Digestion Digestion Prepares food for cellular intake Nutrients

Digestion

Digestion ¢ Prepares food for cellular intake Nutrients must be small enough to be absorbed l Nutrients broken down by mechanical and chemical means l Occurs in digestive tract ¢ Food moved by peristalsis ¢

The Mouth to the Small Intestine ¢ Digestion begins in mouth Mastication breaks up food l Tongue and palate mix in saliva l Moistened food passed: l • Into pharynx → through esophagus →into stomach ¢ Churning of stomach further breaks down food by: l Mixing with enzyme pepsin and HCl

The Mouth to the Small Intestine (con’t) ¢ Partially digested food passes through pylorus into duodenum ¢ Digestion completed after passing through other parts of small intestine (jejunum and ileum) ¢ Digested nutrients absorbed into circulation

Accessory Organs

Accessory Organs ¢ Liver l ¢ Gallbladder l ¢ Secretes bile to break down fats Bile stored here until needed Pancreas l Produces mixture of digestive enzymes

The Large Intestine ¢ ¢ ¢ Undigested food, water, digestive juices Begins with cecum Colon twists and turns: l l l ¢ ¢ ¢ Ascending colon Transverse colon Descending colon Water reabsorbed, feces formed Waste material passes into sigmoid colon Waste stored in rectum; eliminated through anus

Clinical Aspects of Digestion ¢ ¢ Gastrointestinal tract Infection l ¢ Can be caused by variety of organisms Ulcers l l l Lesion of skin or mucous membrane Marked by inflammation or tissue damage Can be diagnosed by: • Endoscopy • Barium study (Radiography with contrast medium)

Cancer ¢ ¢ Colon and rectum most likely affected area Risk factors: l l l ¢ ¢ Diet low in fiber, high in fat Heredity Chronic inflammation of colon (colitis) Polyps often become cancerous Symptom: bleeding into intestine

Cancer (con’t) Internal observations performed with endoscopes ¢ Treatment may require surgical removal of portion of GI tract ¢ May create a stoma for waste elimination l Surgery is called –ostomy, with root named for involved organ (e. g. colostomy) l

Obstructions ¢ Hernia l ¢ Pyloric stenosis l ¢ Protrusion of organ through abnormal opening Opening between stomach and small intestine too narrow Intussusception l Slipping of part of intestine into part below

Obstructions (con’t) ¢ Volvulus l ¢ Ileus l ¢ Intestinal twisting Intestinal obstruction caused by lack of peristalsis Hemorrhoids l Varicose veins in rectum

Appendicitis ¢ Results from infection of appendix ¢ Surgery required to: Avoid rupture l Prevent peritonitis l

Inflammatory Bowel Disease ¢ Crohn disease l l ¢ Chronic inflammation of intestinal wall segments, usually ileum May causes: • Pain • Diarrhea • Abscess • Formation of fistula Ulcerative colitis l Continuous inflammation of colon lining, usually rectum

Hepatitis ¢ ¢ Inflammation of the liver More than six types of viral infections l Hepatitis A • Spread by fecal-oral contamination l Hepatitis B • Spread by blood and other body fluids l Vaccines available for Hepatitis A and B

Cirrhosis ¢ ¢ Chronic liver disease mainly caused by excess consumption of alcohol Characterized by: l l ¢ Hepatomegaly Edema Ascites Jaundice As it progresses: l l l Splenomegaly Internal bleeding Brain damage

Gallstones ¢ Cholecystitis l ¢ Cholelithiasis l l ¢ Presence of stones in gallbladder Usually associated with cholecystitis Diagnosed by: l l l ¢ Inflammation of gallbladder Ultrasonography Radiography Endoscopic retrograde cholangiopancreatography Treatment may involve: l l Drugs to dissolve stones Cholecystectomy

Pancreatitis Inflammation of pancreas ¢ May result from: ¢ Alcohol abuse l Drug toxicity l Bile obstruction l Infections l Other causes l ¢ Disease often subsides with only treatment of symptoms