Chapter 21a The Digestive System

About this Chapter Digestion function and processes Anatomy of the digestive system Motility Secretion Regulation of GI function Digestion and absorption

About this Chapter The cephalic phase The gastric phase The intestinal phase Immune functions of the GI tract

Activities of the Digestive System Ingestion Digestion Mechanical Chemical / Secretion Motility Peristaltic Segmentation Absorption Immunity Elimination Note: 1.Which of these activities occur at each region of the GI tract. 2.Explain how these activities occur, control (hormones or neural), enzymes and structural mechanisms, no need to name the transporters.

Figure 21-1 Digestive Function and Processes The volume of fluid entering the GI tract must equal the volume leaving 9 liters per day 7.5 L from small intestine 1.4 L from large intestine 0.1 L in feces 9.0 L removed from lumen 2.0 L food and drink 1.5 L saliva (salivary glands) 0.5 L bile (liver) 2.0 L gastric secretions 1.5 L pancreatic secretions 1.5 L intestinal secretions 9.0 L Total input into lumen Absorption Excretion Fluid input into digestive system Fluid removed from digestive system Ingestion Secretion

Figure 21-2 Four Basic Processes of the Digestive System SECRETION DIGESTION ABSORPTION MOTILITY Lumen of digestive tractWallInterstitial fluid Blood Food

Figure 21-3a Digestive System Anatomy Trace through digestive system, not specific regions in addition to major parts. Also note accessory structures. Most simply: Oral cavity  pharynx  esophagus  stomach  small intestine  large intestine  rectum Accessory Salivary glands Pancreas Liver and gall bladder THE DIGESTIVE SYSTEM Oral cavity Salivary glands Esophagus Pancreas Stomach Small intestine Rectum Large intestine (a) Gallbladder Liver ANATOMY SUMMARY

Digestive System Anatomy Stomach Fundus  body  antrum (pylorus) Pyloric valve Small intestine Duodenum  jejunum  ileum Accessory organs: pancreas and liver Large intestine: colon (ascending, transverse, descending and sigmoid colons) and rectum Anus

Figure 21-3a–b, d Digestive System Anatomy A closer look at the structure of the stomach and small intestine THE DIGESTIVE SYSTEM Oral cavity Salivary glands Esophagus Pancreas Stomach Small intestine Rectum Large intestine (a) Gallbladder Liver ANATOMY SUMMARY STRUCTURE OF THE STOMACH AND INTESTINE Esophagus Antrum Pylorus Rugae: Surface folding increases area Fundus Diaphragm Body (b) The stomach Plica Mesentery Villi Submucosal glands Serosa Submucosa Mucosa (d) Structure of the small intestine Circular muscle Longitudinal muscle

Digestive System Anatomy Layers: same throughout, but modified for different functions Mucosa Created from Epithelial cells Lamina propria Muscularis mucosae Modifications increase surface area  Rugae / Plica and villi / crypts Submucosa Muscularis externa Serosa

Digestive System Anatomy Figure 21-3c SECTIONAL VIEW OF THE STOMACH (c) Epithelium Lymph vessel Myenteric plexus Artery and vein Lamina propria Muscularis mucosae Mucosa Submucosa Circular muscle Longitudinal muscle Serosa Opening to gastric gland Oblique muscle Muscularis externa

Digestive System Anatomy Figure 21-3e (e) Mucosa Muscularis mucosae Submucosa Circular muscle Longitudinal muscle Serosa Crypt Peyer’s patch Lymph vessel Myenteric plexus Submucosal artery and vein Submucosal plexus Villi Muscularis externa SECTIONAL VIEW OF THE SMALL INTESTINE

Digestive System Anatomy PLAY Interactive Physiology® Animation: Digestive System: Anatomy Review: Overall Function of the GI System

Motility Tonic contractions Sustained Occur in smooth muscle sphincters and stomach Keep bolus from moving backwards Phasic contractions Last a few seconds Peristalsis moves bolus forward Segmentation mixes

Figure 21-5a Contractions in the GI Tract Peristalsis promotes forward movement

Figure 21-5b Motility Segemental contractions promote mixing PLAY Interactive Physiology® Animation: Digestive System: Motility

Figure 21-6 Secretion 9 liters / day 7 of which from secretions Parietal cells secrete hydrochloric acid into the lumen of the stomach. Other sources include: duodenum / pancreas / salivary glands Interstitial fluid Lumen of stomach K+K+ H+H+ CO 2 H2OH2O CA CA = Carbonic anhydrase ATP Parietal cell Cl – HCO 3 – H + + OH – K+K+ Cl – Capillary

Figure 21-7 Secretion Anatomy of the exocrine and endocrine pancreas acini and islets Duct cells secrete NaHCO 3 Pancreatic islet cells Acinar cells Pancreatic acini Lumen

Figure 21-8 Secretion Bicarbonate secretion in the pancreas and duodenum K+K+ 2 Cl – Na + K+K+ CFTR channel Pancreatic duct cell or duodenal cell Interstitial fluid Lumen of pancreas or intestine K+K+ CO 2 H 2 O + CO 2 H 2 O, Na + CA HCO 3 – HCO 3 – + H + ATP Na + Cl – Capillary

Secretion Cl – secretion by intestinal and colonic crypt cells Figure 21-9 K+K+ Na + 2 Cl – Na + K+K+ K+K+ Na +, K + and Cl – enter by cotransport. Cl – enters lumen through CFTR channel. Na + is reabsorbed. 3 Negative Cl – in lumen attracts Na + by paracellular pathway. Water follows. Interstitial fluid Na +, H 2 O Cl – CFTR channel Lumen ATP

Secretion Digestive enzymes secreted into mouth, stomach and intestine Mucous cells in stomach and goblet cells in intestine Saliva is an exocrine secretion Liver secretes bile PLAY Interactive Physiology® Animation: Digestive System: Secretion