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Control of Bladder Function 13-May-17 Urinary Bldder 1 Urinary System Kidney Ureter Aorta Urinary bladder From Hansen T. Sherrief; Texbook of Physiology CD 13-May-17 Urinary Bldder 2 Urinary Bladder Urinary bladder Orifice of ureter Detrusor muscles Ureter Trigone of bladder Prostatic urethra From Hansen T. Sherrief; Texbook of Physiology CD 13-May-17 Urinary Bldder 3 Urinary Bladder Urinary bladder Detrusor muscles – Stores urine – Periodically evacuates completely urine Ureter It is made up of smooth muscles – Detrusor muscle • Fibers extend in all directions • Spiral, longitudinal, circular – Fused to form syncytium Seminal vesicle Prostate From Hansen T. Sherrief; Texbook of Physiology CD 13-May-17 Urinary Bldder 4 Urinary Bladder Detrusor muscles When contracted can Ureter – Increase pressure in bladder by 40 – 60 mm Hg Seminal vesicle Prostate From Hansen T. Sherrief; Texbook of Physiology CD 13-May-17 Urinary Bldder 5 Urinary Bladder On the posterior wall of bladder – Small triangular area called • Trigone Orifice of ureter Trigone of bladder Prostatic urethra Lower part of trigone opens into posterior urethra The ureters enter the bladder at the upper ends of the trigone From Hansen T. Sherrief; Texbook of Physiology CD 13-May-17 Urinary Bldder 6 Innervation Parasympathetic Pelvic nerve from sacral 2,3,4 Contain both sensory and motor fibers Sympathetic fibers T11 – 12 L1,2 Inhibitory to detrusor excitatory to sphincter Internal sphincter External sphincter Parasympathetic fibers S 2,3,4 Excitatory to detrusor Inhibitory to sphincter From Hansen T. Sherrief; Texbook of Physiology CD 13-May-17 Urinary Bldder 7 Innervation Sensory fibers Sympathetic fibers T11 – 12 L1,2 Inhibitory to detrusor excitatory to sphincter Internal sphincter External sphincter Parasympathetic fibers S 2,3,4 Excitatory to detrusor Inhibitory to sphincter – For pain – Detect the degree of stretch in bladder wall – Initiate reflexes for bladder emptying From Hansen T. Sherrief; Texbook of Physiology CD 13-May-17 Urinary Bldder 8 Innervation The motor fibers Sympathetic fibers T11 – 12 L1,2 Inhibitory to detrusor excitatory to sphincter Internal sphincter External sphincter – Excite the detrusor muscles – Inhibit the internal sphincter around the trigone Parasympathetic fibers S 2,3,4 Excitatory to detrusor Inhibitory to sphincter From Hansen T. Sherrief; Texbook of Physiology CD 13-May-17 Urinary Bldder 9 Innervation The sympathetic nerves Sympathetic fibers T11 – 12 L1,2 Inhibitory to detrusor excitatory to sphincter Internal sphincter External sphincter – From lower thoracic and upper lumber segments • T11 , 12 & L 1,2,3 Parasympathetic fibers S 2,3,4 Excitatory to detrusor Inhibitory to sphincter Sympathetic activity – Inhibit the detrusor – Excite the trigone – Sphincter vesicae From Hansen T. Sherrief; Texbook of Physiology CD 13-May-17 Urinary Bldder 10 Sphincter Mechanism In both male and females There are two sphincter elements – Internal sphincter • Smooth muscle at the bladder neck – External sphincter • Skeletal muscle • Located at the level of membranous urethra 13-May-17 Urinary Bldder 11 Sphincter Mechanism Bladder neck sphincter – Detrusor muscle plus – Large amount of elastic tissue – Muscle in this area is called internal sphincter (sphincter vesicae) Not a true circular sphincter – Thickening formed by • Interlaced and converged muscle fibres 13-May-17 Urinary Bldder 12 Sphincter Mechanism Receive both – Parasympathetic nerves – Sympathetic In relaxed filling state – Bladder neck will remain closed – Provide continence mechanism 13-May-17 Urinary Bldder 13 Sphincter Mechanism With contraction – Detrusor muscle pull open the bladder neck 13-May-17 Urinary Bldder 14 Sphincter Mechanism Beyond the posterior urethra, – The urethra passes through – Urogenital diaphragm • Contain layers of muscles Form the external sphincter – Made up of voluntary muscles 13-May-17 Urinary Bldder 15 Ureters Ducts of Bellini Proximal portionof collection system Sympathetics Parasympathetics 13-May-17 Ducts of Bellini have circular muscles Proximal portion of collecting system – Pacemaker activity – Initiate peristalsis T10 T11 T12 S2 S3 S4 Urinary Bldder 16 Ureters Ducts of Bellini Proximal portionof collection system Wave of peristalsis – Stretches calices – Inherent pacemaker activity Forcing urine into bladder Sympathetics Parasympathetics 13-May-17 Urine flowing from collecting ducts into renal calices T10 T11 T12 S2 S3 S4 Initiates peristaltic contractions – Spread to renal pelvis down the ureters Urinary Bldder 17 Ureters Ducts of Bellini Proximal portionof collection system Muscle tone and peristalsis – Influenced by rate of urine excretion Wave of peristalsis In diuresis Forcing urine into bladder Sympathetics Parasympathetics 13-May-17 – Frequency of peristalsis T10 T11 T12 S2 S3 S4 Urinary Bldder 18 Ureters Ducts of Bellini Proximal portionof collection system Wave of peristalsis Forcing urine into bladder Sympathetics Parasympathetics 13-May-17 T10 T11 T12 S2 S3 S4 Walls of ureters innervated by ANS Peristaltic contractions in ureters – Enhanced by parasympathetic – Inhibited by sympathetics Urinary Bldder 19 Ureters Ducts of Bellini Proximal portionof collection system – Compress the ureters – Prevent backward flow of urine into ureters during micturition Wave of peristalsis Forcing urine into bladder Sympathetics Parasympathetics 13-May-17 Normal tone of detrusor muscles Each peristaltic wave T10 T11 T12 – Intra-ureteral pressure – Force urine to flow into bladder S2 S3 S4 Urinary Bldder 20 Uretero-renal Reflex Well supplied by pain fibers When ureters become obstructed (renal stones) – Intense reflex constriction occurs accompanied by severe pain – Ureteric colic 13-May-17 Urinary Bldder 21 Uretero-renal Reflex The pain causes reflex – Constriction of renal arterioles – Urine output from the kidney Uretero-renal reflex – Prevent excess flow of urine – When ureters are blocked 13-May-17 Urinary Bldder 22 Filling of Bladder During the collecting phase – Emptying is prevented or made difficult • By neural activity Sympathetics – Inhibit detrusor muscles – Excite internal sphincter Pudendal fibers Urethral pressure From Hansen T. Sherrief; Texbook of Physiology CD 13-May-17 Urinary Bldder 23 Filling of Bladder Pudendal fibers – Excite external sphincter – Intra-urethral pressure • Maintain continence Pudendal fibers Urethral pressure From Hansen T. Sherrief; Texbook of Physiology CD 13-May-17 Urinary Bldder 24 Urinary Bladder Bladder fills at a rate of 50 ml/hr – Plasticity of smooth muscle • Stretch (stress) relaxation – Ensure that pressure inside the bladder • Increases only slightly 13-May-17 Urinary Bldder 25 Urinary Bladder When bladder collects 150 –250 ml urine – 1st signs of brief urge to urinate appears – 250 –500 ml of urine • Evacuation phase begins 13-May-17 Urinary Bldder 26 Intravesicle pressure (cm H2O) Cystometry Cystometry 80 – Relationship between 60 • Intravesicle pressure & volume • Governed by Laplace’s law 40 20 • P = (2T)/R 0 0 100 200 300 400 500 Intravesicle volume (ml) 13-May-17 Urinary Bldder 27 Intravesicle pressure (cm H2O) Cystometry As urine collect in the bladder 80 – Bladder distend – Both T & R increase so 60 40 • Pressure does not increase appreciably in the initial phases 20 0 0 100 200 300 400 500 Intravesicle volume (ml) 13-May-17 Urinary Bldder – Until critical volume is attained 28 Micturition Reflex As bladder fill with urine Cortex Impulses to spinal cord Brain stem – Stretch receptors are stimulated – Sensory signal relayed to spinal cord (sacral segment) Stretch of muscle during filling Cause reflex contraction of detrusor muscle Bladder pressure Urethral pressure – Micturition reflex – Micturition contraction From Hansen T. Sherrief; Texbook of Physiology CD 13-May-17 Urinary Bldder 29 Micturition Reflex Cortex Impulses to spinal cord Brain stem Stretch of muscle during filling When the bladder is partially full – Reflex can relax spontaneously As blood continues to fill Bladder pressure Urethral pressure – Reflex becomes more frequent – Strength of contraction of detrusor muscle – Intra-vesicle pressure – More stimulation of stretch receptors From Hansen T. Sherrief; Texbook of Physiology CD 13-May-17 Urinary Bldder 30 Micturition Reflex Cortex Impulses to spinal cord Brain stem Stretch of muscle during filling But once the reflex – Has not succeeded in emptying the bladder – It is inhibited – Can remain inhibited for several hours Bladder pressure Urethral pressure From Hansen T. Sherrief; Texbook of Physiology CD 13-May-17 Urinary Bldder 31 Micturition Reflex Cortex Impulses to spinal cord Brain stem But as the bladder becomes more filled with urine – Reflex becomes more powerful Stretch of muscle during filling Initiate reflex inhibition of Bladder pressure Urethral pressure – External sphincter via pudendal nerves Causing urination to occur From Hansen T. Sherrief; Texbook of Physiology CD 13-May-17 Urinary Bldder 32 Evacuation of Urinary Bladder During evacuation – Perineal muscle relax – Voluntary sphincter around urethra relax – Trigone contract • Leads to occlusion of ureteral-vesicle junction • Prevent reflux of urine into ureters 13-May-17 Urinary Bldder 33 Evacuation of Urinary Bladder Contraction of trigone also – Pulls open the posterior portion of bladder neck • Become funnel shaped Detrusor muscle contract – Intra-vesicle pressure begins to rise • This pressure is directed downwards towards urethra 13-May-17 Urinary Bldder 34 Evacuation of Urinary Bladder Voiding begins – Detrusor maintain contraction until bladder is empty When bladder is empty – Detrusor relax – Bladder neck is allowed to close – Urethra and perineal muscles tone return to normal – Trigone resumes its normal tone 13-May-17 Urinary Bldder 35 Paracentral lobule Fibers from paracentral lobule descend to the micturition center to the pelvic and pudendal nerve Detrusor muscles An initial relaxation of perineal muscles is followed by contraction of detrusor muscle. Bladder neck closed when detrusor muscle relaxes assisted by elastic recoil 13-May-17 Signals reaching the brain, initiate desire to hold As the Detrusor muscle contracts abdominal wall muscle and diaphragm contract, abdominal pressure. Stretch receptors stimulated External vesical sphincter relaxes. Bladder neck opens. Voiding occurs with at pressure of 50 to 150 cm water. Urinary Bldder 36 Facilitation & Inhibition Cortex Impulses to spinal cord Brain stem Stretch of muscle during filling Micturition reflex – Spinal cord phenomenon Can be inhibited or facilitated by brain centers Bladder pressure Urethral pressure – Brain stem, pons – Several centers located in cerebral cortex From Hansen T. Sherrief; Texbook of Physiology CD 13-May-17 Urinary Bldder 37 Facilitation & Inhibition Cortex Impulses to spinal cord Brain stem Stretch of muscle during filling When micturition is desired Higher centers – Keep micturition reflex partially inhibited Higher centers can prevent micturition Bladder pressure Urethral pressure – Even if reflex does occur • Tonic contration of external sphincter From Hansen T. Sherrief; Texbook of Physiology CD 13-May-17 Urinary Bldder 38 Facilitation & Inhibition Cortex Impulses to spinal cord Brain stem Stretch of muscle during filling Bladder pressure Urethral pressure From Hansen T. Sherrief; Texbook of Physiology CD 13-May-17 When it is time to urinate Higher centers can facilitate sacral micturition centers – Initiate micturition reflex – At the same time inhibit external sphincter Urination can occur Urinary Bldder 39