Final answer:
Extravasation is the process by which blood and its components leak out of the vascular system due to injury or during immune responses such as diapedesis. It is also involved in cancer physiology and treatments, with particular relevance to the EPR effect in solid tumors.
Step-by-step explanation:
Extravasation involves the extra-vascular leakage of various components of the blood when a blood vessel is compromised. In the case of an injury, where a blood vessel is severed, blood and blood components, such as erythrocytes (red blood cells) and leukocytes (white blood cells), can leak out of the vascular system. Furthermore, this process is essential for the immune response, known as diapedesis, where leukocytes emigrate from the bloodstream and move through the capillary walls to reach infected or inflamed tissue.
Notably, in diseases such as cancer, the process of extravasation can be altered. The structure of blood vessels in solid tumors is often abnormal, leading to an increased permeability that facilitates the escape of substances into the tumor tissue, which is a phenomenon exploited in targeted cancer therapies like the enhanced permeability and retention (EPR) effect. In the context of phagocytosis, extravasated white blood cells employ this migration to perform their function in the defense against pathogens, engulfing and destroying them within a phagolysosome.