Question

There are multiple events that can initiate the release of HCl in the stomach. Two such events are the sight and smell of food. Choose the answer below that is NOT true of this particular phase of gastric acid secretion.  

There are multiple events that can initiate the release of HCl in the stomach. Two such events are the sight and smell of food. Choose the answer below that is NOT true of this particular phase of gastric acid secretion.

The motor nerves of this pathway are part of the somatic motor division.

The nerves involved are long reflexes.

This prepares the stomach for food before its arrival in the stomach.

Multiple areas of the brain are involved in processing the stimuli.

Answer 1

Question:

There are multiple events that can initiate the release the HCl from the stomach. Two such events are the sight and smell of food. Choose the answer below that is not true of this particular phase of gastric secretion.

Answer: The motor nerves of this pathway are part of the somatic motor division.

Explanation: Human digestion involves three phases namely cephalic phase, gastric phase and intestinal phase. The above question is an example of cephalic phase of digestion or gastric acid secretion which involves the secretion of gastric acid HCl from the gastric glands of the stomach in response to the sight and smell of the food, merely by thinking about food even though the food has not actually entered the stomach.

This cephalic phase of gastric acid secretion is initiated by the smell and sight of the food which causes the higher centers of cerebral cortex to fire nerve signals along with the appetite regulating centers like hypothalamus and amygdala. Nerve signals from these centers are carried to the stomach by the vagus nerve (10th cranial nerve) which causes the secretion of gastric acid and prepares the stomach for the incoming food even before the food has actually entered the stomach.

Thus, the cephalic phase of gastric acid secretion is an example of autonomic nervous system activity as it is mediated by parasympathetic fibers of the vagus nerve. Autonomic nervous system controls the smooth visceral muscles and glands. This is not a somatic motor neuron activity as somatic motor neuron controls the voluntary skeletal muscles.

Cephalic phase of gastric acid secretion is also an example of long reflexes. Long reflexes are those reflexes which originate outsider the gastrointestinal tract and are controlled by higher centers of the brain. They regulate large peristaltic waves as well as secretions of gastric glands under the control of brain and spinal cord. Other examples of long reflexes are vomiting reflexes and defecation reflexes.

On the contrary, short reflexes both originate and integrates in the gastrointestinal tract itself without the involvement of brain or spinal cord. Examples of short reflexes is gastrocolic reflex in which distension or increased activity in the stomach leads to relaxation of ileocecal valve and increased activity of the colon. Other examples of short reflexes are intestino-intestinal relaxes, ileogastric reflexes, etc.