urinary bladder +micturation

• Urinary bladder functions as a temporary storage organ that can empty at an appropriate time
• The bladder is situated in the pelvic cavity when empty, but expands superiorly into the abdominal cavity when it becomes full
• The urinary bladder is an abdominal organ at birth, positioned at the extraperitoneal area of the lower abdominal wall. Around the 5th or 6th year of age, the bladder gradually descends into the area of the true (minor) pelvis
• Parts of the urinary bladder

  • Apex
  • Base
  • Superior surface
  • Inferolateral surfaces
• Trigone


  The smooth triangular area between the openings of the ureters and urethra on the inside of the bladder
• Nerve supply to the bladder

  Sympathetic nerve transmits impulses from pain receptors to the upper lumbar segment, resulting in the perception of pain sensation from the urethra & bladder. Pelvic nerve transmits impulses from tension & pain receptors in the bladder wall to the sacral region of the spinal cord, resulting in reflex micturition & sensation of bladder fullness. Pudendal nerve transmits impulses for the sensation of distention of the urethra, passage of urine through the urethra, and maintains the tonic contractions of the skeletal muscle fibers of the external sphincter
• Efferent supply to the bladder

  Sympathetic supply is inhibitory to the bladder wall, motor to the internal urethral sphincter, seminal vesicle, ejaculatory duct & prostatic musculature. Parasympathetic supply is motor to the bladder wall, inhibitory to the internal urethral sphincter. Somatic supply is motor to the external urethral sphincter
• Micturition reflexes start to appear at the first stage. They are progressively intensified in the subsequent stages up to stage 4
• Sensations related to urge to void urine

  • From 300 – 400 ml ⇒ sense of fullness of the bladder
  • From 400 – 600 ml ⇒ sense of discomfort
  • From 600 – 700 ml ⇒ sense of pain
• Micturition reflexes


  1. Start to appear at the first stage and are progressively intensified in subsequent stages up to stage 4

  2. Can be voluntarily suppressed
• At about 700 ml, there is a break point where micturition cannot be suppressed
• Phases of micturition


  • Storage phase (filling phase)
  • Voiding phase (emptying phase)
• After urination


  1. The female urethra empties by gravity

  2. Urine remaining in the male urethra is expelled by several contractions of the bulbocavernosus muscle
• Central coordination of micturition

  1. Occurs in the pontine micturition centre

  2. Parietal lobes and thalamus receive and coordinate detrusor afferent stimuli

  3. Frontal lobes and basal ganglia provide modulation with inhibitory signals
• Cortical centers facilitate micturition by

  • Discharging signals that lead to stimulation of sacral micturition center
  • Inhibition of pudendal nerves resulting in relaxation of external urethral sphincter
  • Contraction of anterior abdominal muscle & diaphragm to increase intra-abdominal pressure and intra-vesical pressure
• If the condition is favourable

  • Higher centers will inhibit the micturition reflex by inhibition of sacral micturition center
  • Stimulation of pudendal nerves resulting in contraction of external urethral sphincter
  • Holding of urine under sympathetic regulation (hypogastric nerve)
• Urinary flow rate decreases in older individuals, possibly due to age-related decrease in detrusor contractility
• Low estrogen levels after menopause can lead to atrophy of urethral mucosal epithelium and other related issues
• Most older men have benign prostatic hyperplasia, potentially leading to bladder outlet obstruction and voiding symptoms
• Age-related changes can lead to an atonic bladder (hypotonic bladder) due to destruction of sensory nerve fibers
• Treatment for abnormal micturition may involve antimuscarinic drugs, bladder catheterization, and correction of underlying causes
• Neurogenic problems related to micturition may be treated with anticholinesterases to increase detrusor contraction
• Cholinergic drugs are not effective for neurogenic bladder issues
• Antidepressants can make abnormalities of micturition worse
• Neurogenic problems


  Treated with anticholinesterases to increase detrusor contraction
• Cholinergic drugs are not effective for neurogenic problems
• Automatic bladder (Spastic neurogenic bladder)


  During spinal shock, the urinary bladder loses tone and becomes flaccid and unresponsive. Later, urine overflows by dribbling
• Automatic bladder (Spastic neurogenic bladder)


  After spinal shock has passed, the voiding reflex returns without voluntary and higher centre control. Whenever the bladder is filled, there is automatic evacuation
• Uninhibited neurogenic bladder


  Due to a lesion in some parts of the brain stem, there is continuous excitation of spinal micturition centres, leading to uncontrollable micturition
• Nocturnal micturition (Bed wetting)


  Occurs in infants and children below 3 years due to incomplete myelination of motor nerve fibers of the bladder, resulting in loss of voluntary control of micturition
• Overactive bladder syndrome


  Causes detrusor instability, uncontrolled bladder contractions, associated with stroke, spinal injury, MS, and certain medications. Symptoms include urinary urgency, nocturia, frequency, and urge incontinence
• Overactive bladder syndrome treatment

  Includes lifestyle changes, muscarinic receptor antagonists, β3-adrenoceptor agonists, topical vaginal oestrogen-replacement therapy, and synthetic antidiuretic hormone analogue
• Urethral sphincter incompetence


  Causes dribbling and/or continuous leakage associated with incomplete bladder emptying, due to impaired detrusor contractility and/or bladder outlet obstruction
• Painful bladder syndrome/interstitial cystitis (PBS/IC)

  Characterized by bladder pain, altered bladder epithelial expression, central sensitization, and increased activation of bladder sensory neurons