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Digestive System What does it do? Function To prepare food/nutrients for absorption What must happen to food before it can be absorbed? (What is absorption?) (What can easily be absorbed?) How does a bacteria obtain nutrients from food? Digestion Two types of digestion – physical/mechanical digestion: breaking the food into smaller pieces (to increase surface area) – Chemical digestion: breaking large molecules down into smaller molecules (by use of enzymes) Is it inside? GI tract The digestive system is essentially a tube that runs through the body This ‘tube’ is called the GASTROINTESTINAL (GI) TRACT The space inside the GI tract is called the LUMEN Accessory organs Several organs lie adjacent to the GI tract at different points and secrete substances which facilitate digestion and/or absorption Salivary glands, liver, gall bladder and pancreas Basic terms Ingestion: food enters the GI tract Digestion: food is mechanically and chemically broken down Absorption: nutrients pass through a cell membrane and enter the body Egestion: unabsorbed and waste materials leave the GI tract Soft palate mouth Parotid gland Sublingual gland pharynx Submaxillary gland epiglottis Esophagus Liver Stomach Gall bladder Pancreas Bile duct Pancreatic duct duodenum Transverse colon Small intestine Descending colon Large intestine Ascending colon caecum rectum appendix anus The Mouth Mechanical digestion (some chemical) Teeth Tongue Salivary Glands Teeth Incisors – flat-edged – cutting Canines – triangle – grasping and tearing Molars – square – grinding/crushing Tongue Used to move food around the mouth Forms chewed up food into BOLUS – wet ball of food Salivary Glands Salivary Glands Produce saliva which – Moisten – Soften – Lubricate Saliva also contains amylase which begins the breakdown of starch Pharynx and Epiglottis Pharynx and Epiglottis Pharynx: joint passage for air and food where the oral and nasal cavities meet Epiglottis: flap of tissue which prevents food from going down airway Esophagus Esophagus Tube connecting mouth to stomach Bolus is propelled to the stomach via PERISTALSIS Peristalsis: wave-like muscular contractions Stomach Stomach Thick, muscular organ with three layers of muscle churns food with gastric juices Cells produce hydrochloric acid, pepsin and mucus Small molecules like water, amino acids and alcohol can be directly absorbed Gastric Pits Stomach secretions Parietal cells produce HYDROCHLORIC ACID which make the stomach acidic Chief cells produce PEPSIN which begins digestion of protein Other cells produce MUCUS which protect the stomach lining CHYME The mixture of blended up food and acid is known as CHYME Small Intestine Small Intestine Long, narrow tube 2-3cm in diameter but approximately 7m long Consists of three sections: duodenum, jejunem and ileum Site of chemical digestion and absorption Pancreas and Liver add secretions to chyme Villi and Microvilli Villi and Microvilli Increase surface area for absorption Secretions in the small intestine The pancreas and liver add secretions to the chyme in the duodenum in order to: – Neutralize the acid – Continue chemical digestion – Improve absorption The Pancreas Produces BICARBONATE which neutralizes the stomach acid Also produces many DIGESTIVE ENZYMES which break down food Digestive Enzymes Proteases break down protein (Trypsin, Chymotrypsin, exopeptidases) Lipases break down fat Amylases break down starch The Liver and Gall Bladder The liver produces BILE which is stored in the gall bladder Bile emulsifies fat This allows it to be broken down by lipases and absorbed Bile Large Intestine Large Intestine Tube 6cm in diameter and 1.5m long Primary function is to reabsorb water and form stool Bacteria in the large intestine produce vitamin K Large Intestine Caecum is the ‘dead-end’ that lies below where the small intestine connects to the large intestine The appendix is the finger-like extension off of the caecum The appendix is theorized to act as a reservoir for bacteria Rectum and Anus Rectum and Anus The rectum is the area where stool is stored immediately before egestion The anus is the opening