PH 131 Gastrointestinal Lecture 4 (1) PDF

PH 131: GASTROINTESTINAL SYSTEM Vivien Fe F. Fadrilan-Camacho, MD, MPH, FPAFP Director, Office of International and Local Linkages, UP Manila Associate Professor and Assistant to the Dean for Academic Affairs Department of Environmental and Occupational Health...

PH 131: GASTROINTESTINAL SYSTEM Vivien Fe F. Fadrilan-Camacho, MD, MPH, FPAFP Director, Office of International and Local Linkages, UP Manila Associate Professor and Assistant to the Dean for Academic Affairs Department of Environmental and Occupational Health College of Public Health University of the Philippines Manila 1  This material is solely for the use of students enrolled in PH 131. Do not distribute without Learning Outcomes permission. At the end of the session, the student should be able to: 1. discuss the function of gastrointestinal system 2. describe the anatomy and physiological processes of the gastrointestinal system 3. discuss common gastrointestinal disorders 3  Digestive System Function Acquires nutrients from environment Anabolism – Uses raw materials to synthesize essential compounds Catabolism – Decomposes substances to provide energy cells need to function 4  Digestive Processes Ingestion Movement of food Digestion – Mechanical digestion – Chemical digestion Absorption Defecation/Excretion 5 General Structure Digestive organs divided into 2 main groups – GI (alimentary) tract – Accessory structures cheeks, teeth, tongue, salivary glands liver, gallbladder, pancreas 6 Nervous Regulation of the GI System The enteric nervous system (ENS) is an extensive network of the submucosal and myenteric plexuses within the walls of the digestive tract (figure 24.4). This network of neurons and associated neuroglial cells is a division of the autonomic nervous system. There are three major types of enteric neurons: (1) Enteric sensory neurons detect changes in the chemical composition of digestive tract contents or detect mechanical changes, such as stretch of the digestive tract wall; (2) enteric motor neurons stimulate or inhibit smooth muscle contraction and glandular secretion in the digestive system; (3) enteric interneurons connect enteric sensory and motor neurons. SEAMEO TROPMED Philippines COLLEGE OF PUBLIC HEALTH Regional Centre for Public Health, Hospital Administration, University of the Philippines Manila Environmental and Occupational Health 7  SEAMEO TROPMED Philippines COLLEGE OF PUBLIC HEALTH Regional Centre for Public Health, Hospital Administration, University of the Philippines Manila Environmental and Occupational Health 8  SEAMEO TROPMED Philippines COLLEGE OF PUBLIC HEALTH Regional Centre for Public Health, Hospital Administration, University of the Philippines Manila Environmental and Occupational Health 9  SEAMEO TROPMED Philippines COLLEGE OF PUBLIC HEALTH Regional Centre for Public Health, Hospital Administration, University of the Philippines Manila Environmental and Occupational Health 10  SEAMEO TROPMED Philippines COLLEGE OF PUBLIC HEALTH Regional Centre for Public Health, Hospital Administration, University of the Philippines Manila Environmental and Occupational Health 11  This material is solely for the use of students enrolled in PH 131. Do not distribute without Salivary Glands permission. 3 pairs salivary glands – Parotid glands – Submandibular glands – Sublingual glands 12  Salivary Glands Composition of Saliva – 99.5% water, 0.5% solutes Na+, K+, Cl-, HCO3 -, and PO4 -, proteins, waste products lysozyme salivary amylase – digests carbohydrates – Saliva composition differs among the 3 glands parotid - watery saliva, amylase submandibular - thicker mucous, amylase sublingual - mostly mucous, a little amylase 13  Salivary Glands Functions of Saliva – Water dissolves food for taste and digestion – Mucous moistens and lubricates food – Mucous lubricates oral surfaces for smooth actions in swallowing and speech – Cl- ions activate amylase – HCO3 and PO4 ions buffer bacterial acids – IgA, lysozymes: protect against microorganisms 14  Salivary Glands Secretion of Saliva - 1-1.5 L l day – Primarily under nervous control Parasympathetic (ANS) à normal salivary secretions – saliva swallowed – most reabsorbed Sympathetic (ANS) à reduced flow (dry mouth) – Food (mechanically, chemically) stimulates salivation behavioral – memories from cortex starts digestion continues after ingestion is complete irritating foods or nausea 15  Physiology of Digestion in Mouth Mechanical digestion – Chewing = mastication – Food mixed with saliva – Shaped into a bolus Chemical digestion – salivary amylase breaks down and converts polysaccharides (starches) to disaccharides (maltose) and monosaccharides (glucose) 16  Physiology of Deglutition (Swallowing) Moving bolus from mouth to stomach – Three phases – Facilitated by saliva, mucous secretions – Involves mouth, pharynx, esophagus 1. Buccal phase w Voluntary w Moves bolus to oropharynx 17  Physiology of Deglutition 2. Pharyngeal phase – Involuntary – Receptors in oropharynx stimulate medulla and pons to: 1. Block mouth with tongue 2. Block nasopharynx with soft palate 3. Raise larynx to seal epiglottis, blocking airways 4. Relax upper esophageal sphincter – Bolus is moved through pharynx into esophagus 18  Physiology of Deglutition 3. Esophageal stage – Upper esophageal sphincter closes – Gastroesopaheal sphincter opens – Esophagus controls involuntary peristaltic movement – Epiglottis reopens – Bolus moves from esophagus to stomach 19 Swallowing Reflex, Phases and Overview of Neural Control SEAMEO TROPMED Philippines COLLEGE OF PUBLIC HEALTH Regional Centre for Public Health, Hospital Administration, University of the Philippines Manila Environmental and Occupational Health 20 Esophagus Peristalsis – Involuntary, rhythmic contraction of muscularis – Controlled by medullary centers – A movement activity: inner circular layer of smooth muscle contracts behind bolus to push it forward; outer longitudinal muscle contracts to pull esophagus wall up 21 Esophagus Physiology – Upper esophageal sphincter – Peristalsis – Lower esophageal (“cardiac”) sphincter – Sharp transition from nonkeratinized stratified squamous epithelium to simple columnar epithilium – Esophageal epithelium resistant to abrasion but not to acid and proteolytic enzyme attack – acid reflux disease 22  SEAMEO TROPMED Philippines COLLEGE OF PUBLIC HEALTH Regional Centre for Public Health, Hospital Administration, University of the Philippines Manila Environmental and Occupational Health 23  Stomach Physiology of digestion - Mechanical digestion – peristaltic movement (mixing waves) back and forth between body and pylorus – 3 muscle layers: longitudinal, circular, and oblique – chyme 24  Stomach Physiology of digestion - Chemical digestion – parietal cells secrete intrinsic factor for Vitamin B12 absorption – parietal cells secrete HCl by active transport kills microbes, denatures proteins causes some acid hydrolysis of food molecules stimulates secretion of hormones for bile & pancreatic juice flow – chief cells secrete pepsinogen (inactive precursor) activated to pepsin by HCl acid and by other pepsins only an effective protease at acid pH Pepsin - cleaves proteins into smaller peptides 25  Stomach: Mucosa Gastric gland chief cells – Secrete pepsinogen (inactive precursor) activated to pepsin by HCl acid and by other activated pepsin enzymes only an effective protease at acid pH cleaves proteins into smaller peptides – Secrete rennin in neonates curdles milk to increase time for gastric processing – Secrete gastric lipase in neonates splits short chain triglycerides common in milk limited role in digestion since it works best at pH 5-6 26 Stomach: Mucosa Simple columnar epithelium with goblet cells and gastric pits – Secretes 2-3 L l day Gastric gland parietal cells – Secrete intrinsic factor for B12 absorption – Secrete HCl by active transport kills microbes, denatures proteins causes some acid hydrolysis of food molecules stimulates secretion of hormones for bile & pancreatic juice flow Goblet & gastric pit mucous cells secrete mucin – 1-3 mm mucus layer in the stomach prevents self-digestion 27 Stomach: Mucosa Gastric gland G cells (enteroendocrine) – Secrete gastrin, histamine, serotonin, somatostatin Absorption – Impermeable to diffusion of most molecules into the bloodstream – Absorbs a few lipid soluble compounds: certain drugs (e,g., aspirin) alcohol 28 29 Stomach: Regulation of Secretion and Motility Regulated by combination of neuronal and hormonal factors 3 phases 1. Cephalic 2. Gastric 3. Intestinal 30  SEAMEO TROPMED Philippines COLLEGE OF PUBLIC HEALTH Regional Centre for Public Health, Hospital Administration, University of the Philippines Manila Environmental and Occupational Health 32  SEAMEO TROPMED Philippines COLLEGE OF PUBLIC HEALTH Regional Centre for Public Health, Hospital Administration, University of the Philippines Manila Environmental and Occupational Health 33  SEAMEO TROPMED Philippines COLLEGE OF PUBLIC HEALTH Regional Centre for Public Health, Hospital Administration, University of the Philippines Manila Environmental and Occupational Health 34 Stomach: Regulation of Gastric Emptying Food normally passes through stomach in 4 hours Hormonal/neuronal reflexes regulate gastric emptying Large meals and large amounts of liquid increase stomach distension à increasing rate of emptying Stomach emptying inhibited by the enterogastric reflex, enterogastrones, and fat in the duodenum 35  This material is solely for the use of students Pancreas enrolled in PH 131. Do not distribute without permission. Lies posterior to stomach – From duodenum toward spleen Is bound to posterior wall of abdominal cavity Is wrapped in thin, connective tissue capsule Functions of the Pancreas 1. Endocrine cells of the pancreatic islets: Secrete insulin and glucagon into bloodstream 2. Exocrine cells: Acinar cells and epithelial cells of duct system secrete pancreatic juice 36  Pancreas Pancreatic juice – 1.2-1.5 L/day – Mostly water some salts, bicarbonate, enzymes alkaline, pH 7.1-8.2 buffers acidic gastric juice, stops pepsin activity, creates proper alkaline pH for enzymes acting in the intestine – Enzymes include: pancreatic amylase – breaks down starches trypsinogen, chymotrypsinogen, procarboxypeptidase (inactive zymogens) – when activated, breaks down proteins pancreatic lipase – breaks down complex lipids ribonuclease and deoxyribonuclease – breaks down nucleic acids 37 Regulation of Pancreatic Secretion Neural control from parasympathetic division of ANS via vagus nerve Autoregulation by sensing the presence of fatty acids and amino acids in the acidic chyme Hormonal control by the secretion of enteroendocrines from duodenum – Secretin – stimulates secretion of water, HCO3 - – CCK – stimulates secretion of enzymes 38  This material is solely for the use of students LIVER enrolled in PH 131. Do not distribute without permission. SEAMEO TROPMED Philippines COLLEGE OF PUBLIC HEALTH Regional Centre for Public Health, Hospital Administration, University of the Philippines Manila Environmental and Occupational Health 39  This material is solely for the use of students enrolled in PH 131. Do not distribute without permission. SEAMEO TROPMED Philippines COLLEGE OF PUBLIC HEALTH Regional Centre for Public Health, Hospital Administration, University of the Philippines Manila Environmental and Occupational Health 40  Liver Function The Physiology of the Liver 1. Metabolic regulation 2. Hematological regulation 3. Bile production 41  Liver Function Metabolic Regulation – The liver regulates: 1. Composition of circulating blood 2. Nutrient metabolism (carbohydrate, lipid & amino acid) 3. Waste product removal 4. Vitamin Storage (A, D, E & K) 5. Nutrient storage (iron) 6. Drug inactivation 42  Liver Function Composition of Circulating Blood – All blood leaving absorptive surfaces of digestive tract Enters hepatic portal system Flows into the liver – Liver cells extract nutrients or toxins from blood Before they reach systemic circulation through hepatic veins – Liver removes and stores excess nutrients Corrects nutrient deficiencies by mobilizing stored reserves or performing synthetic activities 43  Liver Function Hematological Regulation – Largest blood reservoir in the body Receives 25% of cardiac output Functions of Hematological Regulation 1. Phagocytosis and antigen presentation 2. Synthesis of plasma proteins 3. Removal of circulating hormones 4. Removal of antibodies 5. Removal or storage of toxins 6. Synthesis and secretion of bile 44  Liver Sinusoids are patrolled by monocyte-derived stellate reticuloendothelial (Kupffer's) cells – Phagocytize damaged blood cells, bacteria, and other microbes – Phagocytize some foreign molecules such as toxins – Hepatocytes can also store or breakdown toxic molecules 45  Liver Hepatocytes – Receive, process and store nutrients from meals – Process heme and cholesterol breakdown products to make bile components 46  SEAMEO TROPMED Philippines COLLEGE OF PUBLIC HEALTH Regional Centre for Public Health, Hospital Administration, University of the Philippines Manila Environmental and Occupational Health 47  Liver Bile – 800-1000 ml/day – Yellow, brownish, or olive-green liquid – pH 7.6-8.6, mostly water, bile salts, bile acids, cholesterol, lecithin (phospholipid), bile pigments, ions – Part digestive secretion, part excretory product bile salts help in emulsification of ingested fats bilirubin and other bile pigments are wastes from lipid catabolism 48  SEAMEO TROPMED Philippines COLLEGE OF PUBLIC HEALTH Regional Centre for Public Health, Hospital Administration, University of the Philippines Manila Environmental and Occupational Health 49  Liver Physiology of the liver – processes vital to life – Carbohydrate metabolism – regulates blood glucose levels glycogenesis (insulin) glycogenolysis (glucagon) gluconeogenesis (glucagon) – Lipid metabolism - stores, metabolizes some triglycerides synthesizes new cholesterol degrades excess cholesterol for bile salt production – Protein metabolism - deaminates AA’s by removing amino groups (-NH2) from AA’s – deaminated AA's used for ATP production or changed to carbohydrates or fats as needed – detoxifies ammonia (NH3) by synthesizing urea (1 CO2 + 2 NH3 = urea) can convert AA's from one to another (transamination) 50 synthesizes and secretes most plasma proteins  Liver Physiology of the liver - processes vital to life – Storage – oil-soluble vitamins, iron, other nutrients and minerals – Phagocytosis – Removal of dietary toxins, hormones, drugs detoxify or store or secrete compounds into bile metabolize thyroid, steroid hormones – Synthesis of bile salts – Excretion of bile - bilirubin Pathologies of the liver – hepatitis (viral, toxic), cirrhosis, cancer 51  Gall Bladder Pear-shaped sac, 7-10 cm long Physiology – stores and concentrates bile between meals – CCK stimulates bile release for fatty meals – when the small intestine is empty, the hepatopancreatic sphincter closes, forcing bile into the gallbladder for storage 52  SEAMEO TROPMED Philippines COLLEGE OF PUBLIC HEALTH Regional Centre for Public Health, Hospital Administration, University of the Philippines Manila Environmental and Occupational Health 53  Small Intestine: Segmentation primary action of small intestine when food is present a form of mechanical digestion a mixing activity alternate contraction, relaxation of antagonistic smooth (circular and longitudinal) muscle segments in the intestine controlled by the autonomic nervous system 54  Small Intestine: Peristalsis as absorption continues, distension decreases and true peristalsis starts a movement which propels chyme onward these weak movements which occur only after most nutrients have been absorbed 55  Small Intestine: Motility and Secretion Intestinal secretions – 1-2 L/day, pH 7.6 – mostly water and mucus – bicarbonate buffer neutralizes gastric acid – provide enzymes for final chemical digestion Regulation of intestinal secretion and motility – stimulated by distension and acidic chyme – local reflexes increase Ach release – VIP stimulates production of intestinal secretions – basal motility is controlled by autorhythmic pacemakers – local hormones and parasympathetic ANS reflexes increase motility 56 Small Intestine: Chemical Digestion Intestinal secretions – 1-2 L/day, pH 7.6 – mostly water and mucus – along with pancreatic secretions provide acid neutralization, final chemical digestion, and more water for absorption Brush border enzymes – brush border enzymes complete digestion of protein and carbohydrate molecules 57  Small Intestine: Chemical Digestion Brush border enzymes – Enteropeptidase (enterokinase) converts trypsinogen to trypsin Trypsin activates other zymogens – Various other brush border enzymes complete digestion of protein and carbohydrate molecules 58  Small Intestine: Chemical Digestion Complete digestion is a function of bile, pancreatic secretions and intestinal secretions – Although produced by different organs, they all function in the small intestine Prior to small intestine, only limited activity – mouth – salivary amylase – stomach pepsin lingual lipase 59  Small Intestine: Chemical Digestion Chemical digestion in the small intestine: – Carbohydrate digestion pancreatic amylase digests starches disaccharidases liberate monosaccharides – Protein digestion pancreatic proteases (trypsin, chymotrypsin, carboxypeptidase) finished by brush border proteases in the lining epithelium – Lipid digestion bile salts for emulsification pancreatic lipase – Nucleic acid digestion pancreatic ribonuclease and deoxyribonuclease brush border enzymes digest nucleotides 60  Small Intestine: Absorption About 90% of all absorption takes place in small intestine Nutrients enter capillaries via diffusion, facilitated diffusion, or active transport Nutrients are transported in the blood to the liver via the hepatic portal circulation 61 Small Intestine: Water Absorption Total volume added to the small intestine/day - 9.3 L – ~2.3 L from ingestion – ~7.0 L from secretions Small intestine absorbs ~8.3 L /day – passive absorption following nutrient molecules – osmosis The rest of the water (~1.0L/day) passes to large intestine where most is reabsorbed (~0.9 L/day) 62  Functions Large Intestine – Completion of absorption, especially final absorption of H2O – Normal flora manufacture certain vitamins (B complex, K) – Formation and expulsion of feces Anatomy – 1.5 m L, 6.5 cm W – Divided into 4 general areas: cecum colon rectum anal canal 63  Large Intestine: Digestion Mechanical digestion – Chyme passage regulated by ileocecal sphincter valve generally closed - slow passage following a meal à gastroileal reflex: ileal motility increases, sphincter relaxes, chyme moves to the cecum when the cecum is full, the sphincter contracts – Colon movements start when chyme passes sphincter haustral churning – haustra relaxed, distended until full – then contract, squeeze contents into next haustrum peristalsis is slow mass peristalsis (gastrocolic reflex) – during or immediately following a meal, 3-4 times day – strong peristaltic waves from middle of transverse colon – push contents into the rectum 64  Large Intestine: Digestion Chemical digestion – much mucus but no enzymes are secreted – some digestion of chyme by bacteria in colon final breakdown of substances, mostly carbohydrates bacteria produce some vitamins, B complex and K some bacterial metabolites are toxic, but the liver normally deals successfully with them 65  Large Intestine Absorption and feces formation – Chyme after 3-10 hours in the large intestine, chyme becomes solidified (due to water reabsorption) into feces large intestine absorbs water, electrolytes, some vitamins and any toxins – Feces water, inorganic salts, sloughed off intestinal epithelial cells, bacteria, products of bacterial decomposition, undigested parts of food most water is reabsorbed in small intestine, but the large intestine is also important in water reabsorption 66  Large Intestine Physiology of defecation – Mass peristalsis pushes fecal matter into rectum distension stimulates stretch receptors initiating reflex for defecation – Parasympathetic ANS stimulated by stretch receptors stimulates contraction of rectum shortens and increases pressure in rectum parasympathetic stimulation relaxes internal sphincter – Conscious stimulation relaxes external sphincter feces expelled 67  This material is solely for the use of students VIDEOS enrolled in PH 131. Do not distribute without permission. Digestive System Part 1 Digestive System Part 2 Digestive System Part 3 SEAMEO TROPMED Philippines COLLEGE OF PUBLIC HEALTH Regional Centre for Public Health, Hospital Administration, University of the Philippines Manila Environmental and Occupational Health 68 CASE: SEAMEO TROPMED Philippines COLLEGE OF PUBLIC HEALTH Regional Centre for Public Health, Hospital Administration, University of the Philippines Manila Environmental and Occupational Health 69 ACUTE GASTROENTERITIS involvement of the stomach and the intestines in an inflammatory process. It is usually caused by infection which are food or water-borne but may also result from allergic reactions to foods or drugs. Inflammation of the gastric mucosa stimulates vomiting, whereas diarrhea results when the inflammation of the intestines causes increased motility, impaired absorption, and in some cases, increased secretions. Nausea and abdominal cramps are usually present. Fever and malaise are also common. SEAMEO TROPMED Philippines COLLEGE OF PUBLIC HEALTH Regional Centre for Public Health, Hospital Administration, University of the Philippines Manila Environmental and Occupational Health 70 ACUTE GASTROENTERITIS Most infections are mild and self-limiting, but occasionally serious illness results when the host is immunosuppressed or the agent is more virulent. Often a food- or water-borne illness will involve a large number of cases; in some outbreaks entire communities may be infected. It is imperative that in times of disaster clear instructions be given about the safety of food and water. Safe sanitation must be put in place as quickly as possible to prevent further illness requiring the use of scarce health resources. SEAMEO TROPMED Philippines COLLEGE OF PUBLIC HEALTH Regional Centre for Public Health, Hospital Administration, University of the Philippines Manila Environmental and Occupational Health 71 ACUTE GASTROENTERITIS The infection is usually self-limiting, although supportive treatment may be needed for fluid and electrolyte losses, particularly in young children and the elderly. A stool culture is helpful in identifying the causative organism in persistent cases. Escherichia coli ( E. coli) is usually a harmless microbe that is normally resident in the intestine. - Some infective types can adhere to the mucosa and secrete an enterotoxin, causing gastroenteritis, particularly among children in nursery schools or travelers in the form of common “traveler’s diarrhea.” SEAMEO TROPMED Philippines COLLEGE OF PUBLIC HEALTH Regional Centre for Public Health, Hospital Administration, University of the Philippines Manila Environmental and Occupational Health 72  Public Health Interventions Regular handwashing Access to safe food and water sources – multisectoral efforts Food and water safety practices Environmental sanitation Patient/Community education - prevention - red flags (signs of dehydration) SEAMEO TROPMED Philippines COLLEGE OF PUBLIC HEALTH Regional Centre for Public Health, Hospital Administration, University of the Philippines Manila Environmental and Occupational Health 73 CASE 32 y/o female call-center agent complains of 1-week history of epigastric pain and bloatedness and nausea. Because of her work, she frequently skips her meal or does not eat on time. She also loves to drink coffee to help her awake during her shift at night. SEAMEO TROPMED Philippines COLLEGE OF PUBLIC HEALTH Regional Centre for Public Health, Hospital Administration, University of the Philippines Manila Environmental and Occupational Health 74 GASTRITIS Gastritis may be acute or CAUSES: chronic. Infection by many types of Acute gastritis may be a microorganisms (e.g., bacteria and mild, transient irritation viruses) with only vague signs, or it Allergies to foods such as shellfish or drugs may be a more severe Ingestion of spicy or irritating foods, ulcerative or hemorrhagic such as hot peppers, particularly if the episode. person is unaccustomed to a spicy diet Excessive alcohol intake, caffeinated The gastric mucosa is and carbonated drinks inflamed and appears red Ingestion of aspirin or other and edematous. ulcerogenic drugs (especially on an empty stomach SEAMEO TROPMED Philippines COLLEGE OF PUBLIC HEALTH Regional Centre for Public Health, Hospital Administration, University of the Philippines Manila Environmental and Occupational Health 75 GASTRITIS Symptoms: Anorexia, nausea, or vomiting, epigastric pain, cramps, or general discomfort usually self-limiting, with complete regeneration of the gastric mucosa in a day or two. In persons with severe or prolonged vomiting, there is a danger of dehydration, electrolyte loss, and metabolic acidosis, all of which require treatment. Certain infections may require treatment with antimicrobial drugs. SEAMEO TROPMED Philippines COLLEGE OF PUBLIC HEALTH Regional Centre for Public Health, Hospital Administration, University of the Philippines Manila Environmental and Occupational Health 76 Gastroesophageal Reflux Disease (GERD) or Heartburn GERD involves the periodic flow of gastric contents into the esophagus. The severity of GERD depends on the competence of the lower esophageal sphincter (LES) or the relative pressures on either side of the LES. Also called “heartburn” because the refluxed acid causes a painful, burning sensation in the chest. The pain is usually short-lived but may be confused with the pain of an ulcer or a heart attack. Overeating (especially fatty and fried foods), lying down immediately after a meal, consuming too much alcohol or caffeine, smoking, and wearing extremely tight clothing can all cause gastroesophageal reflux. SEAMEO TROPMED Philippines COLLEGE OF PUBLIC HEALTH Regional Centre for Public Health, Hospital Administration, University of the Philippines Manila Environmental and Occupational Health 77 Prevention and Management Medications: Anti H2 Histamine receptors e.g ranitidine or Proton pump inhibitors (PPI) like omeprazole Eliminating factors that reduce LES pressure, such as caffeine, fatty foods, alcohol intake, cigarette smoking, and certain drugs, may relieve the discomfort. Avoidance of spicy foods and use of medication may reduce reflux and inflammation. Patient education SEAMEO TROPMED Philippines COLLEGE OF PUBLIC HEALTH Regional Centre for Public Health, Hospital Administration, University of the Philippines Manila Environmental and Occupational Health 78 References Seely, R., Vanputte, C., Regan, J., Russo, A. Seely’s Anatomy and Physiology, 10th ed. Gould, B., Dyer, R. Pathophysiology for the Health Professions, 4th ed. SEAMEO TROPMED Philippines COLLEGE OF PUBLIC HEALTH Regional Centre for Public Health, Hospital Administration, University of the Philippines Manila Environmental and Occupational Health 79