Introduction to Basic Physiology
In order to understand how toxic substances cause harmful changes in organs, tissues, or cells, knowledge of normal physiology and anatomy is needed. This section is an overview of normal physiology, especially as related to the normal body components and how they function. While we show how some xenobiotics can damage the different body components, detailed examples of toxic cellular and biochemical reactions will be covered in later sections.
Complexity of the Body
The body is immensely complex with numerous components, all of which perform precise functions necessary for the body to maintain health and well-being. Malfunction of any component can result in disease or a breakdown of a portion of the body. Toxic substances can damage an organ or organ system so that it cannot function properly, leading to death or sickness of the organism (for example, liver or kidney failure). However, in nearly all cases, the toxic substance actually exerts its harmful effect directly on specific cells or biochemicals within the affected organ. These cell and chemical changes in turn cause the tissue or organ to malfunction.
Specific Toxic Effects
Most toxic substances are usually specific in their toxic damage to particular tissues or organs, referred to as the "target tissues" or "target organs." Toxic effects may affect only a specific type of cell or biochemical reaction. For example:
Systemic Toxic Effects
On the other hand, the effect of some toxic substances may be generalized and potentially damage all cells and thus all tissues and all organs.
Complexity of the Body
The body is immensely complex with numerous components, all of which perform precise functions necessary for the body to maintain health and well-being. Malfunction of any component can result in disease or a breakdown of a portion of the body. Toxic substances can damage an organ or organ system so that it cannot function properly, leading to death or sickness of the organism (for example, liver or kidney failure). However, in nearly all cases, the toxic substance actually exerts its harmful effect directly on specific cells or biochemicals within the affected organ. These cell and chemical changes in turn cause the tissue or organ to malfunction.
Specific Toxic Effects
Most toxic substances are usually specific in their toxic damage to particular tissues or organs, referred to as the "target tissues" or "target organs." Toxic effects may affect only a specific type of cell or biochemical reaction. For example:
- The toxic effect of carbon monoxide is due to its binding to a specific molecule (hemoglobin) of a specific cell (red blood cell).
- Organophosphate toxic substances, which inhibit an enzyme (acetylcholinesterase) responsible for modulating neurotransmission at nerve endings.
Systemic Toxic Effects
On the other hand, the effect of some toxic substances may be generalized and potentially damage all cells and thus all tissues and all organs.
- An example is the production of free radicals by whole body radiation. Radiation interacts with cellular water to produce highly reactive free radicals that can damage cellular components. The result can be a range of effects from the death of the cell, to cell malfunction, and to the failure of normal cell division (for example, cancer).
- An example of a multi-organ chemical toxic substance is lead, which damages several types of cells, including kidney cells, nerve cells, and red blood cells.