Regulation of body functions; glands

The body is a unified system whose cells, tissues and organs work in harmony; this is achieved in two ways. In humoral regulation, chemicals made by secretory glands – hormones – spread through blood, lymph and tissue fluid and strengthen or weaken the work of organs; they act strongly even in tiny amounts. In nervous regulation, receptors detect a stimulus and produce electrical signals – nerve impulses; sensory nerves carry impulses to the spinal cord and brain, and motor nerves carry them from the brain to organs. The nervous route is fast and precise, while the humoral route is slower and lasts longer. Thanks to both, the constancy of the internal environment – homeostasis – is kept: for instance, when blood sugar rises, the liver converts it into the storage substance glycogen.