The receptor decides which cells respond
- The idea
- Predict
- See it
- Why
- Check
The idea
“A hormone acts on the cells it reaches, or the ones it can get inside.”
A hormone sounds like a package, so the cells it's delivered to should react. Blood delivers it nearly everywhere, and most cells ignore it.
The short version
The mistake: A hormone acts on the cells it reaches, or the ones it can get inside.
What's actually true: A cell responds to a signal only if it has a receptor for it, however many cells the signal reaches or enters.
- A cell responds to a signal only if it makes a receptor whose shape fits it. Those cells are the signal's target cells.
- A hormone in the blood reaches nearly every cell. Cells without its receptor sit in the same blood and do nothing.
- Steroid hormones like estrogen cross almost any cell's membrane. They still act only in cells that make their receptor, a protein inside the cell.
On the exam: Ask which cells have the receptor. Getting there, or getting in, doesn't decide who responds.