What are the main causes, symptoms, and treatment approaches for mood disorders such as depression and bipolar disorder?

Mood disorders are mental health conditions characterized by disturbances in mood, emotions, and behavior. Depression involves persistent feelings of sadness, hopelessness, and loss of interest or pleasure in activities. Bipolar disorder, also known as manic-depressive illness, involves alternating periods of depression and mania or hypomania. Treatment approaches may include psychotherapy, medication (e.g., antidepressants, mood stabilizers), lifestyle modifications, and support networks.