Gastroenterology: Introduction and Terminology

Definition and Scope

Gastroenterology is the medical specialty focused on the study, diagnosis, and treatment of diseases affecting the gastrointestinal (GI) system. This field encompasses the anatomy, physiology, and pathology of the digestive tract and its accessory organs.

• Gastr/o-: Refers to the stomach.

• Enter/o-: Refers to the intestine.

• -logy: Means the study of.

Example: The term gastroenterology literally means "the study of the stomach and intestines."

Anatomy of the Gastrointestinal System

Overview of the GI System

The gastrointestinal system is a continuous tube extending from the mouth to the anus, including accessory organs. Its primary functions are digestion, absorption of nutrients, and elimination of waste.

• Major organs: oral cavity, pharynx, esophagus, stomach, small intestine, large intestine, rectum, and anus.

• Accessory organs: salivary glands, liver, gallbladder, and pancreas.

Oral Cavity and Pharynx

The oral cavity is the entry point for food and contains structures essential for the initial stages of digestion.

• Teeth: Mechanically break down food.

• Tongue: Assists in mixing food and contains taste receptors.

• Hard and soft palates: Form the roof of the mouth; the soft palate and uvula help direct food during swallowing.

• Pharynx: Common passageway for food and air, divided into nasopharynx, oropharynx, and laryngopharynx.

Salivary Glands

Salivary glands secrete saliva, which contains enzymes that begin the chemical breakdown of carbohydrates.

• Parotid glands: Located anterior to the ears.

• Sublingual glands: Located under the tongue.

• Submandibular glands: Located beneath the mandible.

Esophagus and Stomach

The esophagus is a muscular tube that transports food from the pharynx to the stomach via peristalsis. The stomach is a muscular organ divided into four regions: cardia, fundus, body, and pylorus. It performs both mechanical and chemical digestion.

• Lower esophageal sphincter: Prevents reflux of stomach contents.

• Pyloric sphincter: Regulates passage of chyme into the duodenum.

• Omentum: Fatty membrane protecting abdominal organs.

Diseases of the Upper GI Tract

Dyspepsia

Dyspepsia, or indigestion, is discomfort or pain in the upper abdomen. Causes include excess stomach acid, acid reflux, overeating, spicy foods, or stress.

Esophageal Varices

Esophageal varices are dilated veins in the esophageal mucosa, often due to portal hypertension. They are prone to bleeding, especially if irritated by food.

Gastric Ulcer

A gastric ulcer is an open sore in the stomach lining, often caused by Helicobacter pylori infection or chronic NSAID use. Symptoms include pain, bleeding, and risk of perforation.

Diagnostic and Medical Procedures

Endoscopic Retrograde Cholangiopancreatography (ERCP)

ERCP is a procedure using an endoscope and contrast dye to visualize the bile and pancreatic ducts. It is used to diagnose and treat obstructions or strictures.

Nasogastric (NG) Tube

An NG tube is inserted through the nose into the stomach for feeding or medication administration when oral intake is not possible.

Percutaneous Endoscopic Gastrostomy (PEG) Tube

A PEG tube is a permanent feeding tube placed through the abdominal wall into the stomach for long-term nutritional support.

Upper Gastrointestinal Series

This radiologic procedure involves swallowing barium contrast to visualize the upper GI tract on x-ray, aiding in the diagnosis of structural abnormalities.

Anatomy of the Lower Gastrointestinal System

Small Intestine

The small intestine is a long, coiled tube where most digestion and absorption occur. It consists of three segments: duodenum, jejunum, and ileum. Villi line the mucosa, increasing surface area for absorption.

• Duodenum: First segment, receives chyme and digestive enzymes.

• Jejunum: Middle segment, primary site for nutrient absorption.

• Ileum: Final segment, absorbs bile acids and vitamin B12.

Large Intestine

The large intestine absorbs water and forms feces. It includes the cecum (with appendix), colon (ascending, transverse, descending, sigmoid), rectum, and anus. Haustra are pouches that expand to accommodate waste.

Diseases of the Intestines

Intussusception and Volvulus

Intussusception occurs when one segment of intestine telescopes into another, while volvulus is a twisting of the intestine. Both conditions obstruct peristalsis and blood flow, requiring urgent intervention.

Diverticula and Diverticulitis

Diverticula are pouches in the colon wall where feces can become trapped. Infection of a diverticulum leads to diverticulitis, which can cause pain and complications.

Crohn Disease

Crohn disease is a chronic inflammatory bowel disease characterized by thickening of the intestinal wall, ulceration, and partial obstruction. It can affect any part of the GI tract but most commonly involves the ileum.

Colonic Polyps

Polyps are growths on the mucosal surface of the colon. They may be sessile (flat) or pedunculated (on a stalk) and can become cancerous if not removed.

Colostomy and Stoma

A colostomy is a surgical procedure creating an opening (stoma) from the colon to the abdominal wall for fecal diversion. A colostomy bag collects waste externally.

Colonoscopy

Colonoscopy is an endoscopic procedure to visualize the rectum and colon, allowing for diagnosis, biopsy, and removal of polyps.

Barium Enema

A barium enema is a radiologic procedure in which barium contrast is introduced into the rectum to visualize the colon on x-ray, highlighting structures such as haustra.

Diseases of the Abdominal Wall and Cavity

Hernia

A hernia is the protrusion of intestine through a weakness in the abdominal wall. Types include sliding hernia (movable) and strangulated hernia (trapped, with risk of tissue death).

Peritonitis

Peritonitis is inflammation of the peritoneum, often due to perforation of the GI tract and leakage of contents into the abdominal cavity. It is a medical emergency.

Accessory Organs: Liver, Gallbladder, and Pancreas

Liver

The liver is the largest solid organ, producing bile for fat digestion. Bile flows through the biliary tree to the gallbladder and duodenum. The liver also metabolizes nutrients and detoxifies substances.

Liver Diseases

• Fatty liver: Accumulation of fat, often due to alcoholism or metabolic disorders.

• Cirrhosis: Chronic scarring and loss of function.

• Jaundice: Yellowing of skin and sclera due to bilirubin buildup.

• Liver cancer: Malignant tumors, often detected by imaging.

• Ascites: Fluid accumulation in the abdomen due to portal hypertension.

Gallbladder and Bile Ducts

The gallbladder stores and concentrates bile, releasing it in response to fatty meals. Gallstones can obstruct bile flow, causing pain and jaundice.

• Cholelithiasis: Presence of gallstones.

• Cholecystectomy: Surgical removal of the gallbladder, often performed laparoscopically.

Pancreas

The pancreas secretes digestive enzymes (amylase, lipase, proteases) into the duodenum and also produces hormones (insulin, glucagon) for glucose regulation.

Physiology of Digestion

Mechanical Digestion

Mechanical digestion involves physical breakdown and movement of food through mastication (chewing), deglutition (swallowing), and peristalsis (muscular contractions).

Chemical Digestion

Chemical digestion uses enzymes and acids to break down food into absorbable molecules.

• Amylase: Breaks down carbohydrates.

• Pepsin: Breaks down proteins.

• Gastrin: Stimulates acid and pepsinogen secretion.

• Cholecystokinin: Stimulates gallbladder contraction.

• Bile: Emulsifies fats.

• Lactase: Breaks down lactose.

Absorption and Elimination

Absorption is the uptake of nutrients and water, primarily in the small intestine. Elimination removes undigested waste as feces through defecation.

Summary Table: Major GI Terms and Functions