What Are Hormones?

The system of the internal or ductless glands, functioning with the sympathetic and parasympathetic nervous systems, is constantly engaged in meeting the changing conditions to which the individual is exposed. It does this by means of glandular secretions, which are called hormones.
The sex hormones were for a long time the hormones predominantly used in medicine, and for this reason people tend to identify hormones with the product of the sex glands only. They say, "My doctor gave me hormones," but this is like saying, "My doctor gave me capsules." There are probably hundreds of different hormones produced in the body.
Hormone is a general term, meaning the secretion of any one of the ductless glands, and there are a number of these glands. We call them "ductless" to distinguish them from the glands which have ducts or canals. Sweat glands, tear glands, salivary glands all have ducts and empty externally, on the outside of the body. Other glands, like those in the digestive system, empty within the body into an organ. The duct­less glands empty directly into the blood stream.
The theory that inner fluids regulate the functions of the body goes hack to Hippocrates, who named four cardinal fluids responsible for health or illness: blood, phlegm, yellow bile and black bile. The four humors, as they were called from the Latin word for moisture, survive in our language as descriptive of four types of personality. A cheerful, confident person we call sanguine, from the Latin for blood.