1. word that means produced by a living thing 2. a word that means NOT produced by a living thing

Organ Systems and Organs

Before one can understand how xenobiotics affect these different body components, it's important to understand normal body components and how they function. For this reason, this section provides a basic overview of anatomy and physiology as it relates to toxicity mechanisms.

Basic Body Structure and Organization

We can think of the basic structure and functional organization of the human body as a pyramid or hierarchical arrangement in which the lowest level of organization (the foundation) consists of cells and chemicals. Organs and organ systems represent the highest levels of the body's organization (Figure 1).

Diagram of a six-layer pyramid to represent the hierarchical organization of human body components into the following, from bottom layer to top: chemicals, cells, tissues, organs, organ systems, and organism.

Figure 1. Pyramid represents a hierarchical organization of human body components

(Image Source: NLM)

Simplified definitions of the various levels of organization within the body are:

Organ system — a group of organs that contribute to specific functions within the body. Examples include:

Gastrointestinal system

Nervous system

Organ — a group of tissues precisely arranged so that they can work together to perform specific functions. Examples include:

Liver

Brain

Tissue — a group of cells with similar structure and function. There are only four types of tissues:

Epithelial

Connective

Muscle

Nerve

Cell — the smallest living units in the body. Examples include:

Hepatocyte

Neuron

Chemicals — atoms or molecules that are the building blocks of all matter. Examples include:

Oxygen

Protein

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