You do not need to know every branch of arteries/nerves, or detailed pathways. You just need to know the clinically relevant ones. For example, which artery/nerve can be damaged if you break the shaft of your humerus (deep brachial a./radial n); or if you dislocate your hip posteriorly, which nerve is affected (sciatic n) and of course the clinical findings. That's as far as nerves; for pathways know key regulatory enzyems for all the pathways(like PFK-1, or F2,6BP, Pyruvate kinase, HMG-CoA reductase, etc), also the major hormones (insulin, cortisol, etc, and how/where they act), and definitely all the vitamins and co-factors. Study smart, stick to clinical relevance. Buy First Aid.