Final answer:
Pepsin is an enzyme that digests proteins in the stomach, working best in the acidic pH of 1.5-2.5. Smooth muscles in the stomach wall contract to aid in mechanical digestion, mixing food with digestive juices to form chyme, the semi-liquid mixture passed to the small intestine.
Step-by-step explanation:
Role of Pepsin in Protein Digestion
Pepsin is an enzyme involved in the digestion of protein in the stomach. It is secreted by the chief cells in an inactive form known as pepsinogen. When exposed to the acidic environment of the stomach, specifically to the hydrochloric acid secreted by parietal cells, pepsinogen is activated into pepsin. Pepsin has a substrate specificity, meaning it acts on proteins, breaking them down into smaller peptides by cleaving their peptide bonds.
pH of the Stomach
The pH in the stomach is highly acidic, ranging from 1.5 to 2.5. This acidic environment is essential for pepsin's activity because the enzyme functions optimally at low pH levels. The acidity also helps kill harmful microorganisms present in food.
Involvement of Smooth Muscle
The stomach walls contain layers of smooth muscle, which contract and relax in a coordinated manner to churn and mix the stomach contents. This mechanical digestion helps break down the food into smaller pieces and mix it thoroughly with digestive juices, including pepsin, to enhance protein digestion.
Chyme
Chyme is the semi-liquid mixture of partially digested food and gastric juices in the stomach. Following the mechanical and chemical digestion processes, chyme is gradually released into the small intestine, where further digestion and nutrient absorption will take place.