Endocrine hormones travel throughout the body in the blood.
Deficiencies in the endocrine system are another source of impotence.
Lack of certain hormones in the blood can cause impotence. .
Lack of what in the blood can lead to impotence? 
Options:
1: hormones
2: hemoglobin
3: oxygen
4: iron
5: Energy.
6: t-cells
7: competition
8: Energy