When we eat food, digestive juices are secreted, but these are secreted only when there is some food in the food canal and so long as the food has to be digested. Our muscles move only when stimulated. Our body temperature remains constant even when outside temperature fluctuates.
The various organs perform their respective functions in harmony and at the appropriate time. The nervous system and the endocrine system ensure that the body works in a controlled and coordinated manner.
The nervous system includes the brain, spinal cord, sense organs and nerves while the endocrine system operates through certain chemicals called hormones which are produced by specialized glands and are secreted directly into the blood. The nervous system works with the endocrine system to communicate, integrate and coordinate the functions of various organs and systems in our body.
Do you know why we feel hungry? We want food when our body needs energy. The eyes see the food; brain registers this information and a series of coordinated activities are initiated. Appropriate activities in the nervous system instruct the relevant muscles in the hands and the fingers to pick up the food and put it into the mouth. When sufficient food has been eaten, signals from the hunger centre in the brain indicate a sense of fullness and the individual stops eating.
The food reaches the alimentary canal and several digestive juices (for example, gastric juice, bile and pancreatic juice under the influence of specific endocrine glands) are secreted that help in digestion. After a series of digestive processes, food is absorbed into the blood stream to fulfill the energy requirement. Many of these processes cannot be directly observed but they play a vital role in the digestion of food and providing energy for day-to-day functioning.
The nervous system and the endocrine system work together as a team to control and coordinate all activities such as physical actions, thinking processes and emotional behaviour. Sometimes we may not even be aware of the role that the nervous and endocrine systems play in our health and well being. For example, we do not have to remember to breathe or to digest food.
There is another set of action, known as the reflex action that are usually executed in response to an urgent or dangerous situation. For example, immediate removal of hand if it comes in contact with a hot object.