Gastrointestinal System (GI): Comprehensive Study Guide

Key Terms and Definitions

1. Digestive Tract: A 30-ft long system responsible for breaking down food, absorbing nutrients, and expelling waste.

   • Mouth: Site where digestion begins with enzymes like amylase for carbohydrates.

   • Stomach: Acidic environment (pH ~1-2) for breaking down proteins.

   • Small Intestine: Absorbs nutrients, facilitated by villi and enzymes.

   • Large Intestine: Reabsorbs water and forms stool.

2. Chyme: Semi-liquid mixture of food and gastric secretions formed in the stomach and passed into the intestines.

3. Enzymes:

   • Amylase: Breaks down carbohydrates in the mouth.

   • Peptidase: Breaks down proteins in the stomach.

   • Lipase: Breaks down fats, especially significant post-gallbladder removal.

4. pH Gradient: Varies across the digestive system to optimize enzyme activity (e.g., stomach acid vs. near-neutral intestines).

5. Ulcers: Open sores in the stomach, esophagus, or intestines caused by Helicobacter pylori or NSAID use.

6. Constipation: Infrequent bowel movements caused by low fiber, dehydration, or medication (e.g., opioids).

   • Laxatives: Promote stool passage (bulk-forming, saline, stimulant, softeners).

7. Diarrhea: Frequent, loose stools caused by infections, diet, or drugs.

   • Anti-diarrheal agents: Absorbents, opiates, and fluid/electrolyte replenishers.

8. Emesis: Vomiting, a protective mechanism against toxins or irritants.

   • Antiemetic agents: Drugs to prevent nausea and vomiting (e.g., scopolamine, cannabinoids).

Important Concepts

Digestive System Functions

• Supplies nutrients from food/water to sustain life.

• Each segment has specialized functions (enzymes and pH vary to optimize digestion).

• Protective mucus in the stomach prevents self-digestion by hydrochloric acid (HCl).

Conditions and Relationships

1. Gallbladder Removal:

   • Reduces fat digestion capacity due to bile storage loss.

   • Patients may need a low-fat diet.

2. Ulcers:

   • Caused by H. pylori or NSAIDs inhibiting mucus production.

   • Treatment: Antibiotics, H2 blockers (e.g., ranitidine), PPIs (e.g., omeprazole), antacids, and barrier agents.

3. Constipation and Diarrhea:

   • Balanced fiber intake (25–30g daily) and hydration prevent constipation.

   • Diarrhea can lead to dehydration and electrolyte imbalance; treat with BRAT diet or medications like loperamide.

4. Vomiting:

   • Can be induced by toxins, drugs, or motion sickness.

   • Antiemetics interact with the nervous system to reduce symptoms.

Questions and Answers

General

1. Why is the GI system so long?

   • To maximize surface area for nutrient absorption and efficient digestion.

2. What enzymes are involved in digestion, and where?

   • Amylase (mouth): Carbs.

   • Peptidase (stomach): Proteins.

   • Lipase (small intestine): Fats.

3. What protects the stomach from self-digestion?

   • Mucus produced by foveolar cells forms a protective layer.

Medications

1. What drugs treat ulcers?

   • H2 Blockers: Block histamine receptors (e.g., famotidine).

   • PPIs: Inhibit acid production (e.g., lansoprazole).

   • Antacids: Neutralize stomach acid (e.g., Tums).

   • Barrier Agents: Protect stomach lining (e.g., sucralfate).

2. What are bulk-forming laxatives?

   • Hydrophilic substances like psyllium (Metamucil) that increase stool water content.

3. What is the BRAT diet?

   • Banana, Rice, Applesauce, Toast; used to recover from diarrhea.

Case Studies

1. How does stress influence ulcers?

   • Stress suppresses the immune system, increasing susceptibility to H. pylori infections and ulcers.

2. Why might spicy foods cause discomfort but not ulcers?

   • Spicy foods can irritate the stomach but do not cause ulcers unless H. pylori is present.

Examples and Relationships

• NSAIDs and Stomach Health:

  • NSAIDs reduce protective mucus, increasing ulcer risk.

  • Patients on long-term NSAIDs should consider PPIs or barrier agents.

• Electrolyte Imbalance in Diarrhea:

  • Rapid stool transit prevents water and electrolyte absorption.

  • Oral rehydration solutions (ORS) restore balance.

• Impact of Fiber:

  • Soluble fiber (e.g., oats) regulates digestion and prevents diarrhea.

  • Insoluble fiber (e.g., bran) alleviates constipation.