Salivary Glands
| Bicarbonate fluid | Lubricates food during chewing. |
| Salivary Lipase | Prepares fat for digestion. |
Gastric Secretions
| Acid | Initiates digestion of protein and kills bacteria. |
| Pepsin | Aids in initiation of protein digestion. |
| Gastric Lipase | Initiates digestion of dietary fat. |
| Mucous | Lubricates and protects lining of stomach. |
| Intrinsic Factor | Aids in absorption of Vitamin B12 by small intestine. |
Liver Secretions
| Bile Acids | Detergent that helps dissolve dietary fat. |
| Phospholipids | Promotes absorption of fats. |
| Cholesterol | Excreted in bile. |
| Immunoglobulins | Protect from bacteria and other harmful organisms. |
| Mucus | Protects from bacteria. |
Pancreatic Secretions
| Bicarbonate | Neutralizes acid and protects digestive enzymes. |
| Water and electrolytes | Fluid delivery system for digestive enzymes. |
| Amylase | Digests dietary starch and glycogen. |
| Lipases | Digest dietary fat. |
| Proteases | Digest dietary protein. |
Small Intestine
| Substance | Absorption. |
| Iron | In Duodenum. |
| Vitamin B12 | In Ileum. |
| Bile Acids | Ileum absorbs and recycles to liver. |
| Water and Electrolytes | 90% absorbed in small intestine. |
| Carbohydrates | Enzymes along the tips of the intestinal cell digest prior to absorption, i.e. lactase digests milk, sugar. |
| Protein | After digestion by gastric & pancreatic enzymes. |
| Fat | After digestion by pancreatic enzymes & help of bile. |
Hormonal Regulation and Coordination
| Substance | Absorption. |
| Endocrine | Hormones arrive by blood stream, secreted from a distant site. |
| Insulin | Controls glucose metabolism. |
| Gastrin | Stimulates gastric acid/juice secretion and promotes growth of gastric and intestinal cells. |
| Secretin | Stimulates pancreatic secretion of fluid and bicarbonate, the liver to produce bile, and the stomach to produce pepsin. |
| Motilin | Regulates peristalsis and secretion between meals. |
| Paracrine | Hormones released locally. |
| Substance P | Influences secretion, absorption, blood flow, motility, and immunology. |
Hormones that can act as endocrine or Paracrine substances
| CCK | Signal for gallbladder contraction, pancreatic secretion (and growth), & satiety. |
| Somatostatin | Inhibits secretion by gut cells, nerves, and hormone secreting cells. |
| Neurotensin | Increases blood flow & stimulates secretion. |
Nerve Regulation and Coordination
| Extrinsic Nerves | Come from the unconscious part of brain or from the spinal cord. |
| Acetylcholine | Nerve transmitter stimulates peristalsis and secretion. |
| Adrenaline | Nerve transmitter that relaxes gastric & intestinal muscle & decreases blood flow. |
| Intrinsic Nerves | Are within the muscle walls of the digestive system hollow organs. Intrinsic enteric nervous system acts like a local computer, Initiates patterned program responses reflexively when stimulated, and control & coordinate peristalsis. |
