Hello all AIPMT Biology Aspirants, Learn about chyme, Digestion in Stomach.

Food (Bolus) comes to stomach after travelling through esophagus. It takes about 4 to 8 seconds to travel through esophagus.

• Stomach stores the food for 4-5 hours. So, stomach acts as a reservoir for food before release into small intestine.
• Food mixes thoroughly with the acidic gastric juice of the stomach by the churning movements of its muscular wall called propulsion.
• These movements helps gastric juice to break down large food particles to small particles (small enough to pass through pyloric sphincter), and bolus of food turns to a soupy liquid called called Chyme.
• So, stomach mixes saliva, food, and gastric juice to form chyme.
• Action of salivary amylase stops in stomach due to acidic pH of gastric juice.
• Acidic pH (pH = 2) of the stomach kills many microbes in food.
• On exposure to HCl, proenzyme pepsinogen gets converted into the active enzyme pepsin. Pepsin is a proteolytic (protein-digesting) enzyme in the stomach.
• Pepsin converts proteins into proteoses and peptones (peptides).
• Mucus and bicarbonates present in the gastric juice play an important role in lubrication and
  protection of the mucosal epithelium of stomach from damaging by the highly concentrated HCl.
• HCl provides the acidic pH (pH 1.8) optimal for pepsins.
• Rennin is a proteolytic enzyme found in gastric juice of infants which helps in the digestion of milk proteins. In adults, pepsin helps in digestion of milk protein.
• Small amounts of lipases are also secreted by gastric glands, which splits triglycerides (fats and oils) in fat molecules (such as those found in milk) into fatty acids and monoglycerides.
• Mucous cells of the stomach absorb some water, ions, and short-chain fatty acids, as well as certain drugs (especially aspirin) and alcohol.