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Four General Functions
Ingestion Digestion Absorption Excretion
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Digestion The breaking down of food by both chemical and mechanical means into usable forms.
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Types of Digestion Mechanical Digestion – Physically breaking down of food into smaller pieces: - Grinding of teeth to soften food - Churning of food by smooth muscles to mix with digestive enzymes Chemical Digestion - series of catabolic reactions that break down large molecules into smaller molecules.
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Absorption The passage of digested food from the alimentary canal into the cardiovascular and lymphatic systems for transportation to body cells
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Defecation (Excretion)
The elimination of indigestible substances from the alimentary canal
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Taking food into the body (EATING)
Ingestion Taking food into the body (EATING)
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Processes of the Digestive System
Mastication – chewing Movement of skeletal muscles to close the mandible or jaw to help move the teeth break down food.
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Maceration Muscular waves in the stomach which mix food with the gastric juice forming a liquid paste called chyme. Occurs in the stomach.
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Segmentation Short small mixing movements of the alimentary canal. Muscle contractions to mix the chyme with enzymes and other secretions. Some propulsion of the chyme also occurs.
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Peristalsis Involuntary wave like smooth muscle contractions to propel food chime & wastes through the alimentary canal.
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Haustral Churning Movement of wastes along the large intestine by the contraction of pouches (haustra). Slow, segmental churning helps to facilitate water reabsorption.
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Gastrointestinal Tract (Alimentary Canal)
A continuous tube extending through the ventral cavity extending from the mouth to the anus Organs of the Alimentary Canal mouth - pharynx - esophagus stomach small intestine - large intestine
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Diagram of the Alimentary Canal
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Accessory Organs Organs that help with digestion by secreting chemicals such as enzymes and bile. salivary glands liver gallbladder - pancreas
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Accessory Organs
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Oral Cavity – The Mouth
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Mouth (Oral or Buccal Cavity)
Cheeks Lips Hard Palate Soft Palate Uvula Tongue Papillae Lingual Frenulum
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Salivary Glands Paired accessory structures that lie outside the oral cavity Secrete their contents (saliva) into ducts that empty into the mouth Parotid Glands - underneath the ears Submandibular Glands - under the mandible Sublingual Glands - under the tongue
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Salivary Glands Accessory structures of the digestive system
Deciduous teeth (baby teeth) - 20 Permanent teeth - 32 Incisors (8) - 4 on top, 4 on bottom chisel shaped - front of mouth Canines (4) - 2 on top, 2 on bottom sharp pointed tearing teeth Premolars (8) - 4 on top, 4 on bottom Molars (12) - 6 on top, 6 on bottom broad, flat, crushing teeth
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Saliva and Salivary Amylase
Salivary glands produce saliva which includes 99.5 % water, mucin, bicarbonate ions, and the enzyme, salivary amylase. Salivary amylase helps to chemically break down starch into the disaccharide maltose.
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Digestion in the Mouth Mechanical Digestion
Chewing (Mastication) Tongue manipulates the food Teeth grind up the food and mix it with saliva The result of mechanical digestion is a soft flexible mass of food called a bolus Chemical Digestion Salivary amylase initiates the breakdown of carbohydrates Only chemical digestion in the mouth
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Digestion of Starch by Salivary Amylase
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Teeth
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Tooth Structures
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Anatomy of a Tooth Crown - exposed portion of the tooth above the gum line Neck - constricted junction line in the tooth between the crown and the root Root - one to three projections of the tooth that are embedded in the sockets of the alveolar processes of the mandible and maxillae
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Anatomy of a Tooth Enamel - outermost portion of the tooth, protects the tooth from wear and tear the hardest substance in the body Dentin - calcified connective tissue that gives the tooth its basic shape and rigidity Pulp – fleshy part of the tooth that is enclosed by the dentin. It contains the blood vessels and nerves. Cementum - a bone-like substance that covers the dentin of the root
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Anatomy of a Tooth Gingiva – the gums or epithelial tissue that help to protect the root of the tooth. Periodontal Ligament - dense fibrous connective tissue, anchor teeth in position. Serves as a shock absorber when chewing.
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Anatomy of a Tooth Root Canal – the openings in the root that allows for the passage of blood vessels and nerves.
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Processes of the Digestive System
Deglutition – swallowing
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Swallowing (Deglutition)
Moving food from the mouth to the stomach Voluntary Stage - bolus is moved through the mouth into the oropharynx Pharyngeal Stage - involuntary passage of the bolus through the pharynx and into the esophagus Esophageal Stage - involuntary passage of the bolus through the esophagus and into the stomach
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Pharynx Also called the throat.
Serves as a passageway for food and air. Also helps in the formation of words.
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Esophagus About 10 inches long. Located posterior to the trachea.
Does not participate in digestive processes – transportation of the bolus to the stomach by peristaltic action. Moves food down into the stomach Esophageal hiatus - opening in the diaphragm for the esophagus Joins the stomach at the cardiac opening.
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Peristalsis
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Lining of the Esophagus
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Stomach J-shaped enlargement of the digestive tract located just below the diaphragm Superior portion - continuation of the esophagus Inferior portion empties into the duodenum through the pylorus. Position and size of the stomach varies from individual to individual
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Histology of the Stomach
Composed of the same four tissue types as the other structures of the alimentary canal When the stomach is empty the mucosa lie in large folds called rugae Mucosa contains millions of tiny openings called gastric pits that open into gastric glands Secretes digestive enzymes and a fluid called gastric juice (2-3 liter per day)
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Anatomy of the Stomach Cardiac Opening – where the stomach is connected to the esophagus. Is not a true sphincter as food can flow into and out of the stomach. Fundus -The rounded superior part of the stomach that will expand. Acts as a temporary storage for food. Body -The large central portion of the stomach below the fundus. Pylorus- narrow, inferior region of stomach that connects it to the small intestine.
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Anatomy of the Stomach, p.2
Rugae - Folds of the stomach that allow for stretching with the intake of food. Pyloric Sphincter – the one way valve between the stomach and the duodenum (first part of the small intestine)
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Anatomy of the Stomach
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Stomach Structures
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Secretory Cells of the Gastric Glands
Chief Cells Digestive enzymes Pepsinogen activated by HCl and converted to Pepsin which breaks down protein Parietal Cells HCl – Hydrochloric Acid Goblet Cells Secrete mucus to protect the stomach mucosa from the acidic environment
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Histology of the Stomach
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Gastric Gland
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Mechanical Digestion in the Stomach
Several minutes after food enters, the stomach generates mixing waves that churns the food inside - maceration Food mixes with gastric juices and is converted into a thin liquid called chyme
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Chemical Digestion in the Stomach
Cephalic Phase - reflexes initiated by sensory receptors in the head. Gastric juices are excreted. sight -smell - taste -thought of food Gastric Phase - sensory receptors in the alimentary canal and stomach initiate nervous and hormonal chemical digestive processes Intestinal Phase - secretion of stomach enzymes that removes nutrients from food Can absorb water if dehydrated. Medication like aspirin, ethanol and caffeine.
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Absorption in the Stomach
Does not participate in the absorption of food molecules into the blood However, can absorb some substances through the stomach wall Water Weak glucose concentrations Electrolytes Certain drugs (aspirin) Alcohol
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Small Intestine The next part of the alimentary canal.
Divided into three sections – the duodenum, jejunum, and ileum. In the duodenum, chemical digestion is completed. The majority of nutrients are absorbed in the jejunum and ileum.
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The Small Intestine Duodenum - the beginning of the small intestine where it attaches to the stomach First 6 inches Jejunum - the portion of the small intestine right after the duodenum Normally about 8 ft. long Ileum - the final portion of the small intestine About 12 ft. long Ileocecal valve
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The Small Intestine
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Chemical Digestion of the Small Intestine
Complex series of chemical events that results in the breakdown of carbohydrates, fats, and proteins Result of the collective effort of pancreatic juice, bile, and intestinal juice which contain digestive enzymes Results in absorption - passage of digested nutrients into the blood or lymph
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Plicae Circulares
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Modifictions of the Small Intestine
Villi – Finger-like extensions of the mucosa to increase surface area for absorption of nutrients. Lacteal – lymphatic vessel for lipid absorption.
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Villi in Duodenum
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Absorption in the Small Intestine
90% of absorption takes place within the small intestine Remaining 10% occurs in the stomach and large intestine Absorption of nutrients occurs through the villi by means of: diffusion - facilitated diffusion osmosis - active transport
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Villi of Small Intestine
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Villi with Lacteal
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Small Intestine Absorption
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Nutrient Absorption
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Additional Components of the Small Intestine
Intestinal Juice - slightly alkaline secretion (pH 7.6) secreted by intestinal glands rapidly absorbed by the villi and provides a mechanism for absorption of substances in chyme Peyer’s Patches - lymphatic glands of the small intestine Brunner’s Glands - mucus secreting glands of the small intestine
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Mechanical Digestion of the Small Intestine
Segmentation - localized contraction of muscles of the small intestine in areas containing food Rate of about contractions/minute Sloshing of chyme back and forth within the intestinal lumen Peristalsis - rhythmical contraction of muscles of the small intestines that propels chyme through the intestinal tract
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Large Intestine The last part of the alimentary canal.
Responsible for the absorption of water, compaction of feces, and the production of Vitamin K.
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The Large Intestine About 1.5 m (5 ft) in length
Cecum - beginning of the large intestine Vermiform appendix Colon - large tube-like portion of large intestine Ascending colon Transverse colon Descending colon Sigmoid colon Rectum Anal Canal Anus
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Functions of the Large Intestine
Completion of absorption Reabsorption of water Manufacture of certain vitamins (K) Formation of feces Expulsion of feces from the body
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Histology of the Large Intestine
Walls of the large intestine contain no villi or permanent circular folds in the mucosa layer Epithelial tissue layer contain numerous goblet cells (secretes mucus) Lubricates the colonic contents as it passes through the large intestine
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Haustra - series of characteristic pouch like structures that run the entire length of the colon
Taenia Coli - bands of smooth muscle that are arranged longitudinally along the length of the colon Anal Columns - parallel ridges of mucosa in the anal canal which reduces friction with feces during defecation
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Large Intestine Histology
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Large Intestine Structures
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Mechanical Digestion in the Large Intestine
Haustral Churning - the relaxation and contraction of the individual segments of the colon Peristalsis - rhythmical contraction of the colon that moves the contents along through the length of the colon Mass Peristalsis - a strong peristaltic wave that begins about the middle of the transverse colon and drives the colonic contents into the rectum
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Chemical Digestion in the Large Intestine
Last stage of digestion Due to bacterial action in the large intestine Bacteria ferment any remaining carbohydrates and release hydrogen, carbon dioxide, and methane gas Also converts any remaining proteins into amino acids Absorbs any remaining water and electrolytes
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Feces Formation in the Large Intestine
By the time chyme has remained in the large intestine for hours it has become a solid or semi-solid and is known as feces Consists of water, inorganic salts, sloughed off epithelial cells, products from bacterial decomposition, and indigestible parts of food
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Defecation The emptying of the rectum
Diarrhea - frequent defecation of liquid feces Constipation - infrequent or difficult defecation
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Diagram of Accessory Organs
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Pancreas Oblong gland that lies posterior to the greater curvature of the stomach Connected by the pancreatic duct to the duodenum Composed of clusters of glandular epithelial cells. Pancreas is the only organ classified as both an endocrine AND an exocrine gland.
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Pancreas
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Pancreas Two main types of Pancreatic Cells:
Pancreatic Islets-Islets of Langerhans (1%) Hormones: insulin, glucagon, somatostatin Acini Cells (99%) Digestive pancreatic enzymes
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Pancreatic Juice Alkaline mixture of fluid and digestive enzymes from the acini cells Pancreatic digestive enzymes: Pancreatic amylase - carbohydrate digestion Pancreatic lipase - fat digestion Chymotrypsin-Trypsin-Carboxypeptidase - protein digestion Nucleases - nucleic acid digestion Regulated by the intestinal hormones secretin and cholecystokinin
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Liver and Pancreas
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Liver Located inferior to the diaphragm on the right side of the body
Largest organ of the abdominopelvic cavity Weighs about 1.4 kgs (3 lbs) Completely covered by the peritoneum and a dense layer of connective tissue beneath the peritoneum Responsible for MANY regulatory functions for the body.
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Lobules of the Liver Smaller functional units of the liver
Hepatocytes in the lobules produce bile which is a yellowish, brownish, or olive green liquid (1 quart daily) Composed of bile salts and pigments, lecithin, and several ions pH of Excretory product and digestive secretion Assists in the breakdown of fat molecules (emulsification) Principle bile pigment is bilirubin
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Functions of the Liver Metabolism of carbohydrates, fats, and proteins
Removal of drugs and hormones Synthesis and excretion of bile Storage of vitamins, minerals, and food molecules Phagocytosis of old worn out red and white blood cells Activation of Vitamin D Storage of glucose and glycogen
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The Gallbladder A pear shaped sac about 7 - 10 cm long
Located on the inferior surface of the liver Stores and concentrates bile until it is needed by the small intestine for the emulsification of fat
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Gallbladder
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Summary of Digestion Mouth Ingestion
Mastication – form a bolus as food mixes with saliva. Digestion of carbohydrates with amylase (starch to maltose) Deglutition
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Summary of Digestion Pharynx Peristalsis Esophagus
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Summary of Digestion Stomach
Maceration and formation of chyme as the bolus mixes with gastric juices. Digestion of proteins to dipeptides by the enzyme, pepsin. Peristalsis continues
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Summary of Digestion Small Intestine Segmentation
Digestion of carbohydrates, lipids, and proteins is completed (mostly in the duodenum) Nutrient absorption (mostly in the ileum and jejunum) Peristalsis
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Summary of Digestion Large Intestine Peristalsis Haustral churning
Absorption of some vitamins Absorption of water Formation and compaction of feces. Excretion
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Digestive System Diseases and Homeostatic Imbalances
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Appendicitis Inflammation of the vermiform appendix
Can be caused by an obstruction of the lumen of the appendix by fecal material, a foreign body, stenosis, kinking of the organ, or carcinoma
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Cirrhosis of the Liver Distorted or scarred liver tissue due to chronic inflammation Commonly caused by hepatitis, chemical exposure, parasites, and alcoholism Symptoms include: jaundice, bleeding, edema, and increased sensitivity to drugs and chemicals
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Cirrhosis of the Liver
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Effects of Cirrhosis
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Colorectal Cancer Can occur in all areas of the digestive system. 3rd most common cause of cancer for both males and females. Can be benign or malignant. Overall mortality rate is over 60% Factors contributing to colorectal cancer include genetic predisposition, diet high in fat, protein, insufficient dietary fiber, and low calcium and selenium in the diet
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Colorectal Cancer
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Gall Stones Crystallization of bile in the gallbladder
Medical Term -- Cholelithiasis Can block the bile duct causing intense pain Usually treated with gall stone dissolving drugs, lithotripsy, or surgery
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Gallstones
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Gallstones
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Hepatitis Inflammation of the liver
Can be caused by viruses, drugs, and certain chemicals including steroids and alcohol Many different types of Hepatitis including: Hepatitis A (Infectious Hepatitis) Hepatitis B (Serum Hepatitis)
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Hepatitis A Infectious hepatitis Caused by Hepatitis A virus
Spread by fecal contamination of food, clothing, toys, eating utensils, etc. Generally a mild disease of children and young adults Characterized by anorexia, malaise, jaundice, nausea, diarrhea, fever, and chills
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Hepatitis B Serum hepatitis Caused by the Hepatitis B virus
Transmitted by sexual contact, contaminated syringes, transfusion equipment, saliva, tears, and puncture wounds in the skin Can produce cirrhosis and possibly cancer of the liver
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Hepatitis
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Obesity Clinically classified as obese if: Body Mass Index >30
Females greater than 30% of normal body weight Males greater than 20% of normal body weight
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A serious risk factor for:
U.S. surgeon general has said obesity is a serious threat to the health of Americans A serious risk factor for: Heart Disease - Diabetes Hypertension - Cancers Respiratory Disorders Endocrine Disorders Gastrointestinal Disorders Urinary and Reproductive System Disorders
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Obesity
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Ulcers Crater like lesions that develop in the gastrointestinal tract
Gastric Ulcers ---> Stomach Duodenal Ulcers ---> Duodenum Commonly caused by hypersecretion of gastric juices and acids Contributing factors include: stress, cigarette smoking, certain foods, some medications, and bacterial infections
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Ulcers
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Ulcers
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Celiac Disease A digestive and autoimmune disorder that results in damage to the lining of the small intestine when foods with gluten are eaten. Gluten is a protein found in some grains. The damage to the intestine makes it hard for the body to absorb nutrients, especially fat, calcium, iron, and folate.
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Celiac Disease
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Celiac Disease
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Crohn’s Disase Crohn's disease is a chronic disease that causes inflammation—irritation or swelling—in the gastrointestinal (GI) tract. Most commonly, Crohn's affects the ileum of the small intestine and the beginning of the large intestine.
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Crohn’s Disease
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Crohn’s Disease
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Irritable Bowel Syndrome
Irritable bowel syndrome commonly causes cramping, abdominal pain, bloating, gas, diarrhea and constipation. IBS is a chronic condition. IBS does not cause changes in the tissues of the intestine.
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Irritable Bowel Syndrome
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Bile Pathway
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