**Core Concept**
Hypersensitivity vasculitis, also known as leukocytoclastic vasculitis, is a small vessel vasculitis characterized by inflammation of the blood vessel walls. It is typically caused by an immune complex-mediated reaction, often triggered by infections, medications, or other exogenous agents.

**Why the Correct Answer is Right**
The correct answer is arterioles, which are small muscular blood vessels that branch off from the arteries and lead to capillaries. In hypersensitivity vasculitis, the immune complexes deposit in the walls of the arterioles, triggering an inflammatory response that includes the migration of neutrophils, activation of complement, and release of various cytokines and chemokines. This leads to damage to the endothelial cells, disruption of the basement membrane, and subsequent leakage of fluid, proteins, and blood cells into the surrounding tissue.

**Why Each Wrong Option is Incorrect**
**Option A:** Capillaries are tiny blood vessels where exchange of oxygen, nutrients, and waste products occurs. While capillaries can be affected in various types of vasculitis, they are not the primary site of involvement in hypersensitivity vasculitis.

**Option B:** Venules are small blood vessels that collect blood from capillaries and merge to form larger veins. While venules can be affected in some types of vasculitis, they are not typically involved in hypersensitivity vasculitis.

**Option C:** Arteries are large blood vessels that carry oxygenated blood away from the heart. Arteries are not typically involved in hypersensitivity vasculitis, which primarily affects smaller blood vessels.

**Clinical Pearl / High-Yield Fact**
Hypersensitivity vasculitis typically presents with palpable purpura, which is a characteristic "lumpy" rash on the skin. The rash is often accompanied by symptoms such as fever, joint pain, and abdominal pain.

**Correct Answer:** C.