Final answer:
The gastric glands at the start of the stomach produce gastric juice and contain different types of cells, including parietal cells that secrete hydrochloric acid and intrinsic factor, and chief cells that secrete pepsinogen.
Step-by-step explanation:
The gastric glands located at the very beginning of the stomach are essential in the digestion process. These glands are made up of a variety of secretory cells that produce gastric juice during the gastric phase, which begins when food enters the stomach. The glands are structured with pits lined primarily with mucus cells, and deeper within are the gastric glands themselves which feature different types of cells, each with specific functions. Parietal cells, for one, are found mostly in the middle region of these glands and are responsible for producing hydrochloric acid (HCl) and intrinsic factor. Hydrochloric acid plays a key role in creating the acidic environment necessary to activate pepsinogen to pepsin, the protein-digesting enzyme, and also helps in denaturing proteins and killing ingested bacteria. Intrinsic factor is vital for the absorption of vitamin B12 in the small intestine.
Chief cells, located primarily in the basal regions of gastric glands, secrete pepsinogen. Mucous neck cells, which are found in the upper part of the stomach, produce a different type of mucus than what is secreted by the goblet cells of the surface epithelium, although its exact role is not fully understood. Collectively, the cells in the gastric glands perform crucial roles in the digestive process by secreting substances vital for the breakdown and absorption of food.