The structure that detoxifies harmful substances and synthesizes lipids is the liver.

Here's a breakdown of its functions:

* Detoxification: The liver filters blood from the digestive tract, removing toxins, drugs, and other harmful substances. It breaks down these substances into less harmful forms that can be excreted.

* Lipid Synthesis: The liver plays a crucial role in producing cholesterol, triglycerides, and other lipids essential for various bodily functions.

Let me know if you'd like more details about either of these functions!