Gastroenterology: Introduction and Medical Terminology

Definition and Word Construction

Gastroenterology is the medical specialty focused on the study of the gastrointestinal (GI) system, including its anatomy, physiology, diseases, and treatments. Understanding medical terminology is essential for proficiency in this area.

• Gastr/o-: Refers to the stomach.

• Enter/o-: Refers to the intestine.

• -logy: Means the study of.

• Combined, gastroenterology means the study of the stomach and intestines.

Overview of the Gastrointestinal System

Major Structures and Functions

The GI system consists of a series of organs and glands forming a continuous pathway from the mouth to the anus. Its primary functions are digestion, absorption of nutrients, and elimination of waste.

• Organs: Oral cavity, pharynx, esophagus, stomach, small intestine, large intestine, rectum, and anus.

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

• Main functions: Ingestion, digestion, absorption, and elimination.

Anatomy: Upper Gastrointestinal System

Oral Cavity and Pharynx

The oral cavity is the entry point for food and contains the teeth, gums, tongue, and the hard and soft palates. Food passes from the oral cavity into the pharynx (throat) and then the esophagus.

• Teeth: Responsible for mastication (chewing).

• 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.

Salivary Glands

Salivary glands produce saliva, which begins the process of chemical digestion and lubricates food for swallowing.

• Parotid glands: Located anterior to the ears.

• Sublingual glands: Located under the tongue.

• Submandibular glands: Located beneath the mandible.

Pharynx and Larynx

The pharynx is a shared passageway for food and air, divided into the nasopharynx, oropharynx, and laryngopharynx. The larynx, located inferior to the pharynx, remains open during breathing but closes during swallowing to prevent aspiration.

• Epiglottis: A flap that covers the larynx during swallowing, directing food into the esophagus.

Esophagus

The esophagus is a muscular tube that connects the pharynx to the stomach. Peristalsis, or coordinated muscular contractions, moves food toward the stomach.

Stomach

The stomach is a muscular organ divided into four regions: cardia, fundus, body, and pylorus. It mixes food with gastric juices to form chyme and regulates its passage into the small intestine via sphincters.

• Lower esophageal sphincter: Prevents reflux of stomach contents.

• Pyloric sphincter: Controls the release of chyme into the duodenum.

• Omentum: A 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, which can bleed if irritated. They are often associated with liver disease and portal hypertension.

Gastric Ulcer

A gastric ulcer is an erosion of the stomach lining, often caused by Helicobacter pylori infection or chronic use of NSAIDs. Symptoms include pain and bleeding.

Diagnostic and Medical Procedures: Upper GI

Endoscopic Retrograde Cholangiopancreatography (ERCP)

ERCP is a procedure in which an endoscope is passed through the upper GI tract to visualize the bile and pancreatic ducts using contrast dye. It is used to diagnose and treat biliary and pancreatic diseases.

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 inserted 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: Lower Gastrointestinal System

Small Intestine

The small intestine is a long, narrow tube divided into three segments: duodenum, jejunum, and ileum. It is the primary site for nutrient and water absorption, aided by thousands of villi that increase surface area.

• Duodenum: First segment, about 10 inches long.

• Jejunum: Middle segment, about 8 feet long.

• Ileum: Last segment, about 12 feet long.

Large Intestine

The large intestine absorbs water and forms feces. It consists of the cecum (with the appendix), colon (ascending, transverse, descending, sigmoid), rectum, and anus. The ileocecal valve prevents backflow from the large to the small intestine.

• Haustra: Puckered pouches in the colon that expand to accommodate waste.

Diseases of the Intestines

Intussusception and Volvulus

Intussusception is the telescoping of one part of the intestine 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. Inflammation of these pouches is called diverticulitis, which can lead to infection and complications.

Crohn Disease

Crohn disease is a chronic inflammatory condition of the GI tract, often affecting the ileum and colon. It causes wall thickening, ulcers, and partial obstruction.

Colonic Polyps

Polyps are abnormal growths in the colon mucosa. Sessile polyps are flat, while pedunculated polyps are attached by a stalk. Some polyps can become cancerous.

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

A colonoscopy uses a flexible camera to examine the rectum and colon for polyps, cancer, and other diseases.

Barium Enema

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

Diseases: Abdominal Wall and Abdominopelvic Cavity

Hernia

A hernia occurs when an organ or tissue protrudes through a weak spot in the abdominal wall. Types include sliding hernia (reducible) and strangulated hernia (trapped, with risk of tissue death). Congenital hernias such as omphalocele occur at birth.

Peritonitis

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

Anatomy: Accessory Organs

Liver

The liver is the largest solid organ, producing bile for fat digestion. Bile flows through the biliary tree to the gallbladder and duodenum. Key terms include:

• Hepatocytes: Liver cells producing bile.

• Biliary tree: Network of bile ducts.

• Chol/e-: Bile; cholecyst/o-: Gallbladder; cholangi/o-: Bile duct; choledoch/o-: Common bile duct.

Liver Diseases

Liver diseases include fatty liver (steatosis), cirrhosis (scarring and nodules), jaundice (yellowing of skin and eyes due to bilirubin), and liver cancer (tumors visible on CT scan). Ascites is fluid accumulation in the abdomen due to liver dysfunction.

Gallbladder and Bile Ducts

The gallbladder stores and concentrates bile, releasing it into the duodenum in response to fatty chyme. Gallstones can block bile flow, causing pain and complications.

Pancreas

The pancreas secretes digestive enzymes (amylase, lipase, proteases) into the duodenum to aid in the breakdown of carbohydrates, fats, and proteins.

Physiology: Digestion, Absorption, and Elimination

Mechanical and Chemical Digestion

Digestion involves both mechanical and chemical processes:

• Mechanical digestion: Mastication (chewing), deglutition (swallowing), and peristalsis (muscular movement).

• Chemical digestion: Enzymes and acids break down food into absorbable molecules.

Key enzymes and hormones:

• Amylase: Breaks down carbohydrates (salivary glands, pancreas).

• Pepsin: Breaks down proteins (stomach).

• Gastrin: Stimulates acid and pepsinogen release (stomach).

• Cholecystokinin: Stimulates gallbladder contraction (duodenum).

• Bile: Emulsifies fats (liver, gallbladder).

• Lactase: Breaks down lactose (jejunum).

Absorption

Absorption is the process by which nutrients and water are taken into the bloodstream, primarily in the small intestine. Water is also absorbed in the oral cavity, stomach, and large intestine.

Elimination

Elimination removes undigested waste and water from the body as feces. The process is known as defecation, and gas expelled is called flatus.