Sympathetic stimulation causes all of the following except :
**Core Concept**
Sympathetic stimulation is a key component of the body's "fight or flight" response, mediated by the sympathetic nervous system. This response is characterized by increased heart rate, blood pressure, and energy mobilization, as well as decreased digestion and immune response. The sympathetic nervous system achieves this through the release of neurotransmitters such as norepinephrine and epinephrine.
**Why the Correct Answer is Right**
Sympathetic stimulation causes vasoconstriction in most vascular beds, except for those in skeletal muscle, where vasodilation occurs to increase blood flow and oxygen delivery to the muscles. This selective vasodilation allows for increased blood flow to the muscles, preparing the body for physical activity. The increased heart rate and cardiac output further enhance oxygen delivery to the muscles. Additionally, sympathetic stimulation causes bronchodilation in the lungs, allowing for increased airflow and oxygen intake.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is not a known effect of sympathetic stimulation. While sympathetic stimulation does cause increased heart rate and blood pressure, it is not typically associated with decreased heart rate or blood pressure.
**Option B:** This option is incorrect because it is not a direct effect of sympathetic stimulation. While sympathetic stimulation can cause vasoconstriction in most vascular beds, it is not typically associated with increased blood flow to the kidneys.
**Option C:** This option is incorrect because it is not a direct effect of sympathetic stimulation. While sympathetic stimulation can cause increased heart rate and blood pressure, it is not typically associated with decreased blood flow to the skin.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that sympathetic stimulation has a selective effect on blood flow, prioritizing skeletal muscle over other tissues. This is crucial for the body's "fight or flight" response, allowing for increased blood flow and oxygen delivery to the muscles during physical activity.
**Correct Answer:** D.