THE HUMAN DIGESTIVE SYSTEM

Food passes through the digestive tube in the following orderOral cavitypharynxesophagus(mouth)(throat)(gullet)

Stomachsmall largeintestineintestine

Rectum anus

HUMAN DIGESTIVE SYSTEMLiver, 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.

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

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

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

THE ESOPHAGUSThe 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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THE ESOPHAGUSWhere the esophagus opens into the stomach , there is a ring of muscle called sphincter. There are two sphincters to isolate the stomach.

Cardiac sphincteris located between the esophagus and the stomachPyloric sphincteris located between the stomach and the intestine

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

THE STOMACHThe 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.

GLANDS OF THE STOMACHPyloric glandsSecretes mucusMucus protects the lining of the stomach from being digestedGastric glandsSecretes gastric juice(pH 1.5 to 2.5) GASTRIC JUICE HCl HCl kills the bacteria that are swallowed with foodActivates pepsinogen

Pepsinogen Inactive form of pepsin and activated by HClBreaks down large protein molecules into shorter chains of a.a called polypeptides.

GLANDS OF THE STOMACH

GLANDS OF THE STOMACH

THE STOMACHThe 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 STOMACHThere 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

THE STOMACH2. 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.

THE STOMACHLiquids 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

THE SMALL INTESTINEchymepyloric sphincterduodenumileumjejenum6.5 meters in length2.5 cm in diameterMost of the digestion takes placeFUNCTIONS OF THE SMALL INTESTINE:Most of the chemical digestion takes place and completed in itIt is the site of absorption

THE SMALL INTESTINEIt has a number of structural features that increase the surface area for absorbtion.It is very longIts lining has many foldsThe lining is covered with millions of finger-like projections which are called villiThe 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.

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.

THE SMALL INTESTINEAbsorption 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 intestineThey mix the chyme with the digestive enzymesThey break down food particles mechanicallyThey speed up absorption of digestive end products by bringing the intestinal contents into contact with intestinal wall.

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

PANCREASPancreas 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

PANCREATIC JUICEWhen the acidic chyme from the stomach enters the small intestine, it stimulates cells in the intestinal lining to secrete two hormonesSECRETINCHOLECYSTOKININPancreas to secrete pancreatic juice and pancreatic enzymes stimulatesonto the ampulla of vater in the duodenum part of the small intestinepass throuh the pancreatic duct

PANCREATIC JUICEBicarbonate ionsConverts the acidic chyme into alkaline solutionChyme is neutralised by HCO3- and turns into alkaline solution.H+ + HCO3 - H2 CO3Acid from stomachBicarbonate from liver and pancreasAlkaline because medium of intestine is basicEnzymesAmylaseProteases Lipase

ENZYMES OF PANCREATIC JUICEPancreatic Amylase:Starch + water maltose + dextrinamylase2. Proteases

TrypsinTrypsinogentrypsin(inactive)(active)chymotrypsinanterokinaseThey continue the break down of large protein molecules into amino acids begun in the stomachPolypeptides + waterpeptide + amino acidsTrypsin and chymotrypsin

ENZYMES OF PANCREATIC JUICE3. Lipaselipidfatty acids + glycerollipase4 . NucleasesNucleic acidsnucleotides

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

BILEis secreted from liverstored and concentrated in gall bladderhas no enzyme is alkalineconsists of water, ions, cholesterol and bile salts, pigmentsit passes from gall bladder to duodenum through the bile ductthe 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.

Digestion in small intestine(bile from gall bladder)Bile produced in the liver Hormone cholecystokininstored in the gallbladderreleases bile into theBile ductopens to Small intestine

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

INTESTINAL JUICEThe wall of the small intestine contain millions of intestinal glands, which secrete intestinal juice.

Peptidesamino acids

2. Maltose2 glucose

3. Sucroseglucose+fructose

4. Lactoseglucose+galactose(erepsin)peptidasemaltasesucraselactase

DIGESTION IN INTESTINE

1.Remaining Polypeptide peptides

2. Peptidesamino acids

3. Remaining starch disaccharides

peptidase(erepsin)Pancreatic amylaseTrypsin chymotrypsin

DIGESTION IN INTESTINE4.Maltose2 glucose

5.Sucroseglucose+fructose

6.Lactoseglucose+galactose

7. Lipids fatty acids+ glycerol

8. Nucleic acidsnucleotides

maltasesucraselactaselipasesnucleases

HORMONAL CONTROL OF DIGESTION

HORMONESOURCETARGET TISSUEACTIONFACTORS THAT STIMULATE RELEASEGastrinStomach(Mucosa)Stomach(Gastric glands)Stimulates gastric glands to secrete pepsinogenPresence of food in stomach and certain substances such as caffeineSecretinSmall intestine(Duodenum mucosa)PancreasSignals secretion of sodium bicarbonateAcidic chyme acting on mucosa of duodenum (small intestine) LiverStimulates bile secretionCholecytokininsSmall intestine(Duodenum mucosa)PancreasStimulates release of digestive enzymesPresence of fatty acids and partially digested proteins in duodenum (small intestine)GallbladderStimulates emptying of bile

LARGE INTESTINEUndigested and unabsorbed materials pass from the small intestine through a sphincter into the large intestine.No digestion occursOn 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

FUNCTIONS OF THE LARGEReabsorbtion of water form the food mass 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.

LARGE INTESTINEThis 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.

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