Digestive System OverviewWe 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 foodin 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 matterDefinitions to know:1. Orad- in direction toward mouth. For example, vomiting is ejected orad2. Aborad- in direction away from the mouth in digestive tube- like foods/liquids3. Enteric- related to intestines; less precisely- related to any part or all of the digestive tube4. GI= Gastrointestinal: related to the stomach &/or intestines; less precisely related to any part or all of the digestive tube5. Per os- medication/fluids given by way of mouth6. NPO- not per os: do not give this patient anything by the way of mouth; usually done night and morning before receiving anesthetic surgery7. IP injection: intraperitoneal injection- medication injected into the peritoneal cavity surrounding the intestines8. Perienteral administration- an IP delivery of nutrient & /or fluids b/c patient is unable to swallow or process food normalyGeneric Digestive Tube Segment Functional Anatomy and Histology- Mucosal surface (mucosa)- epithelial lining- touches lumen- Serosal surface (serosa)- outer lining- touches the other 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-SThe 4 basic Digestive Processes1. Motilitya. Contractions of the inner circular and outer longitudinal smooth muscle layersb. Propulsive movements (peristalsis) propels food in abroad (usually) direction: esophagus, stomach, small intestinec. Mixing movements promote digestion and absorption by increasing surface area of the food making small pieces out of larger ones: stomach, small intestined. Controlled by autonomic nervous system hormone- NO SEGMENTATION2. Secretiona. Elaboration of numerous digestive juices into digestive tube lumenb. i.e. THE OUTIDE OF THE BODYc. Secretions consist of water plus digestive enzymes, bile salts, or mucusd. Controlled by autonomic nervous system and hormones3. Digestiona. Breaking down of large food particles and macromolecules intosmaller suitable for absorption by the mucosal absorptive cellsb. Carbohydrates are digested into monosacharidesc. Proteins are digested into amino acids and dipeptidesd. Fats are digested into glycerol and free fatty acids 4. Absorptiona. 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 bedStomach EssentialsThe 3 gastric functions:1. Store ingested food until it can be emptied at a rate that maximizes digestion and absorption in small intestine lumen2. Secrete hydrochloric acid (ph 1-2) and proteases that initiate protein digestion. Acid also kills many ingested bacteria, fungi, viruses3. Pulverize and mix gastric contents secretions into a thick liquidcalled chymeGastric secretions- Mucous cells- mucus o An indigestibe viscous colloido Secreted by goblet cells in esophagus, stomach, and intestineso Primarily mucin protein dissolved in alkaline watero 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 lumeno IF-B12 complex is absorbed in ileum segment of the small intestineo 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 cells2. The cells are joined by tight junctions that prevent HCl from penetrating between them3. A mucus coating over the gastric mucosa serves as a physical battier to acid penetration4. 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 stomach lumen- Pepsin is a proteolytic enzyme that breaks large proteins into smaller peptides- Once you start secreting pepsinogen, you increase pepsin activation- Pepsin activates more pepsin - Low pH also denatures proteins which increases exposure for pepsin attachNegative feedback regulation of gastric motility & secretions- Occurs by hormones: GIP, CCK, Secretin- All are released by small intestine epithelial cells in response to: o Hyperosmolarityo Carbohydrateso Fatso Acidso 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 processGastric AbsorptionOnly 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 atriumExocrine Secretions of the Pancreas & liverAcinar 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 acidsDuctal Cells- Secrete watery bicarbonate rick alkaline solution- Increases pH of acidic chyme from stomach back to neutral pH of 7NOTE: goblet cells secrete mucous into the stomachDiverse Physiological Functions of the Liver- Monitors & process plasma carbohydrates, proteins, fats- Detoxify wastes, hormones, drugs, food additives- Synthesize plasma proteinso Albumino Angiotensinogeno Fibrinogeno Immunoglobins- Synthesize lipoproteins and cholesterol- Stores glycogen, fat, copper, and many