A 34-year-old man presents with a 5-day history of a painful sore on his hand. Physical examination reveals a 0.5-cm abscess on the extensor surface of the left hand that drains a thick, purulent material. Diapedesis of leukocytes into and around this patient’s infected wound occurs primarily at which of the following anatomic locations?

**Core Concept**
The question tests the understanding of the inflammatory process, specifically the migration of leukocytes to the site of infection. This process involves the movement of white blood cells through the blood vessel walls to the site of injury or infection. **Diapedesis** refers to the process by which leukocytes escape from the capillaries into the tissues.

**Why the Correct Answer is Right**
Since the correct answer is not provided, I will explain the general concept. Diapedesis occurs primarily at the **postcapillary venules**. This is because the postcapillary venules have a larger diameter and a thinner wall compared to other blood vessels, making it easier for leukocytes to migrate through. The process is facilitated by the interaction between adhesion molecules on the surface of leukocytes and endothelial cells lining the venules.

**Why Each Wrong Option is Incorrect**
**Option A:** This choice is incorrect because while arterioles do play a role in regulating blood flow to the affected area, they are not the primary site for diapedesis.
**Option B:** This choice is incorrect because capillaries, although involved in the exchange of substances, are not the primary location for the migration of leukocytes.
**Option D:** This choice is incorrect because while lymphatic vessels are involved in the removal of excess fluid and proteins from the interstitial space, they are not the primary site for diapedesis.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the inflammatory process, including diapedesis, is a critical response to infection and injury. Understanding the steps involved in this process can help in diagnosing and managing various conditions.

**Correct Answer:** D. postcapillary venules.

✓ Correct Answer: B. Postcapillary venules