Digestive System Overview

Introduction to the Digestive System

The digestive system, also known as the gastrointestinal (GI) tract, is a continuous tube that processes food, absorbs nutrients, and eliminates waste. It includes both primary and accessory organs, each with specialized functions essential for human health.

• Primary organs: Mouth, pharynx, esophagus, stomach, small intestine, large intestine

• Accessory organs: Salivary glands, liver, gallbladder, pancreas

• Length: Approximately 30 feet in adults

• Main functions:

  • Digestion: Breakdown of food into absorbable components

  • Absorption: Uptake of nutrients into blood or lymph

  • Elimination: Removal of solid waste from the body

Anatomy of the Digestive System

Mouth (Oral Cavity)

The mouth is the entry point for food and is responsible for the initial mechanical and chemical breakdown of food. It is formed by the hard and soft palates, cheeks, tongue, and lips. The vestibule is the space between the cheeks and teeth, and the gingiva (gums) surround the necks of the teeth. The lingual frenulum connects the tongue to the floor of the mouth.

• Tongue: Made of skeletal muscle, divided into root, body, and tip; contains taste buds and papillae

• Salivary glands: Three pairs (parotid, submandibular, sublingual) secrete saliva to moisten food and begin digestion

• Digestion begins in the mouth: Food is broken apart, moistened, and formed into a bolus

Teeth

Humans have two sets of teeth: deciduous (baby) and permanent (adult). Teeth are specialized for cutting, tearing, and grinding food.

• Deciduous teeth: 20 total (8 incisors, 4 canines, 8 molars)

• Permanent teeth: 32 total (8 incisors, 4 canines, 8 premolars, 12 molars)

• Types of teeth:

  • Incisors: Sharp cutting edge

  • Canines: Pointed for tearing

  • Premolars: Grinding surface

  • Molars: Largest, for grinding and pounding

• Tooth structure:

  • Crown: Projects above the gum

  • Root: Embedded in a bony socket (alveolus)

  • Neck: Between crown and root

  • Pulp cavity: Contains dental pulp, vessels, and nerves

  • Dentin: Main solid portion

  • Enamel: Covers crown

  • Cementum: Covers root, anchors periodontal ligament

Pharynx

The pharynx (throat) is a muscular tube that serves as a common passageway for food and air. It is divided into three regions: nasopharynx, oropharynx, and laryngopharynx. The epiglottis prevents food from entering the airway during swallowing.

• Nasopharynx: Above the soft palate

• Oropharynx: Between palate and hyoid bone

• Laryngopharynx: Between hyoid bone and entrance to larynx/esophagus

Esophagus

The esophagus is a muscular tube that transports food from the pharynx to the stomach. The lower esophageal sphincter (LES) regulates passage and prevents reflux. Food is moved by peristalsis, a series of coordinated muscular contractions.

Stomach

The stomach is a muscular, saclike organ that continues the digestive process. It is divided into the fundus (upper), body (main), and antrum (lower). Rugae are folds that allow expansion and contain glands for digestive juices. Food is mixed and reduced to chyme, which passes through the pyloric sphincter into the small intestine.

Small Intestine

The small intestine is the primary site for digestion and absorption. It is divided into three sections: duodenum, jejunum, and ileum. Villi increase the surface area for absorption, and digestive juices from the liver and pancreas aid in nutrient breakdown.

• Duodenum: First 12 inches

• Jejunum: Next 8 feet

• Ileum: Last 12 feet

Large Intestine

The large intestine absorbs water and forms feces. It consists of the cecum, colon, rectum, and anal canal. The colon is further divided into ascending, transverse, descending, and sigmoid sections.

Accessory Organs of Digestion

Salivary Glands

Salivary glands secrete saliva, which contains enzymes that initiate carbohydrate digestion and lubricate food for swallowing. The three major pairs are the parotid, submandibular, and sublingual glands.

Liver

The liver is the largest glandular organ and plays a central role in metabolism, detoxification, and synthesis of important proteins. It produces bile for fat emulsification, stores glycogen, and synthesizes clotting factors.

Gallbladder

The gallbladder stores and concentrates bile produced by the liver. Bile is released into the small intestine to aid in fat digestion.

Pancreas

The pancreas secretes digestive enzymes (pancreatic juice) into the small intestine and produces hormones such as insulin and glucagon for blood sugar regulation.

Medical Terminology: Building Your Vocabulary

Common Terms and Word Parts

• cholecystectomy: Surgical removal of the gallbladder (chol/e = bile, cyst = bladder, -ectomy = excision)

• diarrhea: Abnormal frequency and liquidity of fecal discharge (dia- = through, -rrhea = flow)

• glossectomy: Excision of the tongue (gloss = tongue, -ectomy = excision)

• rectocele: Hernia of the rectum (rect/o = rectum, -cele = hernia)

Drug Highlights

Medications Related to the Digestive System

• Antacids: Neutralize stomach acid (HCl)

• Histamine H2-receptor antagonists: Inhibit gastric acid secretion

• Proton-pump inhibitors (PPIs): Suppress gastric acid secretion

• Laxatives: Relieve constipation

• Antidiarrheal agents: Treat diarrhea

• Antiemetics: Prevent or stop vomiting

• Emetics: Induce vomiting

Diagnostic and Laboratory Tests

Common Tests for Digestive Disorders

• Alcohol toxicology: Measures blood alcohol levels

• Carcinoembryonic antigen (CEA): Monitors cancer therapy

• Cholangiography: X-ray of bile ducts after dye ingestion

• Colonoscopy: Visual examination of the colon with a colonoscope

• Comprehensive metabolic panel (CMP): Blood tests for metabolic function

• Endoscopic retrograde cholangiopancreatography (ERCP): X-ray of biliary and pancreatic ducts

• Esophagogastroduodenoscopy: Endoscopic exam of esophagus, stomach, and small intestine

• Gastric analysis: Tests stomach contents for acid, blood, bacteria, bile, and fatty acids

• Hepatitis panel: Blood test for hepatitis infection markers

• Liver biopsy: Microscopic exam of liver tissue

• Occult blood test: Detects hidden blood in stool

• Ova and parasites (O&P): Stool test for parasites

• Stool culture: Identifies bacteria in stool

• Ultrasonography: Visualizes gallbladder or liver using sound waves

• Upper GI endoscopy: Visual exam of gastric mucosa

Selected Pathologies and Procedures

Appendectomy and Appendicitis

An appendectomy is the surgical removal of the appendix, often performed to treat appendicitis, which is inflammation of the appendix.

Cirrhosis

Cirrhosis is a chronic liver disease characterized by scarring and impaired liver function. Common causes include chronic alcohol use and hepatitis.

Colorectal Cancer

Colorectal cancer affects the colon and rectum. Early detection through colonoscopy is critical for effective treatment.

Diverticulitis

Diverticulitis is inflammation of diverticula (small pouches) in the colon wall, which can cause pain and digestive disturbances.

Gastroesophageal Reflux Disease (GERD)

GERD is a condition where stomach acid frequently flows back into the esophagus, causing irritation. It is often due to dysfunction of the lower esophageal sphincter.

Hemorrhoids

Hemorrhoids are swollen veins in the lower rectum or anus, classified as internal or external. They can cause pain, bleeding, and discomfort.

Peptic Ulcer Disease

Peptic ulcers are sores that develop on the lining of the stomach, duodenum, or esophagus due to the action of gastric acids.

Volvulus

Volvulus is a twisting of the intestine that can cause obstruction and compromise blood flow, requiring prompt medical intervention.

Summary Table: Digestive System Organs and Functions

Key Abbreviations

• GI: Gastrointestinal

• LES: Lower esophageal sphincter

• ERCP: Endoscopic retrograde cholangiopancreatography

• CMP: Comprehensive metabolic panel

• CEA: Carcinoembryonic antigen