The bladder is a distensible, muscular sac for the temporary storage of the urine, which enters it through the ureters. It lies in the retro-pubic space, resting on the pubic symphysis and pubic bones. When empty, the bladder's superior surface is roughly triangular, with an anterior apex. The posterior surface is the base and the ureters enter it postero-laterally. In the male, the base is closely related to the seminal vesicles and terminal part of the vas deferens. In the female, it is related to the lower part of the uterus and upper part of the vagina. The base tapers inferiorly to form the neck, which is supported on each side by condensations of pelvic fascia, known as the pubo-vesical ligaments in the female and pubo-prostatic ligaments in the male. At the inferior angle of the trigone is the internal opening of the urethra.
The arterial supply to the pelvic part of the ureter and the bladder is primarily through the superior and inferior vesical branches of the internal iliac arteries. Venous drainage is into the internal iliac vein, via the vesical venous plexus, lying on the external surface of the bladder.
Lymphatics accompany the blood vessels, draining mainly to internal iliac nodes (the lateral part of the bladder may drain to external iliac nodes).
The innervation of the bladder is entirely autonomic, via the hypogastric plexus. It consists of a parasympathetic component, which is responsible for contracting the smooth muscle of the bladder wall (detrusor muscle) and empties the bladder. There is also a sympathetic component, which appears to be responsible for closing the "internal" involuntary sphincter, located at the junction with the urethra (e.g., during ejaculation).
- Afferent fibres:
- accompany both the sympathetic and parasympathetic nerves
- Those traveling with sympathetic nerves consist mainly of pain fibres and return to the T11-L2 segments of the spinal cord
- Those traveling with parasympathetic fibres are responsible for the sensation of fullness of the bladder (there may also be some pain fibres)
- Hence, stimulation of pain fibres of the bladder can lead to referred pain in the lower abdominal wall (afferents travelling with sympathetics) with or without referred pain in the perineum (afferents with parasympathetics).
As the bladder fills, stretch receptors in its wall are stimulated and impulses pass to the spinal cord. Activation of parasympathetic nerves causes the detrusor muscle to contract and the internal urethral sphincter to relax, directing urine into the urethra. Simultaneously, the main muscle of the urogenital diaphragm, the sphincter urethrae (somatic innervation) is relaxed. This allows urine into the more distal part of the urethra. In infants, micturition is a reflex action and occurs every time distension of the bladder reaches a certain point. Voluntary control during post-natal development is accomplished by conscious contraction of the sphincter urethrae muscle.
- state the course of the ureters, in both the male and female pelvis
- describe the structure, function and location of the bladder
- describe the path of the urethra in the male and female
- state the arterial blood supply and the venous and lymphatic drainage of the bladder and ureters
- state the nerve supply to the bladder and describe its function in micturition
- answer applied anatomical questions.