The human body system that is analogous to the xylem in plants is the circulatory system, specifically the component that involves the transport of fluids.
In plants, xylem is responsible for the transport of water and minerals from the roots to the leaves and other parts of the plant. In humans, the circulatory system (particularly blood vessels) carries oxygen, nutrients, and other essential substances from the heart throughout the body, similar to how xylem transports water and nutrients upwards in plants. While there are notable differences between the two systems, the general function of transportation and support is a commonality.