Final answer:
The constriction of the pyloric sphincter is primarily achieved through the activation of sympathetic nerves innervating the smooth muscle. This action aligns with the general role of the sympathetic nervous system in the fight-or-flight response, which reduces digestive activity. The action of nitric oxide as a vasodilator would not typically constrict the pyloric sphincter.
Step-by-step explanation:
The constriction of the pyloric sphincter, a valve that regulates the flow of partially digested food from the stomach to the small intestine, is modulated by various factors within the autonomic nervous system. Conditions such as increased CO2, increased lactic acid, increased potassium, falling pH (rising hydrogen ion concentration), and inflammatory chemicals, lead to the release of nitric oxide (NO), which acts as a vasodilator and relaxes the smooth muscle cells of blood vessels and organs including the pyloric sphincter itself.
However, the direct constriction of the pyloric sphincter is primarily achieved through the action of the autonomic nervous system. Sympathetic activation, associated with the fight-or-flight response, restricts the activity of enteric neurons, thereby decreasing gastrointestinal (GI) secretion and motility. This suggests that option A) is incorrect, as nitric oxide typically promotes relaxation rather than constriction. Option D) is incorrect as well, because activation of parasympathetic nerves innervating the smooth muscle would increase secretion and motility, thus facilitating opening rather than constriction.
Therefore, the correct answer is C) Activation of sympathetic nerves innervating the smooth muscle leads to constriction of the pyloric sphincter. This reflects the sympathetic nervous system's general role in preparing the body for intense physical activity by slowing down processes that are not immediately necessary, such as digestion.