Do white blood cells leave the vessels and travel into tissues?

Yes, under certain circumstances, white blood cells (leukocytes) can leave the vessels and travel into tissues. This process is called extravasation or diapedesis.

White blood cells are a vital component of the body's immune system, responsible for defending against infections, foreign substances, and damaged cells. They circulate through the bloodstream within the vessels, constantly patrolling for potential threats. However, when these threats are detected in the tissues, white blood cells have the ability to migrate out of the vessels and directly enter the affected tissues to mount an immune response.

Extravasation is initiated when chemical signals, such as inflammatory mediators or chemokines, are released from the site of infection or inflammation. These signals create a concentration gradient that attracts white blood cells to the affected area.

The process of extravasation involves multiple steps:

1. Margination: White blood cells slow down and roll along the inner lining of the blood vessel (endothelium).

2. Adhesion: Selectins and integrins on the surface of white blood cells bind to specific molecules (ligands) on the endothelial cells, causing the white blood cells to firmly attach to the vessel wall.

3. Transmigration: The white blood cells squeeze between the endothelial cells and the underlying basement membrane, pushing aside the endothelial cells and creating temporary gaps in the vessel wall.

4. Chemotaxis: Once in the tissue, white blood cells follow the chemical gradients created by the inflammatory mediators, a process known as chemotaxis, which guides them towards the site of infection or injury.

White blood cells that have extravasated into tissues can perform their various immune functions, including phagocytosis (engulfing and destroying pathogens), releasing antimicrobial substances, and activating other immune cells to mount a coordinated response.

The ability of white blood cells to leave the vessels and enter tissues is crucial for the body's defense against infection and the maintenance of tissue homeostasis. It allows the immune system to reach and eliminate threats directly in the affected areas.