Gastrointestinal System Digestion Anatomy of digestive system (review!) 4 major processes of digestive system: 1.Motility 2.Secretion 3.Digestion 4.Absorption

Phases of Digestion/Absorption 1.Cephalic 2.Gastric 3.Intestinal 4.Defecation

1.Cephalic 2.Gastric 3.Intestinal 4.Defecation Anticipation Begins with sensory input that is sent to the cerebral cortex and then to the hypothalamus to stimulate the PNS Salivation, relaxation of the GE sphincter, relaxation of stomach muscles, increase gastric motility Mastication Mechanical digestion Teeth, tongue Deglutition Bolus formation for swallowing Peristalsis in esophagus

Salivary Glands Parotid Glands Secretes Mucous Secretes Mucous Allows for smooth swallowing of bolus Mumps Sublingual and Submandibular glands secrete Amylase Breaks down complex carbohydrates into simple carbohydrates Breaks down complex carbohydrates into simple carbohydrates

Deglutition

1.Cephalic 2.Gastric 3.Intestinal 4.Defecation Storage Relaxation or contraction as needed. Digestion HCl - Hydrochloric Acid (Parietal cells) Pepsin (Chief cells) Mechanical Immune Protection Ingested pathogens Respiratory mucus

Reflux Esophagitis = Heartburn = GERD Gastroesphogeal Reflux Disease Lower esophageal sphincter dysfunction Why reflux against gravity? Why reflux against gravity?

1.Intrapleural pressure  during inspiration  Wall of esophagus expands  Subatmospheric pressure in esophageal lumen sucks acidic stomach contents into esophagus  May also occur during pregnancy or obesity GERD, cont’d

Mechanical Digestion Oblique, Longitudinal and Circular Gastric Muscles Esophagus does not contain oblique muscles Esophagus does not contain oblique muscles Allows for gastric motility to occur Muscles are sensitive to Parasympathetic input Parasympathetic input Gastrin hormone Gastrin hormone Rugae are used along with the Gastric Muscles for mechanical digestion

Chemical Digestion Gastric Pits Invaginations of the stomach wall Invaginations of the stomach wall Lined with several different types of cells Lined with several different types of cells Chief Cells At the bottom of the pits At the bottom of the pits Secretes pepsinogen Secretes pepsinogen Inactive form of the enzyme pepsin Pepsinogen is converted into pepsin upon mixing with HCl Pepsin breaks down proteins into amino acids Pepsin breaks down proteins into amino acids

Chemical Digestion Cont. Parietal Cells Above Chief Cells Above Chief Cells Secret H + and Cl - into the Gastric Pits Secret H + and Cl - into the Gastric Pits Used for Digestion of foodstuff Used for Digestion of foodstuff Gastric Glands or G cells Secretes the hormone Gastrin Secretes the hormone Gastrin Gastrin secretion increases when the contents of the stomach is basic Gastrin secretion increases when the contents of the stomach is basic Gastrin secretion decreases when the contents of the stomach is acidic Gastrin secretion decreases when the contents of the stomach is acidic Gastrin’s functions are Gastrin’s functions are To increase HCl secretion from the Parietal Cells To increase Gastric Motility

Mucous Cells Secrete Mucous to coat the lumen of the stomach Prevents ulceration Prevents ulceration H. Pylori also responsible for ulcers

Question 18 year old White Female Adult enters into the emergency room. She has been vomiting for over 72 hours. You observe she is also hyperventilating. How is the vomiting and hyperventilation tied together? List two of the possible problems that your patient is experiencing. HINT: Don’t forget the Parietal Cell

1.Cephalic 2.Gastric 3.Intestinal – Chyme (ingesta) enters small intestine 4.Defecation o Neutralization of HCl o NaHCO 3 from pancreas o Running Problem: Peptic Ulcer and antacids, including H 2 antagonists and proton pump inhibitors o Pancreatic enzymes o Digest protein, CHO o Bile acids o Emulsification of Fat o Absorption of H 2 O

Mechanical Digestion Peristalsis and Segmentation Occurs in the small intestine Occurs in the small intestine Food is basically shaken back and forth in small segments along the length of the small intestine Food is basically shaken back and forth in small segments along the length of the small intestine

Chemical Digestion During the segmentation process the food scrapes along the tips of the villi and causes cells to explode off Release Digestive Enzymes Release Digestive Enzymes Rapid Mitosis in the Crypts of Lieberchun or Intestinal crypts Rapid Mitosis in the Crypts of Lieberchun or Intestinal crypts Easily affected by chemo/radiation therapy due to rapid mitosis

Chemical Digestion Release of Digestive Enzymes Pancreas releases digestive enzymes into the duodenum Pancreas releases digestive enzymes into the duodenum Release of Bile Emulsification of Fat Emulsification of Fat Storage and Release by Gall Bladder Storage and Release by Gall Bladder Production of Bile by Liver Production of Bile by Liver Bile contains: Bile contains:Cholesterol Bile Salts LecithinBillirubin

Bacterial fermentation of CHO and proteins Bacterial fermentation of CHO and proteins Lactate, some vitamins are digested and/or absorbed Lactate, some vitamins are digested and/or absorbed More H 2 O absorption More H 2 O absorption Osmotic diarrhea vs. secretory diarrhea Osmotic diarrhea vs. secretory diarrhea Osmotic-solutes prevent H 2 O reabsorption Osmotic-solutes prevent H 2 O reabsorption Lactose intolerance Secretory- bacterial toxins ("flush out' pathogens) Secretory- bacterial toxins ("flush out' pathogens) Defecation Reflex Defecation Reflex 1.Cephalic 2.Gastric 3.Intestinal 4.Defecation

Colon Three Major Functions of the Large Intestine Absorption of H 2 O Absorption of H 2 O Storage of Feces Storage of Feces Usually 24 hours Production of Vitamin K Production of Vitamin K From E. Coli Used in the Blood Clotting Process

All of the following are functions of the oral cavity except A. To mechanically process foods B. To digest proteins C. To lubricate foods D. To digest certain carbohydrates

Passage of a bolus of food down the esophagus is assisted by A. Enzymes and acids B. Striated muscles and tissues C. Peristalsis and gravity D. The pyloric sphincter

The hormone that regulates the activity of the gastric glands is known as A. Progesterone B. Androgen C. Gastrin D. TSH E. Pepsin

Bile, which is formed in the liver, assists the A. Breakdown of proteins B. Absorption of water C. Emulsification of fats D. Formation of feces

All of the following are normally found in the bile except A. Cholesterol B. Bilirubin C. Bile salts D. Proteins

Which of the following hormones causes the pancreas to secrete digestive enzyme? A. Secretin B. Cholecystokinin C. Gastrin inhibiting peptide D. Gastrin E. Pepsinogen

Which of the following hormones stimulates the liver to produce bile? A. Secretin B. Cholecystokinin C. Gastrin inhibiting peptide D. Gastrin E. Leptin

Hydrochloric acid is secreted by which of the secretory cells of the stomach? A. Chief cells B. Mucous neck cells C. Serous cells D. Parietal cells E. G cells

Lactose Intolerance Lactose = glucose + galactose Lactase only found in juvenile mammals Adaptive (dominant) mutation in populations with dairy-based cultures Lactose intolerance in 95% of Native Americans, 95% of Native Americans, 90% of Asian Americans 90% of Asian Americans 70% of African Americans 70% of African Americans 50% of Mexican Americans 50% of Mexican Americans

Regulation of GIT ANS Parasympathetic (R & R) Parasympathetic (R & R) Sympathetic Sympathetic Emotional (cephalic reflexes) E.g., smell of food E.g., smell of food ENS (Enteric Nervous System) Self-contained (intrinsic) Self-contained (intrinsic) GI peptides can have regulatory role as hormones or paracrines E.g., Gastrin, CCK E.g., Gastrin, CCK

CHO Digestion & Absorption ~50% of calories in average American diet ~50% of calories in average American diet Starch (polysaccharide) and sucrose (disaccharide) Starch (polysaccharide) and sucrose (disaccharide) Cellulose (roughage) not digestible Cellulose (roughage) not digestible Enzymes: amylases, disaccharidases (maltase, sucrase, lactase) Enzymes: amylases, disaccharidases (maltase, sucrase, lactase) Absorbed only as monosaccharides (glucose, fructose) Absorbed only as monosaccharides (glucose, fructose) Small intestine Small intestine

Protein Digestion and Absorption Variable digestibility 30-60% of protein not from diet First digestion in Stomach by HCl Proteases secreted as proenzymes Pepsin(-ogen), trypsin, etc. Pepsin(-ogen), trypsin, etc. Absorption of single a.a. and di- and tripeptides Specific receptors required for larger chains Specific receptors required for larger chains May serve as allergens DDAVP

Lipid (fat) Digestion Mostly triglycerides in diet Cholesterol, Fat-soluble vitamins, others. Cholesterol, Fat-soluble vitamins, others. Combination with bile salts creates an emulsion Colipase and lipase allow formation of small micelles Colipase and lipase allow formation of small micelles Absorption of fat via diffusion across apical CM Chylomicrons in the cell are absorbed into lacteals

Other Stuff Water soluble vitamins— mediated transport Fat soluble vitamins via absorption Water, Ions and Minerals Various locations and methods, e.g, diffusion, carrier proteins Various locations and methods, e.g, diffusion, carrier proteins Nucleic Acids

Colon Cancer 2 nd largest cause of cancer deaths Cellulose (indigestible) = fiber, roughage Significance of “roughage” in diet??

Olestra Biotechnology focus Consumers want fat in their foods  search for low cal fat substitutes 1996, Procter & Gamble market Olestra Olestra = Olean = sucrose polyester (sucrose molecule FA) Cannot be digested, nor absorbed Unpleasant side effects Absorption of fat sol. vitamins pot. problem

Motility 2 purposes: Forward movement of food Mechanical mixing GI smooth muscles contract spontaneously Pacemaker cells, (Interstitial Cells of Cajal), connected by gap junctions, generate slow wave potentials AP’s spread throughout longitudinal muscles (gap junctions)  wave of contraction Like cardiac muscle, Ca 2+ can regulate contraction strength Like cardiac muscle, Ca 2+ can regulate contraction strength 1. Motility 2. Secretion 3. Digestion 4. Absorption

Different Patterns of Contraction Tonic Contractions Sustained contraction, usually in the stomach Phasic Contractions Peristaltic contractions progressive waves moving along segments of longitudinal layer  forward propulsion progressive waves moving along segments of longitudinal layer  forward propulsion circular layer contracts proximal to bolus circular layer contracts proximal to bolus Especially esophagus Segmental contractions alternate contraction & relaxation lead to mixing alternate contraction & relaxation lead to mixing A side effect of narcotics A side effect of narcotics

Secretion 9 L of fluid pass through the GIT (only 2 L from food & drink)  Secretion and Reabsorption important Ions and water; similar to renal mechanisms Ions and water; similar to renal mechanismsSaliva Hydrochloric Acid (Parietal Cells) Hydrochloric Acid (Parietal Cells) Bicarbonate (enzyme necessary ?) Bicarbonate (enzyme necessary ?) Enzymes (zymogens) Enzymes (zymogens)zymogens Mucus (Goblet cells) Mucus (Goblet cells) Bile (bile salts – function?) Bile (bile salts – function?) Net Fluid Balance in GI system 1. Motility 2. Secretion 3. Digestion 4. Absorption

Digestion Overview Mechanical breakdown and mixing aid enzymatic breakdown Chewing Chewing Tonic contractions, esp. stomach Tonic contractions, esp. stomach Enzymatic breakdown converts macromolecules into absorbable units Bile emulsifies fats Optimal pH of enzymes indicates location of activity 1.Motility 2.Secretion 3.Digestion 4.Absorption

Absorption Overview Most nutrient absorption takes place in ? Fats absorbed into lacteals Fats absorbed into lacteals Everything else absorbed into portal vein Everything else absorbed into portal vein Alcohol & aspirin across gastric epithelium Additional: H 2 O, ions & some vitamins absorbed in ________________ Mechanisms analogous to renal absorption 1. Motility 2. Secretion 3. Digestion 4. Absorption