Small intestine

Definition

The small intestine is a long, coiled tube in the digestive system where most digestion and absorption of nutrients take place. It connects the stomach to the large intestine and is crucial for breaking down food using enzymes and absorbing essential nutrients into the bloodstream. The small intestine consists of three parts: the duodenum, jejunum, and ileum, each playing a distinct role in the digestive process.

5 Must Know Facts For Your Next Test

1. The small intestine is about 20 feet long in adults, making it much longer than the large intestine.
2. Its inner surface is highly folded and covered with villi and microvilli, which dramatically increase its surface area for nutrient absorption.
3. The small intestine plays a key role in breaking down carbohydrates, proteins, and fats with the help of digestive enzymes from the pancreas and bile from the liver.
4. Most nutrient absorption occurs in the jejunum, while the ileum primarily absorbs bile acids and vitamin B12.
5. The small intestine has a complex interaction with gut bacteria that can influence digestion and overall health.

Review Questions

• What are the main functions of the small intestine in digestion and how do its structural features support these functions?
  • The small intestine's main functions are to digest food and absorb nutrients. Its structure supports these functions through its length, allowing ample time for digestion, and its inner surface lined with villi and microvilli that maximize absorption. The sections of the small intestine also perform specific roles: the duodenum focuses on initial digestion, while the jejunum and ileum specialize in nutrient absorption.
• Evaluate how disorders of the small intestine can affect overall nutrition and health.
  • Disorders such as celiac disease or Crohn's disease can severely impact the small intestine's ability to digest food and absorb nutrients effectively. This can lead to malnutrition, as essential vitamins and minerals may not be absorbed properly. Chronic issues can cause symptoms like diarrhea, weight loss, and fatigue, indicating a serious impact on overall health.
• Synthesize information about how the interactions between digestive enzymes and the small intestine contribute to nutritional absorption.
  • Digestive enzymes play a critical role in breaking down complex nutrients into simpler forms that can be absorbed by the small intestine. For instance, pancreatic enzymes break down proteins into amino acids and carbohydrates into simple sugars. The presence of bile aids in fat emulsification, facilitating fat absorption. This collaboration ensures that nutrients are available in their simplest form, allowing efficient absorption through the intestinal lining into the bloodstream.

Related terms

Duodenum: The first section of the small intestine, where the majority of chemical digestion occurs as it receives bile from the liver and pancreatic juices.

Villi:

Tiny finger-like projections that line the walls of the small intestine, increasing the surface area for nutrient absorption.

Absorption: The process by which nutrients from digested food are taken up by the body through the intestinal walls into the bloodstream.