Digestive System Overview We all need a digestive system because Cells require energy to live and thrive and this energy is ultimately stored in the chemical bonds of the food we consume The digestive system s primary job is to digest and absorb food in a molecular form that cells can harness energy from Nearly 95 of the ingested food undergoes digestion and absorption by the digestive system with the balance forming fecal matter Definitions to know 1 Orad in direction toward mouth For example vomiting is ejected orad like foods liquids 2 Aborad in direction away from the mouth in digestive tube 3 Enteric related to intestines less precisely related to any part or all of the digestive tube 4 GI Gastrointestinal related to the stomach or intestines less precisely related to any part or all of the digestive tube 5 Per os medication fluids given by way of mouth 6 NPO not per os do not give this patient anything by the way of mouth usually done night and morning before receiving anesthetic surgery IP injection intraperitoneal injection medication injected into the peritoneal cavity surrounding the intestines 7 8 Perienteral administration an IP delivery of nutrient or fluids b c patient is unable to swallow or process food normaly Generic Digestive Tube Segment Functional Anatomy and Histology mucosa epithelial lining touches lumen serosa outer lining touches the other Mucosal surface Serosal surface abdominal cavity organs Linings mucosa submocosa muscularis externa serosa NOTE ABSORPTION NEEDS TO TAKE PLACE IN ORDER FOR THE FOOD TO BE INSIDE YOUR BODY Mnemonic M S M S The 4 basic Digestive Processes 1 Motility a Contractions of the inner circular and outer longitudinal smooth muscle layers b Propulsive movements peristalsis propels food in abroad usually direction esophagus stomach small intestine c Mixing movements promote digestion and absorption by increasing surface area of the food making small pieces out of larger ones stomach small intestine d Controlled by autonomic nervous system hormone NO SEGMENTATION 2 Secretion a Elaboration of numerous digestive juices into digestive tube lumen i e THE OUTIDE OF THE BODY b c Secretions consist of water plus digestive enzymes bile salts d Controlled by autonomic nervous system and hormones or mucus 3 Digestion a Breaking down of large food particles and macromolecules into smaller suitable for absorption by the mucosal absorptive cells b Carbohydrates are digested into monosacharides c Proteins are digested into amino acids and dipeptides d Fats are digested into glycerol and free fatty acids 4 Absorption a Movement of small molecules from digestion water vitamins and electrolytes from lumen of the digestive tube across mucosal epithelial cells and into adjacent digestive tube s capillary bed Stomach Essentials The 3 gastric functions 1 Store ingested food until it can be emptied at a rate that maximizes digestion and absorption in small intestine lumen 2 Secrete hydrochloric acid ph 1 2 and proteases that initiate protein digestion Acid also kills many ingested bacteria fungi viruses 3 Pulverize and mix gastric contents secretions into a thick liquid called chyme Gastric secretions Mucous cells mucus o An indigestibe viscous colloid o Secreted by goblet cells in esophagus stomach and intestines o Primarily mucin protein dissolved in alkaline water o High molecular weight and carbohydrate rich glycoprotein o MUCOUS MUCIN GLYCANS Chief cells pepsinogen BOTH MUCOUS AND CHIEF CELLS ARE INFLUENCED BY PARASYMPATHETIC OUTFLOW STIMULATION AND GASTRIN HORMONE Parietal cells HCl and IF o Intrinsic factor binds dietary vitamin B12 in stomach o IF B12 complex is absorbed in ileum segment of the lumen small intestine o B12 DEFICIENCY CAN LEAD TO PERNICIOUS ANEMIA The components of the gastric mucosal barrier enable the stomach to contain acid without injuring itself 1 The luminal membranes of the gastric mucosal cells are impermeable to H so that HCl cannot penetrate into the cells 2 The cells are joined by tight junctions that prevent HCl from 3 A mucus coating over the gastric mucosa serves as a physical battier penetrating between them to acid penetration 4 The HCO3 rich mucus also serves as a chemical barrier that neutralizes acid in the vicinity of the mucosa Even when luminal pH is 2 the mucus pH is 7 Digestion Proteins Parietal cells secrete HCl and intrinsic factor binds to vitamin B12 into the stomach Chief cells secrete pepsinogen Pepsinogen is most effective at low pH acidic environment Pepsinogen is converted to PEPSIN due to the low pH of the Pepsin is a proteolytic enzyme that breaks large proteins into Once you start secreting pepsinogen you increase pepsin stomach lumen smaller peptides activation Pepsin activates more pepsin Low pH also denatures proteins which increases exposure for pepsin attach Negative feedback regulation of gastric motility secretions Occurs by hormones GIP CCK Secretin All are released by small intestine epithelial cells in response to o Hyperosmolarity o Carbohydrates o Fats o Acids o ARE PRESENT IN SMALL INTESTINE LUMEN ESPECIALLY IN THE DUODENUM Carbs negative feedback on acid secretion Fats acids negative feedback on acid secretion and motility Enteric nervous system becomes activated through chyme inhibits gastric motility and acid secretion puts break on process Gastric Absorption Only aspirin and ethanol are rapidly absorbed by the stomach everything else is absorbed in the small intestine Aspirin and ethanol first go through the stomach capillary bed blood then the venous drainage of stomach hepatic portal vein liver inferior vena cava right atrium Exocrine Secretions of the Pancreas liver Acinar Cells Amylases break down large carbohydrates into disaccharides Proteases break down large proteins into smaller peptides Lipases break down fats into monoglycerides and free fatty acids Ductal Cells Secrete watery bicarbonate rick alkaline solution Increases pH of acidic chyme from stomach back to neutral pH of 7 NOTE goblet cells secrete mucous into the stomach Diverse Physiological Functions of the Liver Monitors process plasma carbohydrates proteins fats Detoxify wastes hormones drugs food additives Synthesize plasma proteins o Albumin o Angiotensinogen o Fibrinogen o Immunoglobins Synthesize lipoproteins and cholesterol Stores glycogen fat copper and many vitamins Activates vitamin D in cooperation with kidneys Breaks down and recycles hemoglobin from worn out RBCs forming bilirubin Synthesizes and