Gastrointestinal System - PHA106 Pharmaceutical Biosciences 1 PDF

PHA106 Pharmaceutical Biosciences 1 GASTROINTESTINAL SYSTEM  Learning outcomes  Knowledge of the function and structure of GIT  Understanding of the role of the different organs of the GIT  Knowledge of the chemical events of digestion  Functions of the digestive system...

PHA106 Pharmaceutical Biosciences 1 GASTROINTESTINAL SYSTEM  Learning outcomes  Knowledge of the function and structure of GIT  Understanding of the role of the different organs of the GIT  Knowledge of the chemical events of digestion  Functions of the digestive system  Ingestion  Mechanical processing  Movement of food  Chemical digestion  Absorption  Excretion  Organs of the Digestive System Two main groups Gastrointestinal tract (GIT) or alimentary canal:  Mouth  Pharynx  Oesophagus  Stomach  Small and Large intestine Accessory structures: Teeth Tongue Glandular organs involved in secretions aiding chemical digestion of food  Histology of the digestive tract  Mucosa  Inner lining  Mucous membrane – epithelium & lamina propria  Submucosa  Muscularis externa  Peristalsis  Serosa  Mouth Buccal/oral cavity Lips Vestibule of the mouth Oral cavity proper Hard palate/soft palate Tongue Salivary glands  Parotid, submandibular, sublingual Teeth  Pharynx  Throat  Shared by digestive & respiratory system  Nasopharynx lined by ciliated columnar epithelium  Eustachian tube  Pharyngeal tonsil  Oropharynx  Epiglottis  Squamous epithelium  Laryngopharynx  Connects to oesophagus  Squamous epithelium  Laryngopharynx Oesophagus Oesophagus  Oesophagus  25 cm long hollow muscular tube  Transports solids/liquids from pharynx to stomach  Enters abdominal cavity through oesophageal hiatus in diaphragm  Mucosa & submucosa in large folds  Squamous epithelium  Stomach  4 functions  Storage of food  Mechanical breakdown of food  Chemical breakdown of food  Production of intrinsic factor  Chyme  4 regions  Cardia  Fundus  Body  Pylorus Oesophagus  Histology of the stomach  Columnar epithelium  Mucus covers entire surface  Gastric pits  Gastric glands  Parietal cells – intrinsic factor, HCl, alkaline tide  Chief cells – pepsinogen  Pyloric glands  Small intestine  Digests & absorbs nutrients – 90%  Duodenum  Jejunum  Ileum  Position stabilised in peritoneal cavity by mesentery  Circular folds present in intestine  Villi present on mucosa, brush border  Columnar epithelium Circular fold  Structure of villi  Extensive network of capillaries  Carry nutrients via hepatic portal vein to liver  Absorption of nutrients  Lacteal – lymphatic capillary  Villi are mobile – contractions of muscularis mucosae  Increases absorption  Goblet cells secrete mucus Capillaries  Pancreas  Exocrine organ of the GIT  Produces digestive enzymes & buffers  Enter duodenum via pancreatic duct  Endocrine functions also  Liver/gallbladder This will be discussed in a separate lecture  Large intestine  Stores digestive waste & absorbs water  Bacteria provide source of vitamins  1.5 m long  Frames small intestine  3 sections  Caecum  Colon  Rectum  Large intestine  Caecum collects material from ileum  Begins compaction  Appendix attaches to caecum  Colon has a large diameter & thin walls – expansion  Ascending  Transverse  Descending  Sigmoid  Rectum last 15 cm of GIT  Temporary storage of faeces  Large intestine  Large intestine walls are thin  Lack villi  Abundant mucus cells  No enzymes produced  Physiology of large intestine  10% absorption occurs here  Reabsorption of water  Bacterial residents produce vitamin K, biotin & B5  Bilirubin converted to urobilin/stercobilin  Chemical events of digestion CHO digestion & absorption  Salivary amylases break down starch into di and tri- saccharides  Pancreatic a-amylase breaks down remaining complex CHO  Maltase/sucrase/lactase in brush border convert disaccharides to monosaccharides  Monosaccharides absorbed into bloodstream by facilitated diffusion & cotransport mechanisms  Chemical events of digestion Lipid digestion & absorption  Lingual lipase & pancreatic lipase  Break down triglycerides into fatty acids & monoglycerides  Bile salts improve digestion by emulsifying the lipid into tiny droplets  Micelles form  Diffusion of lipids across plasma membrane  Chylomicrons diffuse into lacteal  Chemical events of digestion Protein digestion & absorption  Only occurs after food has been mechanically processed  First protease to act is pepsin (pH 1.5-2.0)  Pancreatic proteases – trypsin, chymotrypsin, elastase, carboxypeptidase  Amino acids absorbed into bloodstream by facilitated diffusion & cotransport mechanisms  Chemical events of digestion Water absorption  Inactive process occurring along an osmotic gradient  Osmotic equilibrium must be maintained  Intestinal cells continuously absorb nutrients & ions  Solute conc. in lumen decreases  Causes water to move out of lumen into surrounding tissues  Chemical events of digestion Ion absorption  Na ions – absorbed by diffusion, co-transport or active transport  Ca ions - active transport  Lipid-soluble vitamins ADEK – absorbed from micelles with dietary lipids  Water-soluble vitamins B & C – absorbed by diffusion across epithelium  Exception vitamin B12 – is absorbed by active transport when bound to intrinsic factor  Age-related changes  Rate of proliferation of epithelial stem cells declines  Smooth muscle tone decreases  Cumulative damage to GIT  Cancer rates increase  Dehydration  Summary  Knowledge of the function and structure of GIT  Understanding of the role of the different organs of the GIT  Knowledge of the chemical events of digestion  Additional reading Martini 11th edn. Chapter 24