After extravasation, leukocytes emigrate in the tissue towards the site of injury is called as-
## **Core Concept**
The process of leukocytes moving out of the bloodstream and into tissues towards the site of injury involves several steps, including **extravasation** (or diapedesis) and **chemotaxis**. Extravasation refers to the migration of cells out of blood vessels into tissues. Chemotaxis is the directional movement of cells in response to chemical stimuli.
## **Why the Correct Answer is Right**
The correct term for the movement of leukocytes towards the site of injury in tissues is **chemotaxis**. Chemotaxis is a critical process in the inflammatory response, allowing leukocytes to accumulate at the site of injury or infection. This movement is guided by **chemokines** and other chemoattractants that are produced at the site of injury. These chemical signals bind to receptors on the surface of leukocytes, triggering a signaling cascade that results in the directed migration of the leukocytes.
## **Why Each Wrong Option is Incorrect**
- **Option A:** Diapedesis refers to the process of cells moving through the intact walls of blood vessels into tissues. While it is related to the movement of leukocytes out of the bloodstream, it does not specifically refer to the directional movement towards the site of injury.
- **Option B:** Margination refers to the process by which leukocytes move to the periphery of blood vessels and adhere to the endothelial lining, which is an earlier step in the inflammatory response than chemotaxis.
- **Option D:** Rolling is the initial step in leukocyte recruitment, where leukocytes loosely adhere to the endothelial cells lining blood vessels and roll along the vessel wall. This is also an earlier step than chemotaxis.
## **Clinical Pearl / High-Yield Fact**
A key point to remember is that chemotaxis is crucial for the effective recruitment of leukocytes to sites of infection or injury. Defects in chemotaxis can lead to recurrent infections and are associated with certain immunodeficiency disorders.
## **Correct Answer:** C. Chemotaxis