Label the parts I-V of the gastric pit and explain how parietal, chief, and enteroendocrine cells contribute to gastric juice formation.

Here is the solution to your question:

a) Label the parts I-V:
I. Gastric pit (or Surface mucous cells)
II. Mucous neck cells
III. Parietal cells (or Oxyntic cells)
IV. Chief cells (or Zymogenic cells)
V. Enteroendocrine cells (or G cells)

b) How III, IV and V contribute to the formation of gastric juice:

• Parietal cells (III) secrete hydrochloric acid (HCl), which lowers the stomach pH, denatures proteins, and activates pepsinogen. They also secrete intrinsic factor.
• Chief cells (IV) secrete pepsinogen, which is converted to pepsin by HCl to begin protein digestion, and gastric lipase for fat digestion.
• Enteroendocrine cells (V), specifically G cells, secrete the hormone gastrin, which stimulates parietal cells to produce HCl and chief cells to produce pepsinogen, thereby regulating gastric juice production.