Introduction. Digestive System. Introduction. Introduction 5/14/2016. Every cell requires a constant energy source. Digestive processes

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1 Introduction Every cell requires a constant energy source Ingested food is complex Modification is needed to utilize Introduction Digestive system is a tube Gastrointestinal tract Specialized regions Mouth Pharynx Esophagus Large Mouth (oral cavity) Tongue Esophagus Gallbladder Anus Jejunum Ileum Parotid gland Sublingual gland Submandibular gland Pharynx Pancreas (Spleen) Transverse colon Descending colon Ascending colon Cecum Sigmoid colon Vermiform appendix Anal canal Salivary glands Large Figure 23.1 Digestive processes 1. Ingestion 2. Propulsion 3. Mechanical digestion 4. Chemical digestion 5. Absorption 6. Defecation Introduction Ingestion Mechanical digestion Chewing (mouth) Churning (stomach) Segmentation (small ) Chemical digestion Large Defecation Food Pharynx Esophagus Propulsion Swallowing (oropharynx) Peristalsis (esophagus, stomach, small, large ) Blood vessel Mainly H 2O Feces Anus Absorption Lymph vessel Figure

2 Introduction Histology of the alimentary canal Four basic layers (tunics) Tunica mucosa innermost layer Protection and absorption Epithelium and connective tissue Tunica submucosa Connective tissue Binds tube together Tunica muscularis (externa) Double layer of muscle Tunica serosa Single layer of epithelium and connective tissue Forms the visceral peritoneum Nerve Artery Vein Mesentery Lymphatic vessel Gland in mucosa Intrinsic nerve plexuses Myenteric nerve plexus Submucosal nerve plexus Duct of gland outside alimentary canal Glands in submucosa Mucosa Epithelium Lamina propria Muscularis mucosae Submucosa Muscularis externa Longitudinal muscle Circular muscle Serosa Epithelium Connective tissue Lumen Mucosa-associated lymphoid tissue Figure 23.6 Introduction Peritoneum Membrane that lines abdominal cavity Serous membrane remember, that means 2 layers! Parietal peritoneum = outer layer (attached to abdominal wall) Visceral peritoneum = inner layer (wrapped around visceral organs) Space in between = peritoneal cavity Introduction Introduction Mesentery Folds in the peritoneum Attached to intestinal tract Encapsulate blood vessels, nerves, fat stores that supply the Omenta Folds in peritoneum Connect stomach to another organ Examples: Lesser omentum connects stomach to liver Greater omentum connects stomach to colon Lesser omentum 2

3 Parietal peritoneum Visceral peritoneum Peritoneal cavity Abdominopelvic cavity Alimentary canal organ Vertebra Peritoneum Schematic cross sections of abdominal cavity illustrate the peritoneums and mesenteries. Dorsal mesentery Ventral mesentery (d) Lesser omentum Pancreas Transverse mesocolon Transverse colon Mesentery Greater omentum Jejunum Ileum Visceral peritoneum Parietal peritoneum Urinary bladder Figure 23.5a Figure 23.30d Mouth Cheek, palate, tongue Opens into oropharynx Salivary glands Soft palate Palatoglossal arch Hard palate Oral cavity Palatine tonsil Tongue Oropharynx Lingual tonsil Epiglottis Hyoid bone Laryngopharynx Uvula Esophagus Trachea Sagittal section of the oral cavity and pharynx Figure 23.7a Salivary glands secrete about 1250 ml of saliva per day! Tongue Teeth Ducts of sublingual gland Frenulum of tongue Sublingual gland Mylohyoid muscle (cut) Anterior belly of digastric muscle Submandibular gland Parotid gland Parotid duct Masseter muscle Body of mandible (cut) Posterior belly of digastric muscle Submandibular duct (b) Mucous cells Serous cells forming demilunes Teeth Held in place by periodontal ligaments Gingiva covers bone 2 dentitions Deciduous Permanent Figure

4 Teeth 20 deciduous 32 permanent Incisors Central (6 8 mo) Lateral (8 10 mo) Canine (eyetooth) (16 20 mo) Molars First molar (10 15 mo) Second molar (about 2 yr) Deciduous (milk) teeth Incisors Central (7 yr) Lateral (8 yr) Canine (eyetooth) (11 yr) Premolars (bicuspids) First premolar (11 yr) Second premolar (12 13 yr) Molars First molar (6 7 yr) Second molar (12 13 yr) Third molar (wisdom tooth) (17 25 yr) Permanent teeth Teeth Anatomy Crown Covered by enamel Dentin Pulp cavity Roots Function Break down food Mixed with saliva to form bolus Figure 23.10a Crown Neck Root Enamel Dentin Dentinal tubules Pulp cavity (contains blood vessels and nerves) Gingiva (gum) Cementum Root canal Periodontal ligament Apical foramen Bone Esophagus Pharynx to stomach Moves bolus to stomach Peristalsis Cardiac (gastroesophageal) sphincter Heartburn Histology Mucosa Stratified squamous epithelium Abundant mucous glands Serosa Entirely connective tissue Figure Mouth (oral cavity) Tongue Esophagus Gallbladder Anus Jejunum Ileum Parotid gland Sublingual gland Submandibular gland Pharynx Pancreas (Spleen) Transverse colon Descending colon Ascending colon Cecum Sigmoid colon Vermiform appendix Anal canal Salivary glands Large Relaxed muscles Circular muscles contract Bolus of food Longitudinal muscles contract Gastroesophageal sphincter closed 4 Food is moved through the esophagus to the stomach by peristalsis. Figure 23.1 Figure 23.13, step 4 4

5 5/14/2016 Relaxed muscles 5 The gastroesophageal sphincter opens, and food enters the stomach. Mucosa (contains a stratified squamous epithelium) Submucosa (areolar connective tissue) Lumen Muscularis externa Gastroesophageal sphincter opens Longitudinal layer Circular layer Adventitia (fibrous connective tissue) Figure 23.13, step 5 Figure 23.12a Cardia simple columnar epithelium Mucosa (contains a stratified squamous epithelium) Fundus Esophagus Muscularis externa Longitudinal layer Circular layer Oblique layer Lesser curvature Serosa Body Lumen Rugae of mucosa Greater curvature Esophagus stomach junction (b) Pyloric canal Pyloric sphincter (valve) at pylorus Pyloric antrum Figure 23.12b Figure 23.14a Falciform ligament Gallbladder Spleen From cardiac orifice to pyloric sphincter Rugae (flatten as stomach fills) Ligamentum teres Greater curvature Greater omentum Convex lateral surface Greater omentum Lesser curvature Concave medial surface Lesser omentum Cecum Figure 23.30a 5

6 Gallbladder Lesser omentum Transverse colon Four tunics Muscularis Additional layer of muscle in an oblique orientation Three layers of smooth muscle Cecum Urinary bladder (b) Figure 23.30b Esophagus Muscularis externa Longitudinal layer Circular layer Oblique layer Lesser curvature Cardia Pyloric canal Pyloric sphincter (valve) at pylorus Pyloric antrum Fundus Serosa Body Lumen Rugae of mucosa Greater curvature Figure 23.14a Four tunics Mucosa Gastric glands» Mucous cells = Mucous» Parietal cells = Intrinsic factor and HCl» Zymogenic (chief) cells = Pepsinogen» Enteroendocrine cells = Gastrin and cholecystokinin Surface epithelium Gastric pits Surface epithelium (mucous cells) Mucosa contains gastric glands Mucosa Submucosa (contains submucosal plexus) Muscularis externa (contains myenteric plexus) Serosa Lamina propria Muscularis mucosae Oblique layer Circular layer Longitudinal layer Layers of the stomach wall (l.s.) wall Gastric pit Gastric gland Mucous neck cells Parietal cell Chief cell Enteroendocrine cell (b) Enlarged view of gastric pits and gastric glands Figure 23.15a Figure 23.15b 6

7 Pepsinogen HCl Pepsin Mitochondria Parietal cell Chief (Zymogenic) cell Enteroendocrine cell (c) Location of the HCl-producing parietal cells and pepsin-secreting chief cells in a gastric gland Chemical digestion in the stomach Protein catabolism polypeptides Secretions HCl Pepsinogen pepsin HCl ph Denatures protein in food Kills many bacteria Intrinsic factor Required for absorption of vitamin B 12 in small Figure 23.15c Chemical digestion in the stomach Enteroendocrine cells Secrete hormone-like substances Gastrin» Stimulates parietal cells to release HCl» Increases gastric motility, emptying Cholecystokinin» Primarily produced by enteroendocrine cells in the duodenum» Inhibits HCl release and gastric emptying» Stimulates pancreas to release digestive enzymes» Stimulates production and release of bile from gall bladder» Contributes to feelings of satiety after eating Chemical digestion in the stomach Chyme Product of stomach digestion Prevention of autodigestion Mucous Gastritis Peptic ulcers Gastric ulcers Duodenal ulcers Control of gastric secretions Neural control Seeing, smelling, tasting, thinking about food stimulates gastric secretions via the vagus nerve Enteric nervous system provides local control independently of brain and spinal cord Spinal cord injury will not damage! Ischemia can damage, but transplants have been performed since 2011 Also subject to ANS control Rest and digest Control of gastric secretions Hormonal control Gastrin Released reflexively by enteroendocrine cells in response to stomach distension, peptides, and low acidity Release stimulated by caffeine 7

8 Control of gastric secretions Stimulatory and inhibitory events occur in three phases 1. Cephalic 2. Gastric 3. Intestinal Cephalic phase Gastric phase Intestinal phase Stimulatory events Inhibitory events 1 Sight and thought Cerebral cortex Lack of Cerebral of food Conditioned reflex stimulatory cortex impulses to 2 Stimulation of Hypothalamus Vagus parasympathetic taste and smell and medulla nerve receptors oblongata center 1 Vagovagal Medulla Vagus Gastrin G cells distension reflexes nerve secretion activates declines stretch receptors Local Overrides Sympathetic reflexes parasympathetic system nervous controls activation 2Food chemicals G cells Gastrin (especially peptides and release caffeine) and rising ph to blood activate chemoreceptors secretory activity Enterogastric reflexes Local 1Presence of low reflex Intestinal ph, partially digested (enteric) Vagal foods, fats, or gastrin nuclei hypertonic solution release Brief in medulla in duodenum when to blood effect stomach begins to Pyloric empty sphincter 1Loss of appetite, depression 1Excessive acidity (ph <2) in stomach 2Emotional upset 1Distension of duodenum; presence of fatty, acidic, hypertonic chyme, and/or irritants in the duodenum Stimulate Inhibit Release of intestinal hormones (secretin, cholecystokinin, vasoactive intestinal peptide) 2Distension; presence of fatty, acidic, partially digested food in the duodenum Figure Control of gastric secretions Stimulatory and inhibitory events occur in three phases 1. Cephalic Hearing, seeing, smelling, tasting, thinking about food Vagusnerve stimulated» Gastric secretion starts Control of gastric secretions Stimulatory and inhibitory events occur in three phases 1.Cephalic 2.Gastric Arrival of food in stomach distension, peptides, low acidity gastrin released» Relaxes pyloric sphincter» Increases stomach motility Control of gastric secretions Stimulatory and inhibitory events occur in three phases 1.Cephalic 2.Gastric 3.Intestinal Chyme reaches duodenum Intestinal distention enterogastric reflex Release of secretin, CCK, VIP» Inhibit stomach motility and delay emptying Cephalic phase Gastric phase Intestinal phase Stimulatory events Inhibitory events 1 Sight and thought Cerebral cortex Lack of Cerebral of food Conditioned reflex stimulatory cortex impulses to 2 Stimulation of Hypothalamus Vagus parasympathetic taste and smell and medulla nerve receptors oblongata center 1 Vagovagal Medulla Vagus Gastrin G cells distension reflexes nerve secretion activates declines stretch receptors Local Overrides Sympathetic reflexes parasympathetic system nervous controls activation 2Food chemicals G cells Gastrin (especially peptides and release caffeine) and rising ph to blood activate chemoreceptors secretory activity Enterogastric reflexes Local 1Presence of low reflex Intestinal ph, partially digested (enteric) Vagal foods, fats, or gastrin nuclei hypertonic solution release Brief in medulla in duodenum when to blood effect stomach begins to Pyloric empty sphincter Release of intestinal hormones (secretin, cholecystokinin, vasoactive intestinal peptide) Stimulate Inhibit 1Loss of appetite, depression 1Excessive acidity (ph <2) in stomach 2Emotional upset 1Distension of duodenum; presence of fatty, acidic, hypertonic chyme, and/or irritants in the duodenum 2Distension; presence of fatty, acidic, partially digested food in the duodenum Figure

9 Presence of fatty, hypertonic, acidic chyme in duodenum Pyloric valve closed 1 Propulsion:Peristaltic waves move from the fundus toward the pylorus. Pyloric valve closed Pyloric valve slightly opened 2 Grinding: The most 3 Retropulsion:The pyloric vigorous peristalsis and end of the stomach acts as a mixing action occur pump that delivers small close to the pylorus. amounts of chyme into the duodenum, simultaneously forcing most of its contained material backward into the stomach. Enterogastric Reflex Initial stimulus Physiological response Result Duodenal stimuli decline Duodenal enteroendocrine cells Secrete Enterogastrones (secretin, cholecystokinin, vasoactive intestinal peptide) Chemoreceptors and stretch receptors Via short reflexes Enteric neurons Contractile force and rate of stomach emptying decline Target Via long reflexes CNS centers sympathetic activity; parasympathetic activity Stimulate Inhibit Figure Figure Major organ of digestion and absorption 2-4 m long; from pyloric sphincter to ileocecal valve Subdivisions Jejunum Ileum Located within the peritoneal cavity Structural modifications Villi( fingers ) Intestinal glands Mucosa Submucosa Mouth (oral cavity) Tongue Parotid gland Sublingual gland Submandibular gland Salivary glands Vein carrying blood to hepatic portal vessel Esophagus Gallbladder Anus Jejunum Ileum Pharynx Pancreas (Spleen) Transverse colon Descending colon Ascending colon Cecum Sigmoid colon Vermiform appendix Anal canal Large Muscle layers Circular folds Villi Lumen Figure 23.1 Figure 23.22a 9

10 5/14/2016 Microvilli (brush border) Microvilli Absorptive cells Lacteal Goblet cell Blood capillaries Mucosa associated lymphoid tissue Intestinal crypt Vilus Enteroendocrine cells Venule Lymphatic vessel Submucosa Muscularis mucosae Duodenal gland (b) Absorptive cell (b) Figure 23.22b Figure 23.3b Microvilli (brush border) Chemical digestion in the small Food entering SI = partially digested Intestinal juice Water, mucous Crypt cells produce lysozyme Absorptive cells Lacteal Goblet cell Blood capillaries Mucosa associated lymphoid tissue Intestinal crypt Villus Enteroendocrine cells Venule Lymphatic vessel Submucosa Muscularis mucosae Duodenal gland (b) Figure 23.22b Chemical digestion in the small Pancreatic juice Enzymes Amylase» Carbohydrates Lipase» Fats Trypsinogen, chymotrypsinogen, carboxypeptidase» Notice the -ogen» These must be activated to digest protein Sodium bicarbonate Pancreas Epithelial cells Membrane-bound enteropeptidase Trypsinogen Trypsin (inactive) Chymotrypsinogen (inactive) Procarboxypeptidase (inactive) Chymotrypsin Carboxypeptidase Neutralize stomach acid Figure

11 Chemical digestion in the small Intestinal juice Alkaline, mucous rich watery secretion Lysosozymes why are these defensive enzymes so important here? Brush border enzymes Enzymes for carbohydrates and proteins Pancreatic secretions Bicarbonate rich watery secretion Amylases, lipases, proteases, and nucleases Bile Bile salts emulsify lipids Accessory digestive organs Gallbladder Pancreas Sternum Nipple Right lobe of liver Gallbladder Bare area Falciform ligament Left lobe of liver Round ligament (ligamentum teres) Accessory digestive organs Largest internal surface area of any body organ Blood supply Hepatic artery oxygenated blood to the liver Hepatic-portal vein venous blood to the liver Hepatic vein all blood exiting the liver Figure 23.24a Hepatic veins Hepatic portal vein Inferior vena cava (not part of hepatic portal system) Gastric veins Spleen Inferior vena cava Splenic vein Right gastroepiploic vein Inferior mesenteric vein Superior mesenteric vein Large (c) The hepatic portal circulation. Lobule (b) Central vein Connective tissue septum Figure 19.29c Figure 23.25a, b 11

12 Interlobular veins (to hepatic vein) Central vein Sinusoids Plates of hepatocytes Bile canaliculi Bile duct (receives bile from bile canaliculi) Fenestrated lining (endothelial cells) of sinusoids Accessory digestive organs Microscopic compartments = lobules Lined by hepatocytes = screen blood» Store nutrients» Manage toxins» Produce bile Portal vein Hepatic macrophages in sinusoid walls Bile duct Portal venule Portal arteriole Portal triad Accessory digestive organs Hepatocyte functions Process blood borne nutrients» Store fat-soluble vitamins and minerals» Glucose is stored as glycogen Perform detoxification» Stores fat soluble toxins Produce ~900 ml bile per day» Note: gall bladder does not MAKE bile, only stores excess Makes heparin and other plasma proteins Catabolizes nitrogenous wastes Mucosa with folds Gallbladder Major duodenal papilla Hepatopancreatic ampulla and sphincter Cystic, Hepatic and Bile ducts Right and left hepatic ducts of liver Cystic duct Common hepatic duct Bile duct and sphincter Accessory pancreatic duct Tail of pancreas Pancreas Jejunum Main pancreatic duct and sphincter Head of pancreas Figure Accessory digestive organs Bile Yellow-green, alkaline solution Bile salts» Cholesterol derivatives that function in fat emulsification & absorption Lack of bile = grayish stools with fatty streaks (acholic feces) Accessory digestive organs Bile Bilirubin» Pigment formed from heme» Metabolized to form urobilinogen stercobilin 12

13 Accessory digestive organs Gallbladder Thin-walled muscular sac on the ventral surface of the liver Stores and concentrates bile by absorbing its water and ions Releases bile via the cystic duct» Flows into the bile duct Accessory digestive organs Pancreas Function Delivers digestive fluids and NaHCO 3 to duodenum via pancreatic duct Tissue types Endocrine» Islets of Langerhans insulin and glucagon Exocrine» Acinar tissue pancreatic juice Mouth (oral cavity) Tongue Esophagus Gallbladder Anus Jejunum Ileum Parotid gland Sublingual gland Submandibular gland Pharynx Pancreas (Spleen) Transverse colon Descending colon Ascending colon Cecum Sigmoid colon Vermiform appendix Anal canal Salivary glands Large Figure 23.1 Right and left hepatic ducts of liver Cystic duct Common hepatic duct Bile duct and sphincter Accessory pancreatic duct duct Acinar cells Basement membrane Zymogen granules Mucosa with folds Gallbladder Major duodenal papilla Hepatopancreatic ampullaand sphincter Tail of pancreas Pancreas Jejunum Main pancreatic duct and sphincter Head of pancreas Exocrine pancreas Rough endoplasmic reticulum Figure Figure 23.26a 13

14 Slide 1 Accessory digestive organs Pancreas Secretion mediated by hormones (where were these hormones made?) Secretin» Released in response to acid» Stimulates release of base from pancreas» Also stimulates release of pancreatic secretions and bile Cholecystokinin» Released when protein and fat enter» Stimulates the release of pancreatic secretions and bile 1 Chyme entering duodenum causes release of cholecystokinin (CCK) and secretin from duodenal enteroendocrine cells. 2 CCK (red dots) and secretin (yellow dots) enter the bloodstream. 3 CCK induces secretion of enzyme-rich pancreatic juice. Secretin causes secretion of HCO 3 -rich pancreatic juice. 4 Bile salts and, to a lesser extent, secretin transported via bloodstream stimulate liver to produce bile more rapidly. 5 CCK (via bloodstream) causes gallbladder to contract and hepatopancreatic sphincter to relax; bile enters duodenum. 6 During cephalic and gastric phases, vagalnerve stimulation causes weak contractions of gallbladder. Figure Large About 1.5 meters in length in a cadaver (SI about 6m long) Functions Vitamins, water, and electrolytes are reclaimed Propulsion of feces toward the anus Colon is not essential for life Right colic (hepatic) flexure Transverse colon Superior mesenteric artery Haustrum Ascending colon IIeum IIeocecal valve Cecum Vermiform appendix Left colic (splenic) flexure Transverse mesocolon Epiploic appendages Descending colon Cut edge of mesentery Teniae coli Sigmoid colon Anal canal External anal sphincter Figure 23.29a Regions Cecum Colon Anal canal Regions Cecum Blind pouch Appendix attaches to this area Bacteria Immune function Fermentation chamber in some other species Examples: horse, rabbit, koala 14

15 Regions Colon Ascending Retroperitoneal Transverse Anchored via mesocolons(mesenteries) Descending Retroperitoneal Sigmoid Anchored via mesocolons(mesenteries) Greater omentum Transverse colon Transverse mesocolon Descending colon Jejunum Mesentery Sigmoid mesocolon Sigmoid colon Ileum (c) Figure 23.30c (d) Lesser omentum Pancreas Transverse mesocolon Transverse colon Mesentery Greater omentum Jejunum Ileum Visceral peritoneum Parietal peritoneum Urinary bladder Regions Rectal valves stop feces from being passed with gas Anal canal Last segment of the large Internal anal sphincter Smooth muscle (involuntary) Spinal reflex arcs External anal sphincter Skeletal muscle (voluntary) Figure 23.30d Rectal valve Hemorrhoidal veins Levator ani muscle Anal canal External anal sphincter Internal anal sphincter Anal columns Pectinate line Anal sinuses Anus (b) Defecation Mass movements force feces into rectum Distension initiates spinal defecation reflex Parasympathetic signals Stimulate contraction of the sigmoid colon and rectum Relax the internal anal sphincter Conscious control allows relaxation of external anal sphincter Valsalva smaneuver Figure 23.29b 15

16 Impulses from cerebral cortex (conscious control) Voluntary motor nerve to external anal sphincter External anal sphincter (skeletal muscle) Sensory nerve fibers Sigmoid colon Stretch receptors in wall Involuntary motor nerve (parasympathetic division) Internal anal sphincter (smooth muscle) 3 If it is convenient to defecate, voluntary motor neurons are inhibited, allowing the external anal sphincter to relax so that feces may pass. 1 Distension, or stretch, of the rectal walls due to movement of feces into the rectum stimulates stretch receptors there. The receptors transmit signals along afferent fibers to spinal cord neurons. 2 A spinal reflex is initiated in which parasympathetic motor (efferent) fibers stimulate contraction of the rectal walls and relaxation of the internal anal sphincter. Figure Digestion Ingested materials must be broken down for absorption Majority of absorption in small Water and alcohol in stomach mucosa Water, some salts and water-soluble vitamins in large Non-absorbable materials removed by defecation Fate of Digested Materials Carbohydrates Glucose, fructose, and galactoseare directly absorbed Glucose: metabolized by nearly all cells Fructose: metabolized almost entirely by the liver Converted to glucose -> stored as glycogen Converted to glycerol -> triglycerides Galactose: metabolized to glucose, mostly in the liver Fate of Digested Materials Carbohydrates Cellulose Humans lack the enzymes to digest Metabolized by bacteria VitaminsK and B 12 are byproducts (very small amounts) Fate of Digested Materials Carbohydrate digestion Foodstuff Starch and disaccharides Oligosaccharides and disaccharides Lactose Maltose Sucrose Galactose Glucose Fructose Enzyme(s) and source Salivary amylase Pancreatic amylase Brush border enzymes in small (dextrinase, glucoamylase, lactase, maltase, and sucrase) Site of action Mouth Path of absorption 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. Proteins Amino acids, dipeptides, and some tripeptides Absorbed by active transport Further metabolism in cells free amino acids bloodstream Figure (1 of 4) 16

17 Protein digestion Foodstuff Protein Large polypeptides polypeptides, small peptides Amino acids (some dipeptides and tripeptides) Enzyme(s) and source Pepsin (stomach glands) in presence of HCl Pancreatic enzymes (trypsin, chymotrypsin, carboxypeptidase) Brush border enzymes (aminopeptidase, carboxypeptidase, and dipeptidase) Site of action Path of absorption Amino acids are absorbed by cotransport with sodium ions. Some dipeptides and tripeptides are absorbed via cotransport with H + + and hydrolyzed to amino acids within the cells. 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. Pancreatic proteases Lumen of Na + Na + Absorptive epithelial cell Amino acid carrier Amino acids of protein fragments Brush border enzymes Apical membrane (microvilli) 1 Proteins and protein fragments are digested to amino acids by pancreatic proteases (trypsin, chymotrypsin, and carboxypeptidase), and by brush border enzymes (carboxypeptidase, aminopeptidase, and dipeptidase) of mucosal cells. 2 The amino acids are then absorbed by active transport into the absorptive cells, and move to their opposite side (transcytosis). Active transport Passive transport Capillary 3 The amino acids leave the villus epithelial cell by facilitated diffusion and enter the capillary via intercellular clefts. Figure (2 of 4) Figure Fate of Digested Materials Lipids Emuslified by bile salts and digested by lipase into monoglycerides and FFAs Micelles formed (lipid and bile salts) and move between microvilli Lipids diffuse into intestinal epithelium (bile salts later reabsorbed in ileum) Fate of Digested Materials Lipids Within intestinal cells Triglycerides are formed Combined with proteins and cholesterol in the cell Chylomicrons Enter lymphatics through lacteal Enter blood vascular system Fat globule Fate of Digested Materials Bile salts Fat droplets coated with bile salts Epithelial cells of small Micelles made up of fatty acids, monoglycerides, and bile salts 3 Fatty acids and monoglycerides leave micelles and diffuse into epithelial cells. There they are recombined and packaged with other lipoid substances and proteins to form chylomicrons. Lacteal 1 Large fat globules are emulsified (physically broken up into smaller fat droplets) by bile salts in the duodenum. 2 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. 4 Chylomicrons are extruded from the epithelial cells by exocytosis. The chylomicrons enter lacteals. They are carried away from the by lymph. Lipids Plasma enzymes generate FFAs and glycerol Pass thru capillary wall to serve tissues The remaining protein-cholesterol combo returns to liver Additional proteins added HDL and LDL created (carriers for lipids) Figure

18 Fat digestion Foodstuff Unemulsified fats Monoglycerides and fatty acids Glycerol and fatty acids Enzyme(s) and source Emulsification by the detergent action of bile salts ducted in from the liver Pancreatic lipases Site of action Path of absorption 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, and 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. Fate of Digested Materials Water After digested nutrients removed, large volumes of salt and water remain in LI Active Na + uptake passive Cl - and water uptake Undigested materials (cellulose) cause water to be retained in LI Antibiotics may kill bacteria digestion impaired Figure (3 of 4) Disorders of the Colon cancer Second most common cause of cancer death in U.S. in men 98,000 new cases annually 48,000 deaths/year Diagnosis Colonoscopy Fiberoptic endoscope Polyps often occur before tumor Disorders of the Colon cancer Contributing factors Contact time with carcinogenic material in colon Diets high in animal material = slowed motility P53 (tumor suppressor gene) mutation Hereditary component Disorders of the Gallstones A.K.A. cholelithiasis Bile salts precipitate Block bile ducts Jaundice due to bilirubin Treatment Lithotripsy Medications Cholecystectomy Disorders of the Celiac disease Autoimmune disease Immune system destroys intestinal villiin response to gluten No villi= no nutrient absorption 18