Intraprostatic dht & type 2-5a-reductase important in development of bph: bph is not developed in men who are castrated before puberty. Castration causes enlarged prostate to shrink: static factors are anatomic enlargement of prostate gland, produces a physical block at bladder neck & thus urinary flow obstruction. This must be recognized when drug therapy considered: dynamic factors may become more extreme if patient stressed or in pain. Results in increased alpha-adrenergic tone & excessive contraction of prostatic stromal tissue. Medication-related symptoms: testosterone replacement used to treat primary & secondary hypogonadism. Patients with bph w/narrowed urethral lumen, loss of detrusor contraction could result in urinary retention: diuretics can produce polyuria. Clinical presentation: symptoms of bph divided into 2 categories: obstructive & irritative, obstructive symptoms, prostatism or bladder outlet obstruction, results when dynamic & static factors reduce bladder emptying. Urinary flow rate decreases, bladder emptying is incomplete & slow, straining, urinary retention, suprapubic pain due to bladder overdistention.