Final answer:
The process by which leukocytes migrate from blood capillaries into tissues by squeezing through endothelial cells is called diapedesis or emigration. This movement is crucial for immune defense and is guided by chemotaxis in response to chemical signals from injured or infected cells.
Step-by-step explanation:
The migration of leukocytes through the endothelium of blood capillaries into the surrounding tissues is called diapedesis, also known as emigration. This process allows the leukocytes to enter tissues where they may take up fixed positions in lymphatic tissue, bone marrow, spleen, the thymus, or other organs. During diapedesis, leukocytes move through tissue spaces similar to amoebas, responding to chemical signals through a process known as positive chemotaxis.
Key to the body's defense, leukocytes exit the bloodstream by squeezing through adjacent cells in the blood vessel wall. They subsequently perform defensive functions, and depending on their function post-migration, may be designated as macrophages or microglia. Clinical medicine often uses differential counts of leukocytes as significant indicators for diagnostics and treatment strategies, highlighting the importance of understanding leukocyte behavior.