PowerPoint ® Lecture Slides prepared by Barbara Heard, Atlantic Cape Community College C H A P T E R © 2013 Pearson Education, Inc.© Annie Leibovitz/Contact Press Images The Digestive System: Part C 23

© 2013 Pearson Education, Inc. Pancreas Location –Mostly retroperitoneal, deep to greater curvature of stomach –Head encircled by duodenum; tail abuts spleen

© 2013 Pearson Education, Inc. Pancreas Endocrine function –Pancreatic islets secrete insulin and glucagon Exocrine function –Acini (clusters of secretory cells) secrete pancreatic juice To duodenum via main pancreatic duct Zymogen granules of acini cells contain proenzymes

© 2013 Pearson Education, Inc. Small duct Acinar cell Basement membrane Zymogen granules Rough endoplasmic reticulum One acinus Duct cell Figure 23.26a Structure of the enzyme-producing tissue of the pancreas.

© 2013 Pearson Education, Inc. Acinar cells Pancreatic duct Figure 23.26b Structure of the enzyme-producing tissue of the pancreas.

© 2013 Pearson Education, Inc. Pancreatic Juice 1200 – 1500 ml/day Watery alkaline solution (pH 8) neutralizes chyme Electrolytes (primarily HCO 3 – ) Enzymes –Amylase, lipases, nucleases secreted in active form but require ions or bile for optimal activity –Proteases secreted in inactive form

© 2013 Pearson Education, Inc. Pancreatic Juice Protease activation in duodenum –Trypsinogen activated to trypsin by brush border enzyme enteropeptidase –Procarboxypeptidase and chymotrypsinogen activated by trypsin

© 2013 Pearson Education, Inc. Figure Activation of pancreatic proteases in the small intestine. Stomach Pancreas Epithelial cells Membrane-bound enteropeptidase Trypsinogen (inactive) Chymotrypsinogen (inactive) Procarboxypeptidase (inactive) Trypsin Chymotrypsin Carboxypeptidase

© 2013 Pearson Education, Inc. Regulation of Bile Secretion Bile secretion stimulated by –Bile salts in enterohepatic circulation –Secretin from intestinal cells exposed to HCl and fatty chyme Hepatopancreatic sphincter closed unless digestion active  bile stored in gallbladder –Released to small intestine ~ only with contraction

© 2013 Pearson Education, Inc. Regulation of Bile Secretion Gallbladder contraction stimulated by –Cholecystokinin (CCK) from intestinal cells exposed to acidic, fatty chyme –Vagal stimulation (minor stimulus) CCK also causes –Secretion of pancreatic juice –Hepatopancreatic sphincter to relax

© 2013 Pearson Education, Inc. Regulation of Pancreatic Secretion CCK induces secretion of enzyme-rich pancreatic juice by acini Secretin causes secretion of bicarbonate- rich pancreatic juice by duct cells Vagal stimulation also causes release of pancreatic juice (minor stimulus)

© 2013 Pearson Education, Inc. Figure Mechanisms promoting secretion and release of bile and pancreatic juice. Slide 1 Chyme enter -ing duodenum causes duodenal enteroendocrine cells to release cholecystokinin (CCK) and secretin. CCK (red dots) and secretin (yellow dots) enter the bloodstream. CCK induces secretion of enzyme-rich pancreatic juice. Secretin causes secretion of HCO 3 − -rich pancreatic juice. Bile salts and, to a lesser extent, secretin transported via bloodstream stimulate Liver to produce bile more rapidly. CCK (via blood stream) causes gallbladder to contract and Hepatopancreatic Sphincter to relax. Bile Enters duodenum. During cephalic and gastric phases, vagal Nerve stimu- lates gallbladder to contract weakly. CCK secretion Secretin secretion

© 2013 Pearson Education, Inc. Digestion in the Small Intestine Chyme from stomach contains –Partially digested carbohydrates and proteins –Undigested fats 3–6 hours in small intestine –Most water absorbed –~ All nutrients absorbed Small intestine, like stomach, no role in ingestion or defecation

© 2013 Pearson Education, Inc. Requirements for Digestion and Absorption in the Small Intestine Slow delivery of acidic, hypertonic chyme Delivery of bile, enzymes, and bicarbonate ions from liver and pancreas Mixing

© 2013 Pearson Education, Inc. Motility of the Small Intestine Segmentation –Most common motion of small intestine –Initiated by intrinsic pacemaker cells –Mixes/moves contents toward ileocecal valve –Intensity altered by long & short reflexes; hormones Parasympathetic  ; sympathetic  –Wanes in late intestinal (fasting) phase

© 2013 Pearson Education, Inc. Figure Microvilli of the small intestine. Mucus granules Microvilli forming the brush border Absorptive cell

© 2013 Pearson Education, Inc. Motility of the Small Intestine Peristalsis –Initiated by rise in hormone motilin in late intestinal phase; every 90–120 minutes –Each wave starts distal to previous Migrating motor complex –Meal remnants, bacteria, and debris moved to large intestine –From duodenum  ileum ~ 2 hours

© 2013 Pearson Education, Inc. Figure 23.3a Peristalsis and segmentation. From mouth Peristalsis: Adjacent segments of alimentary tract organs alternately contract and relax, moving food along the tract distally.

© 2013 Pearson Education, Inc. Motility of the Small Intestine Local enteric neurons coordinate intestinal motility Cholinergic sensory neurons may activate myenteric plexus –Causes contraction of circular muscle proximally and of longitudinal muscle distally –Forces chyme along tract

© 2013 Pearson Education, Inc. Motility of the Small Intestine Ileocecal sphincter relaxes, admits chyme into large intestine when –Gastroileal reflex enhances force of segmentation in ileum –Gastrin increases motility of ileum Ileocecal valve flaps close when chyme exerts backward pressure –Prevents regurgitation into ileum

© 2013 Pearson Education, Inc. Large Intestine Unique features –Teniae coli Three bands of longitudinal smooth muscle in muscularis –Haustra Pocketlike sacs caused by tone of teniae coli –Epiploic appendages Fat-filled pouches of visceral peritoneum

© 2013 Pearson Education, Inc. Large Intestine Regions –Cecum –Appendix –Colon –Rectum –Anal canal

© 2013 Pearson Education, Inc. Figure 23.29a Gross anatomy of the large intestine. Right colic (hepatic) flexure Transverse colon Superior mesenteric artery Ascending colon IIeum IIeocecal valve Cecum Appendix Left colic (splenic) flexure Transverse mesocolon Epiploic appendages Descending colon Cut edge of mesentery Tenia coli Sigmoid colon Rectum Anal canal External anal sphincter Haustrum

© 2013 Pearson Education, Inc. Subdivisions of the Large Intestine Cecum – first part of large intestine Appendix – masses of lymphoid tissue –Part of MALT of immune system –Bacterial storehouse  recolonizes gut when necessary –Twisted  enteric bacteria accumulate and multiply

© 2013 Pearson Education, Inc. Colon Retroperitoneal except for transverse and sigmoid regions Ascending colon (right side – to level of right kidney)  right colic (hepatic) flexure  Transverse colon  left colic (splenic) flexure  Descending colon (left side)  Sigmoid colon in pelvis  rectum

© 2013 Pearson Education, Inc. Greater omentum Transverse colon Transverse mesocolon Descending colon Mesentery Sigmoid mesocolon Jejunum Sigmoid colon Ileum Figure 23.30c Mesenteries of the abdominal digestive organs.

© 2013 Pearson Education, Inc. Figure 23.30d Mesenteries of the abdominal digestive organs. Liver Lesser omentum Pancreas Stomach Duodenum Transverse mesocolon Transverse colon Mesentery Greater omentum Jejunum Ileum Visceral peritoneum Parietal peritoneum Urinary bladder Rectum

© 2013 Pearson Education, Inc. Rectum and Anus Rectum –Three rectal valves stop feces from being passed with gas (flatus) Anal canal –Last segment of large intestine –Opens to body exterior at anus Sphincters –Internal anal sphincter—smooth muscle –External anal sphincter—skeletal muscle

© 2013 Pearson Education, Inc. Figure 23.29b Gross anatomy of the large intestine. Rectal valve Rectum Hemorrhoidal veins Levator ani muscle Anal canal External anal sphincter Internal anal sphincter Anal columns Pectinate line Anal sinuses Anus

© 2013 Pearson Education, Inc. Large Intestine: Microscopic Anatomy Thicker mucosa of simple columnar epithelium except in anal canal (stratified squamous to withstand abrasion) No circular folds, villi, digestive secretions Abundant deep crypts with goblet cells Superficial venous plexuses of anal canal form hemorrhoids if inflamed

© 2013 Pearson Education, Inc. Bacterial Flora Enter from small intestine or anus –Colonize colon –Synthesize B complex vitamins and vitamin K –Metabolize some host-derived molecules (mucin, heparin, hyaluronic acid) –Ferment indigestible carbohydrates –Release irritating acids and gases (~500 ml/day)

© 2013 Pearson Education, Inc. Intestinal Flora Viruses and protozoans Bacteria prevented from breaching mucosal barrier –Epithelial cells recruit dendritic cells to mucosa  sample microbial antigens  present to T cells of MALT  IgA antibody- mediated response  restricts microbes

© 2013 Pearson Education, Inc. Digestive Processes in the Large Intestine Residue remains in large intestine 12–24 hours No food breakdown except by enteric bacteria Vitamins (made by bacterial flora), water, and electrolytes (especially Na + and Cl – ) reclaimed Major functions - propulsion of feces to anus; defecation Colon not essential for life

© 2013 Pearson Education, Inc. Motility of the Large Intestine Most contractions of colon –Haustral contractions Slow segmenting movements Haustra sequentially contract in response to distension

© 2013 Pearson Education, Inc. Motility of the Large Intestine Gastrocolic reflex –Initiated by presence of food in stomach –Activates three to four slow powerful peristaltic waves per day in colon (mass movements)

© 2013 Pearson Education, Inc. Homeostatic Imbalance Low fiber diet  narrowed colon  strong contractions  increased pressure on walls  diverticula (herniations of mucosa) Diverticulosis commonly in sigmoid colon –Affects ½ people > 70 years Diverticulitis –Inflamed diverticula; may rupture and leak into peritoneal cavity; may be life threatening

© 2013 Pearson Education, Inc. Homeostatic Imbalance Irritable bowel syndrome –Functional GI disorder –Recurring abdominal pain, stool changes, bloating, flatulence, nausea, depression –Stress common precipitating factor Stress management important in treatment

© 2013 Pearson Education, Inc. Defecation Mass movements force feces toward rectum Distension initiates spinal defecation reflex Parasympathetic signals –Stimulate contraction of sigmoid colon and rectum –Relax internal anal sphincter Conscious control allows relaxation of external anal sphincter

© 2013 Pearson Education, Inc. Figure Defecation reflex. Slide 1 Impulses from cerebral cortex (conscious control) Voluntary motor nerve to external anal sphincter External anal sphincter (skeletal muscle) Sensory nerve fibers Sigmoid colon Rectum Stretch receptors in wall Involuntary motor nerve (parasympathetic division) Internal anal sphincter (smooth muscle) Feces move into and distend the rectum, stimulating stretch receptors there. The receptors transmit signals along afferent fibers to spinal cord neurons. A spinal reflex is initiated in which parasympathetic motor (efferent) fibers stimulate contraction of the rectum and sigmoid colon, and relaxation of the internal anal sphincter. If it is convenient to defecate, voluntary motor neurons are inhibited, allowing the external anal sphincter to relax so feces may pass

© 2013 Pearson Education, Inc. Defecation- replace Muscles of rectum contract to expel feces Assisted by Valsalva's maneuver –Closing of glottis, contraction of diaphragm and abdominal wall muscles  increased intra-abdominal pressure –Levator ani muscle contracts  anal canal lifted superiorly  feces leave body

© 2013 Pearson Education, Inc. Chemical Digestion Digestion –Catabolic; macromolecules  monomers small enough for absorption Enzymes –Intrinsic and accessory gland enzymes break down food Hydrolysis –Water is added to break bonds

© 2013 Pearson Education, Inc. Digestion of Carbohydrates Only monosaccharides can be absorbed Monosaccharides absorbed as ingested –Glucose, fructose, galactose Digestive enzymes –Salivary amylase, pancreatic amylase, and brush border enzymes (dextrinase, glucoamylase, lactase, maltase, and sucrase) –Break down disaccharides sucrose, lactose, maltose; polysaccharides glycogen and starch

© 2013 Pearson Education, Inc. Digestion of Carbohydrates Starch digestion –Salivary amylase (saliva)  oligosaccharides at pH 6.75 – 7.00 –Pancreatic amylase (small intestine)  breaks down any that escaped salivary amylase  oligosaccharides –Brush border enzymes (dextrinase, glucoamylase, lactase, maltase, sucrase)  oligosaccharides  monosaccharides

© 2013 Pearson Education, Inc. Figure Flowchart of digestion and absorption of foodstuffs. (1 of 4) Foodstuff Enzyme(s) and source Site of actionPath of absorption Starch and disaccharides Oligosaccharides and disaccharides Carbohydrate digestion Lactose Maltose Sucrose GalactoseGlucoseFructose Salivary amylase Pancreatic amylase Brush border enzymes in small intestine (dextrinase, gluco- amylase, lactase, maltase, and sucrase) Mouth Small intestine Small intestine Glucose and galactose are absorbed via cotransport with sodium ions. Fructose passes via facilitated diffusion. All monosaccharides leave the epithelial cells via facilitated diffusion, enter the capillary blood in the villi, and are transported to the liver via the hepatic portal vein.

© 2013 Pearson Education, Inc. Digestion of Proteins Source is dietary, digestive enzymes, mucosal cells; digested to amino acid monomers Begins with pepsin in stomach at pH 1.5 – 2.5 –Inactive in high pH of duodenum Pancreatic proteases –Trypsin, chymotrypsin, and carboxypeptidase Brush border enzymes –Aminopeptidases, carboxypeptidases, and dipeptidases

© 2013 Pearson Education, Inc. Figure Protein digestion and absorption in the small intestine. Slide 1 Lumen of intestine Pancreatic proteases Amino acids of protein fragments Brush border enzymes Na + Absorptive epithelial cell Apical membrane (microvilli) Amino acid carrier Capillary Proteins and protein fragments are digested to amino acids by pancreatic proteases (trypsin, chymotrypsin, and carboxy- peptidase), and by brush border enzymes (carboxypeptidase, aminopeptidase, and dipeptidase) of mucosal cells. The amino acids are then absorbed by active transport into the absorptive cells, and move to their opposite side. The amino acids leave the villus epithelial cell by facilitated diffusion and enter the capillary via intercellular clefts. Na

© 2013 Pearson Education, Inc. Figure Flowchart of digestion and absorption of foodstuffs. (2 of 4) Protein digestion Proteins Large polypeptides Small polypeptides, small peptides Amino acids (some dipeptides and tripeptides) Pepsin (stomach glands) in presence of HCl Pancreatic enzymes (trypsin, chymotrypsin, carboxypeptidase) Brush border enzymes (aminopeptidase, carboxypeptidase, and dipeptidase) Stomach Small intestine Small intestine Amino acids are absorbed via cotransport with sodium ions. Some dipeptides and tripeptides are absorbed via cotransport with H + and hydrolyzed to amino acids within the cells. Infrequently, transcytosis of small peptides occurs. Amino acids leave the epithelial cells by facilitated diffusion, enter the capillary blood in the villi, and are transported to the liver via the hepatic portal vein. FoodstuffEnzyme(s) and sourceSite of actionPath of absorption

© 2013 Pearson Education, Inc. Digestion of Lipids Pre-treatment—emulsification by bile salts –Does not break bonds Enzymes—pancreatic lipases –  Fatty acids and monoglycerides Absorption of glycerol and short chain fatty acids –Absorbed into the capillary blood in villi –Transported via the hepatic portal vein

© 2013 Pearson Education, Inc. Fat globule Bile salts in the duodenum emulsify large fat globules (physically break them up into smaller fat droplets). Digestion of fat by the pancreatic enzyme lipase yields free fatty acids and monoglycerides. These then associate with bile salts to form micelles which “ferry” them to the intestinal mucosa. Micelles made up of fatty acids, monoglycerides, and bile salts Bile salts Fat droplets coated with bile salts Fatty acids and monoglycerides leave micelles and diffuse into epithelial cells. There they are recombined and packaged with other fatty substances and proteins to form chylomicrons. Chylomicrons are extruded from the epithelial cells by exocytosis. The chylomicrons enter lacteals and are carried away from the intestine in lymph. Lacteal Epithelial cells of small intestine Figure Emulsification, digestion, and absorption of fats. Slide 1

© 2013 Pearson Education, Inc. Figure Flowchart of digestion and absorption of foodstuffs. (3 of 4) Fat digestion Unemulsified triglycerides Lingual lipase Gastric lipase Emulsification by the detergent action of bile salts ducted in from the liver Pancreatic lipases Monoglycerides (or diglycerides with gastric lipase) and fatty acids Mouth Stomach Small intestine Small intestine Fatty acids and monoglycerides enter the intestinal cells via diffusion. Fatty acids and monoglycerides are recombined to form triglycerides and then combined with other lipids and proteins within the cells. The resulting chylomicrons are extruded by exocytosis. The chylomicrons enter the lacteals of the villi and are transported to the systemic circulation via the lymph in the thoracic duct. Some short-chain fatty acids are absorbed, move into the capillary blood in the villi by diffusion, and are transported to the liver via the hepatic portal vein. FoodstuffEnzyme(s) and sourceSite of actionPath of absorption

© 2013 Pearson Education, Inc. Digestion of Nucleic Acids Enzymes –Pancreatic ribonuclease and deoxyribonuclease  nucleotide monomers –Brush border enzyme nucleosidases and phosphatases  free bases, pentose sugars, phosphate ions

© 2013 Pearson Education, Inc. Figure Flowchart of digestion and absorption of foodstuffs. (4 of 4) Nucleic acid digestion Nucleic acids Pentose sugars, N-containing bases, phosphate ions Pancreatic ribo- nuclease and deoxyribonuclease Brush border enzymes (nucleosidases and phosphatases) Small intestine Small intestine Units enter intestinal cells by active transport via membrane carriers. Units are absorbed into capillary blood in the villi and transported to the liver via the hepatic portal vein. FoodstuffEnzyme(s) and sourceSite of actionPath of absorption

© 2013 Pearson Education, Inc. Absorption ~ All food; 80% electrolytes; most water absorbed in small intestine –Most prior to ileum Ileum reclaims bile salts Most absorbed by active transport  blood –Exception - lipids

© 2013 Pearson Education, Inc. Absorption of Carbohydrates Glucose and galactose –Secondary active transport (cotransport) with Na +  epithelial cells –Move out of epithelial cells by facilitated diffusion  capillary beds in villi Fructose –Facilitated diffusion to enter and exit cells

© 2013 Pearson Education, Inc. Absorption of Carbohydrates- OMIT Glucose and galactose –Secondary active transport (cotransport) with Na +  epithelial cells –Move out of epithelial cells by facilitated diffusion  capillary beds in villi Fructose –Facilitated diffusion to enter and exit cells

© 2013 Pearson Education, Inc. Absorption of Protein- OMIT Amino acids transported by several types of carriers –Most coupled to active transport of Na + Dipeptides and tripeptides actively absorbed by H + -dependent cotransport; digested to amino acids within epithelial cells Enter capillary blood by diffusion

© 2013 Pearson Education, Inc. Homeostatic Imbalance Whole proteins not usually absorbed Can be taken up by endocytosis/exocytosis –Most common in newborns  food allergies Usually disappear with mucosa maturation –Allows IgA antibodies in breast milk to reach infant's bloodstream  passive immunity

© 2013 Pearson Education, Inc. Absorption of Lipids- OMIT Absorption of monoglycerides and fatty acids –Cluster with bile salts and lecithin to form micelles –Released by micelles to diffuse into epithelial cells –Combined with lecithin, phospholipids, cholesterol, & coated with proteins to form chylomicrons –Enter lacteals; transported to systemic circulation –Hydrolyzed to free fatty acids and glycerol by lipoprotein lipase of capillary endothelium Cells can use for energy or stored fat Absorption of short chain fatty acids –Diffuse into portal blood for distribution

© 2013 Pearson Education, Inc. Absorption of Nucleic Acids- OMIT Absorption –Active transport across epithelium  bloodstream

© 2013 Pearson Education, Inc. Absorption of Vitamins- OMIT In small intestine –Fat-soluble vitamins (A, D, E, and K) carried by micelles; diffuse into absorptive cells –Water-soluble vitamins (vitamin C and B vitamins) absorbed by diffusion or by passive or active transporters. –Vitamin B 12 (large, charged molecule) binds with intrinsic factor, and is absorbed by endocytosis

© 2013 Pearson Education, Inc. Absorption of Vitamins- OMIT In large intestine –Vitamin K and B vitamins from bacterial metabolism are absorbed

© 2013 Pearson Education, Inc. Absorption of Electrolytes- OMIT Most ions actively along length of small intestine Iron and calcium are absorbed in duodenum Na + coupled with active absorption of glucose and amino acids Cl – transported actively K + diffuses in response to osmotic gradients; lost if poor water absorption Usually amount in intestine is amount absorbed

© 2013 Pearson Education, Inc. Absorption of Electrolytes- OMIT Iron and calcium absorption related to need –Ionic iron stored in mucosal cells with ferritin –When needed, transported in blood by transferrin Ca 2+ absorption regulated by vitamin D and parathyroid hormone (PTH)

© 2013 Pearson Education, Inc. Absorption of Water 9L water, most from GI tract secretions, enter small intestine –95% absorbed in the small intestine by osmosis –Most of rest absorbed in large intestine Net osmosis occurs if concentration gradient established by active transport of solutes Water uptake coupled with solute uptake

© 2013 Pearson Education, Inc. Malabsorption of Nutrients Causes –Anything that interferes with delivery of bile or pancreatic juice –Damaged intestinal mucosa (e.g., bacterial infection; some antibiotics)

© 2013 Pearson Education, Inc. Malabsorption of Nutrients Gluten-sensitive enteropathy (celiac disease) –Immune reaction to gluten –Gluten causes immune cell damage to intestinal villi and brush border –Treated by eliminating gluten from diet (all grains but rice and corn)

© 2013 Pearson Education, Inc. Developmental Aspects Oral membrane  mouth opening Cloacal membrane  anus By week 5 alimentary canal continuous tube from mouth to anus Shortly after, accessory organs bud from mucosa

© 2013 Pearson Education, Inc. Figure Embryonic development of the digestive system. Brain Oral membrane Heart Yolk sac Cloacal membrane Body stalk Endoderm Proctodeum Hindgut Spinal cord Midgut Site of liver development Foregut Stomodeum Lung bud LiverStomach Bile duct Cystic duct Gall- bladder Ventral pancreatic bud Dorsal pancreatic bud Duodenum

© 2013 Pearson Education, Inc. Homeostatic Imbalance Cleft palate and cleft lip Tracheoesophageal fistula –Opening between esophagus and trachea Cystic fibrosis –Genetic disease  thick mucus  can block pancreatic duct

© 2013 Pearson Education, Inc. Developmental Aspects Fetal nutrition via placenta, but GI tract stimulated to mature by amniotic fluid swallowed in utero Newborn's rooting reflex helps infant find nipple; sucking reflex aids in swallowing Newborns double birth weight in six months; adult diet by 2 years Cholecystitis, ulcers – problems of middle age

© 2013 Pearson Education, Inc. Developmental Aspects During old age –GI tract activity declines, less digestive juice, absorption less efficient, peristalsis slows  less frequent bowel movements –Taste/smell less acute; periodontal disease often develops –Diverticulosis, fecal incontinence, and cancer of GI tract fairly common

© 2013 Pearson Education, Inc. Cancer Stomach and colon cancers rarely have early signs or symptoms Metastasized colon cancers frequently cause secondary liver cancer Prevention –Regular dental and medical examination