The Digestive System … Notes I

1. The Digestive System … Notes I Structure (Anatomy)/Function (Physiology) …see “Notes” handout

2. mouth tongue epiglottis esophagus trachea cardiac sphincter liver stomach pyloric sphincter gall bladder pancreas bile duct duodenum ileum colon Ileo-caecal valve appendix rectum anus anal sphincter The Stylized Digestive System

3. esophagus gall-bladder stomach bile duct pancreas duodenum The Accessory Digestive Structures

4. The Pancreas • Posterior to stomach • Both an endocrine and exocrine gland • Hormone producing • Insulin (increases body’s ability to use glucose and store it as glycogen in the liver). • Glucagon (promotes the break down of glycogen in the liver to glucose). • Produces digestive juices (pancreatic juice) • Releases pancreatic juice through pancreatic duct to duodenum • Pancreatic juice contains …

5. Water • Sodium bicarbonate (NaHCO3) • Nucleases • Lipase • Pancreatic amylase • Trypsinogen (which becomes trypsin, a protease) Be sure you can discuss the function of each of these in digestion!

6. The Liver • Large organ …Posterior to diaphragm • Richly supplied with blood • Functions: • Regulate the glucose level in blood. • Glucose should comprise about 0.1% of blood plasma. If the level is too high, glucose will be converted to and stored as glycogen by the liver. If it is too low, glycogen breakdown into glucose occurs (recall the roles of insulin and glucagon).

7. Produce urea Urea is a toxic substance produced by the liver from nitrogenous waste products. Body cells produce the waste ammonia, which is transported through blood to the liver. Additionally, the liver is able to deaminate amino acids and produce glucose to help maintain blood glucose levels (process of gluconeogenesis). The liver converts these nitrogenous wastes into urea, which is removed from blood by the kidneys during urine formation.

8. Detoxify blood The liver destroys other toxins in blood. An example is alcohol.The liver metabolizes alcohol into fatty acids, which can cause permanent scarring of the liver tissue - a condition known as cirrhosis.

9. Produce bile Bile is stored in the gall bladder until a hormone (CCK) signals its release. Bile is an emulsifier of fats. As such, it mechanically breaks fat clusters into smaller pieces. This increases their surface area, thereby increasing the efficiency of the lipase enzyme, which chemically breaks them down into fatty acids and glycerol.

10. Produce various blood proteins (globulins) Examples include albumin (helps maintain osmotic pressure of blood) and fibrinogen and prothrombin (important for blood clotting).

11. Destroy old red blood cells Red blood cells have an average life span of 4 months… millions die every day. Disassembled by the liver, the useful components of red blood cells are recycled. For example, iron from hemoglobin is reused by bone marrow in the manufacture of new red blood cells. The rest of the hemoglobin molecule is "worn out" and gets converted to bilirubin and biliverdin. These green pigment molecules are added to bile for excretion through the digestive system.

12. The Digestive Process… …stay tuned!