The hypothalamus is a small part of the human brain that constantly monitors information from all parts of the body and in response to specific inputs regulates organs that make up the endocrine system to produce hormones that influence the entire body. Other organs that are part of the endocrine system include the pituitary gland, the pancreas, the thyroid gland, the adrenal glands, etc.
The endocrine glands control activities in the body with the help of hormones that are released into the blood stream and influence organs that have cells sensitive to the hormones released.
The ability of the brain to directly control activities of the body is quite limited. For example, let's assume a person encounters a situation that requires him to quickly get ready for a fight or flight response. To be able to tackle the situation, there are changes required in the activity of several organs, for example the heart rate and rate of breathing would have to rise so that more oxygen is pumped to the muscles, the kidneys would have to release glucose to allow for fuel for the cells, the brain would have to start noticing small details specific to tackling the situation, among many others. It is not possible for the brain to directly control changes in all the organs mentioned. There are just too many things to be done for the nervous system to directly do them. All of the person's ability to think has to be utilized to quickly create a plan of action and control muscles to implement the plan. The actions of the endocrine system in such situations takes care of all the other essential aspects. This is one of the reasons why the body systems have developed in this manner. It is this that allows the complete body to respond appropriately to whatever a person faces without the person having to consciously control each organ of the body, something that is impossible for anyone to do.
The nervous systems is a system of neurons that enables signals to move between the brain and body. The nervous system is responsible for our bodily reaction to heat and involuntary functions like our heart beat. Whereas the endocrine systems is like a communication system between our organs that secrete chemical messages through the blood stream of the body. For example hormones is apart of this process. These two systems are connect by the hypothalamus which indicates bodily needs like hunger and sexual appetite. So for example when we are hunger the stomach secretes acid to. This act of the stomach is sent through the endocrine system which then reacts with the nervous system in the hypothalamus to make us feel weak with hunger.