Digestive System 1B

17.6: Stomach The stomach is a J-shaped, pouch-like organ, about 25-30 centimeters long It hangs inferior to the diaphragm in the upper-left portion of the abdominal cavity The stomach has two layers of smooth muscle An inner circular layer An outer longitudinal layer (There may be a third inner layer of oblique fibers.)

Parts of the Stomach Greater curvature Esophagus Lower esophageal Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Esophagus Lower esophageal sphincter Fundus Circular fibers Esophagus Body Cardia Longitudinal fibers Pyloric sphincter Lesser curvature Greater curvature Duodenum Pyloric opening Esophagus Pyloric canal Pylorus Oblique fibers Pyloric antrum Gastric folds (rugae) (b) Longitudinal fibers (a)

Parts of the Stomach Fundus Pyloric sphincter Gastric folds Duodenum Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fundus Pyloric sphincter Gastric folds Duodenum Body Pylorus © Dr. Kent M. Van De Graaff

Gastric Secretions The mucous membrane of the stomach has tubular gastric glands that secrete: Pepsinogen From the chief cells Inactive form of pepsin Pepsin From pepsinogen in the presence of hydrochloric acid Is a protein splitting enzyme Hydrochloric acid From the parietal cells Needed to convert pepsinogen to pepsin Mucus From the goblet cells and the mucous glands Protective to stomach wall Intrinsic factor Is required for vitamin B12 absorption

b: © The McGraw-Hill Companies, Inc./Al Telser, photographer Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Portion of a gastric gland Gastric pits Gastric pit Mucous cell Mucous cell Mucosa Parietal cell Gastric gland Portion of a gastric gland Parietal cell Submucosa Muscle layers Chief cell Serosa Chief cell (a) (b) b: © The McGraw-Hill Companies, Inc./Al Telser, photographer

Gastric Absorption Gastric enzymes begin breaking down proteins, but the stomach is not well-adapted to absorb digestive products Why not ??? The stomach does absorb: Some water Certain salts Certain lipid-soluble drugs Alcohol

Mixing and Emptying Actions Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Stomach Food entering Duodenum Pyloric sphincter contracted Chyme Pyloric sphincter relaxed (a) (b) (c)

Nerve impulses inhibit peristalsis in stomach wall From CNS Vagus Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 4 Nerve impulses inhibit peristalsis in stomach wall From CNS Vagus nerve To CNS 1 Duodenum fills with chyme 3 Sensory nerve impulses travel to central nervous system 2 Sensory stretch receptors are stimulated

17.7: Pancreas The pancreas has a dual function as both an endocrine gland and exocrine gland The exocrine function is to secrete digestive juice called pancreatic juice

Structure of the Pancreas Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Right hepatic duct Left hepatic duct Cystic duct Common hepatic duct Bile duct Gallbladder Pancreatic duct Pyloric sphincter Minor duodenal papilla Duodenum Tail of pancreas Major duodenal papilla Bile duct Pancreatic duct Sphincter muscles Head of pancreas Major duodenal papilla Intestinal lumen Hepatopancreatic ampulla Hepatopancreatic sphincter

Pancreatic Juice Pancreatic juice contains enzymes that digest carbohydrates, fats, proteins, and nucleic acids, and include: Pancreatic amylase – splits glycogen into disaccharides Pancreatic lipase – breaks down triglycerides Trypsinogen, chymotrypsinogen, and carboxypeptidase Digest proteins Nucleases – digest nucleic acids Bicarbonate ions – make pancreatic juice alkaline

Regulation of Pancreatic Secretion Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Acidic chyme enters duodenum 1 4 Pancreatic juice rich in bicarbonate ions passes down pancreatic ducts to the duodenum Bicarbonate ions neutralize acidic chyme 5 Secretin stimulates pancreas to secrete bicarbonate ions 3 2 Intestinal mucosa releases secretin into bloodstream Bloodstream Hormonal signals released into bloodstream Stimulation of effector organ

17.8: Liver The liver is the largest internal organ It is located in the upper-right abdominal quadrant just beneath the diaphragm

Liver Structure Inferior vena cava Gallbladder Quadrate lobe Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Inferior vena cava Gallbladder Quadrate lobe Coronary ligament Right lobe Left lobe Cystic duct Falciform ligament Hepatic duct Hepatic artery Hepatic portal vein Right lobe Left lobe Round ligament Bile duct Gallbladder Inferior vena cava Caudate lobe (a) (b)

c: © The McGraw-Hill Companies, Inc./Al Telser, photographer Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Bile duct Branch of hepatic portal vein Branch of hepatic artery Plates of liver cells Central vein Branch of hepatic portal vein Bile canaliculi Bile ductule Hepatic sinusoids Bile duct (a) Branches of hepatic artery Sinusoids (b) (c) c: © The McGraw-Hill Companies, Inc./Al Telser, photographer

Liver Functions The liver carries on many important metabolic activities, including: Produces glycogen from glucose Breaks down glycogen into glucose Converts non-carbohydrates to glucose Oxidizes fatty acids Synthesizes lipoproteins, phospholipids, and cholesterol Converts carbohydrates and proteins into fats Deaminating amino acids Forms urea Synthesizes plasma proteins Converts some amino acids to other amino acids Stores glycogen, iron, and vitamins A, D, and B12 Phagocytosis of worn out RBCs and foreign substances Removes toxins such as alcohol and certain drugs from the blood

Composition of Bile Emulsify fats Bile is a yellowish-green liquid that hepatic cells continuously secrete Bile contains: Water Bile salts: Emulsify fats Help absorb fatty acids, cholesterol, and fat-soluble vitamins Bile pigments Cholesterol Electrolytes

Gallbladder Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

© Carroll Weiss/Camera M.D. Studios Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. © Carroll Weiss/Camera M.D. Studios

Regulation of Bile Release Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cystic duct Common hepatic duct Gallbladder 3 CCK stimulates muscular layer of gallbladder wall to contract Bile duct 1 Chyme with fat enters duodenum 4 Bile passes down the cystic duct and bile duct to duodenum 5 Hepatopancreatic sphincter relaxes and bile enters duodenum Pancreatic duct Cells from the intestinal mucosa secrete the hormone cholecystokinin (CCK) into the bloodstream 2 Duodenum Hormonal signals released into bloodstream Bloodstream Stimulation of effector organ

Functions of Bile Salts Bile salts aid digestive enzymes They reduce surface tension and break fat globules into droplets (like soap or detergent) and this is called emulsification They enhance absorption of fatty acids and cholesterol They help absorb fat-soluble vitamins A, D, E and K Bile salts are recycled as they return to the liver