For depression diagnoses, does one make a clear distinction between endogenous and exogenous causes of depression? Roughly speaking, we might imagine that people have depression predominantly for one of two reasons:


Endogenously induced: The person has some inherent inballance between different neurotransmittors; some part of the persons's brain that regulates emotions is damaged et cetera.
Exogenously induced: The person has no friends; the person has been left by several of his/her partners; the person is unemployed and can't get a job et cetera.


Obviously, in many cases it will not be this black and white.
Whew, OK. I am going to take a crack at this. The question asks about depression diagnoses, so I will interpret and focus on that accordingly. I think we can all agree that making any clear distinction between endogenous and exogenous causes of depression is difficult, since 1) liken to the Nature vs. Nurture question, people generally agree that Major Depression is a result of multiple factors, and 2) clinicians disagree on which (exogenous vs. endogenous) tends to be the &quot;primary&quot; cause of depression [1].
When it comes to making a clinical diagnosis, psychiatrists and other mental health professionals will use the multi-axial system in documentation. Axis IV is a part of the system, and is where exogenous factors can be reported as psychosocial and environmental problems that may affect the diagnosis, treatment, and prognosis [2]. In addition, the clinician should know to keep in mind that psychosocial problems may develop as a consequence of the patient's psychopathology!
Examples of commonly listed psychosocial and environmental problems include family problems (illness, death), social environment (isolation), educational/occupational problems, economic problems, etc., etc.

The evaluation of stressors is based on a clinician's assessment of the stress that an average person with similar sociocultural values and circumstances would experience from psychosocial stressors [1].
The judgement is based on the degree of change that the stressor causes in the person's life, the degree to which the event is desired and under the person's control, and the number of stressors.


Tidbits

To make a quick note about endogenous factors, it is interesting to note that the most consistent abnormality in those with depressive disorders is increased frequency of abnormal hyperintensities in subcortical regions of the brain...
A long-standing clinical observation is that stressful life events more often precede first, rather than subsequent, episodes of mood disorders.
^ One theory proposed is that the stress accompanying a first episode results in long-lasting changes in the brain's biology... so a person has a high(er) risk of experiencing subsequent episodes of (a) mood disorder(s), even without an external stressor [1].
While some clinicians believe that life events play the primary or principal role in depression, others suggest that life events have only a limited role in the onset and timing of depression.
What may seem to be a relatively mild stressor to outsiders may be devastating to the patient due to particular/personal idiosyncratic meanings the patient attach to the event.
Edward Bibring thought perhaps depression is [the result of] the phenomenon that sets in when a person becomes cognizant of a discrepancy between his high ideals and the inability to meet the goals appropriate to reach said ideals.


I suppose I did not provide an adequate answer to your question. Given what I have looked into, it appears that individuality plays a ginormous factor in determining one's personal cause(es), and not only do clinicians disagree on the source of depression, but it appears that when clinicians make their diagnosis/diagnoses, a clear distinction between endogenous and exogenous influences is not made. At least, generally speaking...
References

Kaplan and Sadock's Synopsis of Psychiatry
DSM-IV-TR® Diagnostic and Statistical Manual of Mental Disorders