The GI System 1 & 2 (2023) PDF

WEEK 14 MPharm Programme The Gastro-intestinal System 1 Dr G Boachie-Ansah [email protected] Dale 113 ext. 2617 MPharm PHA112 GI System WEEK Outline of Lectures 14 The main functions of the GI or Digestive System Organisation & functional anatomy of the gastrointestina...

WEEK 14 MPharm Programme The Gastro-intestinal System 1 Dr G Boachie-Ansah [email protected] Dale 113 ext. 2617 MPharm PHA112 GI System WEEK Outline of Lectures 14 The main functions of the GI or Digestive System Organisation & functional anatomy of the gastrointestinal (digestive) system Digestive processes in the mouth & stomach Digestive processes in the small intestine Digestive processes in the large intestine Slide 2 of 83 MPharm PHA112 GI System WEEK Learning Outcomes 14 At the end of this lecture, you should be able to: Describe the basic anatomy & main functions of the gastro-intestinal (digestive) system Explain the digestive processes that take place in the major parts of the digestive tract Describe the neural & chemical control of the gastro-intestinal (digestive) system Discuss the major sites of absorption in the gastrointestinal (digestive) system Slide 3 of 83 MPharm PHA112 GI System The GI System WEEK 14 A group of organs that work together to break down ingested food into smaller, absorbable nutrient molecules that can then be absorbed into blood for distribution to all the cells in the body Slide 4 of 83 MPharm PHA112 GI System WEEK The GI System 14 Main functions Digests or biochemically breaks down ingested food into small, simple nutrient molecules Absorbs & transfers the nutrients, electrolytes & water from the ingested food into systemic circulation Makes the preformed organic nutrient molecules in ingested food available to body cells as sources of fuel or energy building blocks Slide 5 of 83 MPharm PHA112 GI System WEEK The GI System 14 Performs 5 basic digestive processes Motility Secretion Digestion Absorption Storage & elimination of indigestible food Slide 6 of 83 MPharm PHA112 GI System WEEK The Digestive System 14 Motility Muscular contractions that mix & move the contents of the digestive tract forward Two types of digestive motility Propulsive movements propel or push contents forward through the digestive tract Mixing movements mix food with digestive juices & promote digestion facilitate absorption of digested food Slide 7 of 83 MPharm PHA112 GI System The GI System WEEK 14 Secretion Several digestive juices secreted in GI tract in response to specific neural or hormonal stimulation Consist of water, electrolytes & specific organic constituents (enzymes, mucus, etc) Include both exocrine & endocrine secretions Exocrine H2O, HCl, HCO3-, bile, lipase, pepsin, amylase, trypsin & histamine Endocrine Gastrin, secretin, CCK, VIP & somatostatin Slide 8 of 83 MPharm PHA112 GI System WEEK The GI System 14 Digestion Biochemical breakdown of complex foodstuffs into smaller, absorbable units Accomplished by enzyme-mediated hydrolysis Complex foodstuffs & their absorbable units Carbohydrates → monosaccharides Proteins → amino acids Fats → glycerol & fatty acids Slide 9 of 83 MPharm PHA112 GI System WEEK The GI System 14 Absorption Transfer of small digested units, along with water, vitamins & electrolytes, from the GI tract into blood or lymph Occurs largely & most completely in the small intestine Slide 10 of 83 MPharm PHA112 GI System WEEK 14 Slide 11 of 83 Functional Anatomy of The Gastro-intestinal (Digestive) System MPharm PHA112 GI System WEEK 14 Slide 12 of 83 The GI System MPharm PHA112 GI System The GI System WEEK 14 Gross Structure & Organisation Also called the Gastrointestinal (GI) Tract Comprises 2 main components The alimentary canal long, continuous hollow tube stretching from the mouth to the anus (~30 feet long) Accessory organs & glands Salivary glands Liver & Pancreas Slide 13 of 83 MPharm PHA112 GI System WEEK 14 Alimentary canal – Continuous from mouth to anus – Consists of • • • • • Mouth Pharynx Oesophagus Stomach Small intestine Accessory digestive organs – Salivary glands – Exocrine pancreas – Biliary system • Liver • Gallbladder – Duodenum – Jejunum – Ileum • Large intestine – Caecum – Appendix – Colon – Rectum • Anus Slide 14 of 83 MPharm PHA112 GI System WEEK The GI System 14 The Alimentary Canal Gross Functional Organisation Divided into 3 main parts Upper part the mouth, oesophagus & stomach serves as food intake source & receptacle site of initial digestive processes Slide 15 of 83 MPharm PHA112 GI System WEEK The GI System 14 The Alimentary Canal Gross Functional Organisation Divided into 3 main parts (cont’d) Middle part the small intestine – duodenum, jejunum & ileum site of main digestive & absorptive processes Slide 16 of 83 MPharm PHA112 GI System WEEK The GI System 14 The Alimentary Canal Gross Functional Organisation Divided into 3 main parts (cont’d) Lower part the large intestine – caecum, colon & rectum serves as the storage channel for efficient elimination of waste Slide 17 of 83 MPharm PHA112 GI System WEEK 14 Wall Structure of Alimentary Canal Slide 18 of 83 MPharm PHA112 GI System WEEK 14 Wall Structure of Alimentary Canal Slide 19 of 83 MPharm PHA112 GI System WEEK 14 Wall Structure of Alimentary Canal Comprises 4 layers Mucosa innermost, moist, folded lining of epithelial cells, connective tissue & smooth muscle cells main functions protective barrier against pathogens, etc secretes mucus, digestive enzymes & hormones absorbs digested nutrients into the blood undergoes rapid cell division & regeneration Slide 20 of 83 MPharm PHA112 GI System WEEK 14 Wall Structure of Alimentary Canal Comprises 4 layers Submucosa dense connective tissue layer containing blood and lymphatic vessels, lymphoid follicles & nerve fibres contains the submucosal nerve plexus of Meissner main functions provides the digestive tract with distensibility and elasticity glands secrete digestive enzymes nerve plexus helps regulate gut motility Slide 21 of 83 MPharm PHA112 GI System WEEK 14 Wall Structure of Alimentary Canal Comprises 4 layers Muscularis externa consists of inner layer of circular smooth muscle & outer layer of longitudinal smooth muscle myenteric plexus of Auerbach lies in between main functions contractions facilitate mixing & movement of food contents (peristalsis & segmentation) intrinsic nerve plexus helps regulate gut motility Slide 22 of 83 MPharm PHA112 GI System WEEK 14 Wall Structure of Alimentary Canal Comprises 4 layers Serosa outer connective tissue & epithelial covering continuous with the mesentery main functions secretes a watery, slippery serous fluid  lubrication and  friction between digestive organs & surrounding viscera Slide 23 of 83 MPharm PHA112 GI System WEEK 14 Complex Extrinsic & Intrinsic Regulation of Digestive Function Mediated via Interstitial cells of Cajal (pacemaker cells)  slow-wave potentials (BER)  spontaneous rhythmic electrical activity Intrinsic nerve plexuses (ENS)  GI muscle contraction or relaxation Extrinsic nerves (ANS)  increase or decrease GI contraction & secretion Gastrointestinal hormones  increase or decrease GI contraction & secretion Local sensory receptors – chemoreceptors, mechanoreceptors & osmoreceptors Slide 24 of 83 MPharm PHA112 GI System WEEK 14 Slide 25 of 83 Complex Extrinsic & Intrinsic Regulation of Digestive Function MPharm PHA112 GI System WEEK 14 Slide 26 of 83 Complex Extrinsic & Intrinsic Regulation of Digestive Function MPharm PHA112 GI System WEEK Digestive Processes 14 Slide 27 of 83 MPharm PHA112 GI System WEEK 14 Digestive Processes From Mouth to Stomach Slide 28 of 83 MPharm PHA112 GI System WEEK 14 From Mouth to Stomach Mastication (chewing) Aids in mechanical breakdown of larger food units Mixes food with saliva which contains salivary amylase  partial digestion of starch Saliva moistens ingested food, lubricates & exerts antibacterial effect Deglutition (swallowing) oropharyngeal stage oesophageal stage Slide 29 of 83 MPharm PHA112 GI System WEEK Swallowing 14 Oropharyngeal stage Movement of the bolus through the pharynx into the oesophagus Slide 30 of 83 MPharm PHA112 GI System Swallowing WEEK 14 Oesophageal stage Slide 31 of 83 MPharm PHA112 GI System WEEK 14 MPharm Programme The Gastro-intestinal System 2 Dr G Boachie-Ansah [email protected] Dale 113 ext. 2617 MPharm PHA112 GI System The Stomach WEEK 14 J-shaped sac-like chamber The most distensible part of GI tract Main functions Stores ingested food Secretes gastric juice (acid, mucus & intrinsic factor, digestive enzymes - pepsin, lipase) Mixes food with gastric juice initiates digestion of proteins & fat kills bacteria Moves food (chyme) at controlled & steady rate into the duodenum Slide 33 of 83 MPharm PHA112 GI System WEEK 14 Slide 34 of 83 The Stomach MPharm PHA112 GI System WEEK 14 Gastric Mucosal Folds, Gastric Pits & Gastric Glands Slide 35 of 83 MPharm PHA112 GI System WEEK 14 Structure of Gastric Gland Slide 36 of 83 MPharm PHA112 GI System WEEK 14 Slide 37 of 83 MPharm PHA112 GI System Gastric Glands WEEK 14 Important Gastric Secretory Products Product Source Functions Hydrochloric acid Parietal cell Hydrolysis; sterilization of meal Intrinsic factor Parietal cell Vitamin B12 absorption Pepsinogen Chief cell Protein digestion Mucus, bicarbonate Surface mucous cells Gastroprotection Trefoil factors Surface mucous cells Gastroprotection Histamine ECL cells Regulation of gastric secretion Gastrin G cells Regulation of gastric secretion Gastrin releasing peptide (GRP) Nerves Regulation of gastric secretion Acetylcholine (ACh) Nerves Regulation of gastric secretion Somatostatin D cells Regulation of gastric secretion Slide 38 of 83 MPharm PHA112 GI System WEEK 14 Pepsinogen Activation in The stomach Slide 39 of 83 MPharm PHA112 GI System WEEK 14 Mechanism of Gastric HCl Secretion Slide 40 of 83 MPharm PHA112 GI System WEEK 14 Parietal Cell – Receptor Activation of the Proton Pump Slide 41 of 83 MPharm PHA112 GI System WEEK 14 Parietal Cell – Receptor Activation of Proton Pump Slide 42 of 83 MPharm PHA112 GI System WEEK 14 Parietal Cell Receptor Activation of Proton Pump Slide 43 of 83 MPharm PHA112 GI System WEEK 14 Control of Gastric Secretion The 3 Phases of Gastric Secretion Cephalic (“head”) phase Triggered by factors arising before food enters the stomach – thought, smell, sight or taste of food Gastric phase Triggered by factors resulting from the presence of food in the stomach Intestinal Phase Triggered by factors resulting from movement of food from stomach into duodenum Slide 44 of 83 MPharm PHA112 GI System WEEK 14 Control of Gastric Secretion Excitatory Cephalic & Gastric Phases Slide 45 of 83 MPharm PHA112 GI System WEEK 14 Control of Gastric Secretion Inhibitory Intestinal Phase Slide 46 of 83 MPharm PHA112 GI System WEEK 14 Control of Gastric Secretion Inhibitory Duodenal Mechanisms Slide 47 of 83 MPharm PHA112 GI System WEEK 14 Slide 48 of 83 Control of Gastric Secretion MPharm PHA112 GI System WEEK 14 Digestion & Absorption in the Stomach Carbohydrate digestion by salivary amylase continues partial inhibition of amylase by acidity Proteins are partially digested by pepsin in the antrum Only alcohol & aspirin are absorbed Slide 49 of 83 MPharm PHA112 GI System WEEK 14 The Gastric Mucosal Barrier Slide 50 of 83 MPharm PHA112 GI System WEEK 14 The Gastric Mucosal Barrier Protects Stomach from Damage Cell membranes of gastric mucosal cells are impermeable to HCl Tight junctions between adjacent gastric mucosal (epithelial) cells are impermeable to HCl The HCO3–-rich mucus serves both as protective physical barrier & as chemical barrier that neutralizes acid close to gastric mucosa Rapid rate of cell division – entire stomach lining replaced in 3 days Prostaglandins inhibit acid secretion & promote alkaline mucus secretion Slide 51 of 83 MPharm PHA112 GI System WEEK 14 Digestive Processes From Small Intestine To Large Intestine Slide 52 of 83 MPharm PHA112 GI System WEEK The Small Intestine 14 Digestive & Absorptive Functions Main site for digestion & absorption of ingested food Secretes aqueous salt & mucus solution for lubrication & protection Utilizes segmentation & peristaltic contractions to mix & propel chyme, and facilitate absorption Digestion occurs via action of bile, pancreatic enzymes & intestinal (brush-border) enzymes Absorption occurs along the entire length – but largely in the duodenum & jejunum Slide 53 of 83 MPharm PHA112 GI System WEEK The Small Intestine 14 Structure-function Relationships Mucosal surface thrown into permanent circular folds  3-fold  in surface area Microscopic finger-like projections (villi) project from circular folds  10-fold  in surface area Villi are covered by epithelial cells Epithelial cells have numerous smaller, hair-like projections, called microvilli or brush border  20-fold  in surface area 3 types of digestive enzymes are expressed on the membranes of microvilli or brush border – enteropeptidase, disaccharidases & aminopeptidases Slide 54 of 83 MPharm PHA112 GI System WEEK 14 Intestinal Circular Folds, Villi & Microvilli Slide 55 of 83 MPharm PHA112 GI System WEEK 14 The Structure of Intestinal Villi Slide 56 of 83 MPharm PHA112 GI System