Jejunum

Definition

The jejunum is the second part of the small intestine, located between the duodenum and the ileum. It plays a critical role in the absorption of nutrients, particularly lipids, following digestion. Its highly folded mucosal surface increases the area for absorption, making it essential for efficiently taking up fatty acids and other nutrients from digested food.

5 Must Know Facts For Your Next Test

1. The jejunum comprises about 2.5 meters (around 8 feet) of the small intestine's total length and is situated primarily in the upper left quadrant of the abdominal cavity.
2. It has a thicker wall and larger lumen compared to the ileum, which facilitates better nutrient absorption.
3. The jejunum has a rich blood supply through the mesenteric arteries, ensuring efficient transport of absorbed nutrients into circulation.
4. Villi and microvilli on the jejunal surface greatly enhance its absorptive capacity, making it highly effective for lipid uptake.
5. Absorption of fatty acids in the jejunum is enhanced by emulsification from bile salts, which break down fats into smaller droplets.

Review Questions

• How does the structure of the jejunum facilitate its role in nutrient absorption?
  • The jejunum's structure is specifically designed to optimize nutrient absorption. It has a highly folded mucosal surface with numerous villi and microvilli that dramatically increase its surface area. This structural adaptation allows for more efficient uptake of nutrients, particularly lipids, by providing more sites for interaction with digested food. Additionally, its thicker walls support better blood flow, enhancing nutrient transport into the bloodstream.
• Compare and contrast the functions of the jejunum with those of the duodenum in lipid digestion and absorption.
  • While both the jejunum and duodenum are integral to lipid digestion and absorption, their functions differ significantly. The duodenum is primarily where initial digestion occurs; it receives bile from the gallbladder to emulsify fats and pancreatic enzymes to further break them down. In contrast, the jejunum focuses on absorbing these digested lipids into the bloodstream through its extensive surface area. Thus, while the duodenum sets up lipid digestion, the jejunum is where most absorption happens.
• Evaluate the impact of impaired jejunal function on overall lipid metabolism in the human body.
  • Impaired jejunal function can significantly disrupt lipid metabolism. If the jejunum is damaged or diseased, its ability to absorb fatty acids and other lipids is compromised. This can lead to malabsorption syndromes, resulting in deficiencies of essential fatty acids and fat-soluble vitamins. Moreover, poor lipid absorption may cause excessive fat in stool (steatorrhea) and can impact energy levels and overall health due to inadequate nutrient supply. Thus, a healthy jejunum is crucial for maintaining proper lipid metabolism and overall nutritional status.

Related terms

Duodenum: The first part of the small intestine, where most chemical digestion occurs, including the mixing of food with bile and pancreatic juices.

Ileum: The final part of the small intestine, responsible for absorbing vitamin B12 and bile salts, and connecting to the large intestine.

Chylomicrons:

Lipoprotein particles formed in the intestinal cells that transport absorbed lipids from the intestines to other locations in the body.