Sympathetic system has adrenergic nerve endings at all sites except?
**Core Concept**
The sympathetic nervous system is a part of the autonomic nervous system that controls various involuntary functions, including the 'fight or flight' response. It has adrenergic nerve endings that release **norepinephrine** as the primary neurotransmitter. However, there are specific exceptions where the sympathetic system does not have adrenergic nerve endings.
**Why the Correct Answer is Right**
The correct answer is related to the unique exception in the sympathetic nervous system where adrenergic nerve endings are not found. This exception is related to the **sweat glands**, which are innervated by the sympathetic cholinergic fibers, not adrenergic.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because it does not represent the exception to adrenergic nerve endings in the sympathetic system.
**Option B:** Incorrect as it is not the site lacking adrenergic nerve endings.
**Option C:** Incorrect because it is not relevant to the exception.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that the sympathetic nervous system primarily uses **norepinephrine** for its adrenergic effects, except at the sweat glands, where **acetylcholine** is the neurotransmitter released by sympathetic cholinergic fibers.
**Correct Answer:** D. Sweat glands.