Answer:
The direct answer to the question: What is the cephalic, gastric and intestinal phases, is, that these three make part of the full process of food digestion and they happen in that exact order, as a person prepares to eat, eats, and then digests the food he/she has eaten.
Step-by-step explanation:
The processing of food, is a complex system in which not just the digestive, but the accesory organs, and the central nervous system, play a central role. This process has the purpose of providing the necessary nutrients for the body to function.
In the cephalic phase, a person becomes stimulated by the sight, thought, touch, or any sense, for that matter, that has to do with food. It stimulates the central nervous system, particularly the hypothalamus, to activate the stomach, especially the secretion of HCI, gastrin, and other such enzymes, so that these organs are prepared for food digestion. It also increases the production of saliva, and mucus, in the mouth, by way of the vagus nerve,so that digestion of food, especially of fats and proteins, is more efficient.
In the gastric phase, the enzymes produced, and the cells activated, like the parietal cells, due to stomach stretching and also pH changes, produce the movements, production of enzymes, and the release of water, that will mix togather to form the chyme, which is the partly digested foods, and other elements.
The final phase, known as the intestinal phase, happens in the duodenum, when it stretches, and at the presence of such enymes as gastrin, and the low pH. In this phase, fat and carbohydrate digestion, as well as the final phase of protein digestion, as well as absorption, will take place. It will also include the inhibition of the stomach, and activation of the pancreas and liver, to produce further enzymes that will help with, especially, the absorption and management of sugars, fats, and amino acids.
This is in general, and very broadly, what these three phases of digestion are.