OVERVIEWOVERVIEW

The Digestive System The Digestive System

Digestive SystemDigestive System The The digestive systemdigestive system is is

also called the also called the gastrointestinal (GI)gastrointestinal (GI) system.system.

This system is This system is responsible for the responsible for the physical and chemical physical and chemical bbreakdownreakdown of food so it of food so it can be taken into the can be taken into the blood stream and used by blood stream and used by all body all body ccells andells and tissuestissues..

Many organs work Many organs work together to form the together to form the digestive system.digestive system.

The alimentary/GI The alimentary/GI tract canal or tract is a tract canal or tract is a long muscular tube long muscular tube that begins at the that begins at the mouth.mouth.

Included in the Included in the alimentary alimentary tracttract is the is the oral cavity, pharynx, oral cavity, pharynx, esophagus, stomach esophagus, stomach and intestines.and intestines.

The accessoryThe accessory organsorgans in this system are the in this system are the salivary glands, salivary glands, tongue, tongue, teethteeth, liver, , liver, gallbladder and gallbladder and pancreas. pancreas.

In theIn the digestivedigestive system, food is system, food is changed into usable changed into usable nutrients by nutrients by mechanical action mechanical action and and chemicalschemicals called called enzymesenzymes..

Proteins are changed Proteins are changed to to amino acidsamino acids; ; Carbohydrates are Carbohydrates are changed into simple changed into simple SUGARS SUGARS like like glucoseglucose..

Fats are changed intoFats are changed into FATTY acids and FATTY acids and glycerol. glycerol.

The nondigestable The nondigestable parts of the food parts of the food consumed are moved consumed are moved along into the along into the intestinesintestines, and are , and are finally excreted from finally excreted from the body as feces.the body as feces.

Several organs Several organs contribute to the contribute to the function of the function of the digestive system and digestive system and many disease many disease conditions affect conditions affect them.them.

The MouthThe Mouth

The digestive process The digestive process begins in the mouth begins in the mouth where food is chewed where food is chewed so it can be easily so it can be easily swallowed. swallowed.

The tongue is a The tongue is a skeletal muscle skeletal muscle covered with covered with taste taste budsbuds..

The tongue and the teeth work together to The tongue and the teeth work together to chew the food chew the food masticationmastication, the tongue , the tongue then propels the food backward to the then propels the food backward to the pharynx.pharynx.

The tongue also helps in The tongue also helps in SPEECHSPEECH..

The mouth also houses The mouth also houses the the SALIVARYSALIVARY glands glands which secrets a digestive which secrets a digestive enyzme.enyzme.

The pharynx connects the The pharynx connects the mouth to the esophagus, mouth to the esophagus, the pharynx serves as a the pharynx serves as a PASSAGEWAYPASSAGEWAY for both for both food and air.food and air.

Food goes into the Food goes into the esophagus, air goes esophagus, air goes into the trachea on its into the trachea on its way to the lungs.way to the lungs.

The EsophagusThe Esophagus

The esophagus is a tube The esophagus is a tube 10 to 1210 to 12 inches in length inches in length that carries the food to that carries the food to the stomach.the stomach.

Muscular contractions call Muscular contractions call peristalicperistalic waves which waves which move the food through move the food through the entire digestive tract the entire digestive tract begin in the begin in the ESOPHAGUSESOPHAGUS. .

StomachStomach

The stomach is a strong The stomach is a strong hollow elastic hollow elastic MUSCULARMUSCULAR organ with organ with circular muscles at each circular muscles at each end. end.

These These CIRCULARCIRCULAR muscles called sphincters muscles called sphincters hold the food in the hold the food in the STOMACHSTOMACH until it is until it is throughly mixed with throughly mixed with digestive enzymes. digestive enzymes.

When there is no food When there is no food in the stomach, folds in the stomach, folds called called RUGAERUGAE form in form in the mucous the mucous membrane of the membrane of the stomach.stomach.

These many folds These many folds allow for the stomach allow for the stomach to enlarge as it fills to enlarge as it fills with food.with food.

Millions of Millions of GASTRIC GASTRIC GLANDSGLANDS in the stomach in the stomach secrete a gastric juice. secrete a gastric juice.

This gastric This gastric juice juice contains;contains; pepsinpepsin, , necessary for the necessary for the breakdown of breakdown of PROTEINPROTEIN; ; hydrochloric acidhydrochloric acid, , necessary to dissolve necessary to dissolve minerals found in theminerals found in the

foods and provides the foods and provides the stomach a strong stomach a strong ACIDACID environment environment which is needed to which is needed to DESTORDESTORYY the the bacteria and bacteria and microorganisms that microorganisms that enter the stomach in enter the stomach in the food we eat.the food we eat.

The stomach cells also produce the The stomach cells also produce the intrinsic factorintrinsic factor which helps the body which helps the body absorb absorb vitamin B12vitamin B12..

The action of the gastric juice on the food, The action of the gastric juice on the food, assisted by the churning of the stomach assisted by the churning of the stomach produces a semi liquid called produces a semi liquid called Chyme.Chyme.

When the When the chymechyme is ready to leave the is ready to leave the stomach, the pyloric sphincter opens and stomach, the pyloric sphincter opens and allows the food to enter the duodenum. allows the food to enter the duodenum.

The The contraction and relaxationcontraction and relaxation of the of the smooth muscles called smooth muscles called peristalsisperistalsis move move the food along the alimentary tract.the food along the alimentary tract.

INTESTINESINTESTINES

The small The small intestineintestine is is a coiled tube 20 to 25 a coiled tube 20 to 25 feet in length and one feet in length and one inch in diameter. The inch in diameter. The small intestine is small intestine is divided into three divided into three parts:parts:

Parts of the intestineParts of the intestine

The first The first 10 – 1210 – 12 inches is the inches is the duodenum.duodenum.

The next 8 to 10 feet The next 8 to 10 feet is called the is called the jejunum.jejunum.

The final 12 feet or so The final 12 feet or so is called the is called the ileum.ileum.

The small intestine The small intestine contains many contains many intestinal glands intestinal glands which produce which produce intestinal intestinal juice. juice.

In addition In addition bile from bile from the liverthe liver and and pancreatic juices from pancreatic juices from the the pancreaspancreas empty empty into the duodenum.into the duodenum.

Bile, manufactured by the Bile, manufactured by the liverliver is needed is needed for the digestion of fat. The pancreatic for the digestion of fat. The pancreatic juice contains strong juice contains strong enzymesenzymes that that continue the digestion of protein, act on continue the digestion of protein, act on starch and digest fat. The combined starch and digest fat. The combined action of bile, pancreatic juice, and action of bile, pancreatic juice, and intestinal juice complete the breakdown of intestinal juice complete the breakdown of food which can then be absorbed by the food which can then be absorbed by the blood stream.blood stream.

This This absorptionabsorption is is possible because the possible because the small intestine is small intestine is covered with many covered with many projections called projections called villi.villi.

Each tiny villi contains Each tiny villi contains bloodblood and lymph and lymph capillaries.capillaries.

The usable nutrients The usable nutrients pass through the villi pass through the villi into the blood stream.into the blood stream.

The lymph capillaries The lymph capillaries absorb some of the absorb some of the fat fat ingested in the ingested in the food eaten. The food eaten. The portion of food that is portion of food that is undigestibleundigestible passes passes into the large into the large intestine.intestine.

Accessory organsAccessory organs

During the process of digestion, the liver, a During the process of digestion, the liver, a large organ in the upper right of the large organ in the upper right of the abdomen, produces bile which is stored in abdomen, produces bile which is stored in the gallbladder. The gallbladder, a small the gallbladder. The gallbladder, a small muscular sac, releases bile when the muscular sac, releases bile when the chyme passes into the duodenum.chyme passes into the duodenum.

The bile contains The bile contains mineral salts which mineral salts which may crystallize and may crystallize and form form gall stonesgall stones, , causing obstruction of causing obstruction of the bile flow.the bile flow.

The liverThe liver

The liver does several The liver does several other other vitalvital functions functions besides producing besides producing bile: Removal of bile: Removal of poisonspoisons absorbed in absorbed in the intestines, storage the intestines, storage of excess sugar in a of excess sugar in a form called form called glycogenglycogen, , storage of certain storage of certain vitaminsvitamins..

Formation of Formation of antibodies, production antibodies, production of certain proteins of certain proteins necessary for blood necessary for blood clotting, removal of clotting, removal of waste products from waste products from protein called urea.protein called urea.

The pancreasThe pancreas

The pancreas in The pancreas in addition to producing addition to producing digestive juices, also digestive juices, also produces produces insulininsulin, a , a hormone secreted hormone secreted directly into the directly into the bloodblood..

Insulin is necessary Insulin is necessary for metabolism or for metabolism or burning of burning of carbohydratescarbohydrates..

The Large IntestineThe Large Intestine

The large intestine or The large intestine or coloncolon is about 5 feet is about 5 feet long and 2 inches in long and 2 inches in diameter. The large diameter. The large intestine begins at the intestine begins at the lower right corner of lower right corner of the abdomen and is the abdomen and is called the ascending called the ascending colon as it continues colon as it continues upward.upward.

Large intestineLarge intestine

Then it lies across the Then it lies across the upper abdomen which upper abdomen which is called the is called the transversetransverse colon, and colon, and continues down the continues down the left side where it is left side where it is called the called the descendingdescending colon.colon.

At the junction of the At the junction of the large and small large and small intestine is a valve intestine is a valve called the called the ileocecal ileocecal valve. Just below this valve. Just below this valve is the valve is the appendixappendix which has no which has no digestive function.digestive function.

The appendixThe appendix

The appendix is a The appendix is a fingerlike projection fingerlike projection containing a blind sac containing a blind sac which may become which may become irritated and inflamed.irritated and inflamed.

As the descending As the descending colon reaches the colon reaches the pelvis, it makes a “pelvis, it makes a “S”S” shapedshaped bend, known bend, known as the sigmoid colon.as the sigmoid colon.

The final portion of The final portion of the sigmoid extends the sigmoid extends to form the 7-8inch to form the 7-8inch RectumRectum, which opens , which opens exteriorly to the anus.exteriorly to the anus.

The function of the The function of the large intestine is large intestine is concerned with concerned with water water absorption, bacterial absorption, bacterial action and formation action and formation of of fecesfeces..

As the digested food enters the colon it As the digested food enters the colon it contains a great deal of liquid. In the contains a great deal of liquid. In the colon the water absorption and bacterial colon the water absorption and bacterial action turn this liquid into a semisolid form action turn this liquid into a semisolid form and and gas.gas.

FecesFeces is the term given to this mass, is the term given to this mass, sometimes called stool.sometimes called stool.

The peristalsis which is moving the The peristalsis which is moving the undigested food along continues until it undigested food along continues until it enters the rectumenters the rectum..

When the rectum becomes distended, a When the rectum becomes distended, a defecation defecation reflex is trigger alloing the reflex is trigger alloing the emptying of the bowels. (Bowel emptying of the bowels. (Bowel movement)movement)

The process of defecation is under The process of defecation is under conscious control despite the reflex action.conscious control despite the reflex action.

If the urge to defecate is ignored, may If the urge to defecate is ignored, may result in result in constipation.constipation.

DiseasesDiseases

Gastritis – irritation and inflammation of Gastritis – irritation and inflammation of the stomach lining. (gastric Flu)the stomach lining. (gastric Flu)

Ulcers – a lesions or erosion of the lining Ulcers – a lesions or erosion of the lining of the of the stomach or smallstomach or small intestinesintestines

Hepatitis – an inflammation of the Hepatitis – an inflammation of the liverliver.. Cirrhosis – a chronic disease of the liver Cirrhosis – a chronic disease of the liver

causing liver cells to be replaced with causing liver cells to be replaced with scarscar tissuetissue which is non functioning. which is non functioning.

DiseasesDiseases

Constipation – The inability to expell the Constipation – The inability to expell the contents of the rectum.contents of the rectum.

ColitisColitis – an inflammatory disease of the – an inflammatory disease of the colon.colon.

Hemorrhoids – enlarged Hemorrhoids – enlarged veinsveins in the in the rectum.rectum.

Appendicitis – inflammation of the Appendicitis – inflammation of the appendix.appendix.

DiseasesDiseases

Cholecystitis or cholelithiasisCholecystitis or cholelithiasis – inflamation – inflamation of the gall bladder often caused by the of the gall bladder often caused by the formation of formation of crystallized crystallized mineral salts.mineral salts.

Tumors which may either be malignant Tumors which may either be malignant (cancers) or benign (Non cancerous) may (cancers) or benign (Non cancerous) may also affect the digestive system.also affect the digestive system.