Chapter 25-2 The Digestive System

LaPointe Spring ‘12 Slide # 2 Functions of the stomach Bulk storage of undigested food Mechanical breakdown of food - churning Disruption of chemical bonds via acids and enzymes - makes chyme Production of intrinsic factor - required for vitamin B12 absorption

LaPointe Spring ‘12 Slide # 3 Anatomy of the stomach Lesser and greater curvatures Cardia – superior, medial portion by the esophagus, contains mucus glands Fundus – portion superior to stomach-esophageal junction Body – area between the fundus and the curve of the J (pyloris) Pyloric region – antrum, pyloric canal, pylorus adjacent to the duodenum

LaPointe Spring ‘12 Slide # 4 Stomach anatomy Pyloric Sphincter Guards exit from stomach to intestine Rugae Ridges and folds in relaxed stomach Muscularis externa has 3 layers oblique circular longitudnal

LaPointe Spring ‘12 Slide # 5 The Stomach Note the Saladin text book calls the narrow opening of the stomach to the duodenum the pylorus (see fig for labeling) Pyloric region

LaPointe Spring ‘12 Slide # 6 Histology of the stomach Stomach glands (pyloric, cardiac, and gastric) open into gastric pits Parietal cells secrete Intrinsic factor, and HCl Chief cells secrete Pepsinogen pepsin rennin (chymosin) -(coagulates milk) and gastric lipase -produced in newborn infants

LaPointe Spring ‘12 Slide # 7 Histology of the stomach Pyloric glands Mucous secretion containing several hormones Enteroendocrine cells G cells secrete gastrin - stimulates stomach contraction + secretions D cells secrete somatostatin-inhibits gastrin release

LaPointe Spring ‘12 Slide # 8 The Stomach Lining (see fig for comparison of pyloric and gastric glands) Marieb, Figure 23.15a, b

LaPointe Spring ‘12 Slide # 9 Secretion of Hydrochloric Acid Alkaline tide Parietal cells Stimulated by Gastrin, ACh (vagus nerve), histamine (local control) (Also see Saladin 25.14) Seeley, Stephens and Tate

LaPointe Spring ‘12 Slide # 10 Regulation of gastric activity (fig 25.18) Cephalic phase (long reflex) - CNS, sensory input, via vagus nerve prepares stomach to receive ingested material Gastric phase begins with the arrival of food in the stomach neural (short and long reflexes) - stretch receptors, chemoreceptors hormonal - gastrin local responses (paracrine)- histamine release Intestinal phase controls the rate of gastric emptying

LaPointe Spring ‘12 Slide # 11 Intestinal phase Neural - enterogastric reflex (short and long reflexes) - inhibits gastrin secretion decreases acid secretion and motility Hormonal Cholecstokinin (CCK) - (lipids) inhibits gastric secretion and stimulates bile secretion Gastric inhibitory protein (GIP) - (lipids) inhibits gastric secretion, stimulates pancreas to release insulin Secretin (decrease pH) inhibits gastric secretion stimulates pancreas buffer secretion Gastrin - intestinal G cells

LaPointe Spring ‘12 Slide # 12 Digestion and absorption in the stomach Proteins Preliminary digestion (positive feedback loop) Pepsin (see fig 25.15) HCl Carbohydrates salivary  amylase limited digestion of as long as pH remains > 4.5 Very little absorption of nutrients Some drugs and alcohol are absorbed

LaPointe Spring ‘12 Slide # 13 Small intestine Important digestive and absorptive functions Exocrine glands release enzymes proteases and peptidases amylase, other enzymes that digest sugars lipases Receives enzymes, bile, and buffers provided by pancreas, liver, gall bladder

LaPointe Spring ‘12 Slide # 14 Regions of the Small Intestine Martini Figure 24.16a Cecum Ileocecal valve

LaPointe Spring ‘12 Slide # 15 Small intestine - gross anatomy Duodenum first ~ 10 inches; churning, receives pancreatic and liver secretions contains openings for bile duct and pancreatic ducts digestion and absorption Jejunum - ~ 8 feet; chemical digestion and absorption Ileum - ~12 feet; continued absorption, aggregated lymphoid nodules (Peyer’s patches) protect against bacteria Ileocecal sphincter Transition between small and large intestine

LaPointe Spring ‘12 Slide # 16 Marieb Figure The Duodenum Minor duodenal papilla

LaPointe Spring ‘12 Slide # 17 Histology of the small intestine Plicae circular folds of the intestinal lining Villi Fingerlike projections of the mucosa Increases the absorptive area ~600x cells have microvilli Lacteals Terminal lymphatic in villus, transports lipids

LaPointe Spring ‘12 Slide # 18

LaPointe Spring ‘12 Slide # 19 Histology of the Intestine

LaPointe Spring ‘12 Slide # 20 Intestinal juices Duodenal glands (Brunner’s glands) Produce watery mucus, buffers and few enzymes Moisten chyme Help buffer acids + increase pH to alkaline range (7-8) Maintain digestive material in solution Protect intestinal lining Small amounts of intestinal enzymes

LaPointe Spring ‘12 Slide # 21 Cells in the intestine Made in crypts of Lieberkuhn Absorptive cells Goblet cells Paneth cells (may be part of immune system) Endocrine cells

LaPointe Spring ‘12 Slide # 22 Intestinal movements Peristalsis Segmentation Gastroenteric reflexes Initiated by stretch receptors in stomach Gastroileal reflex Triggers relaxation of ileocecal valve permits emptying into the large intestine

LaPointe Spring ‘12 Slide # 23 The pancreas Exocrine functions In acini Enzymes Buffers (HCO 3 - ) Pancreatic duct penetrates duodenal wall Endocrine functions In islet cells Insulin and glucagons

LaPointe Spring ‘12 Slide # 24 The pancreas Exocrine functions Pancreatic juice secreted into small intestine Carbohydrases - alpha amylase Lipases Nucleases (deoxyribonucleases and ribonucleases) Proteolytic enzymes (proteases) proenzymes (trypsinogen, chymotrypsinogen, procarboxypeptidase, and specialized enzymes - e.g. proelastase or procollagenase )

LaPointe Spring ‘12 Slide # 25 Protein digestion COOHNH 2 COOH

LaPointe Spring ‘12 Slide # 26 Pancreas anatomy Posterior to the stomach and extends laterally from the duodenum to the spleen Pancreatic duct empty into the duodenal ampulla along with the bile duct Accessory pancreatic duct

LaPointe Spring ‘12 Slide # 27 The Pancreas Pancreatic duct & ampulla Acces. Pancreatic duct

LaPointe Spring ‘12 Slide # 28 (increases buffer secretion) (increases enzyme secretion) Control of Pancreatic Secretion

LaPointe Spring ‘12 Slide # 29 Pancreas Histology Islet (endocrine)

LaPointe Spring ‘12 Slide # 30 The liver Largest visceral organ Performs metabolic and hematological regulation and produces bile Maintains glucose levels by storing glycogen or the hydrolysis of stored glycogen (glycogenolysis) Makes glucose from non-carbohydrate precursors (gluconeogenisis) Lipid storage and release (fatty acids and cholesterol) Conversion of amino acids to lipids or glucose

LaPointe Spring ‘12 Slide # 31 The liver (continued) Stores vitamins Fat soluble (A,D,E,K) and vitamin B12 iron storage - ferritin Drug, hormone, and protein inactivation and removal from the blood (cytochromes) Deamination and conversion of ammonia to urea Makes bile Makes albumin, fibrinogen and other blood proteins

LaPointe Spring ‘12 Slide # 32 Anatomy of the Liver

LaPointe Spring ‘12 Slide # 33 Portal areas (hepatic triad) at corners of lobules branches of the hepatic portal vein, hepatic artery, bile duct Central vein fed by sinusoids, form hepatic veins Hepatocytes form irregular plates arranged in spoke- like fashion, make bile and plasma proteins Bile canaliculi carry bile made in hepatocytes to bile ductules Bile ductules lead to portal areas Kupffer cells - phagocytes Liver lobule

LaPointe Spring ‘12 Slide # 34 Liver Histology Marieb Figure 23.24a, b Triad locations

LaPointe Spring ‘12 Slide # 35 Liver lobule

LaPointe Spring ‘12 Slide # 36 Liver Histology

LaPointe Spring ‘12 Slide # 37 Liver Histology Marieb Figure 23.24d Hepatic

LaPointe Spring ‘12 Slide # 38 Bile ducts Ductules unite to form bile ducts, these converge to form the left and right hepatic ducts which meet to make the common hepatic duct Common hepatic duct meets cystic duct (from the gall bladder) to form common bile duct