Question

Explain salivary secretion of mouth takes place on the seeing a favourite dish

Answer 1

The phrase "Mouth watering" is actually pretty accurate. There are two types of saliva:
1. Mucous:
It is exactly what it sounds like-thick, sticky and full of mucous.
2. Serous:
Serous saliva, on the other hand, is nearly all water. and that's what floods in your mouth at the smell, sight or thought of delicious food.
It is actually a response to the stimulus sensed by the sensory organs, eyes and nose. As soon as nervous system transfers the message, in response the salivary glands produce the saliva. Thus, your mouth waters as you see your favorite dish.

Answer 2

When a person sees, smells or even thinks about food a signal is sent to the brain's salivary centre. The brain subconsciously reacts with an increased secretion of saliva. So the mouth waters on seeing a favourite dish.

The medulla oblongata is the part of the brain which is responsible for the salivary reflex. It sends neurotransmitters to the glands to produce the saliva. 

Saliva is composed of  99.5% water and 0.5% proteins, electrolytes and lipids. It helps the teeth to chew the food and prepare it for digestion. Saliva is essential for keeping the mouth and teeth healthy and hygenic.