Gastrointestinal Tract (GIT) PDF

THE GASTRO- INTESTINAL TRACT (GIT) BY: EVA F. REYES RMT, MPH  LEARNING OBJECTIVES: 1. Describe the functional anatomy of the GIT 2. Discuss the secretory activities of the GIT 3. Discuss the the motor activity of the GIT 4. Discuss and outline the digestion and absorption of foodst...

THE GASTRO- INTESTINAL TRACT (GIT) BY: EVA F. REYES RMT, MPH  LEARNING OBJECTIVES: 1. Describe the functional anatomy of the GIT 2. Discuss the secretory activities of the GIT 3. Discuss the the motor activity of the GIT 4. Discuss and outline the digestion and absorption of foodstuffs 5. Explain the accessory organs involved in digestion 6. Know and understand the pathophysiology of GIT disorders  The Gastrointestinal Tract or the Alimentary Tract or Gut: Provides body with continual supply of water, electrolytes and nutrients.  FUNCTIONS OF GIT 1. Ingestion of food 2. Digestion of food 3. Secretion of digestive juice 4. Absorption of water, salt, vitamins and end-products of food digestion 5. Excretion of heavy metals, toxins, alkaloids, etc. 6. Helps erythropoiesis by secreting intrinsic factor needed for vit. B12 absorption.  PHASES 1. Movement of food through alimentary tract. 2. Secretion of digestive juices. 3. Absorption of the digestive foods, water and various electrolytes. 4. Circulation of blood through GI organs to carry absorbed substances. 5. Control of functions by nervous and humoral system. THE LAYERS OF INTESTINAL WALL 1. Serosa ; 2. Longitudinal muscle layer; 3. Circular muscle layer; 4. Submucosa; 5. Mucosa The GIT has intrinsic nervous system of its own called the Enteric Nervous System It begins in the esophagus and extends all the way to anus. This enteric nervous system is composed of two layers of neurons and connection fibers: 1. Myenteric or Auerbach’s Plexus (outer) 2. Meissners’ Plexus or submucosal layer (inner)  MYENTERIC OR AUERBACH’S PLEXUS (OUTER) Lies between the longitudinal and circular muscle layer Controls GIT movements The principal effects of myenteric stimulation 1. Increase tonic contraction or tone of the gut wall 2. Increase intensity of the rhythmic contractions 3. Increase velocity of conduction of excitatory waves along the gut wall MEISSNERS’ PLEXUS OR SUBMUCOSAL LAYER (INNER) Lies in the submucosa Controls secretion and blood flow The GIT also receives extensive Parasympathetic and sympathetic innervation which is capable of altering the specific parts of it. 1. Parasympathetic supply to the gut is divided into: Cranial ( 110th) Vagus nerve Sacral ( 2nd, 3rd, 4th spinal pelvic nerves) Execute defecation reflexes and provide extensive innervation to the esophagus, stomach, pancreas and the first half of the large intestine. Stimulation of these nerves causes general increase activity of the entire enteric nervous system 2. The sympathetic fibers originate in the spinal cord ( between T-5 and L2) ; inhibits GIT activity ELECTRICAL ACTIVITY OF GIT SMOOTH MUSCLE 1. Slow Waves or Basic Electrical Rhythm (BER) Caused by - Slow undulation of activity of Na-K pump Frequency: side to side a. 3/min in body of stomach b. 12/min in duodenum c. 8-9/min in terminal ileum 2. Spike potentials these are true action potentials that occur when resting membrane potential of GIT smooth muscle rises above -40 mV Caused by opening of slow Ca-Na channel Functions: Ca++ ions that enter GIT smooth muscle fiber during spike potential cause GIT smooth muscle to contract (peristalsis)  FUNCTIONAL TYPES OF MOVEMENT OF THE GIT 1. Mixing movements GIT will mix its contents at all times. Caused by either peristaltic contractions or local constrictive contractions of the gut wall 2. Propulsive movement Causes food to move forward along the tract 3. Peristalsis - basic propulsive movement of GIT. Brought about by the stimulation of myenteric plexus Irritation Extrinsic nervous signals  FUNCTIONAL TYPES OF MOVEMENT OF THE GIT Occurs in: 1. GIT 2. Bile ducts 3. Other glandular ducts through out the body 4. Smooth muscle tubes of the body Stimulus: distension of the gut (wall contracts 2-3 cm)  LAW OF THE GUT I. INGESTION OF FOOD The amount of food a person ingests is determined by the intrinsic desire for food called HUNGER. The type of food that a person preferentially seek is determined by APPETITE. MOUTH As food enters the mouth, it is mixed with saliva which contains ptyalin w/c contains amylase (digest starches)  SECRETION OF SALIVA The principal glands of salivation are the PAROTID, SUB MADIBULAR, and the SUB- LINGUAL GLANDS, in addition there are small BUCCAL GLANDS. Saliva contains two major types of protein secretions: 1. Serous Secretion containing PTYALIN (an alpha amylase), the enzyme for digesting starches. 2. Mucous Secretion containing MUCIN for lubricating purpose.  SECRETION OF SALIVA The parotid glands secrete entirely the serous type of secretion while the submandibular and the sublingual glands secrete both the serous and mucus. The saliva contains large quantities of potassium and bicarbonate ions and less of sodium and chloride ions.  FUNCTIONS OF SALIVA 1. Mechanical Functions a. Keeps mouth moist and helps speech b. Helps mastication of food c. Prevents injury to mucous membrane 2. Digestive Functions: Ptyalin splits up starch into maltose 3. Excretory Functions: Excretes urea, heavy metals, thiocyanate, drugs and alkaloids, ethyl alcohol, virulent micro-organisms. 4. Oral Hygiene: Saliva keeps oral hygiene by: a. Flow of saliva washes away pathogenic bacteria and food particles (metabolites for pathogens) b. Thiocyanate and proteolytic enzymes (eg. lysozyme) have bactericidal properties. 5. Helps in secretion of taste 6. Helps water balance by thirst mechanism II. MASTICATION OR CHEWING Used in chewing: 1. Posterior Teeth (molars) – grinding 2. Anterior Teeth (incisors) – cutting 3. Jaw Muscles – close the teeth with force of 55 pounds Chewing reflex initiates the rebound contraction III. SWALLOWING OR DEGLUTTITION Can be subdivided into: a. Voluntary Stage – initiates swallowing process b. Pharyngeal Stage – Involuntary and goes all the way into the esophagus Pharynx: is subdivided into Nasopharynx – part of respiratory passageway Oropharynx – Posterior of oral cavity Laryngopharynx – connected to the esophagus Pharyngoesophageal sphincter: Swallowing (open) = relaxed; Respiration (closed) = contracted c. Esophageal Stage – involuntary phase which promotes passage of food through the pharynx into the stomach Stages of Movements: 1. Primary Peristalsis A propelling mechanism that employs 2. Secondary Peristalsis alternating contraction and relaxation. 3. Gravity (standing) Esophagus (gullet) – carries the bolus to the stomach Upper third: Striated muscles controlled by skeletal muscle impulse Lower two thirds: smooth muscles Gastroesophageal Sphincter – prevents backflow of stomach content into the esophagus Valvelike closure of distal end of the esophagus prevents intense intra-abdominal pressure. (e.g., coughing) Stomach: where the initial breakdown of proteins starts. Physiological Divisions of the stomach: 1) Corpus or Body ( including fundus) 2) Antrum MOTOR FUNCTION OF THE STOMACH 1. Storage of large quantities of food until it can be accommodated in the lower portion of the gastrointestinal tract. (1 hour) 2. Mixing of this food with gastric secretions until it forms a semi fluid mixture called CHYME 3. Slow emptying of the food from the stomach into the small intestine. CHYME - A murky, milky semi-fluid or paste w/c results from the food mixed with stomach secretions. The degree of fluidity of chyme depends on: a. stomach secretions b. amount of food c. degree of digestion MOTOR FUNCTION OF THE STOMACH Mixing and propulsion of food in stomach: 1. Weak Peristaltic Constrictor Waves (Mixing Waves) Move toward antrum once every 20 sec. Controlled by basic electrical rhythm (BER). Begin near midpoint of stomach. Functions: a. cause gastric secretions to mix with stored food. b. provide weak propulsion to move mixed contents into the antrum. 2. Powerful Peristaltic Constrictor Rings. Some of weak peristaltic constrictor waves become extremely intense (powerful peristaltic constrictor rings). Functions: a. force antral contents under high pressure toward pylorus b. Mix stomach contents due to retropulsion of antral contents toward body of stomach from pylorus. Hunger Contractions They are rhythmical peristaltic contractions in the body of the stomach which causes hunger pangs (mild pain in the pit of stomach) Begin: 12-24 hours after last meal. Extreme contractions (last for 2-3 min) most intense in young healthy people and increased in low level of sugar  PHASES OF GASTRIC SECRETION (1500 mL/day) 1. Cephalic Phase Occurs even before food enters the stomach Results from sight, smell, thought or taste of food ↑ appetite = ↑ stimulation 2. Gastric Phase Food in the stomach excites gastric mechanism that causes secretion of gastric juice Associated with eating a meal Last for hours as long as the food is still in the stomach 3. Intestinal Phase Presence of food in the upper portion of the small intestine, particularly in the duodenum, can cause the stomach to secrete small amount of gastric juice.  TYPES OF STOMACH GLANDS 1. Single-cell Mucous Gland Located in: Whole stomach mucosa Secrete: Mucus 2. Oxyntic (Gastric) Glands Located in: Body and fundus, except lesser curvature TYPES OF CELLS AND THEIR SECRETIONS: a. Mucous neck cells: Secrete mucus and some pepsinogen. b. Peptic or chief cells: Secrete pepsinogen. c. Oxyntic or parietal cells: Secrete HCI and intrinsic factor.  ENZYMES IN 3. Pyloric Glands: Located in: Antrum of GASTRIC JUICE stomach Secrete: 1. Pepsinogen: Activated by HCI into a. Mucus for protection of pepsinogen. Has proteolytic activity. pyloric mucosa 2. Gastric Lipase: digest butterfat b. Some pepsinogen 3. Gastric amylase: digestion of c. Gastrin starches (minor) 4. Cardiac Glands: 4. Gelatinase: Liquefies some meat Located in: 1cm immediately products surrounding entry point of 5. Rennin – digest milk proteins(infants) esophagus. Secrete: Mucus for DAILY SECRETION AND pH of protection of gastro- GASTRIC JUICE: esophageal junction. 1. Daily secretion: 1200-1500 ml 2. pH-0.9 - 1.5 SMALL INTESTINES PYLORIC VALVE: Prevents intestinal contents to backflow into the stomach. SMALL INTESTINES: Where most of the chemical and mechanical digestion is carried out Where digestion of proteins into amino acids occur. Average length = 8-10 ft MOVEMENTS OF SMALL INTESTINE 1. Mixing Contractions (Segmentation) When a portion of small intestine becomes distended with chyme, stretch of intestinal wall elicits localized concentric contractions spaced at intervals along intestine, giving a segmented appearance Segmentation contraction" chop" the chyme, and mix it with small intestinal secretions. 2. Propulsive Movement (Peristalsis) Chyme is propelled analward by peristaltic waves caused by; a. Entry of chyme into duodenum b. Gastro-enteric reflex Peristaltic Rush A powerful and rapid peristalsis in the small intestine caused by irritation of the intestinal mucosa (eg. Diarrhea) Initiated by 1. Nervous reflexes involving autonomic nervous system and brain stem. 2. Intrinsic enhancement of the myenteric plexus reflexes within the gut wall. Goal: relieving the small intestine of irritative chyme and excessive distention ENZYME IN SMALL INTESTINAL SECRETIONS Secreted by: Epithelial cells of small intestinal mucosa especially those covering the villi.(absorption) Include: 1. Enterokinase 2. Proteolytic enzymes a. Aminopolypeptidase b. Dipeptides 3. Carbohydrate-splitting enzyme a. Lactase (lactose) = Glucose + Galactose → Glucose b. Sucrase (sucrose) = Glucose + Fructose c. Maltase (maltose) = Glucose d. Alpha-dextrinase = Glucose  ABSORPTION 1. Absorption of Water: by osmosis (Amt. absorbed: 99%) 2. Absorption of Na: Amount absorbed: 25-35 gm/day a. Active transport (lateral membrane) b. Diffusion (brush border) 3. Absorption of Ions: a. Ca = Active transport b. Fe = Active transport c. K,Mg,and PO4 = Active transport 4. Absorption of Glucose: by Na-glucose CO-transport 5. Absorption of Galactose (same as Glucose) 6. Absorption of Fructose (converted to Glucоsе): absorbed by facilitated diffusion 7. Absorption of Proteins a. Amino acids=sodium-amino acid cotransport b. Dipeptides, tripeptides and whole proteins absorbed by pinocytosis STARCHES – Polysaccharide Ptyalin (saliva): 20 - 40% Pancreatic amylase: 50- 80% MALTOSE and 3 to 9 GLUCOSE POLYMERS Disaccharide LACTOSE SUCROSE Sucrase Lactase (intestine) (intestine) GLUCOSE GALACTOSE FRUCTOSE  DIGESTION FATS (Bile + Agitation) Fats Emulsified fat Pancreatic Lipase Fatty acids and Emulsified fat 2 - monoglycerides DIGESTIONS OF PROTIENS Pepsin Proteoses Proteins Peptones Polypeptides Trypsin, Chymotrypsin, Carboxypolypeptidase Polypeptides Peptidases + Amino Acids Amino Acids ILEOCECAL VALVE Prevents backflow of fecal contents from the colon into the small intestine. It can resist reverse pressure of 50-60 cm H20  FUNCTIONS OF THE COLON 1. Absorption of water and electrolytes from the chyme to form solid feces (upper part) 2. Storage of fecal matter until it can be expelled (lower part) Thus, the fecal matter in the large intestine is slowly dug into and rolled over, then, fluid and dissolved substances are absorbed until 80 to 200 ml of feces are expelled each day. 3. Produce vit. K and B vit.  MOVEMENTS OF COLON Movements of the colon is therefore classified into: 1. Mixing movements Haustration 2. Propulsive Movement - Mass Movements characterized by: a. a constrictive ring which occurs at a distented or irritated point in the colon b. forcing fecal matter en masse by mass movement DEFECATION 1. Internal Anal Sphincter (Involuntary) - a circulate mass of smooth muscle that lies inside the anus. 2. External Anal Sphincter (Voluntary) - composed of striated muscles that surround the internal sphincter. Types of Defecation reflex: 1. Intrinsic Defecation Reflex(enteric) 2. Parasympathetic Defecation Reflex  COMPOSITION OF FECES 1.3/4 water 2.1/4 solid 3.30% dead bacteria 4.10-20% fat 5.10-20 % inorganic matter NORMAL HUMAN MICROBIOTA OF 6.2-3% protein THE GI TRACT: 7.30% undigested roughage of the Staphylococcus spp. food Enterococcus Normal brown color: Stercobilin & Enterobacteraciae (ex. Escherichia Urobilin (caused by coli) Enterobacteriaceae) Clostridium spp. Odor: caused by Indole, Skatole & Anaerobic gram-positive cocci Mercaptans Abnormal color of feces: Clay/Pale color - due to obstructive jaundice (biliary obstruction) Green color - due to biliverdin Yellow color - due to bilirubin Black color - due to iron or hemorrhage in upper GIT Red color - due to hemorrhage in lower GIT (hemorrhoids, anal fissures, diverticulosis) ACCESORY ORGANS OF THE DIGESTIVE SYSTEM I. PANCREAS Pancreatic Secretion: The pancreatic digestive enzymes are secreted by the pancreatic acini. They are secreted in response to the presence of chyme in upper portion of small intestine. Pancreatic juices are determined by the types of food in the chyme. Characteristics of Pancreatic Juice Pancreatic secretion contains enzymes for digesting all three major types of food, proteins, carbohydrates and fats. Enzymes of Pancreatic Juice: 1. Proteolytic Enzymes INACTIVE ACTIVE ACTIVATORS Trypsinogen Trypsin Enterokinse Chymotrypsinogen Chymotrypsin Trypsin Procarboxypolypeptidase Carboxypolypeptidase Trypsin DAILY SECRETION AND pH of PANCREATIC SECETION: Daily secretion - 1000 pH = 8.0 1. Carbohydrate – splitting enzyme Pancreatic Amylase(Amylopsin): splits starch into maltose 2. Lipolytic Enzyme a. Pancreatic Lipase(Steapsin): with the aid of bile, it splits fats into monoglycerides, fatty acids and glycerol b. Cholesterol Esterase: necessary in the absorption of cholesterol by promoting esterification of cholesterol and fatty acids with the aid of bile salts c. Phospholipase – splits phospholipids into fats  REGULATION OF PANCREATIC SECRETION 1. Nervous Regulation: during cephalic and gastric phase of stomach secretion, vagal stimulation of pancreas. 2. Hormonal Regulation a. Secretin (secreted in response to acidic chyme) causes pancreas to secrete large quantities of fluid containing high concentration of HCO3. b. Cholecystokinin (secreted in response to fat and peptides in chyme) causes pancreas to secrete large quantities of digestive enzymes and bile c. Gastrin (secreted during gastric phase of stomach secretion) cause secretion of excess pancreatic enzymes. II. GALLBLADDER pear-shaped organ that stores and concentrates bile from the liver. FUNCTIONS OF BILE: 1. Emulsifies fat and helps their absorption by forming micelles 2. Excretes metals, toxins bacteria and bile pigments 3. Bile salts stimulate intestinal peristalsis 4. Neutralizes acidic chyme  BILE Secreted by: Liver Composition: 1. Water 2. Inorganic Salt 3. Bile Salts: has emulsifying or detergent function 4. Bile Pigments: Bilirubin and biliverdin 5. Lipids: cholesterol, lecithin, and traces of fatty acid Daily Secretion: 700 to 1200 ml pH: 7.7 to 8.6 III. LIVER Major role in metabolism Glycogen storage, plasma protein synthesis and drug detoxification Capable of natural regeneration Responsible for protein and fat metabolism  Roles in Carbohydrate Metabolism: 1. Gluconeogenesis (formation of glucose from certain amino acids, lactate, or glycerol) 2. Glycogenolysis (formation of glucose from glycogen) 3. Glycogenesis (formation of glycogen from glucose) Performs several roles in Lipid Metabolism 1. Cholesterol synthesis 2. Production of triglycerides (fats) Breaks down hemoglobin  Produces coagulation factors I (fibrinogen), II (prothrombin), V , VII, IX, X, XI as well as Protein C, Protein S and Antithrombin Converts ammonia to urea Breaks down toxic substances and most medicinal products in a process called drug metabolism. Responsible for immunologic effects in the reticuloendothelial system. The liver contains many immunologically active cells acting as a “sieve” for antigens carried to it via the portal system.  Wrap up: Gastrin ( Pyloric Glands ) Enterochromaffin- like cells ( ECL ) Histamine Hydrochloric Acid (Parietal cell or Oxyntic cells) and intrinsic factor+ mucus Acetylcholine ( Vagus Nerves ) Pepsinogen (Peptic cells or Chief cells) -pepsin Secretin ( S cells of duodenum a nd jejunum ) –bicarbonate Cholecystokinin ( I cells of D. and upper J ) – digestive enzymes in acini of pancreas Proteolytic enzymes ( Trypsinogen etc. ) ; Amylopsin and Lipolytic enzymes ( P. lipase or steapsin etc. ) Gallbladder cont. as dictated by CCK (release of bile ) in the presence of fats in the diet Ampulla of Vater (sphincter of Oddi) Mucus and enter0kinase ( Brunner’s Glands in the D. ) Brush border(microvilli) In the small intestine are pits ( Krypts of Lieberkuhn ) produce replacement cells of villi goblet cells ( mucus ) enterocytes ( water and electrolyte Mucus by large intestine is provided by Krypts of Lieberkuhn witn no villi.  GIT PATHO- PHYSIOLOGY  GIT DISORDERS Paralysis in swallowing mechanism: Causes: 1. Damage to 5th, 9th or 10th cranial nerves 2. Damage of swallowing center as in poliomyelitis or encephalitis. 3. Failure of neuromuscular transmission as in myasthenia gravis. 4. Muscular atrophy 5. Deep anesthesia  EFFECTS: 1. Swallowing cannot occur 2. Failure of glottis to close - food passes into the lungs 3. Failure of soft palate and uvula to close - food passes into the nose a. Achlasia - a condition in which lower esophageal sphincter fails to relax during swallowing, so the food cannot empty into the stomach; caused by: absence of myenteric plexus b. Mega esophagus - a result of achlasia, the esophagus becomes enlarged 1. Gastritis: inflammation of gastric mucosa caused by gastric mucosa damage. 2. Gastric Atrophy: wasting or divination in size of gastric mucosa so that gastric activity is lost. Will result in: Achlorhydria - inability to secrete HCL (pH cannot fall below 6.5) Hypoclorhydria - diminished secretion HCL Pernicious Anemia - loss of intrinsic factor 3. Peptic Ulcer it is an excoriated area of mucous caused by digestive action of gastric juice. Causes a. Excess acid and pepsin secretion b. Abnormal mucus secretion c. Dec. Mucus secretion d. Hereditary e. Alcohol, aspirin f. Psychogenic factors that cause stress anxiety g. Inc. Vagal stimulation h. Inc. Sympathetic stimulation 4. Appendicitis Inflammation of appendix due to infection Symptoms: a. Crampy pain referred to mid-abdomen b. Inhibition of GIT motility c. Acute small intestinal obstruction d. Vomiting 5. Constipation Slow movement of feces with large quantities of dry hard feces due to low fiber diet 6. Hirschprungs Disease(Megacolon) Accumulation of large quantities of feces in the colon,thereby increasing its size(birth defect) 7. Blind Loop Syndrome Caused by overgrowth of bacteria within the lumen of small intestine 8. Hepatitis A viral condition that inflames a person’s liver which causes it to lose its ability to function 9. Cholecystitis Inflammation of the gallbladder 10.Celiac Disease A disorder in which a person’s digestive system is damaged by the response of the immune system to gluten 11.Diverticulitis Inflammation of the diverticula(formation of pouches on the outside of the colon 12.Inflammatory Bowel Disease Chronic inflammation of the intestines 13.Esophageal Atresia The esophagus does not connect to the stomach(newborn) 14.Acute Pancreatitis Due to blockage of pancreatic duct 15.Diarrhea Abnormally frequent evacuation of watery stools due to rapid movements of fecal matter  GIT IRRITATION 1. VOMITING: Reflex loss of upper - gastrointestinal contents through the mouth caused by irritation, over- distention or over- excitability of the upper GIT 2. MOTION SICKNESS: Caused by rapidly changing motions of the body which also results to vomiting 3. NAUSEA: A disagreeable sensation that occurs before vomiting(antiperistalsis) 4. Flatus: Caused by gasses entering the GIT from: swallowed air gasses formed by the result of bacterial action gasses that diffuse from the blood into the GIT  REFERENCE Hall, J. (2016). Guyton and Hall Textbook of Medical Physiology (13th ed). Elsevier STUDY MGA CHONG………