Function of Ureter and Urinary Bladder

The Ureter Autonomic nervous system Function – transports urine from renal pelvis to urinary bladder Innervation – Autonomic nervous system Forms a plexus under the outer connective tissue coat of the ureter

The Ureter Innervation: Paraympathetic – afferents and efferents vagus nerve supplies the upper part sacral parasympathetics supply the lower part mediate movements of the ureter

The Ureter Innervation: Sympathetic – afferents and efferents supply from spinal segments T11 – L1 afferents convey pain from ureter; usually caused by intermittent obstruction efferents are inhibitory to smooth muscles; but not a significant effect

The Ureter Motility: Peristalsis – Entry of urine into the ureter initiates peristaltic activity in the upper end of ureter Pacemakers in the calyceal system This peristaltic activity is propagated down Has intrinsic capacity to produce peristalsis in the absence of external innvervation

The Ureter Motility: External neural control – Parasympathetics enhance peristalsis Sympathetic action depends on the receptor type; Alpha receptors enhance peristalsis Beta receptors inhibit peristalsis (predominant)

The Ureter Peristalsis: Obstruction to flow increases tone and peristalsis Capable of transporting much higher rates of urine flow than normal

Bladder Function Storage Emptying

Bladder Function Innervation – afferent : 1. Bladder fullness and desire to pass urine - PARASYMPATHETIC enter the spinal cord via the posterior roots of sacral spinal segments 2, 3 and 4. - participate in reflexes at spinal level - ascend via spinothalamic tracts Upper urethra – upper urethral distension: reflex activity 2. Pain sensation - (overdistension and spasm) - SYMPATHETIC enter the spinal cord at lumbar 1 and 2 spinal levels

Bladder Function Innervation – efferent : 1. Detrusor - parasympathetic - preganglionic fibres originate from the spinal segments S1, 2 and 3 some of these fibres are cholinergic while others secrete other neurotransmitters such as prostaglandins, VIP these nerves contract the detrusor sympathetic - derived mainly from L1 and 2 spinal segments these fibres relax the bladder wall, acting through beta receptors (predominantly)

Bladder Function Innervation – efferent : 2. Internal Sphincter - Parasympathetic nerves from the same source as above causes relaxation Sympathetic nerves from the same source as above cause contraction acting through alpha receptors 3. External sphincter - Somatic nerves from S2, 3 and 4 sacral segments supplied via the pudendal nerve

Inferior mesenteric ganglion Pelvic Nerves Pudendal Nerve

A recording of bladder pressure against volume Cystometrogram A recording of bladder pressure against volume

Bladder Filling 1. As urine enters the bladder, the bladder volume increases, initially without a significant rise in pressure within (plasticity, receptive relaxation) 2. The detrusor muscle is actively relaxed by the sympathetic nerves 3. Thus there is minimal excitation of afferents that bring in bladder fullness sensation. 4. In the adult as the bladder volume reaches about 300 -400 ml the intra-vesical pressure starts to increase and so do the afferent impulses

Bladder Filling 5. At a volume of about 400ml, the increasing afferent impulses give rise to the sensation of bladder fullness and desire to pass urine 6. If the circumstances are appropriate the higher centres facilitate the micturition reflex and the bladder empties 7. If the circumstances are inappropriate, the higher centres inhibit the micturition reflex. In this case the bladder pressure comes down again after some time and the sensation of fullness disappears

Bladder Filling 8. If not emptied, the bladder collects more urine and from time to time sensation of fullness and the desire to pass urine occurs. At each such subsequent occasion the pressure will be higher than in the previous occasion 9. On each of these occasions the higher centres can facilitate or inhibit the reflex 10. If the reflex is repeatedly inhibited there comes a time when the badder pressure will be able to overcome the sphincter contraction and at this point one is not able to voluntarily inhibit micturition, which occurs reflexly.

Bladder Emptying This needs the facilitation of the micturition reflex by the higher centres. Although it is a reflex, it needs to be facilitated voluntarily. This facilitation can be performed voluntarily when the desire to pass urine occurs or even before the bladder fullness sensation is perceived

Bladder Emptying 1. The frontal cortex ceases the inhibitory influence on the brain stem / sacral autonomic motor centres 2. Preganglionic parasympathetic fibres are then free to be stimulated by the input from the afferent nerves 3. These excitatory influences contract the detrusor with dilatation of the internal sphincter, causing the starting of emptying of the bladder 4. Distension of the proximal urethra with urine increase the sensory output from the urethra, which inhibits the somatic motor supply to the external sphincter 5. Bladder empties completely

Bladder Emptying 6. After emptying the bladder wall relaxes and internal and external sphincters regain tone 7. Voiding is further helped by the contraction of the abdominal muscles and forced expiration on a closed glottis. 8. Flow of urine backwards into the ureter (vesicoureteral reflux) is prevented by the oblique path of the ureter through the bladder musculature

Influence by Higher Centres Essential for normal activation of reflex Pontine reticular formation (pontine micturition centre) Bladder Innervation

- Micturition Centres - + + Bladder Innervation Cortical centres Periaqueductal area Pontine tegmentum - + Pontine reticular formation (pontine micturition centre) Bladder Innervation

Continence the ability to retain the urine in the bladder except when voluntarily voiding 1. As the bladder fills and intravesical pressure increases bladder tends to empty itself. This is prevented by reflex contraction of the internal sphincter 2. Increased intraabdominal pressure associated with voluntary or reflex activity tends to empty the bladder. This is counteracted by contraction of the external sphincter 3. It is possible to voluntarily stop voiding during micturition. This is done by contracting the external sphincter

Incontinence Emptying of the urinary bladder without voluntary control Neurological dysfunction – of the innervation of the bladder Sphincter dysfunction

Defects of Bladder Innervation Pelvic nerve lesions Generally both afferent and efferent nerves are affected Afferent – loss of bladder sensation, incontinence with involuntary bladder wall contraction Efferent – bladder sensation present, no effective bladder contraction, overflow incontinence Spinal cord lesions above sacral level – disconnection from higher centres No bladder sensation, incontinence

Micturition Ureter transports urine to the urinary bladder by peristalsis – mediated by intrinsic activity and facilitated by parasympathetics The bladder is innervated by sympathetics (L1, 2) and parasympathetics (S1, 2, 3) Sympathetics act on the detrusor and the internal sphincter to facilitate storage and parasympathetics facilitate emptying Somatic efferents control the external sphincter – play an important role in continence Micturition centres in the brain stem are essential for normal bladder function