Pepsinogen is an inactive enzyme produced by the stomach's lining cells, specifically the chief cells. It plays a crucial role in the digestion of proteins. When food enters the stomach, pepsinogen is converted into its active form, pepsin, in the presence of stomach acid, primarily hydrochloric acid. Once activated, pepsin breaks down proteins into smaller peptides, aiding in their digestion. This process is essential for nutrient absorption in the small intestine. The regulation of pepsinogen secretion is vital for maintaining proper digestive function and preventing damage to the stomach lining.