Related topics: bladder cancer; cystoscopy; cystitis.
The urinary bladder is a hollow, musculomembranous and uneven organ, responsible for collecting the urine coming from the kidneys and conveyed inside it by the ureters. It therefore acts as a temporary reservoir, filling up between one urination and the other and occasionally emptying itself to eliminate externally. , through the urethra, the accumulated urine.
Macroscopically, the bladder is divided into three regions: fundus (or base), body and apex. At the bottom of the bladder there are, one on each side, the outlets of the ureters; the area between these and the orifice of the urethra is called the bladder trigone.
The bladder has a maximum capacity of about 200-400 ml, with considerable individual variability; in particular situations, for example in episodes of urinary stasis, the organ can still accumulate more than one liter of urine. This ability is linked to the peculiar structure of the bladder wall, in which four tunics are recognized, which from inside to "external are called: mucous tunic, submucosal tunic, muscular tunic and serous tunic.
The mucous membrane is characterized by a transitional lining epithelium, consisting of multiple cell layers that adapt their shape to the degree of filling of the bladder. When the organ is empty, the superficial cells have an umbrella or mushroom-head shape, the intermediate ones resemble a club and the lower ones have a rounded shape. making the epithelium much thinner and more multilayered.
The transitional epithelium rests on a lamina propria rich in connective tissue which, with the exception of the so-called vesical trine, can be raised in folds. These folds constitute reserve surfaces, since they flatten in the event of strong bladder filling. submucosal tunic is made up of a thin layer of connective tissue with interposition of elastic fibers; its function is comparable to a sliding plane, thanks to which the mucous tunic can modify its characteristics in relation to the degree of fullness of the bladder.
Deeper than the submucosa, the muscularis is characterized by three layers of smooth muscle fibers which together form the so-called detrusor muscle of the bladder. Although didactically divided into these three layers, in reality these muscular structures are not well differentiable, but they interpenetrate one into the other. In general, however, in the most superficial layer the muscle fiber cells are arranged in longitudinal bundles, which intertwine under the mucosa; in the intermediate layer, on the other hand, the fibrocells take on a circular pattern and thicken at the base of the bladder around the internal urethral orifice, forming the so-called smooth sphincter of the bladder. intermediate forms a valve that prevents the backflow of urine into the same. Like the superficial one, the deepest muscle layer is made up of longitudinal fibers.
The contraction of the detrusor muscle of the bladder and the relaxation of the urethral sphincter are controlled by the parasympathetic nervous system, which therefore promotes urination. Conversely, the contraction of the sphincter and the relaxation of the detrusor (filling phase) are under the control of the sympathetic system.
The serous tunic is represented by the parietal peritoneum, which covers only the upper region of the bladder and its posterolateral faces. In the remaining portions the bladder wall is covered with fibroadipose connective tissue.
