Fact 1: Endocrine hormones travel throughout the body in the blood.

Fact 2: Endocrine cells secrete hormones.

Given the two facts above, answer the question "Cells that secrete hormones travel throughout the body in what?" with the following options: 
- skin
 - deltas
 - blood
 - atoms
 - waves
 - sleep
 - genes
 - breathe


 

   blood      