Structure and Functions of the Human Digestive System

Small Intestine: Structure, Functions, and Role in Nutrient Absorption

The small intestine is a vital organ in the digestive system, responsible for most nutrient absorption. It consists of three sections: the duodenum, jejunum, and ileum.

Structure

• Duodenum: The first section, where enzymes from the pancreas and bile from the liver mix with chyme.
• Jejunum: The middle section, where the majority of nutrients are absorbed.
• Ileum: The final section, responsible for absorbing vitamin B12 and bile salts.

Functions

The primary functions of the small intestine include:

• Breakdown of food using digestive enzymes
• Absorption of essential nutrients, including carbohydrates, proteins, and fats
• Transporting digested food into the bloodstream

Role in Nutrient Absorption

Microvilli lining the small intestine increase surface area for maximum absorption. Nutrients pass into capillaries and lymphatic vessels for distribution throughout the body.

Interaction with Digestive Enzymes

The small intestine works closely with pancreatic enzymes and bile:

• Amylase: Breaks down carbohydrates.
• Lipase: Helps digest fats.
• Proteases: Aid in protein digestion.
• Bile: Helps emulsify fats for easier digestion.