allow healing of the intestinal lining and restore proper nutrient uptake.

Related terms

Duodenum:

The first section of the small intestine where a significant portion of 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.

Pancreatic Enzymes: Digestive enzymes produced by the pancreas that help break down proteins, fats, and carbohydrates in the small intestine.