UNIT B Chapter 9 Digestive System Section 9

UNIT B Chapter 9: Digestive System Section 9. 2 Accessory Organs of Digestion The accessory digestive organs are the pancreas, liver, and gall bladder. TO PREVIOUS SLIDE

UNIT B Chapter 9: Digestive System Hepatic portal system TO PREVIOUS SLIDE Section 9. 2

UNIT B Chapter 9: Digestive System TO PREVIOUS SLIDE Section 9. 2

Bile • • Emulsifying Agent Secreted by liver Excess stored in gall bladder (gall) Secretion stimulated by CCK and Secretin

Liver Function 1. 2. 3. 4. 5. 6. 7. 8. Detoxifying blood Making plasma proteins Maintaining blood glucose levels Producing bile, which contains bile salts that emulsify fat in the small intestine Producing urea, a nitrogenous waste product from the breakdown of amino acids Excrete bilirubin from old RBCs Stores vitamins and minerals: ADEK iron and copper Activates vitamin D

Jaundice • Yellow discoloration of the skin • Due to high levels of bilirubin (from old RBCs)

UNIT B Chapter 9: Digestive System Disorders of the Liver o Hepatitis is inflammation of the liver. o Hepatitis A o Hepatitis B o Hepatitis C TO PREVIOUS SLIDE Section 9. 4

UNIT B Chapter 9: Digestive System Cirrhosis • scarring (fibrosis) of the liver caused by • hepatitis and chronic alcoholism TO PREVIOUS SLIDE Section 9. 4

UNIT B Chapter 9: Digestive System The Gall Bladder Excess bile from the liver is stored in the gall bladder • Bile leaves the gall bladder and proceeds to the duodenum via the common bile duct TO PREVIOUS SLIDE Section 9. 2

Gall Stones

UNIT B Chapter 9: Digestive System Section 9. 4 • Gallstones are small, hard masses that form in the gall bladder. o Mostly Cholesterol o may block the common bile duct and cause jaundice o Treatment: removal of gall bladder. TO PREVIOUS SLIDE

UNIT B Chapter 9: Digestive System The Pancreas Exocrine function : pancreatic juice (buffer and digestive enzymes) Endocrine function: o Hormones: insulin and glucagon, regulate blood glucose (sugar) levels TO PREVIOUS SLIDE Section 9. 2

Acinar Cells secrete Pancreatic Juice: Water, bicarbonate 1. increases p. H in the duodenum (neutralizes gastric acid) 2. protects duodenal wall 3. activates pancreatic enzymes (inactivates pepsin (from the stomach) Enzymes: trypsinogen, lipase, nucleases, and pancreatic amylase

UNIT B Chapter 9: Digestive System Section 9. 2 Islets of Langerhans secrete hormones Insulin • Hormone secreted when blood glucose level is high • Stimulates the uptake of glucose by cells (liver, muscle, adipose tissue) to lower blood glucose Glucagon • Hormone secreted when blood glucose level is low • Stimulates the liver to break glycogen down into glucose to increase blood glucose • Stimulates adipose tissue to break fat down to glycerol and fatty acids (to make glucose) TO PREVIOUS SLIDE

UNIT B Chapter 9: Digestive System Section 9. 3 Digestive Enzymes Digestive enzymes help break down the major components of food: carbohydrates, proteins, nucleic acids, and fats. TO PREVIOUS SLIDE

UNIT B Chapter 9: Digestive System Section 9. 3 Carbohydrate Digestion by Enzymes The digestion of starch (a carbohydrate) begins in the mouth. • Salivary amylase (produced by the salivary glands) digests starch into maltose (a disaccharide) • Pancreatic amylase (produced by the pancreas) and maltase (produced by the small intestine) then convert maltose in the small intestine to glucose (a monosaccharide). Glucose can be absorbed by the small intestine. TO PREVIOUS SLIDE

UNIT B Chapter 9: Digestive System Figure 9. 11 Digestion and absorption of nutrients. a. The breakdown of carbohydrates, such as starch, involves amylase enzymes. TO PREVIOUS SLIDE Section 9. 3

UNIT B Chapter 9: Digestive System Section 9. 3 Carbohydrate Digestion by Enzymes Other disaccharides, such as lactose, have their own enzyme that digests them in the small intestine. • Lactase is an enzyme that digests lactose, a sugar found in milk. o Individuals who have a lactase deficiency often have symptoms of lactose intolerance (diarrhea, gas, cramps) caused by the fermentation of non-digested lactose by intestinal bacteria TO PREVIOUS SLIDE

UNIT B Chapter 9: Digestive System Section 9. 3 Protein Digestion by Enzymes The digestion of proteins begins in the stomach. • Pepsin is an enzyme produced by gastric glands that acts on proteins to produce peptides. • Trypsin (produced by the pancreas) and peptidases (produced in the small intestine) break down peptides into amino acids TO PREVIOUS SLIDE

UNIT B Chapter 9: Digestive System TO PREVIOUS SLIDE Section 9. 3

UNIT B Chapter 9: Digestive System Section 9. 3 Fat Digestion by Enzymes • Lipase (produced by the pancreas) acts in the small intestine and digests fat molecules in the fat droplets after they have been emulsified by bile salts • Glycerol and fatty acids enter the cells of the villi, where they are rejoined and repackaged as lipoprotein droplets (chylomicrons) before entering the lacteals TO PREVIOUS SLIDE

UNIT B Chapter 9: Digestive System TO PREVIOUS SLIDE Section 9. 3

UNIT B Chapter 9: Digestive System Section 9. 3 Regulation of Digestive Enzymes function best at an optimum temperature and p. H that helps maintain the proper shape to fit their substrate. • Since the digestive system is maintained at a constant 37ºC, enzymatic activity is largely controlled by p. H o The p. H of the stomach is between 1 and 2 but can increase to around 7. 4 to 7. 8 when sodium bicarbonate in pancreatic juice is released from the pancreas o This increase in p. H occurs after chyme enters the duodenum, and allows different digestive enzymes to be active depending on the p. H TO PREVIOUS SLIDE

Hormone Released by What Part/ in response to what? Acts on What Part? Gastric juice secreting cells at top of stomach What does it do? GASTRIN upper part of stomach/in response to protein in the stomach Causes secretion of gastric juices SECRETIN Small intestine/Acid chyme Pancreas from stomach Causes pancreas to release Na. HCO 3 and pancreatic enzymes CCK Small intestine/Acid chyme Pancreas and Liver (gall in stomach bladder) Causes liver to secrete bile and pancreas to secrete pancreatic juice. GIP Small intestine/acid chyme Stomach rich in fats enter duodenum Inhibits stomach peristalsis and acid secretion (opposes gastrin)

Hormones that Control Digestion: Hormone GASTRIN SECRETIN Released by What Part/ in response to what? upper part of stomach/in response to protein in the stomach Acts on What Part? Gastric juice secreting cells at top of stomach Small intestine/Acid chyme from stomach Pancreas and parietal cells of stomach CCK Small intestine/Acid (Cholecystok chyme in stomach inin) Pancreas and Liver (gall bladder) What does it do? Causes secretion of gastric juices Also increases the churning action of the stomach Is inhibited by the presence of HCl, Secretin, and GIP – negative feedback loop Causes pancreas to release Na. HCO 3 and pancreatic enzymes Also inhibits gastric acid secretion by the stomach Causes liver to secrete bile and pancreas to secrete pancreatic juice. Also acts as a hunger supressant

Specialized Cells Lining Villi • Absorptive epithelial cell –Contain brush border on lumen/apical side –Brush border: • Enzymes • Nutrient transport molecules • Goblet cell –Secretes mucus