Protein digestion starts in the stomach.
Three types of cells secrete gastric juices.
These gastric juices convert food to acid chyme.
- Mucus cells secrete mucus, which lubricates and protects the cells lining the
- Chief cells secrete pepsinogen,
an inactive enzyme that is converted to pepsin to digest protein.
- Parietal cells secrete hydrochloric acid (HCl),
lowering the pH of the juice.