There are many causes that contribute to and maintain depression. Genes, the brain, peripheral nervous system and endocrine system constitute the physiological mechanisms of depression. Experiences of loss and trauma, and negative, depressive cognitions play a critical role in activating these underlying mechanisms of depression.

Heredity and Genes

There is a significant genetic component to depression. Depression runs in families. Individuals inherit a vulnerability to depression that can become activated under stress, trauma and loss. Further, all people may have a genetic tendency to develop depression when under conditions of chronic stress, loss and trauma.

Neurotransmitters

Neurotransmitters are chemical messengers that enable nerve cells to communicate with each other. Certain neurotransmitters, including serotonin, norepinephrine and dopamine, function in the limbic system of the brain and are implicated in depression. Antidepressants influence the availability of these brain chemicals.

The Brain

The limbic system, comprised of the hypothalamus, amygdala and hippocampus, regulates mood, memory and hormone production and influences emotional and behavioral aspects of depression. Certain regions within the frontal cortex of the brain also influence mood and emotional functioning. Brain trauma, disease or neurotransmitter level dysfunctions that affect these areas of the brain can cause depression.

Endocrine System

The hypothalamus of the brain controls the pituitary and adrenal glands within the endocrine system. These glands release hormones such as norepinephrine, cortisol, and catecholamines that are implicated in depression. Experiences, illnesses and diseases that increase production of these hormones contribute to depression.

Loss and Trauma

The experience of emotional loss and trauma causes alterations in the brain and the endocrine systems that facilitate depression. People with excessive emotional distress develop deficiencies in neurotransmitters and excesses in stress hormones, that in turn alters cognitions, behavior, motivation and emotions that cause and sustain depression.

Negative Cognitions

Negative, self-critical, hopeless thoughts not only reflect underlying emotional states, but also contribute toward the mental and physiological substrate of depression. Negative thoughts trigger physiological responses that perpetuate the depressive emotional states and negative thought processes of depression.

Source:

AllAboutDepression.com: Biological Causes of Depression

HakomInstitute.com: Central and Peripheral Mechanisms in the Neurophysiology of Depression

WrongDiagnosis.com: Misdiagnosis of Depression