Chemicals & Human Health

Toxicology Problem Set

Problem 3: Routes of entry

For help to answer the question:

Which of the following is NOT a possible route of entry for a hazard?
A. ingestion
B. absorption
C. exposure
D. inhalation


To cause harm to a person, a hazard must enter the body. Merely being exposed will not cause harm if the hazard does not actually enter the body. There are three primary ways that a hazard can enter the body:
Ingestion - Chemicals that are ingested enter the body by being eaten. From the digestive track, they can go to the liver or the lymphatic system and then on to the bloodstream. Some chemicals are not absorbed by the digestive track, so they pass through the body and are excreted in the feces.

Inhalation - Chemicals can be breathed into the lungs, called inhalation. The inside surface of the lungs very large and is a poor chemical barrier. Many chemicals that are inhaled can easily and quickly enter the bloodstream from the lung tissue.

Absorption - Chemicals can enter the body by moving through the skin, called absorption. The skin is a very good barrier and provides protection from many hazards, but some substances can penetrate the skin, then enter the blood stream and be carried to all parts of the body.

For example, a pack of cigarettes in a man's shirt pocket does not cause harm to him because nothing from the cigarettes has entered his body. If, however, he smokes one of the cigarettes, the smoke has entered his body through his lungs and can cause harm.

Toxicology Problem Set Chemicals & Human Health

The Southwest Environmental Health Sciences Center
The Biology Project
The University of Arizona
Tuesday, September 16, 1997
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