After the effector cell has being stimulated by acetylcholine (ACh), what enzyme stop the stimulation and allows the effector membrane to repolarize?

A) Beta 1-receptors:
Beta 1-receptors are primarily found in the heart, and their stimulation leads to increased heart rate and contractility. These receptors are not typically involved in vasoconstriction, pupil dilation, or piloerection.

B) Beta 2-receptors:
Beta 2-receptors are primarily located in smooth muscles such as the bronchi and blood vessels. Their stimulation causes smooth muscle relaxation, leading to bronchodilation and vasodilation. Beta 2-receptors are not responsible for the effects of vasoconstriction, piloerection, or pupil dilation described in the question, making this option incorrect.

C) Alpha 2-receptors:
Alpha 2-receptors are involved in the inhibition of norepinephrine release and play a role in regulating sympathetic tone. They are not primarily responsible for vasoconstriction or the other physiological responses listed in the question. Alpha 2-stimulation typically results in decreased sympathetic activity, not the effects described here.

D) Alpha 1-receptors:
Alpha 1-receptors are located on smooth muscle, including the blood vessels, and their stimulation results in vasoconstriction. They are also involved in other actions such as piloerection (hair standing on end), pupil dilation (mydriasis), and closure of the salivary sphincter. Additionally, they play a role in male sexual emission (ejaculation). The physiological responses described in the question—vasoconstriction, piloerection, pupil dilation, and male sexual emission—are all consistent with alpha 1-receptor stimulation.

A) Decreased bowel sounds:
When the sympathetic nervous system (SNS) is activated, such as during stress or a "fight-or-flight" response, blood is redirected away from the gastrointestinal (GI) tract to vital organs like the heart and muscles. This results in decreased gastrointestinal motility and function, which is reflected in a reduction in bowel sounds. Decreased bowel sounds are a direct consequence of reduced blood flow and decreased activity in the GI system.

B) Increased blood glucose level:
While it is true that SNS activation can lead to an increase in blood glucose due to the release of catecholamines (e.g., epinephrine), this response is related to the body’s preparation for physical exertion and not directly a result of blood being diverted from the GI tract. The increase in glucose levels is more about energy mobilization rather than an effect on blood flow to the GI tract.

C) Decreased immune reaction:
Sympathetic stimulation can indeed have effects on immune function, typically suppressing immune responses during a stress response. However, this is not directly linked to blood being diverted away from the GI tract. Immune suppression is more about the body prioritizing immediate survival (e.g., diverting energy to muscles for fight-or-flight) rather than a specific physiological consequence of GI blood flow changes.

D) Increased blood pressure:
Sympathetic nervous system activation does lead to an increase in blood pressure due to vasoconstriction and increased heart rate. However, increased blood pressure is a broader systemic response to SNS stimulation, and it is not directly related to blood being diverted from the GI tract. Blood pressure increases as part of the general "fight-or-flight" response, but it does not specifically indicate changes in GI blood flow.