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THE HUMAN DIGESTIVE SYSTEMDIGESTIVE. Food passes through the digestive tube in the following order Oral cavitypharynxesophagus (mouth)(throat)(gullet)

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Presentation on theme: "THE HUMAN DIGESTIVE SYSTEMDIGESTIVE. Food passes through the digestive tube in the following order Oral cavitypharynxesophagus (mouth)(throat)(gullet)"— Presentation transcript:




4 Food passes through the digestive tube in the following order Oral cavitypharynxesophagus (mouth)(throat)(gullet) Stomachsmall largeintestine Rectum anus

5 HUMAN DIGESTIVE SYSTEM Liver, pancreas and salivary glands lie outside of the digestive tract and they are called as accessory organs. Food is never found within the alimentary canal itself. These organs aid digestion by the secretion of digestive fluids.


7 THE MOUTH AND PHARYNX Mechanical breakdown and chemical digestion occur. Chunks of food are bitten of with the teeth and ground into pieces small enough to swallow The tongue moves and shapes the food mass in the mouth Saliva is secreted into the mouth by three pairs of salivary glands


9 TYPES OF SALIVA Thin, watery secretion that wets the food Thicker, mucuous secretion that acts as a lubricant and causes the food particles to stick together to form a food mass (bolus)

10 Saliva also contains a digestive enzyme called salivary amylase. (This enzyme breaks down starch, which is a polysacharide, into maltose, which is a disaccharide.) When the food has been chewed sufficiently, it is pushed by the tongue to the back of the throat, or pharynx. This starts the automatic swallowing reflex, which forces the food into the esophagus, the tube leading to the stomach. To prevent food and liquids from entering the larynx, it is automatically closed off during swallowing by a flap of tissue called epiglottis. At the same time, breathing stops momentarily and passageways to the nose, ears and mouth are blocked

11 THE ESOPHAGUS The esophagus is a tube through which food passes from pharynx to the stomach. Beginning in the esophagus, the movement of food down the digestive tube is aided by alternate waves of relaxation and contraction in the muscular walls of the alimentary canal. This is called peristalsis.

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13 Where the esophagus opens into the stomach, there is a ring of muscle called sphincter. There are two sphincters to isolate the stomach. THE ESOPHAGUS Cardiac sphincter is located between the esophagus and the stomach Pyloric sphincter is located between the stomach and the intestine


15 When the wave of peristalsis reaches the sphincter, it relaxes and opens, and the food (bolus) enters the stomach. During vomitting, a wave of peristalsis passes upward -reverse peristalsis- causing the cardiac sphincter to open, and the contents of the stomach to be “thrown up”


17 THE STOMACH The stomach is thick-walled muscular sac. Food is stored temporarily in the stomach. Mechanical breakdown and the partial digestion of protein occur. Churning of the stomach causes mechanical break down and helps the mixing of the food with its secretions.


19 GLANDS OF THE STOMACH Pyloric glands Secretes mucus Mucus protects the lining of the stomach from being digested Gastric glands Secretes gastric juice(pH 1.5 to 2.5) GASTRIC JUICE HCl HCl kills the bacteria that are swallowed with food Activates pepsinogen Pepsinogen Inactive form of pepsin and activated by HCl Breaks down large protein molecules into shorter chains of a.a called polypeptides.






25 The breakdown of starch by salivary amylase which begins in the mouth, continues for some time after the food mass reaches the stomach. Gradually however, the low pH of the acid in the stomach inactivates this enzyme and starch breakdown. THE STOMACH

26 There are three mechanisms involved in stimulating the flow of gastric juice. 1.The thought, sight, smell or taste of food stimulates the brain to send messages to the gastric glands, causing them to secrete moderate amounts of gastric juice THE STOMACH

27 2. Food touching the lining of the stomach stimulates the secretion of moderate amounts gastric juice. 3. When a food mass enters the stomach, it stretches the stomach wall. The streching of the stomach wall, as well as the presence of proteins, caffeine, alcohol and certain other substances, stimulates the lining of the stomach to secrete a hormone called gastrin directly into the blood. Gastrin further stimulates the gastric glands in the stomach to secrete large amounts of gastric juice.

28 THE STOMACH Liquids pass through the stomach in 20 minutes or less. Solids on the other hand, must first be reduced to a thin, soupy liquid called chyme

29 THE SMALL INTESTINE chyme pyloric sphincter duodenumileumjejenum 6.5 meters in length 2.5 cm in diameter Most of the digestion takes place FUNCTIONS OF THE SMALL INTESTINE: 1.Most of the chemical digestion takes place and completed in it 2.It is the site of absorption


31 It has a number of structural features that increase the surface area for absorbtion. a)It is very long b)Its lining has many folds c)The lining is covered with millions of finger-like projections which are called villi d)The epithelial cells that make up the intestinal lining have brush borders. In the brush borders, the membranes of cells that face into the intestinal opening have tiny projections called microvilli that further increase the surface area of the cells. THE SMALL INTESTINE





36 Within each villus, there is a network of blood capillaries and in the center of it there is a lacteal. Fatty acids and glycerol are absorbed into tiny lacteals of the lymphatic system.

37 Absorption involves both diffusion and active transport. When food is present, the small intestine is in constant motion. This peristaltic movements have four effect: 1.They squeeze chyme through the intestine 2.They mix the chyme with the digestive enzymes 3.They break down food particles mechanically 4.They speed up absorption of digestive end products by bringing the intestinal contents into contact with intestinal wall. THE SMALL INTESTINE


39 Chyme from the stomach is mixed with Pancreatic juice from pancreas Bile from the liver Intestinal juice from glands in the wall of the intestine *** Fluids in the small intestine are generally alkaline

40 PANCREAS Pancreas is located in the abdominal cavity between stomach and duodenum. It is both endocrine and exocrine gland. It secretes insulin and glucagon form the Islets of Langerhans pH of pancreatic juice is 8.5



43 PANCREATIC JUICE When the acidic chyme from the stomach enters the small intestine, it stimulates cells in the intestinal lining to secrete two hormones SECRETIN CHOLECYSTOKININ Pancreas to secrete pancreatic juice and pancreatic enzymes stimulates onto the ampulla of vater in the duodenum part of the small intestine pass throuh the pancreatic duct



46 PANCREATIC JUICE Bicarbonate ions Converts the acidic chyme into alkaline solution Chyme is neutralised by HCO 3 - and turns into alkaline solution. H + + HCO 3 - H 2 CO 3 Acid from stomach Bicarbonate from liver and pancreas Alkaline because medium of intestine is basic Enzymes 1.Amylase 2.Proteases 3. Lipase

47 ENZYMES OF PANCREATIC JUICE 1.Pancreatic Amylase: Starch + water maltose + dextrin amylase 2. Proteases Trypsin Trypsinogentrypsin (inactive)(active) chymotrypsin anterokinase They continue the break down of large protein molecules into amino acids begun in the stomach Polypeptides + waterpeptide + amino acids Trypsin and chymotrypsin

48 ENZYMES OF PANCREATIC JUICE 3. Lipase lipidfatty acids + glycerol lipase 4. Nucleases Nucleic acidsnucleotides

49 Digestion in small intestine (pancreatic juice) to secrete hormones Acidic chyme cells in intestinal lining Secretin and cholecystokinin stimulate Pancreas to secrete Pancreatic juicePancreatic duct given to Small intestine


51 BILE is secreted from liver stored and concentrated in gall bladder has no enzyme is alkaline consists of water, ions, cholesterol and bile salts, pigments it passes from gall bladder to duodenum through the bile duct the release of bile from the gall bladder is stimulated by cholecystokinin hormone. it aids in the digestion of fats and oils by breaking them up into tiny droplets. This is called emulsification. It increases the surface area for enzyme action. since bile is alkaline, it aids in neutralizing the acidic chyme from stomach.

52 Digestion in small intestine (bile from gall bladder) Bile produced in the liver Hormone cholecystokinin stored in the gallbladder releases bile into the Bile duct opens to Small intestine




56 Bile is transfered from liver to duodenum through the choledoc duct onto the ampulla of vater Numerous oil droplets are physically formed as a result of emulsification.


58 INTESTINAL JUICE The wall of the small intestine contain millions of intestinal glands, which secrete intestinal juice. 1.Peptidesamino acids 2. Maltose2 glucose 3. Sucroseglucose+fructose 4. Lactoseglucose+galactose (erepsin) peptidase maltase sucrase lactase

59 DIGESTION IN INTESTINE 1.Remaining Polypeptide peptides 2. Peptidesamino acids 3. Remaining starch disaccharides peptidase (erepsin) Pancreatic amylase Trypsin chymotrypsin

60 4.Maltose2 glucose 5.Sucroseglucose+fructose 6.Lactoseglucose+galactose 7. Lipids fatty acids+ glycerol 8. Nucleic acidsnucleotides DIGESTION IN INTESTINE maltase sucrase lactase lipases nucleases


62 HORMONESOURCETARGET TISSUE ACTIONFACTORS THAT STIMULATE RELEASE GastrinStomach (Mucosa) Stomach (Gastric glands) Stimulates gastric glands to secrete pepsinogen Presence of food in stomach and certain substances such as caffeine SecretinSmall intestine (Duodenum mucosa) PancreasSignals secretion of sodium bicarbonate Acidic chyme acting on mucosa of duodenum (small intestine) LiverStimulates bile secretion CholecytokininsSmall intestine (Duodenum mucosa) PancreasStimulates release of digestive enzymes Presence of fatty acids and partially digested proteins in duodenum (small intestine) GallbladderStimulates emptying of bile HORMONAL CONTROL OF DIGESTION


64 LARGE INTESTINE Undigested and unabsorbed materials pass from the small intestine through a sphincter into the large intestine. No digestion occurs On the right side of the abdomen, where the small intestine joins the large intestine, is a small pouch the appendix.(It plays no part in the HDS) The appendix becomes infected or inflamed, a condition known as appendicitis

65 FUNCTIONS OF THE LARGE 1.Reabsorbtion of water form the food mass ¾ of water is reabsorbed. If too much water is reabsorbed, constipation results.constipation If too little water is reabsorbed, diarrhea results. 2. The absorption of vitamins (vitamin K and Vitamin B) that are produced by bacteria that normally live in the large intestine. 3. The elimination- removal of undigested and indigestible material from the digestive tract.

66 LARGE INTESTINE This material consists of cellulose, bacteria, bile, mucus and worn-out cells from the digestive tract. As this material travels through the intestine, it becomes feces. Fecal matter is stored in the rectum and periodically eliminated, through the anus.

67 Check If Your Feces Are Healthy Dietary fibers and lactobacillus bifidus are essential for a healthy and comfortable life.The best feces are like bananas. They are modestly hard with no strong smell. Feces are like a barometer of your health and beauty. Check the following questions to see if you have a healthy feces or not. Do they float? They float..................1 point They sink...................2 points How often do you evacuate? Once a day............1 point Not everyday.......2 points How hard are they? Like toothpaste.........1 point Hard.............................2 points What color are your feces? Yellow.....................1 point Dark brown..........2 points How much do they weight? ( 2 pcs of feces a day, each about 2cm in diameter and about 15cm in length ) Over 200g.............1 point Below 200g...........2 points Do your feces smell? Not much.................1 point Bad smell................2 points If you score: 7 to 9 points..........You are quite healthy 10 to 12 points......Be careful what you eat everyday Take more dietary fibres. 13 to 14 points......Warning! If these conditions continue long, you should see a doctor. Like pebbles...2pointsLike paste....1 point Like banana....1 pointVery hard....2 point Liquid....2 pointLike mud....2 point





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