The structure of the stomach and its involvement in digestion (pH, sphincters, rugae, gastric juices)

Question 1

Structure of the stomach

Answer 1

• J – shaped
• Can expand up to 1.5 litres
• Stomach pH is 2-3 (very acidic)
• 1 layer of gastric glands
• 3 layers of muscle (circular, longitudinal and diagonal) that churn food to mechanically break it down
• This churning creates the liquid called chyme

Question 2

Mucosa cells form Gastric juices that contain what?

Answer 2

1. Pepsin (Enzyme)
   Pepsinogen (inactive) + HCl → Pepsin (active)
   Function: Breaks down proteins into small polypeptides.
2. 2. HCL (Hydrochloric Acid)
      Extremely acidic
      Functions:
      Breaks down fibrous tissue in food
      Kills bacteria
      Converts pepsinogen to pepsin
3. Mucus
   Function: Protects the stomach lining from being digested by acids and enzymes.

Question 3

Rugae

Answer 3

• Mucosa form folds called rugae. It allows for expansion of the stomach after consumption of foods and liquids.

Question 4

Sphincter

Answer 4

1. Cardiac Sphincter:
   Location: Beginning of the stomach.
   Action: Opens to let food from the esophagus into the stomach and then closes to keep it there.
2. Pyloric Sphincter:
   Location: End of the stomach.
   Action: Opens to release chyme into the small intestine (duodenum) when ready.
   Memory Aid: “Pyloric = Passes chyme out.”