Hepatic function and nutrient absorption (reabsorption) 4/19

1. Hepatic function and nutrient absorption (reabsorption) 4/19 • What is the function of the Gallbladder? • How does bile help us digest fatty foods? • How does lipase function? • What are the exocrine secretions of the pancreas? • Why is bicarbonate generated in so many different places around the duodenum? • What does the intestinal wall look like at the microscopic level? • How does the intestine move chyme with peristaltic waves of smooth muscle cell contraction? VIP!! • What enzymes degrade protein, carbohydrates and fat? • Can protein, carbohydrates and fat be absorbed if it is not broken up into monomers? • What is the function of the large intestine?

2. Enzymatic digestion occurs in three places: Mouth, Stomach and Small Intestine. What enzymes do we use to do this in each of these three organs? Don’t forget the two types of lipase.

3. The pancreas is unique because it has BOTH exocrine AND endocrine functions,,,,, we quickly die without a pancreas. • 3 Endocrine Hormones Created by Pancreatic Islets: • 1) Glucagon: to maintain plasma glucose during starvation • 2) Insulin: to prevent hyperglycemia after a meal • 3) Somatostatin: inhibits gastrin release and HCl secretion • CCK gets stomach ready to be empty again (rest) and the intestine ready to digest food so nutrients can be absorbed • Acid in duodenum: stimulates CCK secretion! • Nutrients also promote CCK secretion! • CCK Functions: • 1)Contraction of gallbladderBile into duodenum • 2)Stimulates exocrine secretions by the pancreas: • +Pancreatic Enzymes, +Bicarbonate and +Flow rate • 3)Relaxes HEPATOPANCREATIC sphincterBile into duodenum

4. Pancreatic duct and Common bile duct Exit pancreatic duct via Sphincter of Oddi Why are bile and pancreatic secretions rich in bicarbonate? What are Zymogens? Why make them? #1: Trypsinogen>>activated only by enterokinase in the duodenum!!!!!! Secondary Zymogens: Carboxylpeptidase and Chymotrypsin Bile Activated Pancreatic Enzymes: P. amylase, P. lipase, Ribonuclease, Deoxyribonuclease Why do we get so sick without bile? The pancreas creates about 1 ½ liters of exocrine secretion/day from acinar ducts that are rich in water, bicarbonate and zymogens.

5. Intestinal surface promotes four things: 1)Max. surface area, 2)Peristaltic chyme propulsion, 3)Protection against stomach acid/contents, and 4)Replacement cells (24hr/day-7days/WK) • Anatomical divisions: • Circular folds>Villi w Lacteals > Microvilli > Brush Border • Deep Duodenal glands produce bicarbonate along length of intestine in case stomach acid should appear. • Function of brush border and contact digestion • Crypts of Leiberkuhn: • 1) 1-2 liters/day with NaCO3 for pH/fluidity • 2) Epith. Cell division occurs at bottom of Crypts of Lieberkuhn • Why extend Crypts so deep into Submucosa? • What if all Crypts are destroyed? • The cell turn-over-rate of the GI tract is one of the highest in body (2-4 days), what happens when GI cells cant divide? • Consider: Radiation, Toxins, Chemotherapy • This turnover time is important: never ever forget this!

6. Circular foldsVilli with LactealsMicrovilliBrush Border Cell division is most rapid at bottom of crypts! Goblet cells produce extra mucus to keep surface moist and bacteria free.

7. GI smooth muscle cells can contract independently of the CNS because the gut has autorhymicity! The CNS can only ‘modify’ this rate depending on need. • Duodenum usually sets rate for the entire intestine! ‘Migrating Motor Complexes’ are waves of contraction • 12 MMC/min: Duodenum8MMC/min: Jejunum • Contractions occur in Circular and Longitudinal SMC • Contractions mean flow! • This means bacteria are constantly pushed out! • Why is a lack of “digestive sounds” a bad clinical sign? • Irritations in lower intestine may modify gut activity! • What happens to base-line autorhythmic rate when you have diarrhea or indigestion? • What happens to the ability to expel gut material if you are very weak?

8. Intestinal autorhythmically generates waves of contraction. Like the heart, areas with fastest rate determine intestine contraction rate. The Duodenumal region has the fastest rate and the colonic region has the slowest rate of autorhythmicity!What happens to colonic motility if the ileum is injured proximal to the IC valve?

9. The three nutrient types (carbohydrate, proteins and lipids) are broken down into single monomers for maximal absorption (mostly in the jejunum)! Triglygerides are broken into free fatty acids by the action of lipase prior to non-enzymatic absorption.All other nutrients (monosaccharides and amino acids) require specific transport enzymes for significant intestinal absorption to occur.

10. Where are the secretions of the mouth, stomach, pancreas, liver and small intestine reabsorbed? Lets Give Thanks to the Colon!! Some water is reabsorbed with the nutrients along the length of the small intestine, largely the ileum. The large intestine is the last chance to reabsorbed needed materials before you are left with feces in the rectum. • Bile salts can also be reabsorbed into the Portal Circulation! • Ileocecal Valve> entry point to Large Intestine • Cecum>Ascending>Transverse>Descending>Sigmoid • Haustra are the large side pockets

11. Gallbladder: helps store and concentrate bile so extra doses of bile can be released when chyme passes into the duodenum. Bile emulsifies fat and greatly improves digestion. • Concentrates bile X5 to X20 times! • Smooth muscles around gall bladder contract to release bile to the cystic duct • Biliary Calculi (aka Gall stones) Cholelithiasis and lithotripsy • In contrast to kidney stones • Duct Blockages and jaundice! • If the Gallbladder is removed the bile is dumped into the small intestine at a constant rate, not bad bud bile isn’t available for handling meals with lots of fat.

12. How are large chunks of fat broken down into free fatty acids?

13. Dietary Fiber from plants helps us remove cholesterol from the blood by preventing ileal/colonic reabsorption of bile! This helps lower your plasma cholesterol and your heart disease risk!The diagram below represent digestion without fiber.

14. Why is fat content of diet highest on birthday, Thanksgiving, Christmas, New years, Easter, Rhamadan, 4th of july. Why do we have heart attacks on these days? Why do we die on holidays?

15. Some good review questions: 1) What are six functions of the liver? 2) What is the difference between a liver “lobe” and a hepatic “lobule”? 3) What is the function of “bile”? 4) What does the enterohepatic circulation recycle? 5) Name the digestive enzyme that degrades triglycerides.

16. The large intestine (colon) lets us adjust the fluid content of our feces.Problems: Diarrhea (too much H2O) or Constipation (not enough H2O)

17. Where are the secretions of the mouth, stomach, pancreas, liver and small intestine reabsorbed? Lets Give Thanks to the Colon!! Some water is reabsorbed with the nutrients along the length of the small intestine, largely the ileum. The large intestine is the last chance to reabsorbed needed materials before you are left with feces in the rectum. • Bile salts can also be reabsorbed into the Portal Circulation! • Ileocecal Valve> entry point to Large Intestine • Cecum>Ascending>Transverse>Descending>Sigmoid • Haustra are the large side pockets