If fuel and oxidizer are pumped by turbines to the combustion chamber, then why there are so many pipes around? It should only have a two-cylinder shaped turbine assembly. I doubt there are other gases also pushed in other than fuel and oxidizer.
While an ideal engine would just ingest fuel and oxidizer and produce exhaust gas real world engines will have some combination of regenerative cooling, film cooling, turbine exhaust, hydraulic power, ignition systems, pressure sensing, tank pressurization systems, drain/purge/test lines, and electrical connections that just look like pipes for heat protection, and are probably majority of the 'plumbing' visible in the question photo. Some of these may also have bypass or redundant connections.
The possible contents are liquid fuel, liquid oxidiser, vaporised fuel, vaporised oxidiser, fuel rich turbine exhaust, oxidiser rich turbine exhaust, fully burned exhuast, hydraulic pressure, hydraulic return (possibly multiples of these if valves outside engine, ignition system fluids, pneumatic system gases, electricity.
The tubes built into the nozzle perform to very necessary functions.
- the very very, super cold, super dense liquid in these pipes keeps the nozzle from melting or really deforming and becoming too inefficient. When wondering about rockets always consider cost to efficiency and performance to weight. Engines manufactured in higher volumes must meet these criteria. The liquid in the pipes that are part of the nozzle is the super super sub cold and dense fuel. To give up its energy the best way requires it to be a specific temp. The bigger nozzle pipes protects the integrity of the nozzle and preheats the fuel.