Digestion in the Small Intestine

Digestion in the Small Intestine

The small intestine is the primary site for digestion and absorption of nutrients. This process involves the contributions of digestive juices, enzymes, and the transport of nutrients across the intestinal wall.

1. Digestive Juices in the Small Intestine:

• Pancreatic Juice: Contains crucial digestive enzymes such as:

• Trypsin: Digests proteins.

• Amylase: Digests carbohydrates.

• Lipase: Digests lipids.

• Cholesterol ester hydrolase: Digests cholesterol.

• Phospholipase A2: Digests phospholipids.

• Bile: Secreted from the liver, it emulsifies fats, facilitating the efficient action of lipase.

• Intestinal Juice: Secreted from the intestinal glands, containing digestive enzymes such as:

• Peptidase: Digests proteins.

• Sucrase, maltase, lactase: Digests carbohydrates.

• Lipase: Digests lipids.

2. Mucus in the Small Intestine:

• Secreted by:

• Brunner’s Glands: Located in the duodenum, they secrete alkaline mucus to neutralize gastric acid.

• Goblet Cells: Scattered throughout the intestinal lining, they secrete mucus to protect the lining from damage.

• Crypts of Lieberkuhn: Found between intestinal villi, they secrete mucus and digestive enzymes.

3. Digestive Enzymes:

• Protein Digestion:

• Pancreatic Juice: Trypsin

• Intestinal Juice: Peptidase

• Carbohydrate Digestion:

• Pancreatic Juice: Amylase, maltase

• Intestinal Juice: Sucrase, maltase, lactase

• Lipid Digestion:

• Pancreatic Juice: Lipase, cholesterol ester hydrolase, phospholipase A2

• Intestinal Juice: Lipase

4. Secretion of Intestinal Juice:

• Stimulated by:

• Local Stimulation: Contact of food with the intestinal lining.

• Hormones: Hormones like secretin and cholecystokinin stimulate intestinal juice secretion.

5. Nutrient Absorption:

• Na+ Transport: Active transport, generating a gradient for the absorption of other substances.

• Na+ Absorption: Throughout the small intestine.

• Cl- Absorption: Duodenum and jejunum.

• HCO3- Absorption: Duodenum and jejunum.

• Ca2+ Absorption: Duodenum.

• Iron Absorption: Upper small intestine.

• Carbohydrate Absorption: Duodenum and jejunum.

• Protein Absorption: Duodenum, jejunum, and a small amount in the ileum.

• Vitamin B12 Absorption: Ileum.

In conclusion, the small intestine plays a crucial role in digestion and nutrient absorption. This process is facilitated by the combined action of digestive juices, enzymes, and the transport of nutrients across the intestinal wall.