Some of the factors that affect the rate at which particles diffuse include: the particle's molecular weight, temperature, concentration difference, diffusion distance, permeability and surface area.
This region of the stomach is called the 'cardiac' region. How does the mucosa in this region change? Gastric Glands in the fundus (body) of the stomach. The epithelium of the mucosa of the fundus and body of the stomach forms invaginations called gastric pits. The lamina propria contains gastric glands, which open into the bases of the gastric pits. These glands are responsible for the synthesis and secretion of the gastric juice.
The stomach is protected by the epithelial cells, which produce and secrete a bicarbonate-rich solution that coats the mucosa. Bicarbonate is alkaline, a base, and neutralizes the acid secreted by the parietal cells, producing water in the process. This continuous supply of bicarbonate is the main way that your stomach protects itself from autodigestion (the stomach digesting itself) and the overall acidic environment.