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Pancreas
DIAGRAM COMING SOON
Diagram 2.4 Pancreas
The pancreas is also an accessory organ. It has both endocrine and exocrine functions. The endocrine pancreas controls the blood glucose levels by way of the various hormones’ actions.
Glucagon by A (alpha) cells elevates blood glucose levels when one does not have sufficient blood glucose for one’s activity level. On the other hand, Insulin by B (beta) cells reduces blood glucose levels when the blood glucose is high especially when digestion sets in as one consumes high carbohydrates. Another hormone, Somatostatin by D cells are Paracrine and inhibit production of both insulin and glucagons. This is like a control center that monitors the levels if in excessive production, despite the fact that insulin and glucagons antagonize each other.
The exocrine pancreas releases both electrolytes and enzymes. Its main function is to neutralize acid chyme arriving from the stomach, in order to prevent acidic damage to the other organs below the stomach. Sodium and potassium concentrations in pancreatic juices are the same as those in plasma (142 & 4.8 mEq/L, respectively), whereas bicarbonate concentration is much higher than in plasma (100 mEq/L vs 24 mEq/L). There are also other ions like Calcium, magnesium, zinc, phosphate, sulfate.
In the pancreatic juices are the many enzymes that also aid in digestion. There is Amylase: a-amylase that is secreted in its active form. It breaks down glycogen, starch, and most other complex carbohydrates. (carbohydrate digestion). There is also Lipases: Lipase, colipase, phospholipase. They are mostly secreted in their active forms. They serve to hydrolyze water-insoluble esters (requires bile salts to work) and water-soluble esters and conducts fat digestion. The last type are Proteases: trypsin and chymotrypsins which are secreted as inactive proenzymes. Trypsinogen is activated by the small intestine brush border enzyme enterokinase and afterwhich, Trypsin activates other enzymes to carry out protein digestion. The digestion action of enzymes from pancreas is as follows:
Hydrolysis: addition of water molecules as H+ and OH- to break up molecular bonds
1. polysaccharides (carbohydrates) à monosaccharides
2. triglycerides (lipids) à fatty acids
3. peptides (proteins) à amino acids
The control of the pancreatic bicarbonate and enzyme secretions is regulated depending on what flows to the duodenum lumen. If there’s acid in the duodenum lumen, it will increase the secretin release from duodenum mucosa and secretin is then carried in blood to the pancreatic duct cells. Afterwhich, increase secretion of aqueous NaHCO3 solution is then released by the pancreas to the duodenum lumen in which will neutralize the acid. On the other hand, if there is fat and proteins products in the duodenum lumen, it will increase the amount of CCK from duodenum mucosa which is then carried in blood to the pancreatic acrinar cells. This elevates the level of pancreatic digestive enzymes into the duodenum lumen in which will digests the fat and proteins products in the duodenum lumen.
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