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THE HUMAN DIGESTIVE SYSTEM

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1 THE HUMAN DIGESTIVE SYSTEM

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4 Food passes through the digestive tube in the following order
Oral cavity pharynx esophagus (mouth) (throat) (gullet) Stomach small large intestine intestine 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.

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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

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

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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”

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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.

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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 Pepsinogen Inactive form of pepsin and activated by HCl Breaks down large protein molecules into shorter chains of a.a called polypeptides. HCl HCl kills the bacteria that are swallowed with food Activates pepsinogen

20 GLANDS OF THE STOMACH

21 GLANDS OF THE STOMACH

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25 THE STOMACH 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.

26 THE STOMACH There are three mechanisms involved in stimulating the flow of gastric juice. 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

27 THE STOMACH 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 Most of the digestion takes place FUNCTIONS OF THE SMALL INTESTINE:
pyloric sphincter 6.5 meters in length chyme 2.5 cm in diameter duodenum jejenum ileum Most of the digestion takes place FUNCTIONS OF THE SMALL INTESTINE: Most of the chemical digestion takes place and completed in it It is the site of absorption

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31 THE SMALL INTESTINE It has a number of structural features that increase the surface area for absorbtion. It is very long Its lining has many folds The lining is covered with millions of finger-like projections which are called villi 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.

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

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

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

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46 PANCREATIC JUICE Enzymes Bicarbonate ions Amylase
Proteases Lipase Bicarbonate ions Converts the acidic chyme into alkaline solution Chyme is neutralised by HCO3- and turns into alkaline solution. H HCO H2 CO3 Alkaline because medium of intestine is basic Acid from stomach Bicarbonate from liver and pancreas

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

48 ENZYMES OF PANCREATIC JUICE
3. Lipase lipase lipid fatty acids + glycerol 4 . Nucleases Nucleic acids nucleotides

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

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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)
Hormone cholecystokinin stored in the Bile produced in the liver gallbladder releases bile into the Bile duct opens to Small intestine

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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.

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58 INTESTINAL JUICE Peptides amino acids 2. Maltose 2 glucose
The wall of the small intestine contain millions of intestinal glands, which secrete intestinal juice. Peptides amino acids 2. Maltose 2 glucose 3. Sucrose glucose+fructose 4. Lactose glucose+galactose peptidase (erepsin) maltase sucrase lactase

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

60 DIGESTION IN INTESTINE
4.Maltose 2 glucose 5.Sucrose glucose+fructose 6.Lactose glucose+galactose 7. Lipids fatty acids+ glycerol 8. Nucleic acids nucleotides maltase sucrase lactase lipases nucleases

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62 HORMONAL CONTROL OF DIGESTION
HORMONE SOURCE TARGET TISSUE ACTION FACTORS THAT STIMULATE RELEASE Gastrin Stomach (Mucosa) (Gastric glands) Stimulates gastric glands to secrete pepsinogen Presence of food in stomach and certain substances such as caffeine Secretin Small intestine (Duodenum mucosa) Pancreas Signals secretion of sodium bicarbonate Acidic chyme acting on mucosa of duodenum (small intestine) Liver Stimulates bile secretion Cholecytokinins Stimulates release of digestive enzymes Presence of fatty acids and partially digested proteins in duodenum (small intestine) Gallbladder Stimulates emptying of bile

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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 Reabsorbtion of water form the food mass ¾ of water is reabsorbed. If too much water is reabsorbed, constipation results. 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 point They sink points                                                   How often do you evacuate? Once a day point Not everyday points                    How hard are they? Like toothpaste point Hard points                                            What color are your feces? Yellow point Dark brown points                                   How much do they weight? ( 2 pcs of feces a day, each about 2cm in diameter and about 15cm in length ) Over 200g point Below 200g points                                              Do your feces smell? Not much point Bad smell 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...2points Like paste....1 point                                                                Like banana....1 point Very hard....2 point                                                                                  Liquid....2 point Like mud....2 point

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