What is the origin of the substances in the body?

Substances present in the human body can have two origins:

  • Produced by the body, these are known as endogenous substances.
  • Externally produced, these are known as exogenous or xenobiotic substances. 

Endogenous substances :

A veritable biological factory, the body naturally produces hundreds of substances. These substances, known as endogenous substances, are produced by organs, including the endocrine glands, are transported by the bloodstream and contribute to the proper functioning of the body.

"The measurement of these substances provides information on the functioning of the body and allows the assessment of a person's state of health."

Conventional blood tests are usually prescribed by doctors and carried out in medical laboratories. The results are compared with reference values to identify deficiencies or excesses and, if necessary, to take action. 

Examples of frequently measured endogenous substances are: cholesterol (sterol used for hormone production), glucose (sugar), estradiol (female hormone), testosterone (male hormone), thyroxyne (thyroid hormone), etc. 

Exogenous or xenobiotic substances:

As opposed to an "endogenous" substance that is produced by the body, a substance that is foreign to the body is said to be "exogenous" or "xenobiotic". 

Some examples of common xenobiotics: drugs, pesticides, plastics (plasticizers), heavy metals (lead, cadmium, mercury), etc.