Pathophysiology: Chapter Thirty Seven - Part I

Gastrointestinal (GI) system

System that digests food and absorbs nutrients.

GI motility

Movement of contents through the gastrointestinal tract.

GI secretion

Release of substances into the GI tract that support digestion.

Digestion

Breakdown of food into substances that can be absorbed.

Absorption

Movement of nutrients across the intestinal wall into the bloodstream or lymph.

Large intestine

GI segment that prepares waste for elimination.

Upper GI tract

Mouth, esophagus, and stomach; intake and initial digestive processes occur here.

Middle GI tract

Duodenum, jejunum, and ileum; most digestion and absorption occur here.

Lower GI tract

Cecum, colon, and rectum.

Anorexia

Loss or decrease of appetite; may be caused by emotional stress, medications, or illness.

Anorexia nervosa

Eating disorder characterized by fear of gaining weight; different from anorexia as loss of appetite.

Nausea

Unpleasant, conscious sensation of the urge to vomit.

Medullary vomiting center

Brain center whose stimulation produces nausea and participates in vomiting.

Retching

Rhythmic, spasmodic contractions of the diaphragm, chest, and abdominal muscles; usually precedes or alternates with vomiting.

Vomiting (emesis)

Sudden, forceful expulsion of stomach contents through the mouth.

Vomitus

The stomach contents expelled during vomiting.

Vomiting reflex

Sequence involving deep inspiration, airway/glottis closure, gastroesophageal sphincter relaxation, forceful diaphragm and abdominal muscle contraction, and expulsion of stomach contents.

Diarrhea

Excessive frequency of stools; may be acute or chronic.

Large-volume diarrhea

Watery stool associated with increased intestinal secretions or reduced reabsorption; may be secretory or osmotic.

Secretory diarrhea

Large-volume watery diarrhea caused by increased secretion into the intestine; often related to infection.

Osmotic diarrhea

Large-volume watery diarrhea associated with limited reabsorption due to reversal of normal sodium and/or glucose carriers.

Small-volume diarrhea

Diarrhea often associated with inflammatory bowel disease; stool may contain blood, mucus, or pus and may be accompanied by cramps.

Complications of prolonged diarrhea

Dehydration, electrolyte imbalance, acidosis, and malnutrition.

Constipation

Less frequent bowel movements than normal.

Peristalsis

Wave-like intestinal contractions that move contents through the GI tract.

Mechanism of constipation

Decreased intestinal peristalsis causes prolonged transit time and increased water reabsorption from stool.

Causes of constipation

Weak smooth muscle due to age or illness, inadequate dietary fiber or fluids, neurologic disorders, drugs, and obstruction from tumors or strictures.

Hematochezia

Frank, red blood in the stool; usually from lesions in the sigmoid colon or rectum.

Occult blood

Small, hidden amounts of blood in stool that are detectable with a stool test; may result from small bleeding ulcers.

Melena

Dark, tarry stool that may result from significant bleeding in the upper digestive tract.

Esophagus

Fibromuscular tube connecting the lower pharynx to the stomach; approximately 8–10 inches long in adults.

Esophageal location

Lies posterior to the larynx and trachea, descends through the mediastinum between the lungs, and passes through the diaphragm around T11–T12.

Esophageal peristalsis

Involuntary, wave-like muscle contractions that propel contents downward toward the stomach.

Upper third of esophagus

Contains skeletal muscle fibers innervated by the glossopharyngeal (CN IX) and vagus (CN X) nerves.

Lower two-thirds of esophagus

Contains smooth muscle fibers innervated by the vagus (CN X) nerve.

Upper esophageal sphincter (UES)

Sphincter at the upper end of the esophagus; both esophageal sphincters remain closed except during swallowing.

Lower esophageal sphincter (LES)

Sphincter at the lower end of the esophagus; both esophageal sphincters remain closed except during swallowing.

Mastication

Chewing; saliva contains enzymes that break down complex molecules.

Deglutition

The process of swallowing.

Buccal phase of swallowing

Tongue pushes food or drink upward and backward into the pharynx.

Pharyngeal phase of swallowing

Epiglottis closes the entrance to the larynx and the upper esophageal sphincter relaxes, allowing food or drink into the esophagus.

Esophageal phase of swallowing

Food or drink moves downward through the esophagus into the stomach.

Dysphagia

Difficulty swallowing.

Xerostomia

Reduced salivary secretions; may occur with aging, dehydration, or poorly controlled diabetes and can contribute to dysphagia.

Esophageal narrowing

Narrowing that may result from scar tissue after chronic acid reflux or radiation therapy; can cause dysphagia.

Odynophagia

Painful swallowing.

Achalasia

Disorder in which the lower esophageal sphincter fails to relax.

Cause of achalasia

Damage to the enteric nervous system and vagus nerve.

Effects of achalasia

Food cannot enter the stomach normally, enlarges the esophagus above the LES, and remains in the esophagus for prolonged periods.

Achalasia complications

Retained food can cause regurgitation, aspiration into the lungs, and pneumonia.

Achalasia diagnosis

Early diagnosis may use endoscopy and barium studies.

Hiatal hernia

Part of the stomach protrudes through the esophageal hiatus of the diaphragm into the chest cavity.

Cause of hiatal hernia

The opening in the diaphragm becomes enlarged or weakened.

Sliding hiatal hernia

The gastroesophageal junction and upper part of the stomach slide above the diaphragm.

Paraesophageal hiatal hernia

Part of the stomach pushes through the esophageal opening while the gastroesophageal junction remains in its normal position; less common but has a higher risk of serious complications.

Gastroesophageal reflux disease (GERD)

Abnormal reflux of gastric contents into the esophagus and sometimes the oral cavity.

GERD mechanism: LES dysfunction

A weak or incompetent lower esophageal sphincter allows gastric contents to reflux into the esophagus.

GERD mechanism: delayed gastric emptying

Delayed emptying increases gastric pressure and volume, promoting reflux.

GERD mechanism: acid irritation

Refluxed gastric acid irritates the esophageal lining.

GERD diagnostic frequency in slides

Symptoms occurring more than twice per week for several weeks.

Heartburn

Burning sensation behind the sternum; a specific symptom of GERD.

Regurgitation

Backflow of gastric contents into the mouth or throat.

GERD symptom timing and triggers

Symptoms commonly occur 30–60 minutes after meals and worsen with bending forward or lying down.

GERD symptom relief

Symptoms may be relieved by sitting or standing upright.

Additional GERD manifestations

Belching and chest pain.

Barrett esophagus

Replacement of normal esophageal squamous epithelium with abnormal columnar epithelium; listed as a complication of GERD.

What are the four processes that work together in gastrointestinal function?

Motility, secretion, digestion, and absorption.

What is the overall function of the GI system?

To digest food and absorb nutrients.

Where do absorbed nutrients go after crossing the intestinal wall?

Into the bloodstream or lymph.

What is the role of the large intestine?

It prepares waste for elimination.

Which organs make up the upper GI tract, and what occurs there?

Mouth, esophagus, and stomach; intake and initial digestive processes occur there.

Which organs make up the middle GI tract, and what occurs there?

Duodenum, jejunum, and ileum; most digestion and absorption occur there.

Which structures make up the lower GI segment in the slides?

Cecum, colon, and rectum.

What is anorexia?

Loss or decrease of appetite.

What can cause anorexia?

Emotional stress, medications, and illnesses.

How is anorexia different from anorexia nervosa?

Anorexia is loss or decrease of appetite; anorexia nervosa is an eating disorder characterized by fear of gaining weight.

What is nausea, and what causes it according to the slides?

An unpleasant conscious urge to vomit resulting from stimulation of the medullary vomiting center.

What are common causes of nausea listed in the presentation?

Motion sickness, dizziness, migraine headaches, gastroenteritis, food poisoning, and severe pain.

What is retching?

Rhythmic, spasmodic contraction of the diaphragm, chest, and abdominal muscles.

How is retching related to vomiting?

It usually precedes or alternates with vomiting.

What is vomiting (emesis)?

Sudden, forceful expulsion of stomach contents through the mouth.

What is vomitus?

The stomach contents expelled during vomiting.

What protective function does vomiting serve?

It removes harmful substances from the stomach and upper small intestine.

What are the steps of the vomiting reflex?

Deep inspiration; glottis closes; gastroesophageal sphincter relaxes; diaphragm and abdominal muscles contract forcefully; stomach contents are expelled; breathing temporarily stops.

What happens to the airway during the vomiting reflex?

The glottis closes to protect the airway.

What happens to the gastroesophageal sphincter during vomiting?

It relaxes.

What happens to breathing during vomiting?

Breathing temporarily stops during the reflex.

How can prolonged diarrhea affect the body?

It can cause dehydration, electrolyte imbalance, acidosis, and malnutrition.

What is large-volume diarrhea, and what mechanisms can cause it?

Watery stool resulting from increased intestinal secretions or limited reabsorption; it may be secretory or osmotic.

What is secretory diarrhea associated with in the presentation?

Increased secretions into the intestine from plasma; it is often related to infection.

What is osmotic diarrhea associated with in the presentation?

Limited reabsorption due to reversal of normal carriers for sodium and/or glucose.

How does small-volume diarrhea differ from large-volume diarrhea in the slides?

Small-volume diarrhea is often due to inflammatory bowel disease and may contain blood, mucus, or pus with abdominal cramps.

What condition is commonly associated with small-volume diarrhea?

Inflammatory bowel disease.

What is constipation?

Less frequent bowel movements than normal.

What is the pathophysiologic mechanism of constipation?

Decreased intestinal peristalsis prolongs transit time, allowing increased water reabsorption from stool.

What are common causes of constipation?

Weak smooth muscle due to age or illness, inadequate fiber, inadequate fluids, neurologic disorders, drugs, and obstruction from tumors or strictures.

How can decreased peristalsis lead to hard stool?

It prolongs intestinal transit time, allowing more water to be reabsorbed from the stool.

What is hematochezia?

Frank red blood in the stool, usually from lesions in the sigmoid colon or rectum.

What is occult blood in stool?

Small hidden amounts of blood detectable with a stool test; it may be caused by small bleeding ulcers.

What is melena, and what can cause it?

Dark, tarry stool that may result from significant bleeding in the upper digestive tract.