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DIGESTIVE SYSTEM Dr. Manpreet Kaur Dept of Home Science, PGGCG-42, Chandigarh. What is Digestion? Digestion is a process by which the complex and unabsorbable food materials like carbohydrates, proteins and fats are broken down by mechanical and chemical processes to simpler forms i.e. mono saccharides, amino acids & fatty acids & glycerol that can be absorbed through the intestines and then utilized by the cells for various activities. Organs of Digestive System Gastrointestinal tract (GIT) – continuous passageway which contains the food from the time it enters the body, until it leaves; organs include: mouth (oral cavity), pharynx, esophagus, stomach, small intestine, large intestine, rectum, anus Accessory organs - participate in digestive processes; organs include: teeth, tongue, salivary glands, liver, gall bladder, pancreas Mouth (Oral Cavity) Regions include the vestibule & oral cavity proper Roof comprised of hard & soft palate; floor primarily comprised of tongue Mucosa of stratified squamous epithelium (non-keratinized) Joins the pharynx at the fauces THE TONGUE Organ of taste Mastication of food Swallowing of food Articulation Tooth Crown – dentin surrounded by enamel, has hollowed pulp cavity. Neck – at gingival border Root – within mandible & maxilla, has hollowed root canal with blood vessels & nerves. TEMPORARY & PERMANENT TEETH Salivary Glands Are three pairs which secrete saliva It is clear alkaline fluid made of H2O, salts & “salivary Sublingual amylase” gland Submandibular duct Parotid duct Parotid gland Submandibular gland PHARYNX Common passageway for air & food Oropharynx & laryngopharynx lined with stratified squamous epithelium Uvula & epiglottis protect airway when swallowing (“deglutition”) to avoid choking Nasopharynx Uvula Oropharynx Epiglottis Laryngopharynx ESOPHAGUS Muscular 10” tube running from pharynx, posterior to trachea, down thoracic cavity, through “esophageal hiatus” of diaphragm, to lower esophageal (a.k.a. cardiac) sphincter at junction of stomach Functions in “deglutition” through action of peristalsis Mucosa is simple squamous epithelium Variations in muscles– begins as skeletal voluntary muscle at upper 1/3, mixed skeletal & smooth muscle in middle, smooth involuntary muscle by lower 1/3 THE STOMACH Functions of the Stomach Bulk storage of undigested food Mechanical breakdown of food Secretion of gastric juice (water, HCl, mucin, pepsin & renin) to digest food Production of intrinsic factor which helps in absorption of vitamin B12 Liver Largest gland in the body weighing 1550 gms. Located on the right side of the body under the diaphragm Consists of four surfaces suspended from the diaphragm and abdominal wall by the falciform ligament Hepatic artery and portal vein enter the liver & bile duct leaves the liver. Liver is built of lobules which have their own blood supply & small bile ducts which unite to form common bile duct. Connected to the gall bladder via the common hepatic duct THE DUODENUM AND RELATED ORGANS GALLBLADDER 8-10 cm long pouch greenish in colour. It has three coats – Outer peritoneal coat is continuous with peritoneum of liver. Muscular coat helps in contraction. Inner mucous coat It stores bile which is released when required for digestion FUNCTIONS OF LIVER Secretion of bile Storage of glycogen Formation of urea Production of plasma proteins De-saturation of fats Storage of vitamin B12 and iron Production of heat Small Intestine Connects stomach to large intestine; 15-20’ long; 1” diameter; held together in abdominal cavity by “mesentery proper” Cite for completion of chemical digestion & absorption of nutrients comprised of three regions: Duodenum – 10” in length; receives chyme from stomach, secretions from liver, gallbladder & pancreas Jejunum – 8’ long; most digestion & absorption occurs here Ileum – 12’ long; connects to ceacum of large intestine at ilioceacal valve (sphincter) Small Intestine Finger like projections - villi lined with “absorptive cells” - mucosal epithelium of simple columnar epithelium with microvilli “brush border” which increases the absorptive surface by 5 times. Submucosa of each villus contains a capillary network & a “lacteal” (lymphatic capillary) for absorption of nutrients Intestinal glands( glands of liberkuhn) within intestinal crypts secrete “intestinal juice” – provides watery medium to keep enzymes & digestive products in solution for help with absorption Intestinal crypts containing intestinal glands Villi Large Intestine Absorption of water and salts. Excretion of faeces which consists of 50% Dead bacteria and 50% cellulose. Transverse colon Ascending colon Ileocecal sphincter Ceacum Vermiform appendix Descending colon ileum Rectum Anus Sigmoid colon Digestion, Absorption, Transport Digestion Breakdown of food molecules for absorption into circulation Mechanical Process: breaks large food particles to small with teeth, contraction of stomach walls & peristaltic movements. Chemical Process: breaking of covalent bonds by digestive enzymes Absorption and transport Molecules are moved out of digestive tract and into circulation for distribution throughout body Ingestion Mouth mechanical digestion teeth breaking up food by cutting & grinding chemical digestion saliva salivary amylase (ptylin) enzyme digests cooked starch mucin slippery protein (mucus) assists in passage of food protects soft lining of digestive system lubricates food for easier swallowing (bolus) buffers neutralizes acid to prevent tooth decay anti-bacterial chemicals kill bacteria that enter mouth with food Swallowing (& not choking) Epiglottis flap of cartilage closes trachea (windpipe) when swallowing food travels down oesophagus Peristalsis involuntary muscle contractions to move food along the pharynx & oesophagus. Stomach Food Storage can stretch to fit ~2L food Gastric HCl Juice = pH 2 kills bacteria Absorbs iron Water Liquifies food Intrinsic factor Controls absorption of Vit B12 Mucus chemical digestion Pepsinogen breaks down proteins into peptones & proteoses Renin Converts insoluble caseinogen into soluble casein Duodenum 1st section of small intestines acid food from stomach mixes with digestive juices from: pancreas liver gall bladder Pancreatic Juice Non viscous watery fluid. Contains Na, K, HCO3 & water. Bicarbonate lowers pH inhibiting pepsin and providing proper pH for enzymes Enzymatic portion: Trypsinogen Chymotrypsinogen Procarboxypeptidase, Pancreatic amylase Pancreatic lipases (Steapsin) Interaction of duodenal and pancreatic enzymes. Enterokinase from the duodenal mucosa activates trypsinogen to trypsin. Trypsin activates chymotrypsinogen to chymotrypsin Trypsin activates procarboxypeptidase to carboxypeptidase. Trypsin, chymotrypsin and carboxypeptidase digest proteins to peptones & polypeptides. Pancreatic amylase continues digestion of starch to maltose, dextrins & glucose Pancreatic lipase digests lipids to fatty acids & glycerol. Intestinal Juice Clear yellowish fluid which contains water, salts and enzymes. Enzymatic portion: Aminopeptidase Dipeptidase, Maltase Sucrase Lactase Peptidases digest polypeptides, dipeptides & tripeptides into amino acids Maltase converts disaccharide maltose into two units of glucose Sucrase converts disaccharide sucrose into glucose & fructose Lactase converts milk sugar, lactose into glucose & galactose All carbohydrates get converted into simple sugars, proteins into amino acids and fats to fatty acids & glycerol and are absorbed through villi in jejunum & ileum. Organs of Digestive System Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Large Intestine Solid materials pass through the large intestine. These are undigestible solids (cellulose). Water absorbed. Vitamins K and B are reabsorbed with the water. Rectum- solid wastes exit the body.
