Final answer:
Mechanical digestion in the mouth is accomplished by the teeth and jaw through chewing, with assistance from the tongue and the secretion of saliva from the salivary glands which also starts carbohydrate chemical digestion.
Step-by-step explanation:
In the Gastrointestinal Tract, when food is placed in the mouth, mechanical digestion is primarily carried out by two structures: the teeth and the jaw. These structures work in tandem to break down food into smaller, more manageable pieces through the process of chewing, also known as mastication. The tongue also plays a crucial role by positioning and moving the food around in the mouth to ensure even and effective chewing, as well as pushing the mechanically digested food towards the pharynx in preparation for swallowing. While the pharynx and esophagus are involved in the movement of food towards the stomach via the muscular contractions known as peristalsis, they do not directly participate in mechanical digestion.
The salivary glands support the mechanical process by secreting saliva, which moistens the food, making it easier to chew and ultimately swallow. Saliva also initiates the chemical digestion of carbohydrates, thanks to the enzyme amylase, which begins breaking down starches into sugars.