The correct option is D all of the above
GIT or Gastrointestinal tract is regulated by the nervous system (neural control) and the hormones. In this way, the activities of the GIT are controlled and coordinated by the nerves and hormones. They set up a coordination between the different parts of the GIT. The intrinsic neural system (or the enteric neural system) consists of the Meissner’s plexus (found in the submucosa) and the Auerbach’s plexus (found in the muscular layer). The intrinsic neural system controls most of the GIT functions like secretion and motility.
The extrinsic neural system consists of the sympathetic and parasympathetic nervous system which can alter the activity of the enteric neural system in response to reflex activity originating from the GIT itself or from other parts of the body.
The sight, smell or the mere presence of food in the mouth can act as a stimulus for salivation (secretion of saliva). This happens due to the stimulation of the vagus nerve.
Feeling of hunger at a particular time, when food is taken regularly, is an example of conditional reflex.