What is known of the biological factors that underlie the relationship between psychological stress and disease?

It is ambiguous, and a matter open for much debate, as to whether disease is caused by stress or stress is an effect of disease. However it is clear from various research that there is a substantial link between the two and as our knowledge and understanding of the brain and its various functions increases the answers about the causes and possible cures for stress may become more apparent still. Stress is a state of psychological tension caused by certain pressures or forces that are either physical or psychological in nature. For example prolonged exposure to the cold would cause physical stress to the body….(short extract)