Circulatory System- The circulatory system of the quarterbreed is almost unnecessary for its ability to live. The filling heart is connected to the paste brain just to regulate the concentration of filling to some areas. But if the quarterbreed is injured its mock plasma cells made of the filling and skin of the breed completely cover the injury with new dough skin tissue in seconds. Also the filling can replicate itself infinitely until there is no more space for it to [Note: it can only do this in an area with little to no gases and where its very hot, which fits the breed's inner body perfectly], thus making the the removal of the heart organ entirely pointless in the attempt at murdering the quarterbreed.
Digestive system- Anything it consumes turns into its filling like a regular Yukkuri. Its consumption is like the human body in this also. The quarterbreed starts by just shoving the entire food item whole into its mouth. If it can't sucessfully do this, it will try to rip it into other segments and then consume these individually. It then swallows it going through an esophagus-like passage called the Glomp, which can expand itself so as to not damage the food or choke on it. This is controlled through a special nerve from the paste brain. If this is damaged the quarterbreed has a greater risk of choking, but it's not that much of a threat because the passage can convert it into the filling very easily. Afterwards it is taken to a sub-organ system that combines the stomach,liver,pancreas,and gallblader. This is called the Convertion sub system. The previous one was the Gulping sub system. Once the food clears the Glomp passage it enters the quarterbreed's stomach where it tries to convert the consumed food into filling [Note: this is infinitely easy to do if the consumed product is the quarterbreed's filling]. If the stomach cant do it, the liver, pancreas,and gallblader try to pump magic liquids into the food in order to alter its structure to make it more like the filling. If this can't be done no matter what is tried, the amount that was converted is released into the body and the amount that wasn't is excreted through a less complicated intestinal tract, and you can very easily fathom what happens next.
Endocrine System- There are not many specific organs that regulate much complex emotion and feelings in the average quarterbreed. It is all either regulated by the brain or its fucking magic.