Major Depressive Disorder, Critical Literature Review

                    Major Depressive Disorder Name Institutional Affiliation              
Major Depressive Disorder             Major depressive disorder which can also be simply called depression is a mental disorder that causes mood changes which result in sadness, sorrow, irritability, and a sense of loneliness for more than two weeks. Other symptoms include lack of interest in activities that are normally enjoyable, low self-esteem, sleeping problems, reduced concentration, eating problems, among several others. The symptoms may be present all the time or may cease for years only to emerge again later.  Major depressive disorder largely affects an individual’s quality of life (Belmaker & Agam, 2008). The prevalence of depression during a lifetime stands at between 7%-12% in men, and 20%-25% in women. Depressive disorders account for 40.5% of all mental illnesses (Papakostas & Ionescu, 2014). Traditionally perceived as a disease of the elderly adults, the major depressive disorder has crossed the age barrier and is affecting both the old and the young. Studies have shown high major depressive disorder occurrence rates among young people, especially of ages between 12 and 20 years. Cases of young people with major depressive disorder increased to 11.5% in 2014 from 8.7% in 2005 (Mojtabai, Olfson, & Han, 2016). It was also revealed that the increase in cases of the major depressive disorder in young people has not been met by an increase in mental treatment of young people. Environmental, psychological, social, and genetic factors have all been associated with the condition. Risk factors include substance abuse, some medications, family history of the disease, lifestyle changes, and chronic illnesses (Egede & Zheng, 2003). Socioeconomic status changes have been associated with the major depressive disorder in the elderly. Unemployment has also been shown to be a popular trigger for the major depressive disorder (Park, Lee, Sohn, Seong, & Cho, 2015). The major depressive disorder is managed using antidepressant drugs, counselling, and electroconvulsive therapy.  This review seeks to find out the relationship between genetic, psychological, and social factors in causing and maintaining major depressive disorder. Biological Causes of Major Depressive Disorder             Genetics has been strongly associated with the major depressive disorder, and various studies have been carried out to shed more light on this topic. Research has shown that major depressive disorder can be genetically inherited. This is the reason why people with major depressive disorder family history are at a higher risk of getting the disease. Studies in monozygotic and dizygotic twins have shown that major depressive disorder has a 37% heritability rate (Belmaker & Agam, 2008).             Serotonin, dopamine, and norepinephrine are the monoamine neurotransmitters associated with the major depressive disorder. Serotonin controls sleep, eating, mood, and sexual behavior. Norepinephrine is responsible for responding to stressful situations. Dopamine is the neurotransmitter responsible for the sense of pleasure. Lower than normal levels of these neurotransmitters increases the chances of one getting depression. This explains why antidepressants are targeted at increasing the levels of these neurotransmitters in the body. Individuals with disrupted norepinephrinergic systems, cannot handle stress well, and may easily lead to depression. Low levels of dopamine lead to lack of interest or pleasure in previously enjoyable activities. Other neurotransmitters such as glutamate, acetylcholine, and Gamma-aminobutyric acid (GABA) have been shown to have a role in the etiology of the major depressive disorder. The levels and functioning of these neurotransmitters are determined by an individual’s genetics. Certain gene polymorphisms control the functioning of the neurotransmitters and their receptors, hence increase the likelihood of one getting major depressive disorder in a lifetime. For instance, carriers of the short allele of the serotonin transporters have been shown to have a higher prevalence of major depressive disorder (Rot, Mathew, & Charney, 2009). Various hormones are also associated with depression. Underproduction of thyroid hormones by the thyroid gland (hypothyroidism) has been shown to cause depression. Thyroid hormone replacement usually leads to alleviation of depression. Cortisol, produced in the adrenal gland is also highly linked to the major depressive disorder. High levels of cortisol cause depression. Estrogen levels have been associated with the higher incidences of depression in the female population as compared to male counterparts. Low estrogen levels, such as during the post-partum and post-menopausal periods disrupt the functioning of neurotransmitters, increasing vulnerability to depression (Schimidt et al., 2000). Low testosterone levels, especially in men over fifty years has been linked to high incidences of depression.   Psychological Causes of Major Depressive Disorder             Life is fast in the 21^st century. Some individuals have to do more than one job. Others have to cope with tight deadlines, uncooperative colleagues, impatient customers, and heavy workloads. All these make life highly stressful and may lead to depression. Stress has been directly associated with depression. When one is stressed, the cortex of the brain stimulates the hypothalamus to produce corticotropin, releasing hormo...