The Nervous system releases dopamine and other reward chemicals in response to stimuli. Some such stimuli are addictive substances such as nicotine. When this happens the endocrine system sends bodily messages to relax. Having too much of an artificial substance provoking reward chemicals in your brain results in you not responding or producing enough on your own. Thus how addiction begins to occur. Hope this helps!
The duct system leads the semen through the penis towards the egg cells. The glands produce enzymes and proteins that strengthen the sperm and help it survive.
