Micturition is the voiding process of the bladder, effected by a contraction of the muscle around it (the detrusor), simultaneously with a relaxation of the two sphincters of the urethra.
It is a very complex process. To simplify, we can consider it is based on a reflex connection between strain sensors in the wall of the bladder and flow sensors in the urethra on one side, and the detrusor on the other side. When a determined filling level is reached, the strain triggers the contraction of the bladder, and the flow sensors maintain it as long as there is urine passing. Except in the young child, this reflex is under voluntary and reflex control and inhibition, through nervous centers of the cortex of the brain. Other centers in the brain stem and cerebellum have the function of co-ordinating the different commands of micturition and continence, and to integrate them in larger bodily processes. The orthosympathetic system (main neurotransmitters: adrenaline and noradrenaline) is an inhibitor: it relaxes the detrusor and tightens the sphincters; the parasympathetic system (main neurotransmitter: acetylcholine) controls micturitions' processes: it makes the detrusor contract and the sphincter relax. The external sphincter is under the control of the somatic ("voluntary") nerve system. Normally, in adults, continence is complete, and micturition can be started at every time on command. But this latter fact must be relativised: a delay to initiate micturition is observed in the majority of people in the presence of others (Middlemist & al, 1976).
Causes of urine retention include the insufficient contraction of the detrusor, or an excessive resistance to flow in the urethra.
Shy bladder seems to be due to an excessive inhibition of micturition by the brain's centers, and by an overactivity of the orthosympathetic system (stress), which relaxes the detrusor and tightens the sphincters. The psychological background of the disorder is evident: it has characteristics of a social phobia. An underlying organic trouble is indeed quite seldom found. (Rosario & al, 2000).
However, many other causes can trigger micturition troubles, a psychological factor can sometimes only reveal a physical / structural disorder. An strong pointer towards psychological origin is a patient who is able to void properly when alone, and yet has problems within a defined social situation. ( for example: impossible to urinate in public lavatories, but normal stream when alone at home) Contrary to the problems mentioned so far, the constance of the trouble, its fast amplification, other symptoms like frequent need to urinate, blood in urine, pains, the feeling of a bulk in the abdomen or of a displaced organ, abnormal outlets, all those signs must be referred to a doctor for further investigation, to exclude a structural disorder.
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