They all contain the same genome and can activate the same pathways. Same way that your skin and airways can make histamine as an inflammitory signal while your midbrain makes it as a sleep suppressing neurotransmitter (which is why most antihistamines make you sleepy). Genes and pathways and enzymes are quite often not organ specific.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
Notes for future OT posters:
1. Please add the 'open_thread' tag.
2. Check if there is an active Open Thread before posting a new one. (Immediately before; refresh the list-of-threads page before posting.)
3. Open Threads should be posted in Discussion, and not Main.
4. Open Threads should start on Monday, and end on Sunday.