Function of Ureter and

Urinary Bladder

The Ureter

• 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 peristalsisBeta 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 FunctionInnervation – afferent :

1. Bladder fullness and desire to pass urine - PARASYMPATHETICenter 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) - SYMPATHETICenter the spinal cord at lumbar 1 and 2 spinal levels

Bladder FunctionInnervation – 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 FunctionInnervation – 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

CystometrogramA recording of bladder pressure against volume

Bladder Filling1. 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 Filling5. 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 Filling8. 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 EmptyingThis 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 Emptying1. 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 Emptying6. 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

Bladder Innervation

Pontine reticular formation(pontine micturition centre)

Essential for normal activation of reflex

Micturition Centres

Periaqueductal area

Pontine tegmentum

Cortical centres

Bladder Innervation

Pontine reticular formation(pontine micturition centre)

+ -

- +

Continencethe 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

IncontinenceEmptying of the urinary bladder without voluntary control

Neurological dysfunction – of the innervation of the bladder

Sphincter dysfunction

Defects of Bladder Innervation1. 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

2. Spinal cord lesions above sacral level – disconnection from higher centres– No bladder sensation, incontinence

Micturition1. Ureter transports urine to the urinary bladder by peristalsis –

mediated by intrinsic activity and facilitated by parasympathetics2. The bladder is innervated by sympathetics (L1, 2) and

parasympathetics (S1, 2, 3)3. Sympathetics act on the detrusor and the internal sphincter to

facilitate storage and parasympathetics facilitate emptying4. Somatic efferents control the external sphincter – play an

important role in continence5. Micturition centres in the brain stem are essential for normal

bladder function