How do the structures work together? What are the processes / mechanisms involved? (physiology)

ADHD = Attention Deficit Hyperactivity Disorder

Genes affect ADHD when a child is born. If they had an ancestor who had ADHD it could be passed through genes. Bad behavior in pregnancy, such as smoking/drinking could lead to the fetus acquiring ADHD when it is born. Although some may believe that somebody that received a head injury has ADHD, it most likely is that they display fits similar to the disorder. Both sugar and sugar substitute, in large amounts, can lead to both diabetes and ADHD. Food preservatives, in large consumption, end up leading to ADHD.

The dopaminergic areas of the brain are smaller in the brain of a child who has ADHD. The dopaminergic area contains the caudate nucleus, globus pallidus, and the frontal lobes. Activation in the front of the brain is lowered in the mind of a child with the disorder.

Beginnings of ADHD fits usually start from age seven. ADHD affects 4.1% of all adults (above age 18) in the US, and 9% of American children. Males are also four times as likely to develop the disorder than females.

Sources:

Abnormal Psychology by Kring, Johnson, Davison, Neale (Book)

http://www.nimh.nih.gov/health/topics/attention-deficit-hyperactivity-disorder-adhd/index.shtml