Digestion in Stomach — Core Principles
Core Principles
Digestion in the stomach is a vital step where food undergoes both mechanical and chemical breakdown. Mechanically, the stomach's muscular walls churn and mix food with gastric juices, forming a semi-liquid called chyme.
Chemically, specialized gastric glands secrete gastric juice, a potent mixture containing hydrochloric acid (HCl), pepsinogen, gastric lipase, mucus, and intrinsic factor. HCl creates an acidic environment (pH 1.
5-3.5), which denatures proteins, kills pathogens, and activates pepsinogen into pepsin. Pepsin is the primary enzyme for protein digestion, breaking them into smaller polypeptides. Gastric lipase initiates minor fat digestion.
Mucus protects the stomach lining from the corrosive acid and enzymes, while intrinsic factor is crucial for Vitamin B12 absorption. This entire process is tightly regulated by neural and hormonal signals, preparing the chyme for its controlled release into the small intestine.
Often confused with
Side-by-side differences the NEET paper likes to test.
| Aspect | Digestion in Stomach | Digestion in Mouth |
|---|---|---|
| Primary Function | Mechanical breakdown (chewing), initiation of carbohydrate and minor fat digestion. | Mechanical churning, initiation of protein digestion, antimicrobial action. |
| pH Environment | Neutral to slightly alkaline (pH $6.7-7.0$). | Highly acidic (pH $1.5-3.5$). |
| Key Enzymes | Salivary amylase (carbohydrates), Lingual lipase (minor fat). | Pepsin (proteins), Gastric lipase (minor fat). |
| Major Nutrient Digested | Carbohydrates (starch). | Proteins. |
| Protective Mechanism | Saliva moistens and lubricates food, antibodies provide minor defense. | Thick mucus layer and bicarbonate protect against acid and enzymes. |
| Product | Bolus (soft, moist mass of food). | Chyme (acidic, semi-liquid paste). |
Digestion in the mouth primarily involves mechanical chewing and the initial enzymatic breakdown of carbohydrates by salivary amylase in a neutral pH environment, forming a bolus. In contrast, digestion in the stomach is characterized by vigorous mechanical churning and the commencement of protein digestion by pepsin in a highly acidic environment, transforming the bolus into chyme.
The stomach also provides a crucial antimicrobial barrier and secretes intrinsic factor for Vitamin B12 absorption, functions not present in the mouth. These differences highlight the specialized roles of each organ in the digestive continuum.
Why it is tested: Understanding the distinct roles and conditions (pH, enzymes) in different parts of the alimentary canal is fundamental for NEET. Questions often compare and contrast the digestive processes, enzymes, and products at various stages.