OVERVIEW The Digestive System

Digestive System  The digestive system is also called the gastrointestinal (GI) system.  This system is responsible for the physical and chemical breakdown of food so it can be taken into the blood stream and used by all body cells and tissues.

 Many organs work together to form the digestive system.  The alimentary/GI tract canal or tract is a long muscular tube that begins at the mouth.

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

 The accessory organs in this system are the salivary glands, tongue, teeth, liver, gallbladder and pancreas.

 In the digestive system, food is changed into usable nutrients by mechanical action and chemicals called enzymes.

 Proteins are changed to amino acids; Carbohydrates are changed into simple SUGARS like glucose.  Fats are changed into FATTY acids and glycerol.

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

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

The Mouth  The digestive process begins in the mouth where food is chewed so it can be easily swallowed.  The tongue is a skeletal muscle covered with taste buds.

 The tongue and the teeth work together to chew the food mastication, the tongue then propels the food backward to the pharynx.  The tongue also helps in SPEECH.

 The mouth also houses the SALIVARY glands which secrets a digestive enyzme.  The pharynx connects the mouth to the esophagus, the pharynx serves as a PASSAGEWAY for both food and air.

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

The Esophagus  The esophagus is a tube 10 to 12 inches in length that carries the food to the stomach.  Muscular contractions call peristalic waves which move the food through the entire digestive tract begin in the ESOPHAGUS.

Stomach  The stomach is a strong hollow elastic MUSCULAR organ with circular muscles at each end.  These CIRCULAR muscles called sphincters hold the food in the STOMACH until it is throughly mixed with digestive enzymes.

 When there is no food in the stomach, folds called RUGAE form in the mucous membrane of the stomach.  These many folds allow for the stomach to enlarge as it fills with food.

 Millions of GASTRIC GLANDS in the stomach secrete a gastric juice.  This gastric juice contains; pepsin, necessary for the breakdown of PROTEIN; hydrochloric acid, necessary to dissolve minerals found in the foods and provides the stomach a strong ACID environment which is needed to DESTORY the bacteria and microorganisms that enter the stomach in the food we eat.

 The stomach cells also produce the intrinsic factor which helps the body absorb vitamin B12.  The action of the gastric juice on the food, assisted by the churning of the stomach produces a semi liquid called Chyme.

 When the chyme is ready to leave the stomach, the pyloric sphincter opens and allows the food to enter the duodenum.  The contraction and relaxation of the smooth muscles called peristalsis move the food along the alimentary tract.

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

Parts of the intestine  The first 10 – 12 inches is the duodenum.  The next 8 to 10 feet is called the jejunum.  The final 12 feet or so is called the ileum.

 The small intestine contains many intestinal glands which produce intestinal juice.  In addition bile from the liver and pancreatic juices from the pancreas empty into the duodenum.

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

 This absorption is possible because the small intestine is covered with many projections called villi.  Each tiny villi contains blood and lymph capillaries.  The usable nutrients pass through the villi into the blood stream.

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

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

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

The liver  The liver does several other vital functions besides producing bile: Removal of poisons absorbed in the intestines, storage of excess sugar in a form called glycogen, storage of certain vitamins.

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

The pancreas  The pancreas in addition to producing digestive juices, also produces insulin, a hormone secreted directly into the blood.  Insulin is necessary for metabolism or burning of carbohydrates.

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

Large intestine  Then it lies across the upper abdomen which is called the transverse colon, and continues down the left side where it is called the descending colon.

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

The appendix  The appendix is a fingerlike projection containing a blind sac which may become irritated and inflamed.  As the descending colon reaches the pelvis, it makes a “S” shaped bend, known as the sigmoid colon.

 The final portion of the sigmoid extends to form the 7-8inch Rectum, which opens exteriorly to the anus.  The function of the large intestine is concerned with water absorption, bacterial action and formation of feces.

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

 Feces is the term given to this mass, sometimes called stool.  The peristalsis which is moving the undigested food along continues until it enters the rectum.

 When the rectum becomes distended, a defecation reflex is trigger alloing the emptying of the bowels. (Bowel movement)  The process of defecation is under conscious control despite the reflex action.  If the urge to defecate is ignored, may result in constipation.

Diseases  Gastritis – irritation and inflammation of the stomach lining. (gastric Flu)  Ulcers – a lesions or erosion of the lining of the stomach or small intestines  Hepatitis – an inflammation of the liver.  Cirrhosis – a chronic disease of the liver causing liver cells to be replaced with scar tissue which is non functioning.

Diseases  Constipation – The inability to expell the contents of the rectum.  Colitis – an inflammatory disease of the colon.  Hemorrhoids – enlarged veins in the rectum.  Appendicitis – inflammation of the appendix.

Diseases  Cholecystitis or cholelithiasis – inflamation of the gall bladder often caused by the formation of crystallized mineral salts.  Tumors which may either be malignant (cancers) or benign (Non cancerous) may also affect the digestive system.