How do hormones only affect on organ if they are in the blood?
see "Endocrine System" by Encyclopedia Britannica
- Endocrine glands have a LOT of capillaries
- Capillaries carry hormones away from gland
- capillary is place where material easily enters or leaves the blood since the wall of capillary is so thin
- Hormones leave hormone glands in the blood
- Blood - and hormones - travel throughout body and touch EVERY cell
- ...but hormones only affect target tissue
- Target tissue has receptor for hormones
- every hormone is chemical with chemical shape (3D shape; specific charges)
- receptors accept specific shape
- one hormone fits into receptor
- every hormone requires a unique receptor
- receptor receiving hormone "turns on"
- Target activated by hormone