Accessory Organs Pancreas, Liver and Gallbladder

Pancreas Secretes pancreatic juice into pancreatic duct then to the duodenum Function: contains 4 classes of enzymes to break down substances. Location: posterior to stomach; left side

Pancreatic Juice Pancreatic amylase –splits starch and glycogen into disaccharides Pancreatic lipase –splits triglycerides into fatty acids and monoglycerides Proteinases (Trypsin, chymotrypsin, carboxypeptidase) –Breaks up peptide bonds Nucleases –split nucleic acid molecules

Pancreatic Juice Bicarbonate ions make pancreatic juice alkaline to neutralize acidic chyme

Pancreatic Secretion Regulation During cephalic and gastric digestive phases parasympathetic impulses stimulate pancreatic secretion. Secretin: hormone –causes release of pancreatic juice into duodenum – stimulates a bicarbonate-rich fluid. –Activated by the duodenum filling up with chyme

Figure 17.25

Pancreatitis Inflammation of pancreas Caused by activation of enzymes in the pancreas gland –Trypsinogen------trypson

Liver Largest internal organ 2 lobed structure –Large right and small left Each lobe is made up of Hepatic lobules: function unit of the liver Figure 17.28

Liver Lobes are divided into hepatic lobules –hepatic cells around a central vein –hepatic sinusoids lead to the hepatic portal vein –Kupffer cells remove bacteria by phagocytosis –bile canals lead to hepatic ducts which merge at the common bile duct Figure 17.29

Liver Functions 1. Metabolism: Carbohydrate metabolism –stores glycogen, regulates blood glucose levels Lipid metabolism –synthesizes lipoproteins, regulates lipid metabolism **Protein metabolism –deamination of amino acids, forming urea –transamination of amino acids –synthesis of plasma proteins (clotting proteins)

Liver Functions 2. Stores minerals and vitamins –iron is stored as ferritin, Vit A, B 12 and glycogen 3. Detoxification of substances, including alcohol 4. Destruction of damaged red blood cells 5. Phagocytosis of foreign antigens –Contain Kupffer’s cells Remove and destroy microbes, foreign matter and worm platelets and erythrocytes 6. Serves as a bile reservoir and Secretion of bile 7. Blood reservoir

Bile Composition Yellowish-green fluid secreted by hepatic cells Contains water (90%), cholesterol, and electrolytes Contains bile salts* –Emulsify (break down) fats –Makes cholesterol Contains bile pigments –bilirubin, biliverdin –breakdown products of hemoglobin

Figure 17.30

Jaundice Abnormal Skin pigmentation Excess bilirubin in the blood. (Bilirubin is produced by the normal breakdown of red blood cells. Normally bilirubin passes through the liver and is excreted as bile through the intestines)ii Jaundice occurs when bilirubin builds up faster than the liver can break it down and pass it from the body.

Liver Diseases Cirrhosis Jaundice

Gallbladder Bile is produced by the liver and concentrated in the gall bladder. Stores bile between meals Figure 17.32

Gallbladder Cholecystokinin: CCK released in response to proteins and fats in the small intestine, stimulates gall bladder contraction. Bile leaves through the cystic duct to the common bile duct and is squirted into the duodenum of the small intestine.

Function of Bile Salts Bile salts enhance absorption of fatty acids and fat-soluble vitamins. Bile salts reduce surface tension and break fat into small droplets (emulsification). Emulsification increases surface area so lipases can more easily digest fats. The intestinal mucosa reabsorbs nearly all of the bile salts.

Blocked cystict duct

cholecystitis

Small Intestine Extends from the pyloric sphincter to the large intestine Three portions: duodenum, jejunum, ileum Receives secretions from the pancreas and the liver Complete digestion of nutrients in chyme, absorbs products of digestion, transports residue to the large intestine Figure 17.33

Small Intestine Double-layered folds of peritoneum –mesentery: supports intestinal nerves, blood and lymphatic vessels –greater omentum: drapes over the intestine Inner intestinal wall has many tiny projections, the intestinal villi. Each contains blood vessels, nerves and a lacteal Intestinal glands extend into the mucosa Circular folds of the mucosa, plicae circulares, increase surface area

Figure 17.35

Figure 17.36

Figure 17.37

Small Intestine Secretions Mucus is secreted by goblet cells and glands in the submucosa Intestinal mucosa have digestive enzymes on their luminal surfaces –peptidases: split peptides into amino acids –sucrase, maltase, lactase: split disaccharides into monosaccharides –intestinal lipase: splits fats into fatty acids and glycerol