Overview
Food travels through the mouth, pharynx, esophagus, stomach, small intestine (duodenum, jejunum, ileum) and large intestine (cecum, colon, rectum). Waves of smooth muscle contraction (peristalsis) move it along, while sphincters control the flow between sections.
The accessory organs add what the tract cannot make on its own. The liver makes bile and processes nutrients and drugs, the gallbladder stores and concentrates bile, and the pancreas releases digestive enzymes and bicarbonate into the duodenum.
Main functions
- Ingestion and mechanical breakdown of food
- Chemical digestion by acid and enzymes
- Absorption of nutrients, mostly in the small intestine
- Absorption of water and electrolytes in the colon
- Elimination of waste
- Metabolism and detoxification by the liver
Key structures
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Esophagus
The muscular tube that carries food from the pharynx to the stomach.
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Stomach
A muscular J-shaped sac that stores food and begins protein digestion with acid.
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Small intestine
About 6 meters of intestine where most digestion and absorption happen.
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Large intestine (colon and rectum)
The last 1.5 meters of the tract, which absorbs water and forms stool.
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Appendix
A small finger-like pouch attached to the cecum.
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Liver
The largest internal organ: the body's chemical factory and filter.
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Gallbladder and bile ducts
A small pear-shaped sac under the liver that stores and concentrates bile.
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Pancreas
A gland behind the stomach with both digestive (exocrine) and hormonal (endocrine) roles.
Peristalsis and absorption
Peristalsis is a wave of contraction behind the food and relaxation in front of it. The stomach mixes food with hydrochloric acid and pepsin into chyme, which enters the duodenum in small amounts. There, bile emulsifies fat and pancreatic enzymes digest carbohydrates, proteins and fats.
The small intestine absorbs most nutrients through millions of villi; vitamin B12 and bile salts are absorbed in the terminal ileum. The colon absorbs water and electrolytes and houses bacteria that produce vitamin K.
Nursing assessment
- Abdominal exam order: inspect, auscultate, percuss, palpate (auscultate before palpation so you do not change bowel sounds).
- Listen in all four quadrants; normal bowel sounds occur 5–35 times per minute. Listen for 5 minutes before calling them absent.
- Note distension, tenderness, guarding, rebound tenderness and masses.
- Ask about appetite, nausea, vomiting, last bowel movement, stool color and weight change.
- Check for signs of GI bleeding: hematemesis, coffee-ground emesis, melena (black tarry stool) or bright red blood.
Common conditions
| Condition | What happens | Key signs | Nursing priorities |
|---|---|---|---|
| Gastroesophageal reflux disease | Stomach acid flows back into the esophagus | Heartburn after meals or lying down, regurgitation, chronic cough | Small meals, stay upright 2–3 hours after eating, elevate the head of the bed, avoid triggers |
| Peptic ulcer disease | Erosion of the stomach or duodenal lining (H. pylori, NSAIDs) | Epigastric pain; perforation causes sudden severe pain and a rigid abdomen | Monitor for bleeding, teach medication regimens, avoid NSAIDs |
| Appendicitis | Inflamed, obstructed appendix | Periumbilical pain moving to the right lower quadrant (McBurney's point), rebound tenderness, fever | Keep NPO, no heat to the abdomen and no laxatives; sudden pain relief may mean rupture |
| Cholecystitis | Inflamed gallbladder, usually from gallstones | Right upper quadrant pain after fatty meals, radiating to the right shoulder; Murphy's sign | Pain control, low-fat diet, prepare for cholecystectomy |
| Cirrhosis | Scarring of the liver | Jaundice, ascites, bleeding, confusion from high ammonia (hepatic encephalopathy) | Bleeding precautions, daily weights and girth, lactulose as prescribed, avoid alcohol and hepatotoxic drugs |
| Bowel obstruction | Blockage of intestinal flow | Distension, cramping, vomiting, absent flatus; high-pitched bowel sounds early, absent later | NPO, nasogastric decompression, fluids and electrolytes |
| Pancreatitis | Inflammation of the pancreas (gallstones, alcohol) | Severe epigastric pain radiating to the back, high lipase, nausea | NPO initially, pain management, fluid resuscitation, monitor glucose and calcium |
Labs and normal values
| Test | Typical adult range | Why it matters |
|---|---|---|
| ALT / AST | About 4–36 U/L / 0–35 U/L | Rise with liver cell injury; ranges vary by lab |
| Total bilirubin | 0.3–1.0 mg/dL | High levels cause jaundice |
| Albumin | 3.5–5.0 g/dL | Low in malnutrition and liver disease; contributes to edema |
| Ammonia | 10–80 mcg/dL | High in liver failure; causes encephalopathy |
| Lipase | 0–160 U/L | Most specific test for pancreatitis |
| Amylase | 30–110 U/L | Rises in pancreatitis |
| Fecal occult blood | Negative | Positive suggests GI bleeding |
Reference ranges differ between laboratories and textbooks. Use the values your program and facility use.
Exam tips
- Inspect, auscultate, percuss, palpate: the abdomen is the one exam where you listen before you touch.
- Black tarry stools usually mean upper GI bleeding; iron and bismuth can also darken stool.
- Confirm feeding tube placement by X-ray before the first use, then check before each use as policy requires.
Practice questions
8 NCLEX-style questions on the digestive system. Pick an answer to see the rationale.
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In which order does the nurse perform an abdominal assessment?
Show the answer and rationale
Answer B: Inspect, auscultate, percuss, palpate. Palpation and percussion can change bowel sounds, so the nurse listens before touching.
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A client with suspected appendicitis suddenly reports that the pain is gone. What does the nurse suspect?
Show the answer and rationale
Answer B: The appendix ruptured. Sudden relief can mean rupture, which releases pressure but leads to peritonitis.
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Which lab test is most specific for acute pancreatitis?
Show the answer and rationale
Answer B: Lipase. Lipase stays elevated longer and is more specific to the pancreas than amylase.
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A client with cirrhosis is confused and has asterixis. Which lab value does the nurse check?
Show the answer and rationale
Answer A: Ammonia. The failing liver cannot convert ammonia to urea; high ammonia causes hepatic encephalopathy.
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Which teaching helps prevent dumping syndrome after gastric surgery?
Show the answer and rationale
Answer C: Eat small meals low in simple sugars and lie down after eating. Slowing the movement of food into the intestine reduces the fluid shift that causes dumping.
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Which vitamin requires intrinsic factor from the stomach for absorption?
Show the answer and rationale
Answer B: Vitamin B12. Intrinsic factor binds B12 so it can be absorbed in the terminal ileum.
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Which stoma finding should the nurse report immediately?
Show the answer and rationale
Answer C: Dark purple to black. A dusky or black stoma suggests poor blood supply and tissue necrosis.
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In which position should the client lie after a liver biopsy?
Show the answer and rationale
Answer B: Right side. Lying on the right side presses the liver against the chest wall and reduces bleeding at the puncture site.