What process relates to a treatment involving direct insertion into a vein?

The process that involves direct insertion into a vein is termed "intravenous." This method allows for the administration of medications, fluids, or nutrients directly into the bloodstream through a vein. It is commonly used in various medical settings because it provides immediate access to the circulatory system, ensuring rapid effects of the treatment compared to other routes of administration.

Intradermal refers to the injection into the dermis, just under the skin. Intramuscular involves injecting into a muscle tissue, which is absorbed at a different rate than intravenous methods. Subcutaneous involves injecting into the tissue layer between the skin and the muscle. Each of these methods has specific applications and is not associated with direct access to the venous system like intravenous administration is.