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Marieb’s Human Anatomy and Physiology Ninth Edition Marieb w Hoehn Chapter 23 ** Digestive System ** Stomach Small/Large Intestine Salivary Glands Liver Overview….Where have you been? Figures from: Marieb, Human Anatomy &Physiology, Pearson, 2013 2 Stomach M Gastric glands M G cells D cells Stomach can hold about 1-1.5 liters of material Greater curvature Stomach Functions: - Mixing - Reservoir - Secretion of gastric juice - Digestion, anti-bacterial action, facilitates absorption of vitamin B12 - Secretion of gastrin, somatostatin Rugae flatten as stomach fills 3 Blood Supply and Drainage of Stomach Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001 4 Lining and Gastric Glands of Stomach Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001 5 Gastric Secretions • mucus (cardia) • from goblet cells and mucous glands • protective to stomach wall • pepsinogen • from chief cells • inactive form of pepsin • pepsin • from pepsinogen in presence of HCl • protein splitting enzyme • INFANTS ONLY • rennin (chymosin) • gastric lipase • hydrochloric acid • from parietal cells • needed to convert pepsinogen to pepsin • ‘p’ in parietal and ‘p’ in pH • intrinsic factor • from parietal cells • required for vitamin B12 absorption • mucus, gastrin, somatostatin • from pyloric glands • protective to stomach wall • gastrin and somatostatin are hormones 6 Secretion of H+ by Parietal Cells Important functions of the stomach pH (1.5 – 2.0) - kills microorganisms - denatures proteins - breaks down plant material and CT in meats - activates pepsin Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001 7 Liver, Bile ducts, Pancreas and Small Intestine Figures from: Marieb, Human Anatomy &Physiology, Pearson, 2013 8 Three Parts of Small Intestine Figure from: Hole’s Human A&P, 12th edition, 2010 “Mixing bowl”; acid neutralization Bulk of chemical digestion and nutrient absorption occurs here The ‘bowel’ consists of the small and large intestines. Vitamin B12 absorption Main functions of small intestine: 1) chemical digestion 2) absorption of nutrients (90%) from chyme 9 Blood Supply and Drainage of Small Intestine Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001 10 Wall of Small Intestine Figure from: Hole’s Human A&P, 12th edition, 2010 Plicae circulares – permanent circular folds of mucosa that further increase surface area for absorption – do not flatten out with distention like rugae of stomach. Especially prominent in lower duodenum and upper jejunum Submucosa of duodenum contains mucus-secreting glands (Brunner’s glands) that protect the small intestine 11 Intestinal Villi & Glands Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007 Enterocyte = Intestinal Cell Intestinal glands secrete an abundant watery fluid that helps absorb products of digestion. They also contain enteroendocrine cells (enterokinase, gastrin, secretin, CCK) 12 Intestinal Epithelium Figure from: Hole’s Human A&P, 12th edition, 2010 Microvilli further increase the surface area available for absorption in the small intestine Form a ‘brush border’ on the intestine Digestive enzymes are embedded in the membrane of microvilli Main function of plicae, villi, and microvilli is to increase the surface area for absorption (from about 3.6 ft2 to about 2200 ft2!) 13 Secretions of Small Intestine • peptidase – breaks down peptides into amino acids • sucrase, maltase, lactase – break down disaccharides into monosaccharides Brush border • intestinal lipase – breaks down fats into fatty acids and glycerol • enterokinase – converts trypsinogen to trypsin • gastrin/somatostatin – hormones that stimulate/inhibit acid secretion by stomach • cholecystokinin (CCK) – hormone that inhibits gastric glands, stimulates pancreas to release enzymes in pancreatic juice, stimulates gallbladder to release bile, and relaxes hepatopancreatic sphincter (of Oddi) • secretin – stimulates pancreas to release bicarbonate ions in pancreatic juice; stimulates gall bladder to release bicarbonate-rich bile See Table 23.32 in Marieb for a great summary of digestive enzymes 14 Movements of the Small Intestine Movements in local segments can occur without stimulation by parasympathetic NS. However, nervous stimulation accelerates segmentation and peristalsis. • peristalsis – pushing movements • segmentation – ringlike contractions that aid in mixing and slowing peristalsis • overdistended or irritated wall triggers “peristaltic rush” resulting in diarrhea “Long distance” movements are triggered by stomach filling: - gastroenteric reflex (↑ motility and secretion along length of small intestine) - gastroileal reflex (relaxation of ileocecal sphincter) 15 Absorption in the Small Intestine • monosaccharides and amino acids • through facilitated diffusion and active transport • absorbed into blood • electrolytes and water • through diffusion, osmosis, and active transport • absorbed into blood • vitamins • fat-soluble dissolve in dietary fats (vit A,D,E,K) •Water-soluble through diffusion, except B12 (active transport) • Vitamin K (large intestine) – with other lipids • absorbed into blood 16 Absorption of Fats in the Small Intestine Figure from: Hole’s Human A&P, 12th edition, 2010 • fatty acids and glycerol • several steps • absorbed into lymph into blood Chylomicrons contain TG, cholesterol, and phospholipids 17 Large Intestine Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001 * 18 Histology of the Large Intestine Figures from: Hole’s Human A&P, 12th edition, 2010 Walls of large intestine are much thinner than the small intestine, however, the lumen is larger Note lack of villi and presence of numerous goblet cells (mucus) No enzymes produced; any digestion is from previously introduced enzymes or bacteria 19 Functions of Large Intestine • little or no digestive function • absorbs water, bile salts, and electrolytes • secretes mucus (lubrication, binding, protection, pH) • conversion of bilirubin (uro- and stercobilinogen) • houses intestinal flora (~800 species of bacteria) and absorbs vitamins liberated by bacterial action (K, B5, and Biotin); produces intestinal gas (flatus) • forms and stores feces • carries out defecation 20 The Rectum, Anal Canal, and Anus Figure from: Hole’s Human A&P, 12th edition, 2010 Rectal valves Temporary storage of fecal material in rectum triggers the urge to defecate Internal anal sphincter is usually contracted but relaxes in response to distension. External sphincter must be tensed reflexively to retain feces Procto- = anus or rectum (Keratinzed strat. squamous epithelium) 21 Movements of Large Intestine • slower and less frequent than those of small intestine • mixing movements (haustral churning every 30 min) • mass movements - usually follow meals (stimulated by distension of stomach and duodenum) - gastrocolic reflex - duodenocolic reflex - peristaltic wave from transverse colon through rest of large intestine 22 All You Need to Know??? 23 Parasympathetic Defecation Reflex Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007 Note that this reflex opens the internal sphincter and closes the external sphincter Need voluntary relaxation of the external sphincter for defecation 24 Feces • water (75%), solids (25%) • electrolytes • mucus • bacteria (30% of solids) and sloughed epithelial cells • bile pigments altered by bacteria provide color (mainly urobilins and stercobilins) • odor produced by bacterial compounds (indoles and skatoles, phenols, H2S, ammonia) • indigestible materials 25 Major Organs of Digestive System Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007 Organs can be divided into the: -Digestive tract (primary) (alimentary canal); tube extending from mouth to anus (about 30 ft.) -Accessory organs; teeth, tongue, salivary glands, liver, gallbladder, and pancreas 26 Salivary Glands Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007 27 Secretions of Salivary Glands Secretions are about neutral pH and continual due to basal parasympathetic stimulation, but increase after - presence, or anticipation of, food; - parasympathetic stimulation (watery, large volume) - sympathetic stimulation (viscous, small volume) • Parotid glands • clear • primarily water, serous fluid • rich in amylase • mumps virus typically attacks here • Submandibular glands • primarily serous fluid • some mucus, amylase • Sublingual glands • primarily mucus • most viscous 28 Liver [ Hepat(o)- ] Round ligament is part of the falciform ligament that divides the lobes; remnant of fetal umbilical vein. Note that the vena cava does not enter the liver; it passes by Figure from: Martini, Anatomy & Physiology, Pearson Education, 2004 29 Arterial Supply and Venous Drainage of Liver Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001 30 Hepatic Lobule Hepatic lobules are the functional units of the liver (>100,000) Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007 31 Paths of Blood and Bile in Hepatic Lobule Figure from: Hole’s Human A&P, 12th edition, 2010 Liver’s role as an accessory organ in digestion is production of bile Sinusoid Hepatic portal vein → sinusoids → central vein → hepatic veins → inferior vena cava Hepatic artery 32 Liver Functions (over 200!) • Three general categories of function 1) Metabolic regulation • • • • • Interconversion of carbohydrates, lipids, amino acids Removal of wastes Vitamin and mineral metabolism Drug inactivation Know items Storage of fats, glycogen, iron, vit A/B12/D/E/K 2) Hematological regulation • • • • • in red Phagocytosis and antigen presentation; ab removal Synthesis of plasma proteins Removal of circulating hormones Removal of worn-out RBCs (Kupffer cells) Removal or storage of toxins 3) Synthesis and secretion of bile (role in digestion) 33 Gallbladder [Cyst(o)-] Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001 Main function is to store and concentrate bile between meals, and release bile under the influence of CCK 34 Composition of Bile (Chole-) Yellowish-green liquid continually secreted by hepatocytes • water • bile salts (bile acids) • derived from cholesterol • emulsification of fats (increases surface area for digestive enzymes) • helps absorption of fatty acids, cholesterol, and fat-soluble vitamins • 80% are recycled (reabsorbed and reused) – enterohepatic circulation of bile • 20% excreted in feces (disposes of excess cholesterol) • bile pigments (bilirubin and biliverdin from breakdown of RBCs) • electrolytes 35 Regulation of Bile Release from GB Figure from: Hole’s Human A&P, 12th edition, 2010 • fatty chyme entering duodenum stimulates the GB to release bile (via CCK) Secretin causes the bile ducts (and pancreatic ducts) to secrete bile rich in HCO3- 36 Actions of Cholecystokinin (CCK) on Digestion Figure adapted from: Barrett, K., Gastrointestinal Physiology, Lange, 2006 CCK Contraction of Gallbladder Secretion of pancreatic enzymes Reduced emptying of stomach Relaxation of hepatopancreatic sphincter Protein, CHO, lipid absorption and digestion Matching of nutrient delivery to digestive and absorptive capability 37 Pancreas Exocrine (digestive) and endocrine (metabolic) functions Completes digestion of proteins that was started in the stomach 38 Blood Supply and Drainage of Pancreas Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001 39 Pancreatic Juice • pancreatic amylase – splits glycogen into disaccharides • pancreatic lipases – break down triglycerides • pancreatic nucleases – digest nucleic acids • bicarbonate ions – make pancreatic juice alkaline (pH = 8) and neutralize acid coming from stomach • Pancreatic proteolytic enzymes… 40 Pancreatic Proteolytic Enzymes Enteropeptidase (Enterokinase) (brush border of sm. intestine) Trypsinogen Pancreas Know this chart Trypsin Chymotrypsinogen Procarboxypeptidase Proelastase (Proenzymes, Zymogens) Dipeptides, tripeptides, amino acids Chymotrypsin Carboxypeptidase Elastase (Active enzymes) Proteins Purpose of proteolytic enzymes is continued breakdown of proteins that began in the stomach 41 Regulation of Pancreatic Secretions • acidic chyme stimulates release of secretin • secretin stimulates release of watery pancreatic juice with bicarbonate and phosphate (= buffers; to pH) CCK and parasympathetic NS stimulate production and secretion of pancreatic enzymes and zymogens 42 Key Regulation of Pancreas/Intestinal Digestion + Stimulation Acidic Chyme Enters Duodenum (brush border) + + Secretin + + Cholecystokinin (CCK) + + Bile and Pancreatic ducts Gallbladder Contraction Bile Trypsin Chymotrypsinogen Procarboxypeptidase Proelastase Trypsinogen Carboxypeptidase Elastase Proteins Lipases (emulsification) Triglycerides Cholesterol Fat Soluble Vitamins Lacteals Subclavian vein Pancreas Trypsinogen (proenzymes, zymogens) HCO3-, PO43- pH to ≈ 8 (req. for enzyme action) Relaxation of hepatopancreatic sphincter + Enterokinase Fatty acids, monoglycerides Conversion to chylomicrons Nucleases (DNA, RNA) Nucleotides Portal Vein Amylase (glycogen, starches) Mono-, di-, trisaccharides Di- and tripeptides Action of brush border enzymes Monosaccharides Amino acids 43 Life-Span Changes • gums recede • teeth become sensitive • teeth may loosen or fall out • heartburn more frequent • constipation more frequent • nutrient absorption decreases • accessory organs age but the effects are less noticeable 44