Examples of homeostasis include the regulation of body temperature, the pH of extracellular fluid, or the concentrations of sodium, potassium and calcium ions as well as that of glucose in the blood plasma, despite changes in the environment, diet, or level of activity.
Blue-collar workers perform labor jobs and typically work with their hands. The skills necessary for blue-collar work vary by occupation. Some blue-collar occupations require highly skilled personnel who are formally trained and certified.
The terms white-collar and blue-collar became popular in the 1920s. White-collar workers are professionals and usually work in office buildings or the clergy. Their jobs do not involve much, if any, manual labor, and they do not wear uniforms. Blue-collar workers, by contrast, usually have intense physical labor jobs.