Hormones carry messages through the blood
Hormones carry messages through the blood

The endocrine system is a system of glands that secrete chemical messengers called hormones. Endocrine glands release hormones directly into the bloodstream.
Step-by-step lessons on AQA GCSE Biology 5.3.1 Human endocrine system. Each one builds up to exam-style questions. Start with the foundational topics and build up to the higher-tier material.