Biology

Depression is a mental disorder characterized by a feeling of intense sadness for excessively long periods of time that tends to affect with the normal functioning (Fawcett).  However, depression not only affects the mind but also the body (Mayo Clinic Staff).  The manner in which an individual feels, thinks and behaves is altered in depression and daily functioning is seriously affected (Mayo Clinic Staff).  Depression is considered to be a chronic disease that requires persistent treatment in the form of psychotherapy and medication.  There are several forms of depression including major depressive disorder, dysthymic disorder, postpartum depression, Pre-menstrual dysphoric disorder, Seasonal affective disorder, psychotic depression and seasonal affective disorder (NIMH).  Major depression is a condition in which the individual develops a range of symptoms that affect with normal functioning and can be disabling in nature.  There are high chances that an individual would experience an episode of major depression once in their lifetime.  However, there are also chances that the individual may have more than one episode of depression in their life (NIMH).  The symptoms tend to persist for at least 6 months and are characterized by the development of 5 or more symptoms.  If fewer than 5 symptoms occur for at least 2 weeks, then such as episode of depression is termed as minor depression (Ballas).

Depression is the most common mental disorder after anxiety.  Depression can occur in any age group but is more common in teens, young adults, and middle-aged individuals.  Depression can also occur in children and elders.  During the later part of the 20th century, there were more number of substance abuse cases and hence, more and more people with depression have been committing suicide.  Depressive episodes can go on for period between 6 months to 2 years without any treatment.  About 17 of elders have depression, and it may be more common in individuals who have had depression earlier in life (Fawcett).  Depression tends to occur more often in women, especially teens and young adults.  The exact cause for this has not been understood clearly.  Scientists think that a woman is more likely to seek help for depression than men, which means more number of documented cases of depression (Ballas).    Depression can occur along with a number of other disorders including anxiety disorders (such as PTSD, obsessive-compulsive disorder, panic disorder, Generalized anxiety disorder), substance abuse, social phobia, medical illnesses (such as stroke, cancer, HIV, diabetes, heart disease, Parkinsonism, etc).  If depression is treated, there are better chances of the co-existing disorder to improve.  Bipolar disorder is a mental disorder characterized by the development of bouts of mania along with bouts of depression (NIMH).    

Causes
The exact cause for depression has not been understood clearly although experts feel that it is a combination or interplay of genetic, biochemical, environmental and psychosocial factors.  Depression is often found to occur in families.  One reason for this is that it is often inherited, but here may be some kind of learned behavior transmitted down the family (Ballas). Multiple genes are involved in the transmission of depression down families (NIMH).  There may be certain changes observed in the brain scans (observed through neuro-imaging such as CT and MRI scans) of individuals suffering from depression.  Besides, it has also been found the levels of various neurotransmitters (epinephrine, dopamine, and serotonin) present in the brain are abnormal in depression (NIMH).  Certain events in life such as death of a near and dear one, problems with a partner, witnessing or experiencing a stressful situation, chronic stress, disappointments at school, workplace, or at home, brain disorders (dementia, brain tumors, multiple sclerosis), certain medical illnesses, isolation, drugs such as antihypertensive agents and sedatives, childhood trauma, major illnesses, etc, can lead to depression (Ballas).      

Symptoms
Usually the symptoms of depression develop gradually over a few days or weeks.  Some people with depression have problems with experience of emotions and events that were previously enjoyable would become lack luster.  The individual is withdrawn socially and would progressive experience a hopeless life and become more and more helpless.  Functioning at the home, school, workplace or in social settings is seriously compromised (NIMH).  The individual feels lonely, withdrawn, guilty, worthless, restless, irritable, and tired.  Energy levels are low and suicidal ideation is common.  Appetite changes along with weight gain or weight loss are also common.  The individual experiences difficulty with concentration.  Activities that were once enjoyable (such as sex, holidays, social functions, etc) are now painfully stressful (Ballas).  The individual also has problems with thinking, sleeping and body movements (Mayo Clinic Staff).
 
Diagnosis
The diagnosis of depression is made based on the history, family history, drug history, symptoms, signs, blood tests, urine tests, mental evaluation, depression questionnaire, and is established based on certain guidelines mentioned by Diagnostic and Statistical Manual of Mental Disorders  Fourth Edition, Text Revision (DSM-IV-TR).  The history should try to determine previous events of depression, drugs being used or family history of depression.  Laboratory tests such as urine tests, blood tests are done to determining the functioning of various organs of the body and to rule out substance abuse.  A mental evaluation of the patient is conducted to determine the thoughts, feelings, and behavior of the individual (Fawcett).  DSM-IV-TR is guidelines used to diagnose depression based on the experience of 5 or more symptoms for more than 2 weeks.  Depressive symptoms should be existent along with difficulty in functioning (Mayo Clinic Staff).    

Treatment
Depression is treated using medications, psychotherapy and other modalities.  Several antidepressants are useful in treating depression indulging Selective serotonin reuptake inhibitors (SSRIs), Serotonin and nor epinephrine reuptake inhibitors (SNRIs), Nor-epinephrine and dopamine reuptake inhibitors (NDRIs), Tricyclic antidepressants, Monoamine oxidase inhibitors (MAOIs) and atypical antidepressants.  SSRIs are safe, effective and cause lesser side-effects.  SNRIs have similar side-effects as SNRIs but can cause dizziness and sweating (NIMH).  NDRIs does not cause sexual side-effects but can increase the risk of seizures.  Trazodone and mirtazapine are the most often used atypical antidepressants.  TCAs and MAOIs are known to be effective but have a number of side-effects and hence are reserved once the SSRIs or SNRIs do not work or cannot be administered.  If the patient has a co-existing anxiety disorder or other mental disorders, anti-anxiety drugs may be administered (Mayo Clinic Staff).

Psychotherapy is an important part of the treatment for depression.  In these sessions, the patient can understand the unhealthy thoughts and behaviors and develop better means of coping with problems of life.  It can be administered individually or during Group therapy (Fawcett).

Other forms of therapy recommended for Electro-convulsive therapy, residential therapy and hospitalizations.  Depression is usually treated on an outpatient basis and only in the case of serious depression along with sucidical tendencies, would hospitalizations be required  (NIMH).  

Complications
Usually, if the symptoms of depression are treated promptly, using antidepressants, psychotherapy, and other modes, the outcome is good.  However, the toll may be serious especially in those who do not receive any kind of treatment.  Such individuals would have problems for the rest of the lives.  Some of the common complications that may arise from depression include substance abuse, alcohol abuse, problems with relationships, family issues, heart disorders, suicidal ideation, isolation, etc (Mayo Clinic Staff).