Internists are detectives, ferreting out clues to the inner workings of their patients. Their hands pick up subtle differences in the size of lymph nodes. Their ears pick up faint sounds in the lungs. Some of them can even smell metabolic imbalances! In the midst of all the interconnectivity that is homeostasis, they find the soft spot, the organ that's not pulling its weight, the organ that's trying to steal the show. Then, they carefully select a drug from the pharmacy that will set things in order. Willy Wonka would have been an internist.
I mentioned interconnectivity, but that was an understatement. No cell in the body does anything on the sly. Right now, I can consider approximately 2 organ systems simultaneously, and it feels a lot like trying to recall one song while the radio in the background plays a different one. To illustrate, the negative feedback pathway for osmoregulation, below, is about the maximum level of complexity that exists in my understanding today.
In contrast, the image below is a scientific attempt to characterize all biochemical pathways in one cell.
Close up of N3, showing some steps in the metabolism of glucose.
It's no different from learning your way around a new city. At first, you might only know the way between school and home, and then, you might know how to get to the grocery store, but only from home. Eventually, not only can you get everywhere you need to get, but you also know the fastest way from school to the grocery store, whether or not you can stop at the bank or the gas station on your way there, and whether you should stop at the post office before school, on your way to the grocery store, or on your way home at the end of the day.
Eventually, I'm going to have that map in my head!
Physiology is an incredible symphony, isn't it? Our job is to learn to hear each individual instrument and to pick out the melody from the harmonies.