Digestive System

Why This Matters for Nursing: Nutrition, medication absorption, and GI conditions are central to patient care. Understanding digestion helps you assess nutritional status, manage feeding tubes, and administer oral medications effectively.

What You Need to Know

The digestive system breaks down food into nutrients the body can absorb and use for energy, growth, and repair.

Two Types of Digestion:

🧠 Memory Trick

GI Tract Order: "Mother Says Stomach Should Empty Properly"

Mouth → Stomach (via esophagus) → Small intestine → Empty into → Large intestine → Poop out

Or simply: Mouth → Esophagus → Stomach → Small intestine → Large intestine → Rectum

The GI Tract (Alimentary Canal)

Accessory Organs

Enzymes and Digestion

Bile is NOT an enzyme — it emulsifies fat (breaks into smaller droplets) to help lipase work.

Small Intestine: Main Absorption Site

Three Sections:

1. Duodenum — Receives chyme, bile, pancreatic juice; most chemical digestion
2. Jejunum — Primary absorption of nutrients
3. Ileum — Absorbs B12 and bile salts

Absorption Structures:

• Villi — Finger-like projections that increase surface area
• Microvilli — Tiny projections on villi (brush border)
• Huge surface area = efficient absorption

Large Intestine

Key function: Water absorption and feces formation

✏️ Worked Examples

Example 1: Where is most nutrient absorption?

Step 1 — Understand what absorption means. Digestion is breaking food down into small enough pieces. Absorption is when those broken-down pieces actually cross into the bloodstream to be used by the body. These are two different things.

Step 2 — Know which organ is specialized for absorption. The small intestine is covered in structures called villi — finger-like projections that dramatically increase the surface area available to absorb nutrients. Each villus has tiny projections called microvilli (also called the "brush border"). The result: the small intestine has a surface area equivalent to a tennis court, despite being coiled up in your abdomen. That's specifically designed for maximum absorption.

Step 3 — Be specific. Within the small intestine, the jejunum (middle section) is where most nutrient absorption happens. The duodenum does most of the chemical digestion; the ileum absorbs specific things like vitamin B12.

Answer: The small intestine (especially the jejunum) is where most nutrient absorption occurs.

🏥 Nursing connection: Patients with Crohn's disease (inflammation of the GI tract, often affecting the small intestine) often have malabsorption — they eat food but can't absorb nutrients properly. This leads to malnutrition, weight loss, and vitamin deficiencies even when they seem to eat enough.