physiology of micturition 28.03. 11

Physiology of micturition

Micturation is the discharge of urine from the bladder via the urethra.

A autonomic spinal cord reflex.

Facilitated & inhibited by higher centers.

Afferent & efferent through pelvic nerves.

External sphincter is under voluntary control

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Reflex and Voluntary Control of Micturition

• Bladder filling reflexively contracts the bladder

• Internal Sphincter mechanically opens

• Stretch receptors in bladder send inhibitory impulses to external sphincter

• Voluntary signals from cortex can override the reflex or allow it to take place

Disorders of micturition

• the type due to interruption of the afferent nerves from the bladder- tabes dorsalis

• the type due to interruption of both afferent and efferent nerves;

• the type due to interruption of facilitatory and inhibitory pathways descending from the brain.

• residual urine is left in the bladder.

The bladder becomes distended, thin-walled, and hypotonic,

tumors of the cauda equina or filum terminale, the bladder is flaccid and distended

During spinal shock, the bladder is flaccid and unresponsive.

It becomes overfilled, and urine dribbles through the sphincters (overflow incontinence)

spastic neurogenic bladder

Abnormalities of Micturition

• Atonic Bladder Caused by Destruction of Sensory Nerve Fibers. --- overflow incontinence

• Automatic Bladder Caused by Spinal Cord Damage Above the Sacral Region.

• Uninhibited Neurogenic Bladder Caused by Lack of Inhibitory Signals from the Brain.

The cystometrogram

• Phase-1-progressive rise

• Phase-2-sustained rise

Phase-3- rapid rise.

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Micturition reflex

Full bladder – stimulate stretch receptors

sensory signals through pelvic nerve to spinal cord

efferent fibers from S2 S3 S4 sacral segment of spinal cord through parasympathetic nerve

it causes contraction of detrusor muscles of bladder at the same time relaxation of internal sphincter Pudendal nerve to external sphincter if causes its inhibition its

relaxation causes urination

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Physiologic anatomy of the bladder

• Bladder is a smooth muscle chamber – detrusor muscle - two parts

• the body – in which urine collects• The neck – a funnel shaped extension of the body,

connecting with the urethra• Trigone – bladder neck opens into the posterior urethra,

two ureters enter the bladder at the upper angles of the trigone

Micturition

• Micturition is the process by which the urinary bladder empties when it becomes filled. It involves two steps –

1. The bladder fills progressively until the tension in its walls rises above a threshold level

2. Second step is a nervous reflex the micturition reflex

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cystometogram

• Shows the approximate changes in intra vesicular pressure as the bladder fills with urine

• Pressure peaks are called micturition waves in the cystometogram

• caused by the micturition reflex

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Posterior urethra

• Internal sphincter

• External sphincter –voluntary skeletal muscle – under voluntary control

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THE URINARY BLADDER STORES THE URINE

• Gravity and peristaltic contractions propel the urine along the ureter

• Parasympathetic stimulation contracts the bladder and micturition results if the sphincters (internal and external urethral sphincters) relax

• The external sphincter is under voluntary control