Digestive System Disorders Study Notes

Chapter 17: Digestive System Disorders

Structures and Their Functions

• Upper Gastrointestinal Tract
• Liver
• Pancreas
• Lower Gastrointestinal Tract

Functions of the Digestive System

• Processes ingested food and fluids: Breaks them down into their units, controlled by enzymes.
• Absorbs necessary components: Utilizes membrane transport mechanisms; mainly occurs in the small intestine.

Anatomy of the Digestive System

• Structures Involved:
  • Hard palate
  • Mouth
  • Tongue
  • Teeth
  • Salivary Glands (Parotid, Submandibular, Sublingual)
  • Esophagus
  • Oropharynx
  • Stomach (Cardiac sphincter, Pyloric sphincter)
  • Duodenum (includes Duodenal papilla)
  • Large Intestine (Ascending colon, Ileocecal valve, Cecum, Appendix, Transverse colon, Descending colon, Sigmoid colon, Rectum, Anus)
  • Liver
  • Gallbladder
  • Common bile duct
  • Pancreas

Functions of Major Digestive Structures

• Mouth: Chews food, mixes with saliva which adds water and digests carbohydrates.
• Esophagus: Responsible for swallowing.
• Stomach: Mixes and dilutes chyme using gastric secretions (digest proteins and add intrinsic factor).
• Small intestine: Bile emulsifies fat, pancreatic and intestinal secretions assist in comprehensive digestion.
• Colon: Absorbs water and electrolytes; forms solid feces.
• Rectum: Stores feces until defecation.

Layers of the Gut Wall

• Mucosa: Includes the epithelium and mucus-producing cells.
• Submucosa: Connective tissue containing blood vessels, nerves, lymphatics, and secretory glands.
• Smooth Muscle Layers: Includes circular and longitudinal smooth muscle layers.
• Serosa: The visceral peritoneum.

Upper Gastrointestinal Tract

Oral Cavity

• Main site for mechanical breakdown (mastication) and chemical digestion (salivary amylase initiates carbohydrate breakdown).
• Formation of bolus.

Pharynx

• Critical for swallowing (deglutition).

Esophagus

• Structure: Closed except during swallowing, upper part consists of skeletal muscle, lower part consists of smooth muscle.
• Swallowing Mechanism:
  • Soft palate rises.
  • Vocal cords approximate.
  • Epiglottis covers the larynx.
  • Respiration ceases momentarily at the swallowing event.
  • Bolus moves into the esophagus.

Stomach

• Description: Expansible muscular sac that acts as a reservoir for food and fluid.
• Muscle Layers: Contains three layers of smooth muscle that churn and mix food.
• Digestive Functions: Initial digestion of proteins via pepsin (produced from the combination of pepsinogen and hydrochloric acid), formation of chyme, absorption of small and lipid-soluble molecules.

Liver

• Functions as the body's metabolic factory, involved in:
  • Receiving nutrient-rich blood via the hepatic portal vein.
  • Storing nutrients and contributing to carbohydrate, protein, and fat metabolism.
  • Producing plasma proteins, clotting factors, and bile.
  • Breaking down old and damaged red blood cells.

Pancreas

• Exocrine Functions: Arranged in lobules, secretes digestive enzymes including:
  • Trypsin
  • Chymotrypsin
  • Carboxypeptidase
  • Ribonuclease
  • Pancreatic Amylase
  • Bicarbonate ions (HCO3-)
• Joins the bile duct to enter the duodenum.

Lower Gastrointestinal Tract

• Small Intestine: Composed of duodenum, jejunum, and ileum.
  • Contains villi and microvilli that increase absorption surface area.
  • Function: Major site for absorption of nutrients and production of digestive enzymes (mucus, enterokinase, peptidases, nucleosidases, lipase, sucrase, maltase, lactase).

Major Digestive Enzymes and Their Actions

Large Intestine

• Functions:
  • Hosts resident normal flora that break down certain materials and produce Vitamin K.
  • Provides fluid and electrolyte reabsorption.
  • Forms solid feces through mass movement.

Neural and Hormonal Controls

Parasympathetic Nervous System (PNS)

• Primarily via the vagus nerve (Cranial Nerve X).
  • Increases motility and secretions.

Sympathetic Nervous System (SNS)

• Activated by stress or anxiety.
  • Decreases gastrointestinal activity; causes vasoconstriction, leading to reduced secretions and epithelial cell regeneration.

Major Hormonal Controls

Digestion and Absorption

• Carbohydrates: Break down in mouth and small intestine.
• Proteins: Initiated in stomach, continued in small intestine.
• Lipids: Emulsified by bile, further broken down by enzymes into monoglycerides and fatty acids.
• Water-soluble vitamins (B and C): Absorb directly; fat-soluble vitamins (A, D, E, K) absorbed with fats.
• Electrolytes: Absorbed via active transport or diffusion.
• Drugs: Mostly absorbed in the intestine.
• Water: Primarily absorbed by osmosis; about 700 mL secreted and 2300 mL ingested daily.

Common Digestive System Disorders

1. Anorexia, Nausea, Vomiting, and Bulimia: Possible signs of digestive disorders or other systemic conditions.

   • Can lead to dehydration and malnutrition.
   • Vomiting (Emesis): Involves the vomiting center in the medulla, which coordinates the vomiting reflex.
   • Activation triggers physical responses like hypersalivation, closure of the glottis, and abdominal muscle contractions.

2. Diarrhea: Excessive frequency of loose or watery stools, leading to dehydration and electrolyte imbalances.

   • Types of Diarrhea:
     • Large-volume: Due to secretory mechanisms.
     • Small-volume: Often related to inflammatory conditions.
     • Steatorrhea: Indicates malabsorption syndromes.

3. Constipation: Insufficient frequency of bowel movements leading to hard stools.

   • Causes include inadequate fluid/fiber intake, immobility, medications, and obstructions.

4. Fluid and Electrolyte Imbalances: Often due to vomiting and diarrhea; can lead to metabolic acidosis or alkalosis.

5. Pain: Can be classified as visceral, somatic, or referred.

   • Visceral pain: Dull, poorly localized; caused by distention or contraction of hollow organs.
   • Somatic pain: Sharp and localized; linked to inflammation of peritoneal lining.
   • Referred pain: Perceived at a distant site due to nerve convergence.

Diagnostic and Therapeutic Interventions

Basic Diagnostic Tests

• Radiography: Use of contrast mediums.
• Ultrasound: Detects unusual masses.
• Computed Tomography (CT) & MRI: Can show liver and pancreatic conditions.
• Endoscopy: Allows for biopsy.
• Laboratory Analysis: Investigation of stool specimens; blood tests for liver, pancreatic functions.

Common Therapies and Prevention

• Dietary Modifications: Gluten-free diets for celiac disease; restrictions on alcohol, increased fiber intake.
• Stress Reduction: Important for recovery and immune function.
• Medications: Includes antacids, antiemetics, laxatives, antidiarrheals, and specific treatments like sulfasalazine or antibiotics for infections.

Liver and Pancreatic Disorders

Common Liver Conditions

1. Hepatitis: Inflammation caused by several virus types.
2. Cirrhosis: Progressive destruction of liver tissue, leading to functional loss.
3. Liver Cancer: Hepatocellular carcinoma is the most common primary tumor; diagnosed often at advanced stages.

Pancreatic Disorders

1. Acute Pancreatitis: Medical emergency; inflammation results from autodigestion of pancreatic tissue.
2. Pancreatic Cancer: High mortality rate, usually diagnosed late due to vague initial symptoms.

Disorders of the Lower Gastrointestinal Tract

• Celiac Disease: Malabsorption syndrome affecting mostly children.
• Chronic Inflammatory Bowel Disease: Includes Crohn’s Disease and Ulcerative Colitis.
• Irritable Bowel Syndrome: Characterized by varying symptoms of diarrhea and constipation.
• Appendicitis: Inflammation of the appendix; can lead to peritonitis when ruptured.
• Diverticular Disease: Development of diverticula in the colon; can become inflamed leading to diverticulitis.
• Colorectal Cancer: Most often develops from adenomatous polyps, with an emphasis on early diagnosis.
• Intestinal Obstruction: Can be mechanical or functional; leads to accumulation and potential necrosis.
• Peritonitis: Inflammation of the peritoneal cavity due to chemical or bacterial causes, often requiring surgical intervention.