system
Given the following post, respond as if you're commenting on Reddit:
human
How do transplanted organs communicate with the brain after surgery?
gpt
Most organs aren't directly communicating with the brain (ie have no neurons synapsing in them) - they tend to be controlled more by feedback loops and endocrine signalling.  For example, your kidneys control how much salt is excreted based on its sensation of the blood pressure within it (via the renin-angiotensin-aldosterone system).  However, this can also be modulated centrally via hormones such as ADH.  The other commonly tranplanted organs such as livers and lungs similarly rely on mostly non-neuronal mechanisms for control.  

With that said, there are some important connections between organs and the central nervous system that can be disrupted due to a transplant.  For example, heart rate is partially controlled by the tone through the vagus nerve, which provides parasympathetic innervation and slows the heart.  Because this connection is not present in transplanted hearts, they tend to have a much higher resting rate.  On the afferent side of things, transplanted lungs have trouble with sensation to trigger cough reflexes since the ascending fibers are lost - this can lead to increased rates of aspiration and pneumonia.