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micturition (urination)
Physiology:
1) detrusor muscle
a) muscarinic cholinergic innervation, sacral plexus S2-S4
b) contracts bladder causing the bladder to empty
2) bladder outlet
a) internal sphincter
1] alpha-adrenergic innervation, hypogastric plexus, T11-L2
2] contraction of the internal sphincter retains urine in bladder
b) external sphincter
-> somatic innnervation from pudendal nerve
3) storage of urine
a) detrusor relaxation, closure of sphincters
b) normal bladder capacity is 300-600 mL
c) 1st urge to void is between 150-300 mL
4) emptying
a) detrusor contraction & opening of the sphincters
b) detrusor pressure exceeds urethral resistance
5) central nervous system
a) pontine micturition center facilitates urination
b) frontal cortex inhibits urination
Urinary changes with aging
1) decrease in
a) bladder capacity & force of contractions
b) ability to postpone voiding (frequency)
c) urethral compliance
d) strength in pelvic support muscles
2) increase in
a) post-void residual volume (> 100 mL is abnormal)
b) involuntary bladder contractions (urgency)
c) nocturia 1-2X/night
Related
age-associated changes in the urinary system
micturition/postmicturition syncope
oliguria
polyuria
urinary incontinence (UI)
General
physiologic process
References
- nlmpubs.nlm.nih.gov/hstat/ahcpr/
- Urinary Incontinence Syllabus, UCLA Specialty Women's Clinic,
Eslami M, 2001