digetsive system pathi

Gastrointestinal Tract

• Mouth

• Esophagus

• Stomach

• Small intestine

• Large intestine

• Rectum

• Anus

Functions of the Gastrointestinal Tract

• 
  

• Ingestion of food

• Propulsion of food and wastes from the mouth to the anus

• Secretion of mucus, water, and enzymes

• Mechanical digestion of food particles

• Chemical digestion of food particles

• Absorption of digested food

• Elimination of waste products by defecation

• Immune and microbial protection against infection

• Layers GI

• 
  

• Mucosa

• Submucosa

• Muscularis

• Serosa or adventitia

• Controlled by local and autonomic nervous system stimuli

  • Enteric (intramural) plexus

Mouth

• Reservoir for mastication (chewing) and mixing of food with saliva

• 32 permanent teeth in adults

• Thousands of taste buds

  • Distinguish salty, sour, bitter, and sweet and savory (umami) tastes

Salivary Glands

• Three pairs

  • Submandibular

  • Sublingual

  • Parotid

• Secrete about 1 L of saliva per day

• Water with mucus, sodium, bicarbonate, chloride, potassium, and salivary alpha-amylase (carbohydrate digestion)

• Controlled by sympathetic and parasympathetic fibers

Swallowing

• Esophagus

• Peristalsis

  • Coordinated sequential contraction and relaxation of outer longitudinal and inner circular layers of muscles

  • Primary and secondary

• Upper esophageal sphincter

  • Keeps air from entering the esophagus during respiration

• Lower esophageal sphincter

  • Prevents regurgitation from the stomach and caustic injury to the esophagus

Swallowing Phases

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• Oropharyngeal (voluntary)

  • Food formed into bolus and forced toward pharynx

  • Pharynx contracts

  • Respiration inhibited and epiglottis slides down

• Esophageal (involuntary)

  • Food bolus enters esophagus

  • Esophagus relaxes

  • Peristalsis occurs to move food down to lower esophageal sphincter

  • Food bolus enters stomach

Stomach

• A hollow, muscular organ just below diaphragm

• Functions

  • Stores food

  • Secretes digestive juices

  • Mixes food with the juices

  • Propels partially digested food (chyme)

Gastric MotilitySwallowing

• 
  

• Causes relaxation

• Facilitated by gastrin and cholecystokinin

Gastric MotilityMotilin

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• Increases peristalsis

Gastric MotilitySecretin

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• Decreases peristalsis

Gastric Motility-gastric mixing and emptying

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• Retropulsion

• Rate dependent on volume, osmotic pressure, and chemical composition

Gastric Secretion

• Stimulation of gastric secretion

  • Eating

  • Gastrin

  • Paracrine pathways

  • Acetylcholine

  • Chemicals

    • Ethanol, coffee, protein

Gastric Secretion phase

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• Cephalic phase

  • Stimulated by the thought, smell, and taste of food

• Gastric phase

  • Stimulated by distention of the stomach

• Intestinal phase

  • Stimulated by histamine and digested protein

• Gastric glands

Gastric Secretion-The stomach secretes large volumes of gastric juices

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• Acid

• Pepsinogen

• Mucus

• Enzymes

• Hormones

• Intrinsic factor

• Gastroferrin

• 
  

Gastric Secretion-acid

• 
  

• Secreted by parietal cells

• Dissolves food fibers, acts as a bactericide against swallowed microorganisms, and converts pepsinogen to pepsin

Gastric Secretion-pepsin

• 
  

• Secreted by chief cells

• Proteolytic enzyme

  • Breaks down protein and forms polypeptides in the stomach

gastric secretion-mucus

• 
  

• Stimulated by prostaglandins

• Mucosal barrier

• Gastric mucosal blood flow

Small Intestine

• 5 to 6 meters long

• Three segments

  • Duodenum

  • Jejunum

  • Ileum

    • Ileocecal valve

Intestinal Digestion and Absorption

• Initiated in stomach

  • Actions of gastric hydrochloric acid and pepsin

• Continues in proximal portion of small intestine

  • Action of pancreatic enzymes, intestinal enzymes, and bile salts

    • Carbohydrate breakdown

    • Proteins degraded

    • Fats emulsified

• Nutrients absorbed by active transport, diffusion, or facilitated diffusion

Intestinal Motility

• The movements of the small intestine facilitate both digestion and absorption

  • Haustral segmentation

  • Peristalsis

• Neural reflexes facilitate motility, digestion, and absorption

  • Ileogastric reflex

  • Intestinointestinal reflex

  • Gastroileal reflex

Large Intestine

• 1.5 meters long

• Cecum

• Vermiform appendix

• Colon

  • Ascending

  • Transverse

  • Descending

  • Sigmoid

• Rectum

• Anal canal

Large Intestine

• Extrinsic parasympathetic innervation occurs through vagus nerve

• Vagal stimulation increases rhythmic contraction of the proximal colon

• Blood supply is derived primarily from branches of the superior and inferior mesenteric arteries

• Colonic movement primarily segmental

  • Fecal mass massaged

  • Water absorbed

  • Peristaltic movements promote the emptying of the colon

  • Gastrocolic reflex

    • Causes the fecal mass to pass rapidly into the sigmoid colon and rectum

  • Defecation reflex

    • Stimulated by the movement of feces into the sigmoid colon and rectum

Immunity and the GI System-Gut-associated lymphoid tissue (GALT)

• 
  

• Major role in immune defenses by killing many microorganisms

• Mucosal secretions produce antibodies (IgA)

• Paneth cells produce defensins and other antibiotic peptides and lysozymes important to mucosal immunity

• Peyer patches (collections of lymphocytes, plasma cells, and macrophages) produce immunoglobulin A as a component of the gut-associated lymph tissue in the small intestine

Intestinal Microbiome

• Numbers of bacteria increase from proximal to distal GI tract

  • Highest in colon

• Multiple factors affect normal composition of bacterial flora

  • Genetics, diet, environmental, drugs

• Alert immune system to protect against infection

Accessory Organs
of Digestion

• Organs

  • Liver

  • Gallbladder

  • Exocrine pancreas

• Secrete substances necessary for digestion

Liver

• Divided into right and left lobes

  • Right lobe further divided into the caudate and quadrate lobes

• Falciform ligament

• Round ligament

• Coronary ligament

• Glisson capsule

• Blood supply

  • Hepatic artery

  • Hepatic portal vein

Secretion of Bile

• Bile is an alkaline, bitter-tasting, yellowish green fluid that contains bile salts, cholesterol, bilirubin, electrolytes, and water

  • 700 to 1200 mL bile secreted per day

• Bile formed by hepatocytes and secreted into the bile canaliculi

• Enterohepatic circulation

  • Recycling of bile salts

Metabolism of Bilirubin

• Bilirubin is a byproduct of the destruction of aged red blood cells

• Bilirubin gives bile a greenish black color and produces the yellow tinge of jaundice

Vascular and Hematologic Liver Functions

• Stores blood

• Hemostatic functions

  • Synthesizes clotting factors

    • Because bile salts are needed for reabsorption of fats, vitamin K absorption depends on adequate bile production in the liver

Liver Functions

• Metabolism of nutrients

  • Carbohydrates

  • Proteins

  • Fats

• Metabolic detoxification

• Storage of minerals and vitamins

Gallbladder

• Saclike organ that lies on the inferior surface of the liver

• Function (of the gallbladder) is to store and concentrate bile between meals

• Holds about 90 mL of bile

• Begins to contract 30 minutes after eating under the influence of the vagus nerve and cholecystokinin

Exocrine Pancreas

• Composed of acinar cells that secrete enzymes and networks of ducts that secrete alkaline fluids to assist in digestion

  • Pancreatic duct (Wirsung duct)

  • Ampulla of Vater

  • Arterial blood is supplied by branches of the celiac and superior mesenteric arteries

  • Venous blood leaves through tributaries to the portal vein and through the splenic vein

Clinical Manifestations of the Gastrointestinal System-anorexia

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• A lack of a desire to eat despite physiologic stimuli that would normally produce hunger

• Associated with nausea, abdominal pain, diarrhea, psychological stress, and weight loss

Vomiting

• (emesis)

  • The forceful emptying of the stomach and intestinal contents through the mouth

  • Several types of stimuli initiate the vomiting reflex

  • The common symptoms of vomiting are hypersalivation and tachycardia

  • Nausea: subjective experience that is associated with a number of conditions

  • Retching: nonproductive vomiting

  • Projectile vomiting: Spontaneous vomiting that does not follow nausea or retching

Constipation

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• Defined as infrequent or difficult defecation

• Primary condition

  • Normal transit (functional)

  • Slow transit

  • Pelvic floor or outlet dysfunction

• Secondary condition

  • Caused by many different factors such as diet, medications, various disorders, aging

Constipation manifestations

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• 
  

• Straining with defecation

• Hard stools

• Sensation of incomplete emptying

• Manual maneuvers to facilitate stool evacuation

• Fewer than three bowel movements per week

• Treatment is managing underlying disease

Diarrhea

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• Presence of loose, watery stools

  • Acute or persistent

• Large-volume diarrhea

  • Caused by excessive amounts of water or secretions or both in the intestines

• Small-volume diarrhea

  • Volume of feces is not increased, usually results from excessive intestinal motility

• 
  

• Major mechanisms of diarrhea

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• 
  

• Osmotic diarrhea

• Secretory diarrhea

• Motility diarrhea

systemic effects diarrhea

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• 
  

• Electrolyte imbalance

• Weight loss

• Associated with malabsorption syndromes

• Treated with fluid restoration, antimotility or water-absorbent medications, treatment of causal factors

Abdominal Pain

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• Mechanical, inflammatory, or ischemic

• Usually associated with tissue injury and inflammation

• Parietal pain

• Visceral pain

• Referred pain

Gastrointestinal Bleeding

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• Upper gastrointestinal bleeding

  • Esophagus, stomach, or duodenum

• Lower gastrointestinal bleeding

  • Jejunum, ileum, colon, or rectum

• Occult bleeding

• Physiologic response depends on rate and amount of blood loss

• Hematochezia: bright red stools

• Melena: black or tarry stools

• Dysphagia

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• Difficulty swallowing

  • Mechanical obstructions

  • Functional disorders

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• Achalasia

• 
  

• 
  

• Related to loss of inhibitory neurons in the myenteric plexus with smooth muscle atrophy in the middle and lower portions of the esophagus

• Dysphagia

  • Manifestations

• 
  

• 
  

• Stabbing pain at the level of obstruction

• Discomfort after swallowing

• Regurgitation of undigested food

• Unpleasant taste sensation

• Vomiting

• Aspiration

• Weight loss

• Symptoms managed by eating small meals slowly, taking fluid with meals, and sleeping with the head elevated to prevent regurgitation and aspiration

• Gastroesophageal reflux disease (GERD)

• 
  

• Reflux of acid and pepsin from the stomach to the esophagus that causes esophagitis

• Resting tone of the LES tends to be lower than normal

• Conditions that increase abdominal pressure or delay gastric emptying can contribute to the development of reflux esophagitis

Manifestations GERD

• 
  

• 
  

• Heartburn

• Acid regurgitation

• Dysphagia

• Chronic cough

• Asthma attacks

• Laryngitis

• Upper abdominal pain within 1 hour of eating

• Proton pump inhibitors are the agents of choice for controlling symptoms and healing esophagitis

• Gastroparesis

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• Delayed gastric emptying in the absence of mechanical gastric outlet obstruction

• Associated with diabetes mellitus, surgical vagotomy, or fundoplication

• Symptoms include nausea, vomiting, abdominal pain, and postprandial fullness or bloating

• Pyloric obstruction

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• The blocking or narrowing of the opening between the stomach and the duodenum

• Can be acquired or congenital

• Manifestations

  • Epigastric pain and fullness

  • Nausea and vomiting

  • Succussion splash

  • With a prolonged obstruction, malnutrition, dehydration, and extreme debilitation

• Usually conservative management

• Intestinal obstruction

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• An intestinal obstruction is any condition that prevents the flow of chyme through the intestinal lumen

• Simple obstruction

  • Mechanical blockage of the lumen

• Functional obstruction (paralytic ileus)

  • Failure of intestinal motility

  • Often occurs after intestinal or abdominal surgery, pancreatitis, or hypokalemia

• 
  

• Signs of small intestinal obstruction

  • Colicky pains

  • Nausea and vomiting

• Signs of large intestine obstruction

  • Hypogastric pain and abdominal distention

Gastritis

• Inflammatory disorder of the gastric mucosa

• Acute gastritis

  • Caused by injury of the protective mucosal barrier

• Chronic gastritis

  • Chronic fundal gastritis (type A, immune)

  • Chronic antral gastritis (type B, nonimmune)

• Symptoms vague

  • Anorexia, fullness, nausea, vomiting, epigastric pain

Peptic Ulcer Disease

• A break or ulceration in the protective mucosal lining

  • Usually in stomach or proximal duodenum

  • Sometimes in esophagus

• Acute and chronic ulcers

• Duodenal ulcers

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• Most common of the peptic ulcers

• Developmental factors:

  • Helicobacter pylori infection

  • Use of NSAIDs

• Characterized by intermittent pain in the epigastric area

  • Relieved rapidly by ingestion of food or antacids

• Management aimed at relieving the causes and effects of hyperacidity and preventing complications

Gastric Ulcer

• Gastric ulcers tend to develop in the antral region of the stomach, adjacent to the acid-secreting mucosa of the body

• Pathophysiology

  • The primary defect is an increased mucosal permeability to hydrogen ions

  • Gastric secretion tends to be normal or less than normal

• Manifestations and treatment similar to duodenal ulcers except food causes pain

Surgical Treatment of Ulcer

• Most common indications are recurrent or uncontrolled bleeding and perforation of the stomach or duodenum

• Objectives are to reduce stimuli for acid secretion, decrease the number of acid-secreting cells in the stomach, and correct complications of ulcer disease

Inflammatory Bowel Disease

• Ulcerative colitis and Crohn disease

  • Chronic, relapsing inflammatory bowel disorders

    • Genetics

    • Environmental factors

    • Alterations of epithelial barrier functions

    • Altered immune reactions to intestinal flora

Ulcerative Colitis

• Chronic inflammatory disease that causes ulceration of the colonic mucosa

  • Sigmoid colon and rectum

  • Begins in the rectum and may extend proximally to the entire colon

  • Intermittent periods of remission and exacerbation

Ulcerative Colitis Manifestations

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• Diarrhea (10 to 20/day)

• Urgency

• Bloody stools

• Cramping

• Treatment is individualized and depends on severity of symptoms and extent of mucosal involvement

Crohn Disease

• Granulomatous colitis, ileocolitis, or regional enteritis

• Idiopathic inflammatory disorder; affects any part of the digestive tract, from mouth to anus

• Causes “skip lesions”

• Can involve any part of the GI tract

• Ulcerations can produce fissures that extend into the lymphatics

• Symptoms similar to ulcerative colitis

• Anemia may result from malabsorption of vitamin B₁₂ and folic acid

• Treatment similar to ulcerative colitis

Irritable Bowel Syndrome

• Disorder of brain-gut interaction characterized by recurrent abdominal pain with altered bowel habits

• More common in males

• Associated with anxiety, depression, and reduced quality of life

Irritable Bowel Syndrome PresentationPresentations

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• Visceral hypersensitivity or hyperalgesia

• Abnormal intestinal permeability, motility, and secretion

• Postinflammatory (infectious or noninfectious)

• Alteration in gut microbiota (dysbiosis)

• Food allergy/intolerance

• Psychosocial factors

Irritable Bowel Syndrome Manifestations

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• Lower abdominal pain or discomfort and bloating

• Can be grouped

  • Diarrhea-predominant

  • Constipation-predominant

  • Alternating diarrhea/constipation

• Symptoms are usually relieved with defecation and do not interfere with sleep

• No cure, and treatment is individualized

• Diverticula

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• Herniations of mucosa through the muscle layers of the colon wall, especially the sigmoid colon

• Diverticulosis

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• Asymptomatic diverticular disease

• Diverticulitis

• 
  

• The inflammatory stage of diverticulosis

Diverticular Disease
of the Colon

• Diverticula can occur anywhere in the gastrointestinal tract, particularly at weak points in the colon wall

• Complicated diverticulitis includes abscess, fistula, obstruction, bleeding, or perforation

• Symptoms of uncomplicated diverticular disease may be vague or absent

Appendicitis

• Inflammation of the vermiform appendix

• Possible causes:

  • Obstruction, foreign bodies, infection

• Epigastric or periumbilical pain

  • Rebound tenderness to RLQ

• Perforation, peritonitis, and abscess formation are the most serious complications

• Treatment is antibiotics and appendectomy

Complications of
Liver Disorders: Ascites

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• Accumulation of fluid in the peritoneal cavity

• Most common cause is cirrhosis

• Development associated with

  • Portal hypertension

  • Decreased synthesis of albumin by the liver

  • Splanchnic vasodilation

  • Renal sodium and water retention

• 25% mortality in 1 year if associated with cirrhosis

• Causes abdominal distention and increased abdominal girth and weight gain

• Paracentesis

Complications of
Liver Disorders: Hepatic Encephalopathy

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• A neurologic syndrome of impaired behavioral, cognitive, and motor function

• The condition develops rapidly during fulminant hepatitis or slowly during course of liver disease

• Cells in the nervous system are vulnerable to neurotoxins absorbed from the GI tract that, because of liver dysfunction, circulate to the brain

• Early symptoms

  • Subtle changes in personality, memory loss, irritability, disinhibition, lethargy, and sleep disturbances

• Later symptoms

  • Confusion, disorientation to time and space, flapping tremor of the hands (asterixis), slow speech, bradykinesia, stupor, convulsions, and coma

Complications of
Liver Disorders: Jaundice

• 
  

• Caused by hyperbilirubinemia

• Obstructive jaundice

  • Extrahepatic obstruction

  • Intrahepatic obstruction

• Hemolytic jaundice

  • Prehepatic jaundice

  • Excessive hemolysis of red blood cells

• Characterized by dark urine, yellow discoloration of sclera and skin, and light-colored stools

Disorders of the Liver: Acute Liver Failure

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• Rare clinical syndrome resulting in severe impairment or necrosis of liver cells without preexisting liver disease or cirrhosis

• Acetaminophen overdose is leading cause in the United States

Disorders of the Liver: Cirrhosis

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• Irreversible inflammatory, fibrotic liver disease

• Biliary channels become obstructed and cause portal hypertension

• Severity and rate of progression depend on the cause

• Many causes

Disorders of the Liver: Alcoholic Liver Disease

• 
  

• Related to toxic effects of alcohol and coexisting liver disease

  • Alcoholic fatty liver

  • Alcoholic steatohepatitis

  • Alcoholic cirrhosis

• Anorexia, nausea, jaundice, and edema develop with advanced fatty infiltration or the onset of alcoholic steatohepatitis

Disorders of the Liver: Hepatitis

• 
  

• Systemic viral disease that primarily affects the liver

• 5 types (A, B, C, D, and E)

• Can cause acute, icteric illness

  • B and C are most common causes

• Spectrum of manifestations ranges from absence of symptoms to fulminating hepatitis, with rapid onset of liver failure and coma

Disorders of the
Gallbladder: Gallstones

• 
  

• Formation called cholelithiasis

• Risks

  • Obesity

  • Middle age

  • Female

  • Oral contraceptive use

  • Rapid weight loss

  • Native American ancestry

  • Genetic predisposition

  • Gallbladder, pancreas, or ileal disease

• 
  

• Often asymptomatic or vague

• Epigastric and right hypochondrium pain

• Intolerance to fatty foods

• Gallstones

• 
  

• Formed from impaired metabolism of cholesterol, bilirubin, and bile acids

• Type depends on chemical composition

  • Cholesterol

    • Formed from bile that is supersaturated with cholesterol produced by the liver

  • Pigmented brown

    • Formed from calcium bilirubinate and fatty acid soaps that bind with calcium

  • Black

    • Composed of calcium bilirubinate with mucin glycoproteins

    • Associated with chronic liver disease and hemolytic disease

Disorders of the
Gallbladder: Cholecystitis

• 
  

• Inflammation of gallbladder or cystic duct

• Almost always caused by a gallstone lodged in the cystic duct

• Pain is similar to that caused by gallstones

• Fever, leukocytosis, rebound tenderness, and abdominal muscle guarding are common findings

Disorders of the
Pancreas: Pancreatitis

• 
  

• Inflammation of the pancreas

• Develops because of obstruction to the outflow of pancreatic digestive enzymes caused by bile and pancreatic duct obstruction

• Acute or Chronic pancreatitis

Celiac Disease

• Autoimmune disease that damages small intestinal villous epithelium when gluten is ingested

  • Gluten is the protein component in cereal grains (wheat, rye, barley, malt)

• The disease appears to be caused by dietary, genetic, and immunologic factors

Celiac Disease manifestations

• Onset of manifestations depends on the age of the infant when gluten-containing substances are added to the diet

  • Severity of symptoms varies tremendously

• Celiac crisis

• Diagnosis confirmed with serologic autoantibody measurement

• Gluten-free diet for life

Necrotizing Enterocolitis

• Ischemic, inflammatory condition that causes bowel necrosis and perforation

• Most common severe neonatal gastrointestinal emergency

• Primarily affects smallest and most premature infants

• Etiology unclear

Necrotizing Enterocolitis contributing factors

• 
  

• Infections

• Abnormal bacterial colonization

• Intestinal ischemia

• Immature immunity

• Exaggerated inflammatory responses

• Immature intestinal motility

• Altered microcirculatory blood flow and barrier function

• Perinatal stress

• Effects of medications and feeding practices

• Genetic predisposition

Necrotizing Enterocolitis Manifestations

• 
  

• Mild abdominal distention to bowel perforation

• Bloody stools and septicemia

• Evaluation and treatment

  • Clinical manifestations, laboratory results, and plain films of abdomen

  • Cessation of feeding, gastric suction, antibiotics, and surgery

Neonatal Jaundice

• Yellow pigmentation of the skin caused by an increased level of bilirubin in the bloodstream

• Usually becomes clinically apparent when the serum bilirubin concentration is greater than 2 mg/dL

• Physiologic jaundice

  • Common in healthy newborns

  • Caused by lack of maturity of bilirubin uptake and conjugation

  • Associated with hemolytic disease, metabolic and endocrine disorders, liver abnormalities, infections

• Pathologic jaundice

  • 
    

  • Associated with severe illness

  • Risk factors include fetal-maternal blood type incompatibility, premature birth, exclusive breast feeding, maternal age >25 years, male gender, delayed meconium passage, glucose-6-phosphate dehydrogenase deficiency, and excessive birth trauma