Homeostasis is keeping the internal environment of the body as constant as possible. To do this, data are needed concerning the current status of this environment, so the proper actions can be taken to adjust any imbalance.
This internal environment is affected by many internal and external factors. Examples are temperature, glucose, concentration, salt concentration, PH, Co2 concentration, and many other physical and chemical factors.
These factors need to be measured so the proper data is sent to the brain in order for it to take a decision concerning the suitable action.
The five senses measure the external factors as they are full of nerve endings that detect the changes in the outer environment of the body.
Yet, there are nerve endings in many different areas of the body that detect the changes in the internal environment, like glucose level in the body, and these information are also sent to the brain to take the proper decision.