Sophia - Human Biology - Unit 5 Challenge 1. 1 — Endocrine System Understand the structure and function of the endocrine system. Which best describes the endocrine system? • a.) A system that helps distribute oxygen and other nutrients to cells all over the body • b.) A system of vessels, nodes, glands and nodules that returns excess tissue fluid to the blood • c.) A system of glands that produces and secretes hormones into the bloodstream • d.) A system that protects the intern...