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Digestion is the breakdown of large, complex organic molecules into smaller , more simple components that can be absorbed and used by the body. Molecules need to be small enough to diffuse across plasma membranes of the cells lining the intestinal wall through the process of absorption. • Digestion includes all the processes that chemically and mechanically break down food into nutrients • Begins immediately after food is ingested • Includes Mechanical and Chemical digestion – Mechanical digestion is mechanical – changes of the physical state of the food by , • Mastication in the mouth– reducing the food particle size through chewing, and mixes food with saliva • Deglutition • Churning of the contents in the GI lumen (stomach and intestinal movement so they are well mixed with the GI juices • Propelling food through the digestive tract Chemical digestion: changes in chemical composition of food as it travels through the digestive tract; these changes are the result of hydrolysis by Digestive enzymes Digestive enzymes are characterized by Extracellular, organic (protein) catalysts follows the Principles of enzyme action which are A. Specific in their action as proteinases hydrolysis protein ,Lipases hydrolysis fat and saccaridase hydrolysis disaccarides B. Function optimally at a specific pH C. Enzymes are continually being destroyed or eliminated from the body and must continually be synthesized 4 Ingestion : is the consumption of or taking in of nutrients Mastication: chewing. Breaking down of food in the mouth with the help of teeth Deglutition: swallowing of solids or liquids Digestion: breaking down of large nutrient molecules into smaller ones so that they may be absorbed Absorption: transfer of medium and small sized nutrient molecules from GIT lumen into blood Defecation: passage of stools/ faeces from the rectum to the exterior Gastrointestina l (Gl) tract (Alimentary canal) Accessory structures Not in tube path 1. Mouth 1. Salivary gland 2. Oral Cavity 2. Liver 3. Pharynx 4. Esophagus 5. Stomach 6. Small intestine 7. Large intestine 8. Anus 3. Gall bladder 4. Pancreas 6 Three pairs: 1. PAROTID :on side of face (swell with the mumps) 2. SUBLINGUAL: (below tongue) and 3. SUBMANDIBULAR: both in lower jaw produce saliva Functions of Salivary 1. Lubrication : to facilitate mastication of food and make it slides easily through the 2.Saliva coats the oral cavity and esophagus 3.Solubilises dry food: in order to be tasted, the molecules in food must be disolved 4.Oral hygiene: The oral cavity is almost constantly flushed with saliva, which floats away food debris and keeps the mouth relatively clean J-shaped pouch of the Located slightly left of center in the body with Capacity: about 1 litre has two opening a. Cardiac Sphincter:Muscle that surrounds the esophagus at its junction with the stomach , Opens to admit food into the stomach b. Pyloric sphincter : Muscle that surrounds the stomach at its junction with the small intestine: Opens to admit CHYME into the small intestine Functions a. Storage area for ingested food (empties in 2-6 hours) b. Place for digestive enzymes (pepsin and salivary amylase) to work c. Main place for protein digestion d. Absorption of small molecules (e.g. H2O, ethanol) 3 meters or 10 feet in length, Walls highly convoluted to S.A. Interior folds covered with villi: tiny fingerlike projections that further S.A. Divided into 3 parts: a. Duodenum (first 25 cm): Produces digestive enzymes: lactase, peptidase, maltase, nuclease b. Jejunum c. Ileum Functions: 1. 2. Completes digestion Absorption of nutrients a. monosaccharides, amino acids, short peptides, fatty acids are transported into intestinal cells, and diffuse into bloodstream b. Fats diffuse into intestinal cells and are deposited in the lacteal (lymph vessel in the villus) Blood Supply For Gastrointestinal Tract Synthesize and secerte bile that act as detergent – emulsifies fats thus facilitate fate digestion 2. Detoxifies/removes toxic substances as Drugs and Alcohol 3. Stores Gycolgen, Vitamins (A, D, E, K), Fe, other minerals and Cholesterol 4. Activates vitamin D 5. Formation of Fetal RBC 6. Formation of plasma protein: albumin, globulin and fibrinogen 7. Stimulate bone marrow to form RBCs in adult through secretion of erythropoietin hormone 8. Metabolizes absorbed food molecules 1. Carbohydrates 2. Proteins 3. Lipids 1. 12 Has exocrine function through Production of pancreatic juice (digestive enzymes and sodium bicarbonate to neutralize acidic chyme) Has Endoocrine functions through Production of insulin, a hormone that influences the cells’ uptake of glucose from the bloodstream , and Glucagon hormone that share with insulin to adjust blood sugar 5 parts Ascending colon Transverse colo Descending colon Rectum - stores feces Anus- muscles close the rectum until release of feces is appropriate Functions Reabsorption of water Formation of feces Manufacture of some amino acids, growth factors, vitamins B's and K by E.coli)