The only acid that I know in the stomach is: Gastric Acid
(Which is made up of Hydrochloric Acid.)
rennin
Pepsinogen is an inactive precursor of the enzyme pepsin, which is responsible for breaking down proteins in the stomach. Hydrochloric acid activates pepsinogen, converting it into pepsin. The presence of hydrochloric acid in the stomach helps to create an acidic environment that allows pepsin to function optimally.
Both crayfish and starfish have a cardiac stomach and a pyloric stomach. The cardiac stomach is responsible for receiving and grinding food, while the pyloric stomach is responsible for digesting and absorbing nutrients.
The stomach churns the food into smaller and smaller pieces with the help of the strong stomach acid, Hydrochloric acid.
Hydrochloric acid (HCl)
No. The autonomic nervous system is responsible for controlling the muscle activity of your stomach.
The stomach because it has the stomach acid that breaks down food and goes into the digestion system.
Absorption
Although the stomach is responsible for digestion, very little absorption happens in it. Instead, the stomach is more like a washing machine; it agitates foodstuffs. It stirs up ground up food (mechanical digestion from teeth / gums occurs in the mouth), with stomach acids in the stomach and bile salts from the gallbladder assisting in chemical digestion.
Proteins are digested in the stomach. Pepsin is the enzyme, which is responsible for breaking the peptide bond of the proteins.
The stomach, small intestine, and large intestine are the digestive organs responsible for absorbing nutrients.
The dome-shaped portion of the stomach just beneath the diaphragm is called the fundus. It is located in the upper left portion of the stomach and is responsible for storing and mixing ingested food before releasing it into the rest of the stomach for digestion.