Digestive System_ST.ppt


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Digestive System_ST.ppt

  2. 2. INTRODUCTION <ul><li>The utilization of the food we eat occurs in four main stages: </li></ul><ul><li>ingestion – involves the intake of food, and includes both mastication (chewing) and swallowing; </li></ul><ul><li>digestion – breaking up foods into less complex substances so that it can enter the blood stream; </li></ul><ul><li>absorption – the products of digestion (less complex substances) enter the blood stream, so that they can be transported to a part of the body where they are utilized. </li></ul>
  3. 3. <ul><li>The last (fourth) stage is assimilation – when the food substances reach their destination, they get ‘absorbed into’ the cells, and are used for different cellular functions. </li></ul><ul><li>The ‘digestive’ system or alimentary canal is concerned with ingestion, digestion, and absorption. </li></ul><ul><li>This system begins with the mouth or oral cavity, then food passes to the esophagus or food pipe; it then passes to the stomach, on to the intestines and finally opening to the exterior at the muscular anus. </li></ul>
  4. 4. PATH OF FOOD – MOUTH TO ANUS Path of food through the human digestive system includes the following organs and structures : Mouth – pharynx – esophagus – peristalsis – mucus – sphincter muscles – cardiac sphincter – stomach – pyloric sphincter – small intestine (duodenum, jejunum, ileum) – ileocecal valve – large intestine or colon (cecum, appendix, ascending colon, transverse colon, sigmoid colon) – rectum – anus.
  5. 5. IN THE MOUTH <ul><li>Food is taken in at the mouth where ingestion takes place. </li></ul><ul><li>Food is masticated or chewed, digestion also begins in the mouth, but for starch alone . </li></ul><ul><li>In the mouth, the chewed food is mixed with an alkaline fluid, called saliva . </li></ul><ul><li>Saliva contains mucus which acts as a lubricant to ease the passage of food through the rest of the alimentary canal. </li></ul>
  6. 6. <ul><li>The saliva also contains an enzyme called ptyalin which aids the conversion of starch into soluble sugars. </li></ul><ul><li>This digestion is partial , as these sugars have to be broken down into still simpler substances, before they can be absorbed. </li></ul><ul><li>This partial digestion of starch is aided by thorough mastication of food. </li></ul><ul><li>This is why eating slowly, and chewing thoroughly promotes good digestion. </li></ul><ul><li>After being well masticated, food form a bolus (ball) which is swallowed contraction of muscles. </li></ul>
  7. 7. <ul><li>The bolus of food passes to the back </li></ul><ul><li>of the tongue, and enters the pharynx. </li></ul><ul><li>The pharynx opens into both the food pipe (esophagus) and into the wind pipe (larynx, trachea). </li></ul><ul><li>Food is normally prevented from entering the wind pipe, by the presence of a small organ called epiglottis . </li></ul><ul><li>The epiglottis is hinged at the base of the tongue. </li></ul>
  8. 8. <ul><li>Sometimes we eat too quickly, with the result that the food goes the wrong way, enters the windpipe, and even – perhaps – the lungs. </li></ul><ul><li>We cough in order to remove the food particles from the respiratory system. </li></ul>TONGUE SALIVARY GLANDS
  10. 10. PALATE <ul><li>The palate forms the roof of the oral cavity and has an anterior hard palate and posterior soft palate. </li></ul><ul><li>The soft palate and uvula function to close off the nasal cavity during swallowing. </li></ul><ul><li>Associated with the palate in the back of the mouth are palatine tonsils, which help to protect the body against infection. </li></ul><ul><li>Pharyngeal tonsils (adenoids) are on </li></ul><ul><li>the posterior wall of the pharynx, </li></ul><ul><li>above the border of the soft palate. </li></ul>
  11. 11. TEETH Two sets of teeth develop in sockets within the alveolar processes of the maxillary and mandibular bones. The 20 primary teeth are shed in the order they appeared and are replaced by 32 secondary teeth.
  12. 12. Each tooth consists of a crown and a root, and is made of enamel, dentin, pulp, cementum, nerves, and blood vessels. A tooth is held tight in its socket by a periodontal ligament.
  13. 13. ESOPHAGUS <ul><li>Muscular tube which is about 25 cm long. </li></ul><ul><li>It extends between the pharynx and the stomach. </li></ul><ul><li>At the upper end of the esophagus there is a ring of muscle – called a sphincter – which keeps the esophagus closed. </li></ul><ul><li>When food has been chewed, it is pushed into the pharynx. </li></ul><ul><li>The sphincter relaxes, opening the esophagus, and the food is pushed down into it by muscular contractions. </li></ul><ul><li>In 5 to 10 seconds the food comes to the end of the tube. </li></ul>
  14. 14. <ul><li>There, another sphincter relaxes, allowing the food to pass into the stomach. </li></ul>ESOPHAGUS A MUSCULAR TUBE - 25cm LONG MAIN FUNCTION: CONDUCTION OF FOOD FROM PHARYNX TO STOMACH (5-10 SECONDS) SPHINCTER (AT THE BEGINNING OF THE STOMACH)
  15. 15. STOMACH <ul><li>The curved, saclike structure between the esophagus and the small intestine is the stomach. </li></ul><ul><li>It is located just under the diaphragm. </li></ul><ul><li>The lining of the stomach ( = mucous membranes) contains many glands. </li></ul><ul><li>These (exocrine) glands produce hydrochloric acid, digestive enzymes, and mucus. </li></ul><ul><li>The wall of the stomach consists of smooth muscle. </li></ul><ul><li>The average capacity in an adult is 1500 mL </li></ul>
  16. 16. <ul><li>Digestion in the stomach </li></ul><ul><li>The food is transformed into a thick fluid. </li></ul><ul><li>Digestion is aided by the enzymes present in the juice secreted by the gastric glands. </li></ul><ul><li>The food which enters the stomach is alkaline because of the saliva. </li></ul><ul><li>In the stomach it becomes acidic due to the secretion of hydrochloric acid by the gastric glands. </li></ul><ul><li>In the gastric juice there are 2 enzymes – pepsin and renin . </li></ul>
  17. 17. <ul><li>They hydrochloric acid has no digestive properties – but kills bacteria and accelerates the action of the two enzymes. </li></ul><ul><li>Pepsin aids the conversion of complex proteins into simple nitrogen containing compounds called peptones. </li></ul><ul><li>The function of renin is solely to coagulate milk, at least in young animals. </li></ul>
  18. 18. <ul><li>Carbohydrates are not digested in the stomach. </li></ul><ul><li>The semi digested food is called chyme . </li></ul><ul><li>The chyme then slowly passes through the small, narrow tube called the pylorus. </li></ul><ul><li>The pylorus is regulated by a circular muscle known as the pyloric </li></ul><ul><li>sphincter . </li></ul><ul><li>The chyme then enters the </li></ul><ul><li>small intestine. </li></ul>PROTEIN
  19. 19. <ul><li>Peptic ulcer sometimes there is an abnormal break in the continuity (i.e. an ulcer) of the mucosal lining of the stomach and duodenum. </li></ul><ul><li>Normally, there is a protective barrier which prevents the auto (self) digestion of the lining by gastric secretions, specially gastric acid. </li></ul><ul><li>The explanation for the breakdown of this protection in patients with ulcers is not clearly understood. </li></ul>
  20. 20. <ul><li>In patients with ulcers of the duodenum and parts of the stomach close to its opening into the duodenum, excessive gastric acid appears to play a role. </li></ul><ul><li>It is also been recognized that these ulcers are more likely to occur in patients who are tense and anxious, and in those who smoke a lot, eat erratic and well spiced meals. </li></ul>
  21. 21. SMALL INTESTINE <ul><li>Divided into 3 parts the duodenum comes first and is about 25 cm long, the jejunum is next, and constitutes 2/5ths of the remaining length, and the ilium makes up the remaining 3/5ths. </li></ul>
  22. 22. <ul><li>The total average length of the small intestine is 5.9m in women and 6.4m in men. </li></ul><ul><li>This way found to correlate with height, but not with age. </li></ul><ul><li>The lengthy small intestine receives secretions from the pancreas and liver, completes digestion of the nutrients in chyme, absorbs the products of digestion, and transports the remaining residues to the large intestine. </li></ul>
  23. 23. <ul><li>Duodenum </li></ul><ul><li>Receives a fluid secretion by a large gland – the pancreas which lies in the abdominal cavity, behind the stomach. </li></ul><ul><li>The pancreatic juice is produced in the pancreas, and then passes through the pancreatic duct. </li></ul><ul><li>This duct joins the bile duct to form a common duct entering the duodenum. </li></ul>
  24. 24. <ul><li>The pancreatic juice contains 3 enzymes – amylase , which aids the conversion of starch into soluble sugars; trypsin , which aids the conversion of protein and peptones into soluble amino acids; lipase , which aids the conversion of fat into substances (fatty acids) which are absorbed in the presence of bile acid. </li></ul>
  25. 25. PANCREAS <ul><li>The pancreas is about 15 cm long, and lies across, and behind the stomach. </li></ul><ul><li>It is a dual purpose gland. </li></ul><ul><li>The exocrine part secretes pancreatic juice, which helps in the digestion of carbohydrates, fats, and protein. </li></ul><ul><li>The endocrine part consists of groups of cells called the Islets of Langerhans. </li></ul><ul><li>These cells produce hormones called insulin and glucagon . </li></ul><ul><li>These hormones influence the utilization of sugar in the body. </li></ul>
  26. 26. PANCREATIC JUICE Enzymes include pancreatic amylase, pancreatic lipase, trypsin, chymotrypsin, carboxypeptidase, and two nucleases. Protein-digesting enzymes are released in an inactive form and are activated upon reaching the small intestine.
  27. 28. LIVER <ul><li>Situated on the right side of the abdominal cavity just under the diaphragm. </li></ul><ul><li>It is the largest gland in the body. </li></ul><ul><li>One of its functions is to secrete bile , an alkaline liquid which passes via the gallbladder into the duodenum, where it acts on fats in food, and prepares them for digestion. </li></ul><ul><li>The liver is also a store for glycogen, a starchy substance which can be converted to sugars when the body makes demands for extra energy. </li></ul>
  28. 29. <ul><li>Other chemical processes taking place in the liver including the building up of simple amino acids (the products of the digestion of proteins) into the various protein substances needed by the body to build tissues such as skin, bone, hair, and nails. </li></ul>
  29. 32. GALLBLADDER <ul><li>A pear shaped sac, 8 to 10 cm long. </li></ul><ul><li>It is situated under the liver. </li></ul><ul><li>It is a reservoir for bile , produced by the liver. </li></ul><ul><li>The presence of fat in the intestine (duodenum) stimulates the flow of bile from the gallbladder. </li></ul><ul><li>Bile is transported from </li></ul><ul><li>the gallbladder and the </li></ul><ul><li>liver to the duodenum, </li></ul><ul><li>via a tube or duct. </li></ul>
  30. 33. SPLEEN Located in the upper left quadrant. Consists of white pulp (lymphoid tissue) and red pulp. Filters and stores blood.
  31. 34. <ul><li>Jejenum, Ilium </li></ul><ul><li>The lower portions of the small intestine open into the large intestine. </li></ul><ul><li>In the ilium digestion of fats and carbohydrates is completed. </li></ul><ul><li>While in the small intestine, the food is completely digested and much of it is absorbed into the blood stream to be circulated to all parts of the body. </li></ul><ul><li>The inner lining of the small intestine has numerous finger like projections into the lumen (passage), which are called ville (villus). </li></ul><ul><li>Thus the absorbing surface is greatly enlarged. </li></ul>
  32. 37. LARGE INTESTINE (COLON) <ul><li>The colon is the lower part of the digestive tract. </li></ul><ul><li>It measures about 1.5 m long and 5 cm wide when it is full. </li></ul><ul><li>Watery waste material enters the colon from the small intestine. </li></ul><ul><li>In the large intestine a lot of water absorbed during its passage towards the rectum and is discharged in semi solid form, from the anus . </li></ul><ul><li>The colon wall contains a muscular layer and is lined with mucus tissue. </li></ul>
  33. 38. <ul><li>The muscles in the colon wall contract in successive waves called peristalsis . </li></ul><ul><li>This movement is similar to the way of moving a marble through a rubber tube. </li></ul>PERISTALTIC MOVEMENT
  34. 39. APPENDIX <ul><li>A finger sized cul-de-sac or dead end branching off of the initial part of the colon. </li></ul><ul><li>In animals who eat plants exclusively it helps in the digestion of cellulose (starch) into sugar. </li></ul><ul><li>In man the function of the appendix is not clear. </li></ul><ul><li>Man can live normally without an appendix, hence is called vestigial . </li></ul>
  35. 40. <ul><li>Owing to its position, it may get blocked by hard substances (e.g. seeds) and then bacteria which are present in their millions in the large intestine, act on this substance. </li></ul><ul><li>This may result in inflammation of the appendix or appendicitis . </li></ul>
  36. 41. ANAL CANAL <ul><li>The anal canal has 2 openings or sphincters – an internal sphincter and an external sphincter . </li></ul><ul><li>The internal sphincter is under the control of the sympathetic and parasympathetic nerves (the involuntary nerves). </li></ul><ul><li>The sympathetic nerves prevent the sphincter from opening. </li></ul>
  37. 42. <ul><li>In the contrast, the parasympathetic nerves facilitate emptying. </li></ul><ul><li>The external sphincter is under the control of our will , thus allowing defecation (= emptying of the bowels) to occur at appropriate places and times. </li></ul>
  38. 43. FATE OF ABSORBED FOODS <ul><li>The absorption of most digested foods takes place through the villi of the small intestine. </li></ul><ul><li>The blood in smaller blood vessels in the villi absorbs the sugars, and amino acids. </li></ul><ul><li>These vessels join to form wider vessels and eventually one large vein, the portal vein . </li></ul><ul><li>This vessel transports the blood which contains substances from the food (sugar) to the liver. </li></ul><ul><li>In the liver the sugar is once more converted, but this time into more a complex substance – glycogen . </li></ul>
  39. 44. <ul><li>This is the energy store , which is broken down in times of increased energy requirement. </li></ul><ul><li>Amino acids are absorbed into the blood stream and carried to all parts of the body, where some are built into proteins. </li></ul><ul><li>Fatty acids and glycerol pass into the lacteals of the villi, where they are reconstituted into fats. </li></ul><ul><li>Then they are carried away by the lymph vessels . </li></ul><ul><li>Ultimately these vessels open into the blood stream, and fats reach the different parts of the body, bypassing the liver. </li></ul>
  40. 45. <ul><li>This it can be seen that carbohydrates, fats, and proteins are digested and absorbed in different parts of the digestive system. </li></ul><ul><li>Vitamins, salts, and water do not require to be digested and are absorbed unchanged. </li></ul>
  41. 46. PERITONEUM <ul><li>The lining of the abdominal wall and the outer surfaces of the organs (including those of the digestive system) are covered with a membrane called the peritoneum . </li></ul><ul><li>This membrane secretes a fluid which lubricates the organs and prevents friction. </li></ul>Transit time in the stomach, small intestine & large intestine
  42. 47. <ul><li>The first part of a test meal reaches the initial parts of the large intestine within the 4 hours. </li></ul><ul><li>The rest of the undigested food enters the colon in 8 or 9 hours. </li></ul><ul><li>From the last part of the colon, to the anal canal, the transport is slower, easily 72 hours. </li></ul>
  43. 48. NEURAL REGULATION OF THE DIGESTIVE SYSTEM <ul><li>In general, the parasympathetic nerves facilitate emptying by contracting the muscles, while relaxing sphincters. </li></ul><ul><li>The gallbladder also contracts with parasympathetic stimulation. </li></ul><ul><li>In contrast, the sympathetic nerves restrict emptying, by relaxing the muscles, and contracting the sphincters. </li></ul>
  44. 49. FECES <ul><li>Feces are composed of undigested material, water, electrolytes, mucus, and bacteria. </li></ul><ul><li>The color of feces is due to the action of bacteria on bile pigments. </li></ul><ul><li>The odor of feces is due to the action of bacteria. </li></ul>
  45. 50. THANK YOU