How do leukocytes move in and out of blood vessels order to reach sites inflammation or tissue destruction?

Leukocytes, also known as white blood cells, play a crucial role in the body's defense system by protecting against infections, inflammation, and tissue damage. They are able to move in and out of blood vessels in order to reach sites of inflammation or tissue destruction through various mechanisms:

1. Margination: When leukocytes sense chemical signals indicating inflammation or injury, they undergo a process called margination. During margination, leukocytes move from the center of the bloodstream towards the vessel wall. This allows them to come into close contact with the endothelial cells lining the blood vessel.

2. Adhesion: Once leukocytes are in close proximity to the endothelial cells, they adhere to the vessel wall through specific adhesion molecules expressed on their surface. These adhesion molecules bind to complementary molecules on the endothelial cells, such as selectins and integrins.

3. Diapedesis: After adhesion, leukocytes undergo diapedesis, which is the process of squeezing through the gaps between endothelial cells and the underlying basement membrane. This allows them to leave the bloodstream and enter the surrounding tissue.

4. Chemotaxis: Leukocytes are guided towards the site of inflammation or tissue destruction by chemical signals called chemoattractants. These chemoattractants are produced by damaged cells, bacteria, and other immune cells at the site of inflammation. Leukocytes sense the chemoattractants and move towards higher concentrations of these signals through a process called chemotaxis.

5. Extravasation: Once leukocytes have migrated through the vessel wall, they undergo extravasation, which is the process of moving from the perivascular space into the surrounding tissue. This involves further adhesion and migration through the extracellular matrix.

By following these steps, leukocytes are able to leave the bloodstream and reach sites of inflammation or tissue destruction where they can perform their functions, such as phagocytosis, killing pathogens, and releasing cytokines to promote immune responses.