You are only allowed to ask one question at a time so I edited down accordingly. The endocrine system is a collection of glands and organs that secrete different hormones that control various functions throughout the body. Like the nervous system, the endocrine system responds to stimuli only on a slower time scale (hours instead of seconds). The glands and organs secrete hormones, or small chemical molecules that travel through the bloodstream to their target receptors to invoke a chemical response. Different funtions controlled by hormones include growth, sexual responses, and digestion. Some examples of glands include pituitary, adrenal, and thyroid. Examples of hormones include estrogen, testosterone, insulin, and thyroxine.