The Endocrine System The function of the endocrine system is to regulate the body functions by the use of hormones. The structure of the endocrine system is therefore the structure and location of all the main endocrine glands. The pituitary gland, thyroid, pancreas, adrenal glands, and the sex glands (testes) are some of the more important ones, but there are several others. The glands secrete hormones directly in to the blood, which act as messengers. The nature of messenger which is released by the gland, once it has recognised the stimulus is chemical. The messenger is transported in the blood stream, and its speed is relatively slow. The messenger then travels to its target cells, and its effects usually take place over a large length of time. An example of this would be puberty. This is a different process to the nervous system, in the nervous system; the origin of the stimuli is usually from receptor cells, where as in the endocrine system, the origin of the stimuli is the presence of metabolite in the blood. ...