© CU/SONMS/nutrition/CSSAN Digestion &Absorption of every day foods

© UWCM/SONMS/nutrition/MJohn Outcomes Describe the relative position of gastrointestinal structure and organs Define the model of motility with the GI system Briefly explain the key functions of secretion Describe the role of saliva Describe the optimal environment and role of the main digestive enzymes Explain where most of the digestion and absorption of nutrient occurs in relation to macronutrients Briefly explain neuronal and endocrine control of digestion absorption and absorption of nutrients Briefly describe aerobic and anaerobic forms of energy production from food

© UWCM/SONMS/nutrition/MJohn The Digestive tract

© UWCM/SONMS/nutrition/MJohn Movement of food through the GI tract. Motility : –Ingestion: Taking food into the mouth. –Mastication: Chewing food and mixing it with saliva. –Deglutition: Swallowing food. –Peristalsis: Rhythmic wave-like contractions, moving food.

© UWCM/SONMS/nutrition/MJohn Key Functions- Mechanical processing and motility- breaking, mixing propelling food

© UWCM/SONMS/nutrition/MJohn Key Functions: Secretion Releasing of digestive enzymes Digesting- chemical breakdown of food

© UWCM/SONMS/nutrition/MJohn Key Functions: Absorption- P assage of digested nutrients/fluid across the GI wall - to blood/lymph

© UWCM/SONMS/nutrition/MJohn Key Functions: Elimination Expulsion of undigested and unabsorbed residues from the gut

© UWCM/SONMS/nutrition/MJohn Digestion & absorption of beans on toast

© UWCM/SONMS/nutrition/MJohn What does saliva do to food Lubricates –Thins -dilutes for swallowing Anti acid function, –buffers acids, particularly important when there are acids of bacteria Digests: Amylase (Lipase) Bacteriostat Bacteriolytic –Acts on endogenous bacteria

© UWCM/SONMS/nutrition/MJohn Food chunks up here and amylase continues to work until food drops into the stomach Does anything happen here? Holding position

© UWCM/SONMS/nutrition/MJohn Beans & Toast near cardiac Sphincter Amylase continues to work - no acid

© UWCM/SONMS/nutrition/MJohn Stomach Mucosa

© UWCM/SONMS/nutrition/MJohn activates pepsinogen Optimal pH (2-3) for enzymes hydrochloric acid

© UWCM/SONMS/nutrition/MJohn Release pepsinogen & prorennin Into the acid environment Pepsinogen >>>>>>Pepsin Prorennin >>>>>> Rennin –convert proteins to polypeptides The chief (zymogenic) cells

© UWCM/SONMS/nutrition/MJohn Digestion of Beans & Toast Bread - carbohydrates = no action Proteins Beans - proteins to peptides Butter protein to peptides Pepsin Churning turns beans on toast into chyme

© UWCM/SONMS/nutrition/MJohn Mucous cells gastric acid can damage the mucosa Mucous is a protective mucosal barrier against acid and the proteolytic enzymes in gastric juice. –Aspirin, alcohol and an excess of gastric acid can cause chronic cellular damage and eventually gastric erosions or ulcers –If the mucous layer is damaged or reduced then mucous & blood supply is increased (prostaglandin).

© UWCM/SONMS/nutrition/MJohn The Duodenum Brunners glands’at the top ‘ -produce a thick tenacious, alkaline mucous protection Gall bladder-bile Pancreatic juice via the ampulla.

© UWCM/SONMS/nutrition/MJohn CCK stimulates contraction of gall bladder secretion of pancreatic enzymes Secretin stimulates water & Bicarb secretion from the pancreas potentiates CCK Control of Pancreatic Secretion

© UWCM/SONMS/nutrition/MJohn Beans & Toast in the Duodenum Protein in Beans & butter - Pancreatic Proteolytic enzymes Carbohydrates in Bread & Beans Pancreatic amylase Fat in beans & butter Pancreatic Lipase Beans on toast is now chyme

© UWCM/SONMS/nutrition/MJohn Pancreatic Enzymes Pancreatic amylase continues digesting polysaccharides >>>>>> disaccharides  brush border enzymes convert  disaccharides to monosaccharides Proteolytic enzymes –Trypsin, Chymotrypsin - Carboxypolypeptidase  break peptide bonds in polypeptides >>> amino acids Pancreatic lipase & intestinal lipase strip fatty acids from the glycerol backbone.

© UWCM/SONMS/nutrition/MJohn BILE Bile salts emulsify fats Bile contains Cholesterol important in making a fat concentration gradient that allows fatty acids to enter the cell Bile emulsifies the fats in the bean sauce and butter

© UWCM/SONMS/nutrition/MJohn Layers of the Small Bowel

© UWCM/SONMS/nutrition/MJohn Cells of the mucosal epithelium Absorption cells: These form the brush border which also contains several enzymes. –Intestinal Lipase works on lipds from butter –Sucrase act on sucrose from the beans & bead –Lactase works on Lactose from the from butter –Maltase work on maltose from bread The Brush Border Think about the role of fibre

© UWCM/SONMS/nutrition/MJohn Enlarged Villus of Small Bowel Brush Border cell

© UWCM/SONMS/nutrition/MJohn The fate of Beans & Toast Proteins Polypeptides Tri-peptides Di-peptides Amino acidsFat Glycerol and fatty acids Small and long chain fatty acidsSmall and long chain fatty acids Carbohydrates Polysaccharides Disaccharides Sucrose  Maltose  Lactose Monosaccharides  Glucose  Fructose  Galactose

© UWCM/SONMS/nutrition/MJohn "brush border" cell & fat absorption 1,000 microvilli per cell Micelle = aggregations of –free fatty acids, –mono-glycerides in the middle – bile salts at polar ends enabling solution in water. Micelles 'shuttle’ fatty acids & glycerol to the brush border where they can be absorbed into the enterocyte

© UWCM/SONMS/nutrition/MJohn Diffusion Process (Micelle) Butter fat? Vegetable fat? in chyme Now Chyme Think about the role of fibre

© UWCM/SONMS/nutrition/MJohn Absorption of Nutrients via Small bowel

© UWCM/SONMS/nutrition/MJohn Active transport mechanism with NA + or H + Vegetable protein in Beans? Chyme

© UWCM/SONMS/nutrition/MJohn Energy production from food With Oxygen Carbohydrate to Glucose molecule 2 Pyruvate molecules 4 Acetyl CoA Molecules Without Oxygen Carbohydrate to Glucose molecule 2 Pyruvate molecules Lactate 16 times MORE energy 16 times LESS energy

© UWCM/SONMS/nutrition/MJohn Homeostatic controls Controls over digestive system act before food is absorbed into internal environment: Nervous system- thought of food Nerve plexuses in gut wall - distension by food (? air) Endocrine system - e.g. responses to low blood sugar

© UWCM/SONMS/nutrition/MJohn Endocrine Control Specialised glands secrete hormones into blood to reach target organs chemical messenger e.g. pancreas pituitary thyroid etc.

© UWCM/SONMS/nutrition/MJohn 4 Gastrointestinal Hormones Gastrin- secreted by endocrine cells in stomach lining when amino acids & peptides are in stomach. Stimulates secretion of acid into stomach. Secretin- peptide hormone. Stimulates the pancreas to secrete bicarbonate CCK (cholecystokinin)- enhances actions of secretion & stimulates gallbladder contractions GIP (glucose insulinotropic peptide)- released in presence of glucose & fat in small intestine. Stimulates insulin secretion