The Digestive System No Guts - No Glory!
Digestive System Anatomy • Digestive tract – Alimentary tract or canal – GI tract • Accessory organs – Primarily glands • Regions – – – – Mouth or oral cavity Pharynx Esophagus Stomach Small intestine Large intestine Anus
Functions • Ingestion: Introduction of food into stomach • Mastication: Chewing • Propulsion – Deglutition: Swallowing – Peristalsis: Moves material through digestive tract
Functions • • • Mixing: Segmental contraction that occurs in small intestine Secretion: Lubricate, liquefy, digest Digestion: Mechanical and chemical Absorption: Movement from tract into circulation or lymph Elimination: Waste products removed from body
Digestive Tract Histology
Digestive System Regulation • Nervous regulation – Involves enteric nervous system • Types of neurons: sensory, motor, interneurons – Coordinates peristalsis and regulates local reflexes • Chemical regulation – Production of hormones • Gastrin, secretin – Production of paracrine chemicals • Histamine • Help local reflexes in ENS control digestive environments as p. H levels
Peritoneum and Mesenteries • Peritoneum – Visceral: Covers organs – Parietal: Covers interior surface of body wall – Retroperitoneal: Behind peritoneum as kidneys, pancreas, duodenum • Mesenteries – Routes which vessels and nerves pass from body wall to organs – Greater omentum – Lesser omentum
Peritonitis • Acute inflammation of the peritoneal cavity • Caused by: Stab -, or bullet wounds, perforating ulcers of GI tract, ruptured appendix • Bacterial infection, if generalized often fatal • Mega-dose antibiotic therapy
Oral Cavity • Mouth or oral cavity – Vestibule: Space between lips or cheeks and alveolar processes – Oral cavity proper • Lips (labia) and cheeks • Palate: Oral cavity roof – Hard and soft • Palatine tonsils • Tongue: Involved in speech, taste, mastication, swallowing
Teeth • 20 deciduous, 32 permanent teeth • Anatomy • Enamel: Hydroxyapatite Ca 5(PO 4)3 OH, lack of collagen, irreparable • Dentin: similar to bone, avascular, dentinal tubules house extensions of odontoblasts, maintain dentin structure (incl. repair)
Teeth
Teeth – Impacted teeth - fail to emerge from gums, pressure, pain (common with “wisdom teeth”) (3 rd molars) – Root canal therapy - death of nerve, cessation of blood supply pulp cavity frequently becomes infected sterilization treatment filling capping – Dental caries - gradual demineralization, erosion of enamel & dentin, via dental plaques, lactic acid producing bacteria, proteases break down collagen of dentin
Teeth • Dental calculus - dental plaque precipitates calcium salts calculus may compromise seal b/w gingiva & teeth risk of infection gum disease gingivitis (bleeding, swelling, pain) infection spread to jaw bone erosion tooth loss peridontitis • 95% of people > 35, cause of ca. 85% of tooth loss in adults
The Mouth & Associated Organs • Walls of mouth - stratified, squamous epithelium (friction) – gums, hard palate & dorsum of tongue slightly keratinized – upon injury: secretion of defensins (protection against microorganisms in oral flora) • Lips - muscular, red margins poorly keratinized, translucent, no sweat or sebaceous glands
The Mouth & Associated Organs • Cheeks - buccinator muscles • Tongue - intrinsic (shape change) and extrinsic muscle (movement, attached to skull bones)
Salivary Glands • Produce saliva – Prevents bacterial infection – Lubrication – Contains salivary amylase • Breaks down starch • Three pairs – Parotid: Largest – Submandibular – Sublingual: Smallest
Composition of Saliva • • • Hypo-osmotic solution ( 97 -99. 5% water) p. H 6. 75 - 7. 00 Na, K, phosphate, bicarbonate, chloride proteins: amylase, Lysozyme, Ig. A metabolic wastes: urea, uric acid Resident bacteria reduce nitrate (NO 3 -) into nitrite (NO 2 -), converted into NO (nitric oxide), esp. in acidic environment (around gums, acids produced by caries producing bacteria), NO - bactericical
Control of Salivation • 1 -1. 5 l/day • Basal secretion to moisten oral cavity • Increased output via response to stimuli – chemoreceptors, pressoreceptors brain stem parasympathicus output increased salivation esp. in response to acidic foods (fruit juices, vinegar) or hot spices – also triggered via cortical stimulation (thought, smell)
Control of Salivation • Effect of symapthicus – decreases overall secretion – change to thick, mucous secretion – strong sympathicus stimulation vasoconstriction of vessels serving glands near cessation of salivation (dry mouth, difficulty swallowing, talking) – accumulation of food particles enhanced bacterial growth halitosis • Salivary glands Infection – Mumps (myxovirus infection) spread to testes in male adults 25% chance of sterility
Deglutition (Swallowing) • Three phases – Voluntary • Bolus of food moved by tongue from oral cavity to pharynx – Pharyngeal Reflex: Upper esophageal sphincter relaxes, elevated pharynx opens the esophagus, food pushed into esophagus – Esophageal • Reflex: Epiglottis is tipped posteriorly, larynx elevated to prevent food from passing into larynx
Phases of Deglutition (Swallowing)
Esophagus • Heartburn - burning, radiating, substernal pain caused by acid reflux into esophagus, can lead to inflammation & ulceration • Causes: – excessive eating, severe obesity, pregnancy, exercise after meals, hiatus hernia (structural abnormality, stomach protrudes above diaphragm, insufficient cardiac sphincter function, esp. when lying down)
Stomach Anatomy • Openings – Gastroesophageal: To esophagus – Pyloric: To duodenum • Regions – – Cardiac Fundus Body Pyloric
Stomach Histology • Layers – Serosa or visceral peritoneum: Outermost – Muscularis: Three layers • Outer longitudinal • Middle circular • Inner oblique – Submucosa – Mucosa
Stomach Histology • Rugae: Folds in stomach when empty • Gastric pits: Openings for gastric glands – Contain cells • Surface mucous: Mucus • Mucous neck: Mucus • Parietal: Hydrochloric acid and intrinsic factor • Chief: Pepsinogen • Endocrine: Regulatory hormones
Hydrochloric Acid Production Animation 36
Phases of Gastric Secretion Animation 37
Movements in Stomach
Gastritis, Gastric Ulcers – breaching of the mucosal barrier inflammation persistent gastritis erosion of underlying tissue ulcer – pain, risk of hemorrhage – triggered by hypersecretion of HCl, hyposecretion of mucus, 90% of affected patients carry Helicobacter pylori
Gastritis, Gastric Ulcers • Bacteria release cytotoxins and chemotactic proteins immune response (suspected of increasing risk for stomach cancer) • ? Bacterium also found in >40% of healthy people • Treatment: Antibiotics, H 2 -antihistamines, cimetidine (Tagamet ), ranitidine (Zantac ) • Bismuth subsalicylate (Pepto-Bismol ) Bi 3+ toxic to Helicobacter • Antacids neutralize HCl - (Al(OH)3, Mg(OH)2 – Maalox. TC®, Rolaids ®
Vomiting (Emesis) • Triggers – excessive stretching of stomach, alcohol, chemical irritants such as bacterial toxins, drugs, etc. impulse to emetic center (medulla) • Motor response – skeletal muscles of abdominal wall & diaphragm contract, cardiac sphincter relaxes, soft palate rises closing off nasal passages
“there she blows”
Small Intestine • Site of greatest amount of digestion and absorption • Divisions – Duodenum – Jejunum – Ileum: Peyer’s patches or lymph nodules • Modifications – Circular folds or plicae circulares, villi, lacteal, microvilli • Cells of mucosa – Absorptive, goblet, granular, endocrine
Small Intestine Secretions • Mucus – Protects against digestive enzymes and stomach acids • Digestive enzymes – Disaccharidases: Break down disaccharides to monosaccharides – Peptidases: Hydrolyze peptide bonds – Nucleases: Break down nucleic acids • Duodenal glands – Stimulated by vagus nerve, secretin, chemical or tactile irritation of duodenal mucosa
Duodenum and Pancreas
Duodenum Anatomy and Histology
Liver • Lobes – Major: Left and right – Minor: Caudate and quadrate • Ducts – Common hepatic – Cystic • From gallbladder – Common bile • Joins pancreatic duct at hepatopancreatic ampulla
Functions of the Liver • Bile production – Salts emulsify fats, contain pigments as bilirubin 0. 5 – 1 l/day • Storage – Glycogen, fat, vitamins A, D, E, copper and iron • Nutrient interconversion • Detoxification – Hepatocytes remove ammonia and convert to urea • Phagocytosis – Kupffer cells phagocytize worn-out and dying red and white blood cells, some bacteria • Synthesis – Albumins, fibrinogen, globulins, heparin, clotting factors
Hepatitis • Inflammation of liver, mostly due to – Viral infection (strains A-F), some drugs, mushroom toxins • 40% (US) Hepatitis B (blood contact, infusions, needles, sex) • 32% (US) Hepatitis A (less severe, transmitted water born, sewage, lack of hygiene, raw shell fish, (feces-mouth) • Recombinant-DNA produced vaccine against both made in yeast
Hepatitis • Hepatitis C common epidemic in developing countries, water born – no vaccine, but successful drug treatment with anti-inflammatory/immunesuppressive steroids (prednisone), recombinant-DNA made interferon
Liver Cirrhosis & Cancer • Cirrhosis - chronic, progressive inflammation, via chronic alcoholism, hepatitis, and other toxins regeneration of connective tissue faster than hepatocytes scar tissue contracts fibrosis obstruction of hepatic portal veins portal hypertension varicosis - may rupture bleeding, vomiting of blood • Hepatitis B often leads to hepatocarcinoma
Blood and Bile Flow
Duct System
Gallbladder • Bile is stored and concentrated • Stimulated by cholecystokinin and vegal stimulation • Dumps into small intestine • Production of gallstones possible – Drastic dieting with rapid weight loss
Pancreas • Anatomy – Endocrine • Pancreatic islets produce insulin and glucagon – Exocrine • Acini produce digestive enzymes – Regions: Head, body, tail • Secretions – Pancreatic juice (exocrine) • • • Trypsin Chymotrypsin Carboxypeptidase Pancreatic amylase Pancreatic lipases Enzymes that reduce DNA and ribonucleic acid
Bicarbonate Ion Production
Pancreatic Secretion Control
Large Intestine • Extends from ileocecal junction to anus • Consists of cecum, colon, rectum, anal canal • Movements sluggish (18 -24 hours)
Large Intestine • Cecum – Blind sac, vermiform appendix attached • Colon – Ascending, transverse, descending, sigmoid • Rectum – Straight muscular tube • Anal canal – Internal anal sphincter (smooth muscle) – External anal sphincter (skeletal muscle) – Hemorrhoids: Vein enlargement or inflammation
Secretions of Large Intestine • Mucus provides protection – Parasympathetic stimulation increases rate of goblet cell secretion • Pumps – Exchange of bicarbonate ions for chloride ions – Exchange of sodium ions for hydrogen ions
Histology of Large Intestine
Movement in Large Intestine • Mass movements – Common after meals • Local reflexes in enteric plexus – Gastrocolic: Initiated by stomach – Duodenocolic: Initiated by duodenum • Defecation reflex – Distension of the rectal wall by feces • Defecation – Usually accompanied by voluntary movements to expel feces through abdominal cavity pressure caused by inspiration
Reflexes in Colon and Rectum Animation 38
Large Intestine Bacterial Flora – live off undigested material, e. g. complex carbohydrates, cellulose, etc. – produce gases: CH 4, CO 2, H 2, N 2, dimethyl sulfide (CH 3 -S-CH 3) called flatus – synthesize crucial vitamin Bs & K • Diarrhea, constipation
Salmonella Food Poisoning • Many different strains of Salmonella, some cause typhoid fever, other common gastroenteritis – emesis, diarrhea, abdominal cramps, common in children under 10, even more in infants – bacteria common on poultry, eggs, sometimes in unpasteurized milk – rarely causes bacteremia, can affect heart, joints, and brain (meningitis) mostly selflimiting disease (symptoms ca. 5 - 7 d, bacteria present up to 6 month)
Lactose Intolerance • Decrease production of lactase in adulthood – lack of hydrolysis of lactose in into galactose and glucose – accumulation of lactose in intestine (after ingesting dairy products) – acts as osmotic laxative (retains H 2 O in lumen) – metabolized by intestinal flora - production of gases - cramps, abdominal pain • Therapy: Lactase tablets
Gluten Enteropathy • Gluten - protein common in cereals (wheat, rye, barely & oats) • some people - hypersensitive, diarrhea & malabsorption (mechanism? ) • Therapy: Gluten free food products
Genetic Defects affecting GI-tract • Structural malformations e. g. cleft palate, lip, patent opening b/w esophagus and trachea • Cystic Fibrosis – all secretions affected, major symptoms in lung – in GI-tract, pancreatic secretion abnormal, indigestion, severely compromised fat digestion, malabsorption of Vits. A, D, K – in utero: possible blockage of intestine, rupture
Colon Cancer • Second most frequent (after lung cancer) in males • without symptoms for long time • when symptoms appear, mostly metastases have formed (liver, etc. ) • gradual progression of series of mutations • starting as polyps • prevention by early detection, yearly colon examination, surgery • correlation to diet?
Digestion, Absorption, Transport • Digestion – Breakdown of food molecules for absorption into circulation • Mechanical: Breaks large food particles to small • Chemical: Breaking of covalent bonds by digestive enzymes • Absorption and transport – Molecules are moved out of digestive tract and into circulation for distribution throughout body
Carbohydrates • Consist of starches, glycogen, sucrose, lactose, glucose, fructose • Polysaccharides broken down to monosaccharides • Monosaccharides taken up by active transport or facilitated diffusion and carried to liver • Glucose is transported to cells requiring energy – Insulin influences rate of transport
Lipids • Include triglycerides, phospholipids, steroids, fat-soluble vitamins • Emulsification breaks down large lipid droplets to small
Lipoproteins • Types – Chylomicrons • Enter lymph – VLDL – LDL • Transports cholesterol to cells – HDL • Transports cholesterol from cells to liver
Proteins • Pepsin breaks proteins into smaller polypeptide chains • Proteolytic enzymes produce small peptide chains – Dipeptides, tripeptides, amino acids
Water and Ions • Water – Can move in either direction across wall of small intestine depending on osmotic gradients • Ions – Sodium, potassium, calcium, magnesium, phosphate are actively transported