● The process of digestion is accomplished by `color{violet}("mechanical")` and `color{violet}("chemical processes.")`

● The `color{violet}("buccal cavity")` performs two major functions, `color{violet}("mastication of food")` and facilitation of `color{violet}("swallowing.")`

● The `color{violet}("teeth")` and the `color{violet}("tongue")` with the help of `color{violet}("saliva masticate")` and mix up the food thoroughly.

● `color{violet}("Mucus")` in saliva helps in `color{violet}("lubricating and adhering")` the `color{violet}("masticated food particles")` into a `color{brown}("bolus.")`

● The `color{violet}("bolus")` is then conveyed into the `color{violet}("pharynx")` and then into the `color{violet}("oesophagus")` by `color{violet}("swallowing")` or `color{brown}("deglutition.")`

● The `color{violet}("bolus")` further passes down through the `color{violet}("oesophagus")` by successive `color{violet}("waves of muscular")` contractions called `color{violet}("peristalsis.")`

● The `color{violet}("gastro-oesophageal sphincter")` controls the passage of `color{violet}("food")` into the `color{violet}("stomach.")`

● The `color{violet}("saliva secreted")` into the `color{violet}("oral cavity")` contains electrolytes `color{violet}((Na^+, K^+, Cl^–, HCO^–))` and `color{violet}("enzymes, salivary amylase")` and `color{violet}("lysozyme.")`

● The chemical process of digestion is initiated in the `color{violet}("oral cavity")` by the `color{violet}("hydrolytic")` action of the carbohydrate splitting enzyme, the salivary amylase.

● About `color{violet}(30 %)` of starch is `color{violet}("hydrolysed")` here by this enzyme (optimum pH 6.8) into a disaccharide – maltose.

● `color{violet}("Lysozyme")` present in `color{violet}("saliva")` acts as an antibacterial agent that prevents infections.

`"Starch" underset("pH 6.8") overset("Salivary Amylase")→ "Maltose"`

● The `color{violet}("mucosa of stomach")` has `color{violet}("gastric glands.")`

● `color{violet}("Gastric glands")` have three major types of cells namely –

(i) `color{brown}("Mucus neck cells")` which secrete mucus.

(ii) `color{brown}("Peptic or Chief cells")` which secrete the proenzyme pepsinogen.

(iii) `color{brown}("Parietal or Oxyntic cells")` which secrete `HCl` and `color{violet}("intrinsic factor")` (factor essential for absorption of `color{violet}("vitamin" B_(12))` ).