Why do children wet the bed?
To understand enuresis better, it is useful to know how the kidneys and the bladder work.
How the body works
All the blood that flows through our body is filtered in the kidneys. Some of the liquid and nutritive substances are returned to the bloodstream, whilst excess fluid and waste products are concentrated in the form of urine.
The urine descends through the body in tubes called ureters, until it reaches the bladder, a muscle that resembles an elastic balloon - extendable and retractable. The bladder has two jobs: to store urine and to expel it, through another tube which is called the urethra.
During the night
At night, the pituitary gland produces an antidiuretic hormone which slows down urine production. Certain children only produce a very small quantity of this hormone at night and, as a result, their kidneys continue to produce as much urine as they do during the day. This could explain why they always wet the bed.
It could also be possible that their brain doesn't respond to the signal sent by the bladder, or that they have trouble waking up.
In any case, the child doesn't realise that their bladder is full, they don't get up, and they unwittingly expel the urine...in their bed.