Digestive system. Dr. Carmen E. Rexach Physiology Mt San Antonio College

Transcription

1 Digestive system Dr. Carmen E. Rexach Physiology Mt San Antonio College

2 Functions Motility ingestion mastication deglutition peristalsis Secretion exocrine endocrine Digestion Absorption

3 Tunics

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5 Innervation Autonomic nervous system Parasympathetic (vagus nerve) motility secretion Sympathetic decreases peristalsis secretion contraction of sphincters

6 Esophagus Collapsible tube first 1/3 Skeletal muscle last 2/3 Smooth muscle gastroesophageal sphincter

7 Stomach Function food storage initiates protein digestion kills bacteria moves food to SI intrinsic factor Digestion and absorption proteins alcohol/aspirin

8 Gastric Glands Goblet cells mucus Parietal cells HCl Chief cells pepsinogen Argentaffin cells Seratonin (correct) G cells gastrin

9 ph 3 functions of ph in stomach denature ingested protein convert pepsinogen to pepsin destroy bacteria

10 Protective mechanisms Impermeability of gastric mucosa to CO 2 and NH 3 alkaline mucus tight junctions rapid cell division and replacement protective effects of prostaglandins In doudenum bicarbonate from pancreatic juice Brunner s glands Secrete mucinous alkaline solution

11 Peptic ulcers Gastric ulcers Weakened defense mechanisms Duodenal ulcers Increased acid and pepsin production Helicobacter pylori Major factor in both types Present in 100% of gastric ulcer patients and 95% of duodenal ulcer patients Exceptions: Those whose ulcers are the result of overuse of NSAIDS = inhibits prostaglandin production Produces NH 3 and urease damages epithelium and allows H+ to permeate Also linked to increased acid secretion

12 Small intestines Length 3 divisions duodenum jejunum ileum absorption doudenum + jejunum ileum system of folds microvilli, villi, plicae circularis

13 Villi Columnar epithelium goblet cells crypts of Lieberkuhn Glands that secrete intestinal juice at base of the villi brush border surface area enzymes enterokinase microvilli arteriole villus capillaries nerve lacteal Lymph duct vein Muscularis mucosa artery

14 Intestinal motility Major types of contractions peristalsis segmentation Pacesetter potential smooth muscle cells can lead to a/p parasympathetic and sympathetic influences Relaxation NO

15 Large Intestine Structure Haustra Fluid and electrolyte absorption 90% in SI passive osmosis water secretion Defecation

16 Liver

17 Liver lobules: functional unit

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21 Functions of liver Exocrine Endocrine Clotting functions Plasma proteins Organic metabolism Cholesterol metabolism Excretory and degradative functions

22 Exocrine & Endocrine Synthesis and secretion of bile salts ml/day Adds bicarbonate rich solution to bile Secretes IGF-1 = promotes cell division Forms T3 from T4 Secretes Angiotensinogen Metabolizes hormones Secretes immune cytokines

23 Clotting and Plasma proteins Produces prothrombin & fibrinogen Produces bile salts needed for vitamin K absorption Produces plasma albumin, acute phase proteins, binding proteins, and lipoproteins

24 Organic metabolism Converts plasma glucose to glycogen and triglycerides Converts amino acids to fatty acids Produces triglycerides and secretes them as lipoproteins Gluconeogeneisis and glycogenolysis Converts fatty acids into ketones Produces urea

25 Cholesterol metabolism/excretory & degradative functions Synthesizes cholesterol Secretes plasma cholesterol into bile Converts plasma cholesterol into bile salts Secretes bile pigments Excretes toxins via bile Destroys old erythrocytes and lots, lots more!

26 Gallbladder & pancreas Hepatic ducts Common bile duct gallbladder Pancreas Duodenal papillae Pancreatic duct Doudenum

27 Pancreas Endocrine = islets of Langerhans insulin and glucagon, etc. Exocrine = pancreatic acini pancreatic juice composition water bicarb digestive enzymes role of enterokinase

28 Neural and endocrine regulation Long reflex preconditioning Short reflex more local GI hormones Extrinsic controls 3 phases (cephalic, gastric, intestinal) some events without neural or endocrine control

29 GI hormones Gastrin Secretin CCK glucose-dependent insolinotropic peptide (GIP) Glucagon-like peptide 1 (GLP-1) Guanylin

30 Gastrin endocrine cell location antrumof stomach stimulus for release amino acids, peptides in stomach parasympathetic nervous system actions stimulates secretion of HCl and pepsinogen

31 Secretin Endocrine cell location small intestine stimulus for release acid in small intestine action stimulate pancreatic bicarbonate secretion potentiate CCK-stimulated pancreatic enzyme secretion

32 Cholecystokinin (CCK) Endocrine cell location small intestine Stimulus for release amino acids, fatty acids in small intestine Action contraction and emptying of the gall bladder stimulates release of pancreatic enzymes (in the brain: acts as satiety hormone)

33 Glucose-dependent insulinotropic peptide (GIP) Endocrine cell location small intestine Stimulus for release glucose, fat in the small intestine Action inhibits gastric emptying potentiates insulin release

34 Glucagon-like peptide 1 (GLP-1) Endocrine cell location ileum and colon Stimulus for release oral ingestion of nutrients glucose, fats, amino acids (mixed meals) Action inhibits gastric motility stimulates insulin secretion

35 Guanylin Endocrine gland location ileum and colon Action stimulates intestinal Cl - release result: increased NaCl and water in feces

36 Cephalic phase First 30 minutes Smell, sight, and taste of food stimulates vagus nuclei of brain (long reflex) vagus nerve stimulates: parietal and chief cells Gastrin secretion by G cells Also stimulates parietal and chief cells

37 Gastric phase Begins when food arrives in stomach Stimulus distension chemical composition of chyme short polypeptides and amino acids in stomach Positive feedback, cells secrete gastrin HCl and pepsinogen are released Glucose No effect Lipids Inhibition of gastrin secretion ph<2.5 negative feedback inhibition of gastrin

38 Intestinal phase Begins when chyme enters small intestines neural inhibition of gastric emptying and acid secretion due to: increased osmolality stretching enterogastrone stimulus: fat in chyme inhibits gastric acid secretion GIP = insulin secretion if glucose is present CCK = inhibits gastric emptying when chyme in duodenum

39 Intestinal reflexes Gastroileal reflex increased gastric activity = increased motility of ileum = increased chyme through sphincter ileogastric reflex ileal distension = decreased gastric motility intestino-intestinal reflex one segment overdistends = rest relax

40 Regulation pancreatic juice & bile Neural & hormonal Pancreatic juice secretin ph <4.5 in duodenum stimulates bicarbonate production by pancreas camp as a second messenger CCK fat content in chyme production of pancreatic enzymes Ca ++ as second messenger Secretion of bile continuous secretion gallbladder contraction under influence of CCK and secretin

41 Mouth Digestion and absorption of salivary amylase Stomach carbohydrates enzymes denatured Small intestines pancreatic amylase = maltose, maltriose brush border enzymes = monosaccharides secondary active transport with Na + Into capillaries in villus

42 Mouth: Salivary amylase Digestion of Carbohydrates Stomach: Enzymes denatured Duodenum: Pancreatic amylase Brush border enzymes

43 Absorption of carbohydrates

44 Digestion and absorption of proteins Mouth nothing Stomach Pepsin = short chain polypeptides Small Intestines trypsin, chymotrypsin, elastase carboxypeptidase aminopeptidase = from brushborder across into blood Whole proteins babies botulinum toxin Free amino acids Dipeptides tripeptides

45 Digestion of proteins Stomach: Pepsin and HCl Small intestines: Trypsin, chymotrypsin Carboxypeptidase Brush border: aminopeptidases

46 Protein absorption aa Na + -Amino acids move into enterocytes by countertransport, in exchange for two Na +. -They are absorbed into a capillary bed on the basal side of the cell and taken to the liver via the hepatic portal system.

47 Digestion and absorption of lipids Emulsification pancreatic lipase Mixed micelles to brushborder transport across into epithelial cells can be moved inside cell chylomicron into lacteal

48 Digestion of Fat Small intestines: Pancreatic lipase

49 lacteal

50 Lipid transport From lymphatics to thoracic duct Triglycerides removed by lipoprotein lipase on endothelial membranes Free fatty acids and glycerol into tissues Leftovers to liver Remnant particles contain cholesterol Combined with apoproteins to produce VLDL s Deliver triglycerides to other organs Later converted to LDL s when triglyceride has been removed

51 Lipoproteins What are they? Lipid & protein complexes Transport cholesterol & triglycerides in blood Protein allows hydrophobic lipids to remain in suspension Five classes: Based on density, molecular weight, size, chemical composition Chylomicrons VLDL IDL LDL High levels associated with increased risk CVD HDL Low levels associated with increased risk of CVD Best profile = high HDL, low LDL

52 Treatment for morbid obesity

53 Lapband

54 Roux-en-Y Gastric Bypass