8. The Physiology of Micturition Flashcards
What is the body of the bladder?
The temporary store of urine.
What is the trigone of the bladder?
Ureteric orifices and internal urethral orifice are at the angles of a triangle.
What is the neck of the bladder?
Connects the bladder to the urethra.
What does the Latin - detrusor mean?
To push down.
What are the three layers of the detrusor muscle?
Inner longitudinal, middle circular, outer longitudinal.
How does the bladder have strength in all directions of stretch?
The arrangement of the muscle layers.
What supplies the detrusor muscle?
Autonomic nervous sytem, not voluntary control.
What is the spinal nerve supply of the detrusor muscle?
Bilateral.
What is the internal urethral sphincter?
Continuation of the detrusor muscle, made of smooth muscle.
What is at the bladder neck?
Physiological sphincter, no muscle thickening.
What is the primary muscle of continence?
Internal urethral sphincter.
What is the external urethral sphincter?
The anatomical sphincter, localised circular muscle thickening to facilitate action.
What is the external urethral sphincter derived from?
The pelvic floor muscles.
What type of muscle is the external urethral sphincter?
Skeletal, so voluntary control.
How does the external urethral sphincter hold in urine?
Contracts to constrict the urethra.
What is the parasympathetic supply of the detrusor muscle?
Pelvic nerve (S2-S4).
What is the effect of parasympathetic activity on the detrusor muscle?
ACh acts on M3 receptor to cause contraction.
What is the sympathetic supply of the detrusor muscle?
Hypogastric nerve (T10-L2).
What is the effect of sympathetic activity on the detrusor muscle?
NA acts on B3 receptors to cause relaxation.
What is the sympathetic supply of the internal urethral sphincter?
Hypogastric nerve (T10-L2).
What is the effect of sympathetic activity on the internal urethral sphincter?
NA acts on a1 receptors to cause contraction.
What is the somatic supply of the external urethral sphincter?
Pudendal nerve (S2-S4).
Where is the spinal motor outflow of the external urethral sphincter from?
Onof’s nucleus of the ventral horn of the cord.
What is the effect of the somatic supply of the external urethral sphincter?
ACh acts on nicotinic receptors to cause contraction.
What is the basic messaging pathway when the bladder is full?
Brain micturition centres activated -> spinal micturition centres -> parasympathetic neurones.
What causes the detrusor muscle to contract?
Increase in parasympathetic stimulation to the bladder via the pelvic nerve. This causes it to increase intravesicular pressure.
How does the cerebral cortex respond to a full bladder?
Make a conscious, executive decision to urinate. This reduces somatic stimulation to the external urethral sphincter so relaxes.
What leads to bladder emptying through the urethra?
Contraction of the detrusor muscle with paired relaxation of the external urethral sphincter.
Why does the intravesicular pressure of the bladder hardly change with filling?
The walls of the bladder have many folds, which distend when filling with urine.