Which portion of the upper gastrointestinal system is initially responsible for the mechanical breakdown of food? Liver Mouth Esophagus Large intestine

Mouth

Explanation:

The mouth is the part of the upper digestive tract where the process of mechanical digestion begins. Teeth breakdown the food into smaller pieces. With help of tongue, the food pieces are mixed with saliva which in turn is released from salivary glands. This process of mechanical digestion of food is called chewing or mastication. It converts the food into a soft, flexible, easily swallowed mass called a bolus. Food particles in bolus get dissolved in water to facilitate the chemical digestion by enzymes.

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