DIGESTION © 2016 Paul Billiet ODWS

Processes associated with feeding Ingestion Digestion Absorption Excretion Urine, breath, sweat Egestion Faeces Assimiliation © 2016 Paul Billiet ODWS

Digestion The breakdown of polymers into monomers for absorption Polymers are usually insoluble and too large to pass across cell membranes. © 2016 Paul Billiet ODWS

Physical digestion & movement Mastication: using jaws and specialised teeth Peristalsis: circular and longitudinal smooth muscles of the gut wall producing waves of contraction muscles contract Food Food moves down the gut © 2016 Paul Billiet ODWS

Tissue layers TS Small Intestine © 2016 Paul Billiet ODWS

Esophagus wall Circular muscle Longitudinal muscle © 2016 Paul Billiet ODWS

Physical digestion Chewing reduces the food to small particles Increasing the surface area exposed to the enzymes Peristalsis moves the food along the gut & mixes the foods with digestive juices Soluble compounds dissolve Large molecules exposed to digestive enzymes. © 2016 Paul Billiet ODWS

Chemical digestion Using a range of specialised enzymes… that work in different conditions… in different compartments of the organ-system All these enzymes have an optimum temperature of 37°C. © 2016 Paul Billiet ODWS

Chemical digestion - Carbohydrates Polysaccharides Starches & glycogen Amylases Salivary & pancreatic pH 8 Maltose Cellulose No enzymes Undigested © 2016 Paul Billiet ODWS

Chemical digestion - Lipids Fats & oils Lipase Pancreatic pH8 Fatty acids & Glycerol © 2016 Paul Billiet ODWS

Chemical digestion - Proteins Pepsin Stomach pH 1 Peptones Endo-petidase Pancreatic pH 8 Amino acids © 2016 Paul Billiet ODWS

Chemical digestion – Nucleic acids DNA & RNA Nucleases Pancreatic pH8 Nucleotides Evidence suggests that pepsin, in the stomach, can also digest nucleic acids though much more slowly than it digests proteins. © 2016 Paul Billiet ODWS

Absorption The uptake of nutrients from the gut into the blood stream Most takes place in the small intestine Water is absorbed by the colon Alcohol, some minerals and water are absorbed by the stomach lining. © 2016 Paul Billiet ODWS

Absorption across membranes Diffusion Water, gases, alcohol, lipids Facilitated diffusion Water, glucose & amino acids Active transport Na+/K+ also glucose & amino acids Endocytosis Proteins e.g. antibodies. © 2016 Paul Billiet ODWS

The Digestive System Mouth Salivary glands Oesophagus Liver Stomach Gall bladder Pancreas Small intestine Large intestine Appendix Anus © 2016 Paul Billiet ODWS

The Stomach Endoscope view inside stomach Stomach diagram © 2016 Paul Billiet ODWS

Stomach Transit: 0 to 3h Capacity: 1.5dm3 Muscular sack (Circular, longitudinal & diagonal muscles) Churning food into chyme Gastric Pits: HCl Acidic pH: Enzyme activation & bacteriocidal Pepsinogen (inactive)  Pepsin (active) Protease Mucus epithelium  mucus Protection of stomach from acid and protease enzymes Cardiac sphincter & pyloric sphincter (muscular valves) Hold food in stomach for digestion © 2016 Paul Billiet ODWS

TS Small Intestine © 2016 Paul Billiet ODWS

The villus Mouse intestinal villi Microvilli of the epithelium www.nikonsmallworld.com/images/gallery2006/th.. Microvilli of the epithelium 131.229.114.77/.../Portfolio2_files/t_004.jpg © 2016 Paul Billiet ODWS

Small intestine FEATURES FUNCTIONS Intestinal Glands: Enzymes (e.g. lactase) Pancreas and Liver also secrete bile and pancreatic juice Disaccharide digestion Bile – HCO3- and salts for lipid digestion Pancreatic juices HCO3- and enzymes Length (3 5m long), Rugae (folds), Villi & Microvilli Large surface area 200m2 (a) Digestion (b) Absorption Capillaries Transport of digested food. Lacteals (lymph vessels) Fatty acids + monoglycerides. Hepatic portal system All absorbed food is first taken to the LIVER Gut flora (bacteria) Mutualistic & vitamin synthesis © 2016 Paul Billiet ODWS

Large intestine Endoscope view Large intestine © 2016 Paul Billiet ODWS

Large intestine CAECUM/ APPENDIX Transit up to 96h Length 1,5m CAECUM/ APPENDIX Sack at the beginning of the large intestine Bacterial fermentation cellulose (non ruminants) Vestigial in humans COLON No villi but rugae (folds) Water absorption Bacterial activity Mutualistic RECTUM Anal sphincter Holding area for faeces before egestion © 2016 Paul Billiet ODWS