Design a basic system that allows you to regulate a function in the body. What components are needed and why?

The thing that I am trying to control is known as the controlled variable.
If I want to control something I need to know what the target level is. In terms of homeostasis the target level is the set point.
I need to be able to measure the current value of the controlled variable. I use the sensor to make those measurements.
I need to be able to compare the current value of the controlled variable with the setpoint, and decide whether something needs to be done to change the value of the controlled variable. I do that in the controller.
I need to have something that will enable me to change the value of the controlled variable. The things that enable you to change the value of the controlled variable are the effectors.
I need to get information from the sensors to the controller so that it can be used. I use the afferent pathway to deliver information.
I need to get instructions from the controller to the effectors. I use the efferent pathway to deliver instructions.