Evolution into human body took millions of years for universe to design our body.

Respiration being too important for all cells to work, heart was placed closest to lungs so that oxygen could reach the cardiac cells because cardiac muscles work the most.

Arteries were directed upwards to brain brain asap as it cant survive without oxygen and repair is not still developed. Plus thinking requires energy.

 The best of blood with glucose is also given to brain as it likes glucose. 

Being the head in catering , liver directly sends to heart or heart sucks glucose rich blood out of it! Brain has those cell bodies which are heavy in energy demand.

 After-all they have to make those neurotransmitters and then initiate activities in other organs pr tissues by giving the efferent spark.

 But once the muscle ,for instance starts, regular blood supply and fat will keep the fuel on. 

I am to think about mitochondria. It gets oxygen to burn energy out of the glucose. 

So each cell helps its mitochondria burn it. And then use the energy to do its task. 

So nature does crave the body out of something and it is a very detailed, carefully designed [gigantic] work, which took so long 'millions of year' time.