Gastrointestinal System Anatomy and Physiology PDF

Gastrointestinal System Anatomy and Physiology Karen Gil MD, MHSN Gastrointestinal System GI tract Continue multilayered tube Extend from the mouth to the anus Covered by peritoneum 25 cm. long Digestive tract is divided in 1. GI organs Mouth Pharynx Esophagus Stomach Small intestine Large intestine...

Gastrointestinal System Anatomy and Physiology Karen Gil MD, MHSN Gastrointestinal System GI tract Continue multilayered tube Extend from the mouth to the anus Covered by peritoneum 25 cm. long Digestive tract is divided in 1. GI organs Mouth Pharynx Esophagus Stomach Small intestine Large intestine 2. GI acccesory organs Teeth Tongue Salivary glands liver Gallbladder Pancreas Digestive System Six basic functions of the digestive tract 1. Ingests food and liquids 2. Secretes water, acid buffers and enzymes into the lumen 3. Mixing and propulsion of food and secretions through the GI tract Digestive System 4. Digestion: Mechanical digestion to break up and churn food Chemical digestion were large nutrients are enzymatically broken down to smaller molecules 5. Absorption of digestive products into the blood and lymph 6. Defecation of indigestible substances and wastes as feces Histology Layers of the GI tract Mucosa Submucosa Muscularis Serosa Mucosa Mucous membrane Three layers Epithelium that contains mucus-secreting cells and endocrine cells Lamina propria made of areolar connective tissue (blood vessels, lymphatics, MALT) Muscularis Mucosae, thin layer of smooth muscle Nonkeratinized stratified squamous epithelium – mouth, pharynx, esophagus and anal canal (protective function) Simple columnar epithelium- stomach and intestines (secretion and absorption functions), renewal every 5 to 7 days Submucosa Composed of areolar connective tissue Contains blood and lymphatic vessels and submucosa plexus (Plexus of Meissner) Muscularis Composed of smooth muscle and Myenteric plexus (Plexus of Auerbach) The mouth, phaynx and superior and middle parts of the esophagus contains skeletal muscle (voluntary swallowing) and the external anal sphincter (voluntary control on defecation) Smooth muscle help in break down food, mix and propulsion Characteristics of smooth muscle Main layer of the GI tube extending from the esophagus to the anus 1. Longitudinal layer (outer sheet) 2. Circular layer (inner sheet) Serosa Superficial layer suspended in the abdominopelvic cavity Serous membrane composed of areolar connective tissues and simple squamous epithelium Inferior to the diaphragm is called peritoneum Peritoneum visceral covers some organs parietal lines the abdominal wall Retroperitoneal area Peritoneal cavity Peritoneum folds: 1. Greater omentum (drapes over small intestine and transverse colon) 2. Falciform ligament (attaches the liver to the abdominal wall) 3. Lesser omentum (suspends the stomach and duodenum from the liver) 4. Mesentery (binds the small intestine to the posterior abdominal wall) 5. Mesocolon ( binds the large intestine to the posterior abdominal wall) Enteric nervous system Sympathetic Parasympathetic Stimulates enteric neurons activity to increase GI secretion and motility (Auerbach’s) (Meissner’s) Myenteric Plexus control GI motility Submucosal plexus control secretions Myenteric Plexus (Auerbach’s) Localized between the longitudinal and circular layers – Increase tone – Increase rhythmic contractions – Increase the rate of contraction – Increase velocity of contractions Submucosal Plexus (Meisner’s) Localized in submucosa – glandular secretion PERISTALSIS General Concepts Alimentary tract provides Fluids Water & Electrolytes Nutrients Functions Digestion Phases 1. Ingestion Taking food into the mouth 2. Secretion Release of water, acid, buffers, and enzymes into the lumen of the GI tract 3. Mixing and propulsion Churning and propulsion of food through the GI tract Functions 4. Digestion Mechanical and chemical breakdown of food 5. Absorption Passage of digested products from the GI tract into the blood and lymph 6. Defecation The elimination of feces from the GI tract Buccal cavity The mouth chews and lubricates food Start digestion Maneuvers food to the pharynx to swallowing Buccal cavity Mouth Lips Hard and soft palate Extrinsic muscles and intrinsic muscles of the tongue Salivary glands Buccal cavity Mastication Incisors - cutting action Molars - grinding action Incisors 55 lbs vs molars 200 lbs. Salivary glands Daily secretion - 800 – 1500 ml pH= 6.0 – 7.0 Contains 99.5% -water and 0.5% solutes -K+ and HCO3 Major salivary glands (site where most of the saliva is secreted) 1. Parotid -serous secretion 2. Submandibular-serous and mucus 3. Sublingual-mucus Minor glands (mucoid secretion) Buccal Saliva secretion Salivation Controlled by autonomic nervous systems Parasympathetic stimulation (fibers of the facial- VII and glossopharyngeal- IX nerves)promotes continuous secretion of a moderate amount of saliva Sympathetic stimulation dominates during stress, resulting in dryness of the mouth Dehydration – salivary glands stop secreting to conserve water Functions of Saliva Wash away pathogens Wash away food particles Lubrication (food move around easily) Bactericidal action Antibodies (IgA) Mastication Chewing reflex begins mechanical digestion Bolus- rounded softened food mass reflex contraction of Start chemical ingestion mastication muscle breakdown starch into disaccharides by salivary amylase Lingual lipase in saliva start break down triglycerides into fatty acid and diglycerids Bolus ( food) reflex inhibition of mastication muscle Relaxation of jaw Pharynx Pharynx dual role respiration and swallowing Laryngopharynx Larynx Deglutition Swallowing Three stages: 1. Voluntary stage 2. Involuntary pharyngeal stage 3. Involuntary esophageal stage Deglutition https://www.youtube.com/watch?v=wqMCzuIiPaM Voluntary stage Passing the bolus into the oropharynx Pharyngeal stage involuntary Soft palate Pulled upwards closing posterior nares Passing the bolus form the phayrnx to the esophagus Palato pharyngeal folds pulled medially Vocal folds are pulled together Epiglottis swing back over the pharynx Larynx pulls and enlarges the esophagus Esophageal stage (involuntary) Passing the bolus from the esophagus into the stomach Peristalsis: coordinated sequences of contraction and relaxation of the muscularis Esophageal sphincters UES (skeletal muscle) LES (smooth muscle) 1/3 of esophagus posses striated muscle in muscularis controlled by Glosopharyngeal and Vagus nerve Upper esophageal sphincter Esophagus Muscular tube Receives food form the laryngopharynx and passes it into the stomach after crossing the esophageal hiatus (diaphragm) Mucosa – non-keratinized stratified squamous epithelium, lamina propria and superior skeletal muscle that changes to smooth muscle inferiorly Esophageal secretion Mainly mucoid – lubrication – prevents excoriation – buffer Esophageal Disorders A. Anatomical I- Stenosis Congenital Acquired (most common - progressive dysphagia) Chronic inflammation (Reflux esophagitis) II - Atresia - absence III - Fistula - abnormal communication IV - Webs - overgrowth of epithelial cell forming a diaphragm V - Diverticula (acquired outpouching) VI -Varices Related to cirrhosis (ETOH) Congenital Anomalies of the Esophagus Esophageal atresia abscence Tracheoesophageal fistula (TEF) (abnormal communication) Signs: Polyhydramnios (pregnancy) Swallowing problems Infants aspirate their saliva, can drown on it TEF - saliva or gastric secretion flow directly to the trachea 1 case in 3000-4500 births Related to other defects (vertebral, anorectal, cardiovascular, renal) Tx surgery * II. Esophageal Atresia and Tracheo-esophageal Fistulas ** * * Esophageal Diverticula Sac or pouch arising from a tubular organ Classified by the location in the esophagus (upper, middle, lower) Congenital or acquired Zenker diverticulum Pseudodiverticula Herniation of mucosa and submucosa through muscular walls Esophageal Diverticula Dysphagia Chest pain Regurgitation Halitosis Tx Diverticulectomy Esophageal Varices Dilated tortuous vessels which reflects increased portal venous pressure At least 2/3 of cases associated with alcoholic cirrhosis Rupture is associated with massive hemorrhage 40% death rate in the first episode and 50% recurrence rate within 1 year Mechanical disorders I- Achalasia Primary esophageal motility disorder Failure or relaxation of LES with proximal dilation Absence of esophageal peristalsis 1- Primary (more common) Innervation disorder (CN X) 2- Secondary (infections) Signs and symptoms Dysphagia (most common) Regurgitation Chest pain Heartburn Weight loss Complications: ulceration fibrous thickening SCC (5%) at an early age TX Surgery, Botox Esophageal Hernia Sliding (95%) along the central Axis Present in 1-20% of population of which only 9% will have symptoms - heartburn Ulceration, bleeding and rupture are possible complications Paraesophageal Different segment (along greater curvature) Esophageal Hernia Dx: A barium upper gastrointestinal series When symptoms are due to GERD, treatment: Prevention of reflux of gastric contents Improved esophageal clearance Reduction in acid production Modifying lifestyle factors usually responds well to proton-pump inhibitor (PPI) therapy Omeprazole Pantoprazole Surgical treatment involves removing the hernia sac and closing the abnormally wide esophageal hiatus It is necessary only in the very few patients who have complications of GERD despite aggressive PPI treatment Mallory Weiss Syndrome Longitudinal tear at GE junction after forceful vomit Etiology in 5-10% of upper GI bleeding Usually small amount and self limited (chronic ETOH) Diagnosis: Suspected in pt with upper GI bleeding (hematemesis) and history of vomiting Endoscopy Complications: Ulceration Mediastinitis Treatment: Endoscopic therapy (active bleeding) Acid suppression PPI Esophagitis Injury to the mucosa with inflammation Contributing factors Decrease efficiency of anti-reflux mechanism Sliding hiatal hernia Impaired reparative capacity Most commonly due to reflux Complications: bleeding Strictures perforation predisposition for malignancy Eosinophils infiltrate epithelium with neutrophils indicating a severe porocess Esophagitis Treatment Diet (low acid) Decrease acid relflux PPI Omeparzole Pantoprazole Lanzoprazole Barrett's Esophagus Complication of long-standing GE reflux Microspcopically there is replacement of normal squamous epithelium by metaplastic glandular (intestinal) epithelium or goblet cells (mucous producing) Complications: ulceration strictures increase risk 30 X 40 for adenocarcinoma Adenocarcinoma arising from Barrett’s esophagus Esophageal Carcinoma Squamous cell carcinoma (1-2% of all cancer deaths) More common in males (3:1) Long time of evolution with epithelial dysplasia ending in carcinoma Esophageal Carcinoma Signs and symptoms: Dysphagia (most common); initially for solids, eventually progressing to include liquids Weight loss (second most common) Bleeding Epigastric or retrosternal pain Bone pain with metastatic disease Hoarseness Persistent cough Physical findings include the following: Typically, normal examination results unless the cancer has metastasized Hepatomegaly (from hepatic metastases) Lymphadenopathy in the laterocervical or supraclavicular areas (reflecting metastasis) Tx: Surgery Chemotherapy Radiotherapy