Small Intestine Anatomy and Function

Small Intestine Structure and Function

• The small intestine is approximately 20 feet long and its primary function is absorption and digestion.
• It consists of four parts: duodenum, jejunum, ileum, and ileocecal valve.
• The mucosal lining of the small intestine is covered with villi, which are tiny fingerlike projections.
• Each villus contains goblet cells that release digestive enzymes, secrete mucus, and absorb nutrients.
• The villi are also covered with microvilli, which are located on the epithelial cells, forming a double set known as the brush border.
• The brush border increases the surface area of the small intestine, significantly increasing its absorptive capacity.

Digestive Process in the Small Intestine

• The intestinal phase of digestion involves neural and hormonal responses.
• The neural response, the enterogastric reflex, is responsible for opening the pyloric sphincter and decreasing gastric motility and acid production.
• In the duodenum, bile from the liver, enzymes from the pancreas, and chyme from the stomach come together to complete the digestive process.
• The duodenum and jejunum contain receptors that sense acidity, osmotic pressure, and products of digestion such as fats and peptides.

Functions of Small Intestine Segments

• The primary function of the duodenum is to complete the digestive process.
• The primary function of the jejunum is absorption of nutrients such as amino acids, glucose, iron, calcium, and fat-soluble vitamins.
• The primary function of the ileum is the reabsorption of vitamin B12 and the return of bile acids to the liver through the enterohepatic circulation process.
• The gastroileal reflex stimulates the opening of the ileocecal valve, which controls the release of digestive contents into the large intestine.

Test your knowledge on the structure and function of the small intestine, the largest organ in the gastrointestinal system responsible for absorption and digestion. Learn about the different parts such as the duodenum, jejunum, and ileum, along with the role of villi in nutrient absorption.