Final answer:
The stomach's major functions in the gastrointestinal tract are the chemical release of hydrochloric acid, which aids in protein digestion, and the mechanical churning of food due to muscle contractions.
Step-by-step explanation:
The correct answer to the question “What are the primary muscular and chemical functions within the stomach's major organ of the gastrointestinal tract?” is C) Release of hydrochloric acid and mechanical churning of food. The two main roles of the stomach in digestion are mechanical and chemical. The stomach's muscular walls churn the food, completing the mechanical breakdown as smaller pieces are easier to digest chemically. This process is known as peristalsis and is aided by an extra layer of muscle unique to the stomach's structure.
Chemical digestion involves the secretions of the stomach, predominantly hydrochloric acid, which lowers the pH to between 1.5 and 2.5, creating an acidic environment essential for the function of digestive enzymes like pepsin. Pepsin is a critical enzyme for the breakdown of proteins into smaller components. Additionally, a small amount of lipase is secreted for minimal fat digestion in the stomach, and mucus is produced to protect the stomach lining from the acidic pH.