What does the root word "endo-" indicate?

The root word "endo-" comes from the Greek word "endon," which means "within" or "inside." It is commonly used in various scientific and medical terms to indicate something that is internal or located within an organism or structure. For instance, in the term "endoscopy," it refers to the examination of the inside of the body. Similarly, "endocrine" refers to glands that secrete hormones directly into the bloodstream, highlighting their internal functions. This root word helps provide clarity about the location or involvement of processes related to the internal aspects of anatomy or systems. The other options represent different spatial relationships that do not align with the meaning conveyed by "endo-."