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Download Anatomy and Physiology The Digestive System
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The Digestive System Digestive System • The digestive system, also known as the gastrointestinal system, is responsible for the physical and chemical breakdown of food • Breakdown is necessary so food can be taken into bloodstream and used by body cells and tissues • System consists of alimentary canal and accessory organs Food Breakdown • Ingestion – Taking of food into the body • Peristalsis – Physical movement along the tract • Digestion – Mechanical and chemical breakdown of food • Absorption – Passage of food from digestive tract into body • Defecation – Elimination of indigestible substances from body Alimentary Canal • A long, muscular tube that begins at the mouth and includes the mouth (oral cavity), pharynx, esophagus, stomach, small intestine, large intestine, and anus Accessory Organs • Accessory organs are the salivary glands, tongue, teeth, liver, gallbladder, and pancreas Parts of the Alimentary Canal • The mouth, also called the buccal cavity, receives food as it enters body • While food is in mouth, it is – Tasted – Broken down physically by teeth – Lubricated and partially digested by saliva – And swallowed Parts of the Alimentary Canal • The teeth are special structures in mouth that physically break down food by chewing and grinding • Process is called mastication • The tongue is a muscular organ that contains special receptors, called taste buds • Taste buds allow a person to taste sweet, salt, sour, and bitter sensations • The tongue also aids in chewing and swallowing foods Parts of the Alimentary Canal • The hard palate is the bony structure that forms the roof of the mouth and separates the mouth from the nasal cavities • Behind the hard palate is the soft palate, which separates the mouth from the nasopharynx • The uvula, a cone-shaped muscular structure, hangs from the middle of the soft palate and prevents food from entering the nasopharynx during swallowing Parts of the Alimentary Canal • Three pairs of salivary glands – Parotid (cheek/jaw) – Sublingual (beneath tongue) – Submandibular (chin/neck) • They produce a liquid called saliva • Saliva lubricates mouth during speech and chewing and moistens food so it can be swallowed easily • Also contains enzyme called salivary amylase • Salivary amylase begins chemical breakdown of complex carbohydrates, or starches, into sugars that can be taken into the body Parts of the Alimentary Canal • After food is chewed and mixed with saliva, it is called a bolus • When bolus is swallowed, it enters the pharynx (throat) • Pharynx is a tube that carries both air (to trachea) and food (to esophagus) • When a bolus is being swallowed, muscle action causes epiglottis to close over larynx Parts of the Alimentary Canal • The esophagus is the muscular tube dorsal to the trachea • It receives bolus form pharynx and carries it to stomach • Esophagus, and remaining part of alimentary canal, relies on rhythmic, wavelike, involuntary movement of its muscles • Called peristalsis, it moves food in forward direction Parts of the Alimentary Canal • The stomach is an enlarged part of alimentary canal and receives food from esophagus • Mucous membrane lining stomach contains folds called rugae • Folds disappear as stomach fills with food • Two sphincters at stomach ends called – Cardiac sphincter – Pyloric sphincter Parts of the Alimentary Canal • Cardiac sphincter – Circular muscle between esophagus and stomach – Closes after food enters stomach – Prevents food from going back into esophagus • Pyloric sphincter – Circular muscle between stomach and small intestine – Keeps food in stomach until food is ready to enter intestine – Food usually remains in stomach approx. 1-4 hours Parts of the Alimentary Canal • During time food is in stomach, it is converted into a semifluid material, called chyme • Chyme is from gastric juices produced by glands in stomach mixed with bolus • Gastric juices contain HCL and Pepsinogen • HCL kills bacteria, facilitates Fe absorption, and activates the enzyme pepsin (which starts protein digestion) Parts of the Alimentary Canal • When food, in form of chyme, leaves stomach, it enters the small intestine • The small intestine is a coiled section of alimentary canal • Approximately 20 feet in length and one inch in diameter • Divided into three sections – Duodenum – Jejunum – Ileum Parts of the Alimentary Canal • The duodenum is the first nine to ten inches of the small intestine • Bile (from gallbladder and liver) and pancreatic juice (from pancreas) enter this section through ducts, or tubes • The jejunum is approximately eight feet in length and forms middle section • The ileum is the final 12 feet of small intestine, and connects with large intestine at the cecum Parts of the Alimentary Canal • Process of digestion is completed while food is in small intestine • Products of digestion are absorbed into bloodstream for use by body cells • Intestinal juices produced by small intestine contain enzymes maltase, sucrase, and lactase, which break down sugars into simpler forms Parts of the Alimentary Canal • Intestinal juices contain enzymes known as peptidases, which complete the digestion of proteins • Juices also contain steapsin, which aids in the digestion of fat • Bile from liver and gallbladder emulsifies (physically breaks down) fats • Enzymes from pancrease, like amylase (for sugars) and lipase (for fats) also aid in breakdown Parts of the Alimentary Canal • After food has been digested, it is absorbed into bloodstream • Walls of small intestine are lined with fingerlike projections called villi • The villi contain blood capillaries and lacteals Parts of the Alimentary Canal • Capillaries absorb digested nutrients and carry them to liver, where they are either stored or released into circulation for use by body cells • Lacteals absorb most of digested fats and carry them to thoracic duct in lymphatic system, which releases them into circulation • When food has completed its passage through small intestine, only wastes, indigestible materials, and excess water remain Parts of the Alimentary Canal • The large intestine is the final section of the alimentary canal • It is approximately five feet in length and two-and-ahalf inches in diameter • Functions include – Absorption of H2O and any remaining nutrients – Storage of indigestible materials before eliminated – Synthesis (formation) and absorption of some B-complex vitamins and vitamin K by bacteria present – Transportation of waste products out of body Parts of the Alimentary Canal • The large intestine is divided into a series of connected sections • The cecum is the first section, attached to small intestine – contains a small projection called the vermiform appendix • Next section is the colon with several divisions – – – – Ascending colon Transverse colon Descending colon Sigmoid colon Parts of the Alimentary Canal • The rectum is the final six to eight inches of the large intestine and is a storage area for indigestibles and wastes • It has a narrow canal, called the anal canal, which opens at a hole, called the anus • Fecal material, or stool, the final waste product of the digestive process, is expelled through this opening Accessory Organs • The liver – Largest gland in the body – Located under diaphragm; in RUQ of abdomen – Secretes bile • Used to emulsify fats and • Makes fats water soluble – necessary for absorption – Stores sugar in form of glycogen • Glycogen converts to glucose and released into bloodstream when additional blood sugar is needed – – – – – Stores Fe and certain vitamins Produces heparin, which prevents clotting of blood Produces proteins such as fibrinogen and prothrombin Produces cholesterol Detoxifies substances such as alcohol and pesticides, and destroys bacteria taken into blood from intestine Accessory Organs • The gallbladder – Small, muscular sac located under liver and attached to it by connective tissue – Stores and concentrates bile, received from liver – When bile is needed to emulsify fats in digestive tract, the gallbladder contracts and pushes bile through common bile duct into duodenum Accessory Organs • The pancreas – A glandular organ located behind stomach – Produces pancreatic juices containing enzymes to digest food – Juices enter duodenum through pancreatic duct – Enzymes in juices break down sugars, proteins, and fats – Produces insulin, secreted into bloodstream • Regulates metabolism (or burning) of carbohydrates to convert glucose (blood sugar) into energy Diseases/Abnormal Conditions • Appendicitis – Acute inflammation of appendix – Usually resulting from obstruction and infection • Symptoms include – – – – Generalized abd pain, later localizes at RLQ Nausea and vomiting Mild fever Elevated white blood count • Treatment – Appendectomy – If appendix ruptures, infectious material will spill into peritoneal cavity causing peritonitis, a serious condition Diseases/Abnormal Conditions • Cholecystitis – Inflammation of the gallbladder – When gallstones form from crystallized cholesterol, bile salts, and bile pigments, the condition is known as cholelithiasis • Symptoms (frequently occur after eating fatty foods) include – Indigestion – Nausea and vomiting – Pain that starts under the rib cage and radiates to the right shoulder • Treatment – – – – Low-fat diet Lithotripsy (low shock waves used to shatter gallstones) Cholecystectomy If gallstone blocks bile ducts, gallbladder can rupture and cause peritonitis Diseases/Abnormal Conditions • Cirrhosis – Chronic destruction of liver cells accompanied by formation of fibrous connective and scar tissue • Causes include – Hepatitis, bile duct disease, chemical toxins, and malnutrition associated with alcoholism • Symptoms (vary and become more severe as disease progresses) include – Hepatomegaly (enlarged liver), Anemia, Indigestion, Nausea and vomiting, Nosebleeds, Jaundice, and Ascites (accumulation of fluid in peritoneal cavity) – When liver fails, disorientation, hallucinations, hepatic coma, and death occur • Treatment – Directed toward preventing further damage to liver – Alcohol avoidance, proper nutrition, vitamin supplements, rest, infection prevention, and appropriate exercise are encouraged Diseases/Abnormal Conditions • Constipation – When fecal material remains in colon too long, causing excessive reabsorption of water – Feces, or stool, becomes hard, dry, and difficult to eliminate • Causes include – Poor bowel habits, chronic laxative use leading to a “lazy” bowel, diet low in fiber, and certain digestive diseases • Treatment – – – – Usually corrected by a high fiber diet Adequate fluids Exercise Although laxatives are sometimes used to stimulate defecation, frequent laxative use may be habit forming and lead to chronic constipation Diseases/Abnormal Conditions • Diarrhea – Condition characterized by frequent watery stools – Can be extremely dangerous in infants and children because of the excessive fluid loss • Causes include – Infection, stress, diet, irritated colon, toxic substances • Treatment – Directed toward eliminating cause – Providing adequate fluid intake – Modifying diet Diseases/Abnormal Conditions • Diverticulitis – Inflammation of the diverticula, pouches (or sacs) that form in the intestine as the mucosal lining pushes through the surrounding muscle • Causes include – Fecal matter and bacteria becoming trapped in the diverticula – Can result in abscess or rupture leading to peritonitis • Symptoms (vary depending on amount of inflammation) include – Abd pain, irregular bowel movements, flatus, constipation or diarrhea, abd distention, low-grade fever, and nausea and vomiting • Treatment – Antibiotics, stool-softening medications, pain medications, and surgery to remove the affected section of the colon (in severe cases) Diseases/Abnormal Conditions • Gastroenteritis – An inflammation of the mucous membrane that lines the stomach and intestinal tract • Causes include – Food poisoning, infection, and toxins • Symptoms include – Abd cramping, nausea, vomiting, fever and diarrhea • Treatment – Usual methods are rest and increased fluid intake – Severe cases: antibiotics, IV fluids, and medications to slow peristalsis may be used Diseases/Abnormal Conditions • Hemorrhoids – Painful, dilated or varicose veins of the rectum and/or anus • Causes include – Straining to defecate, constipation, pressure during pregnancy, insufficient fluid intake, laxative abuse, and prolonged sitting or standing • Symptoms include – Pain, itching, and bleeding • Treatment – High-fiber diet; increased fluid intake; stool softeners; sitz baths or warm, moist compresses; and, in some cases, a hemorrhoidectomy Diseases/Abnormal Conditions • Hepatitis – A viral inflammation of the liver • Type A, HAV, or infectious hepatitis – highly contagious – transmitted in food or water contaminated by feces of infected person – Vaccine is available to prevent HAV • Type B, HBV, or serum hepatitis – transmitted by blood and serum – more serious than HAV and can lead to chronic hepatitis or cirrhosis of the liver – Vaccine developed to prevent HBV is recommended for all health care workers • Other strains of hepatitis virus identified include types C, D, and E Diseases/Abnormal Conditions • Symptoms of hepatitis include – Fever, Anorexia (lack of appetite), Nausea, Vomiting, Fatigue, Dark-colored urine, Claycolored stool, Enlarged liver, and Jaundice • Treatment methods include – Rest and a diet high in protein and calories and low in fat – A liver transplant may be necessary if the liver is severely damaged Diseases/Abnormal Conditions • Hernia – Or rupture, occurs when an internal organ pushes through a weakened area or natural opening in a body wall • Hiatal Hernia – When the stomach protrudes through the diaphragm and into the chest cavity through the opening for the esophagus • Inguinal Hernia – When a section of the small intestine protrudes through the inguinal rings of the lower abdominal wall • Symptoms include – Heartburn, stomach distention, chest pain, and difficult swallowing • Treatment – A bland diet, small frequent meals, staying upright after eating, and surgical repair – If hernia cannot be reduced (pushed back in place) a herniorrhaphy is performed Diseases/Abnormal Conditions • Pancreatitis – Inflammation of the pancreas – Pancreatic enzymes begin to digest pancreas itself becomes necrotic, inflamed, and edematous; If damage extends to blood vessels in pancreas, hemorrhage and shock occur • Causes – May be caused by excessive alcohol consumption or blockage of pancreatic ducts by gallstones – Many cases are idiopathic, or of unknown cause • Symptoms include – Severe abd pain that radiates to back, nausea, vomiting, diaphoresis, and jaundice if swelling blocks the common bile duct • Treatment depends on cause – Cholecystectomy is performed if gallstones are cause – Analgesics for pain and nutritional support are used if cause is alcoholism or idiopathic • This type of pancreatitis has a poor prognosis and often results in death Diseases/Abnormal Conditions • Peritonitis – Inflammation of the abdominal peritoneal cavity – Usually occurs when a rupture in the intestine allows the intestine contents to enter the peritoneal cavity – A ruptured appendix or gallbladder can cause this condition • Symptoms include – Abd pain and distention, fever, nausea and vomiting • Treatment includes – Antibiotics – Surgical repair of damaged intestine (if necessary) Diseases/Abnormal Conditions • Ulcer – An open sore on the lining of the digestive tract – Peptic ulcers include gastric ulcers and duodenal ulcers • Causes – Major cause is bacterium Helicobacter pylori (H. pylori), that burrows into stomach membranes, allowing stomach acids and digestive juices to create an ulcer • Symptoms include – Burning pain, indigestion, hematemesis, and melena (dark, tarry stool) • Usual treatment methods are – Antacids, a bland diet, decreased stress, and avoidance of irritants such as alcohol, fried foods, tobacco and caffeine – If H. pylori bacteria are present, treatment with antibiotics and PeptoBismol usually cures the condition – Severe cases, surgery is performed to remove the affected area Diseases/Abnormal Conditions • Ulcerative colitis – Severe inflammation of colon accompanied by formation of ulcers & abscesses – Thought to be caused by stress, food allergy, or autoimmune reaction • Main symptom is diarrhea containing blood, pus, and mucous – Other symptoms include wt. loss, weakness, abd pain, anemia, and anorexia – Periods of remission and exacerbation are common • Treatment – Directed toward controlling inflammation, reducing stress, maintaining proper nutrition, and avoiding substances that aggravate condition – In some cases, surgical removal of the affected colon and creation of a colostomy is necessary • Artificial open in colon allows fecal material to be excreted through abd Diseases/Abnormal Conditions Celiac Disease: • an immune (allergic) reaction to gluten, a protein present in cereal grains (wheat, barley and rye) • The lining of the small intestine is affected, decreasing the amount of surface available for the absorption of nutrients. Main Symptoms: • weight loss, bloating, stomach pain after eating, sometimes diarrhea and malnutrition • Eventually, your brain, nervous system, bones, liver and other organs can be deprived of vital nourishment. Diagnosis: • Blood tests • Elevated levels of certain substances in your blood (antibodies) indicate an immune reaction to gluten. These tests detect celiac disease even if you have only mild symptoms or none at all. • Endoscopy Treatment: • A gluten-free diet is essential, and the only treatment for managing celiac disease.
