Final answer:
Infection with the bacterium Helicobacter pylori is the major factor in the development of gastritis and peptic ulcer disease. While NSAIDs, smoking, and stress may contribute, they are not the primary cause without H. pylori infection.
Step-by-step explanation:
The major factor in the development of both gastritis and peptic ulcer disease is infection with H. pylori. While other factors such as the chronic use of non-steroidal anti-inflammatory drugs (NSAIDs), tobacco smoking, and stress can contribute to the development of peptic ulcers, they are not considered the primary cause independent of H. pylori infection. The bacterium Helicobacter pylori is a gram-negative organism that can survive in the acidic environment of the stomach by producing the enzyme urease. This adaptation enables the bacteria to colonize the stomach lining, leading to the breakdown of the mucosal barrier and causing peptic ulcers or gastritis. Treatment of peptic ulcers often involves a course of antibiotics to eradicate H. pylori and medications to reduce stomach acid and promote healing.