MEDICAL BIOLOGY, HUMAN ANATOMY, PHYSIOLOGY, AND PATHOLOGY - Ya.I. Fedonyuk 2010

ANATOMY, PHYSIOLOGY, PATHOLOGY

CHAPTER 7. NUTRITION PROCESS AND ITS PATHOLOGY

ANATOMY AND PHYSIOLOGY OF THE DIGESTIVE ORGANS

SMALL INTESTINE

2. DIGESTION IN THE DUODENUM

2.1. COMPOSITION, PROPERTIES, AND REGULATION OF PANCREATIC JUICE SECRETION

Pancreatic juice is a colorless fluid with an alkaline reaction that contains Enzymes capable of

breaking down Proteins, fats, and CARBOHYDRATES. The alkaline reaction is maintained by bicarbonates.

Proteolytic Enzymes (Trypsin, Chymotrypsin, carboxypeptidase) break down proteins into Peptides and Amino Acids. These enzymes are synthesized by The Pancreas in an inactive state. Trypsinogen (the inactive form of the enzyme) is converted into trypsin (the active form) through the action of enterokinase, which is produced by the intestinal mucosa. Trypsin activates chymotrypsinogen, turning it into chymotrypsin. Unlike the Pepsin found in gastric juice, pancreatic proteolytic enzymes function exclusively in an alkaline environment.

Lipolytic enzymes (lipase, phospholipase) break down fats and Phospholipids into Fatty acids and glycerol. These enzymes operate only in an alkaline medium and act upon fats that have been previously emulsified by Bile.

Amylolytic enzymes (amylase, maltase, lactase) hydrolyze carbohydrates. Amylase breaks down the polysaccharide starch into Disaccharides. Maltase splits the disaccharide maltose into glucose. Lactase breaks down milk sugar into the monosaccharide glucose.

The secretion of pancreatic juice is initially triggered by conditioned stimuli even before food enters the Oral Cavity, such as the smell or appearance of food, or simply talking about food. Secretion is further intensified when food stimulates the receptors of the oral cavity. The Vagus nerve serves as the secretory nerve, with the secretion center located in the Medulla Oblongata. Sympathetic nerves inhibit pancreatic juice secretion; therefore, negative emotions, pain, and other states that stimulate the sympathetic Nervous system suppress this process.

From the moment chyme enters the duodenum, pancreatic secretion reaches its maximum and is mediated by neurohumoral mechanisms. This can be demonstrated experimentally, as the pancreas continues to secrete juice even after its innervating nerves are severed. The humoral stimulators of pancreatic secretion are the Hormones secretin and cholecystokinin-pancreozymin, which are produced by the duodenal mucosa. These hormones are released specifically when acidic chyme enters the alkaline environment of the intestine. The active hormones are then absorbed into the bloodstream, transported to the pancreas, where they stimulate its neuroglandular apparatus and induce juice secretion.

If the chyme has a high fat content, it promotes The production of significant amounts of cholecystokinin-pancreozymin.