Micturition

Micturition Micturition is the process by which the urinary bladder empties when it becomes filled.

Micturition First, the bladder fills progressively until the tension in its walls rises above a threshold level This elicits the second step, which is a nervous reflex called the micturition reflex that empties the bladder If this fails, at least causes a conscious desire to urinate.

Urinary bladder Detrusor muscle body, passing inferiorly and anteriorly into the urogenital triangle and connecting with the urethra 40 to 60 mm

Micturition Filling Regular peristaltic contractions Renal pelvis to the bladder Oblique passage No significant changes in the composition of urine (urothelium) Emptying Detrusor muscle Internal urethral sphincter (Smooth Muscle) External urethral sphincter (Skeletal Muscle) occurring one to five times per minute Urine flowing from the collecting ducts into the renal calyces stretches the calyces and increases their inherent pacemaker activity, which Urothelium complete barrier

Innervation of the Bladder Sympathetic Parasympathetic main function in males is believed to be the prevention of reflux of semen into the bladder during ejaculation. Carry pain sensation Somatic

Filling of the Bladder Bladder muscle has the property of plasticity; when it is stretched, the tension initially produced is not maintained. This relation between intravesical pressure and volume can be studied by a procedure called cystometry.

CYSTOMETROGRAM Insert a catheter and emptying the bladder Then record the pressure while the bladder is filled with 50-mL increments of water or air (cystometry). A plot of intravesical pressure against the volume of fluid in the bladder is called a CYSTOMETROGRAM

Law of Laplace States that “The pressure in a spherical viscus is equal to twice the wall tension divided by the radius” P =2T/R P =2T/R In the case of the bladder, the tension increases as the organ fills, but also the radius increases.

CYSTOMETROGRAM 10 cm water 10 cm H20

CYSTOMETROGRAM II Stretch receptor stimulation Ib Ia

Micturition Reflex Micturition reflex is an autonomic spinal cord reflex But it can also be inhibited or facilitated by centers in the cerebral cortex or brain stem. Stretch reflex 300 to 400 mL stretch receptors in the bladder wall, especially by the receptors in the posterior urethra when

Micturition Reflex Higher control Facilitatory area : Pontine region and posterior hypothalamus Inhibitory area : Midbrain.

Micturition Reflex Receptor : Stretch receptor Afferent : Pelvic nerve S2,3,4 Centre : Sacral portion of the spinal cord Sensory area of cerebral cortex (desire) Efferent : Parasympathetic nerve Pudendal nerve inhibition

Micturition Reflex The perineal muscles and external urethral sphincter are relaxed The detrusor muscle contracts Abdominal muscle contracts Breathing held with glottis clossed Urine passes out through the urethra. Female urethra empties by gravity Male urethra is emptied by several contractions of the bulbocavernosus muscle.

Micturition Reflex Voluntary urination Children Emotional stress Cystitis , stones

Abnormalities of micturition Deafferentation Tabes dorsalis All reflex contractions of the bladder are abolished. The bladder becomes distended, thin-walled, and hypotonic But some contractions occur because of the intrinsic response of the smooth muscle to stretch. Voluntary voiding still possible

Abnormalities of micturition Denervation Afferent and Efferent nerves are both destroyed Tumors of the cauda equina or filum terminale The bladder is flaccid and distended for a while. Gradually, however, the muscle of the "decentralized bladder" becomes active, with many contraction waves that expel dribbles of urine out of the urethra. The bladder becomes shrunken and the bladder wall hypertrophied.

Abnormalities of micturition Spinal Cord Transection During spinal shock, the bladder is flaccid and unresponsive. It becomes overfilled, and urine dribbles through the sphincters (overflow incontinence). After spinal shock has passed, the voiding reflex returns no voluntary control no inhibition or facilitation from higher centers

Abnormalities of micturition Spinal Cord Transection Some paraplegic patients train themselves to initiate voiding by pinching or stroking their thighs, provoking a mild mass reflex In some instances, the voiding reflex becomes hyperactive, bladder capacity is reduced, and the wall becomes hypertrophied. This type of bladder is sometimes called the spastic neurogenic bladder. The reflex hyperactivity is made worse by, and may be caused by, infection in the bladder wall.

Kidney Diseases Edema Uremia Acidosis Anemia Osteomalacia Acute renal failure Chronic renal failure Glomerulonephritis Nephrotic Syndrome Nephrogenic Diabetes Insipidus Hypertension and Kidney Disease

Treatment of Renal Failure Dialysis Renal transplant