In the human body hormones and enzymes are substances that initiate and speed up a majority of the reactions. Enzymes play the role of catalysts in the human body. They speed up many reactions and even allow many to take place which would not occur in the absence of enzymes at the temperature and in the other environmental conditions within the body.

Some examples of the function of enzymes is in our body is in digestion, respiration, energy production, among many others. It would not be entirely inaccurate to say that everything that happens in our body is in some way facilitated by enzymes acting as catalysts.

Hormones on the other hand, do not play the role of catalyst; instead they are chemical messengers which initiate chemical reactions when they are required. Hormones are produced by many organs which can control the activities going in the body using them. Hormones are a means to start or stop reactions as the need arises.