Micturation reflex by Dr Irum

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Transcript of Micturation reflex by Dr Irum

MICTURITION

Dr Irum Junaid

MICTURITION

The process by which the urinary bladder empties when it becomes

filled

Physiological Anatomy of Urinary System

• Kidneys (cortex, medulla, nephron, pelvis )

• Ureters (mucosa, muscle, fibrous)

• Urinary Bladder (body, neck), (mucosa,muscle, fibrous) (detrusor, trigone)

• Urethra • Internal and External

sphincters

Anatomy & Neurophysiology of the Lower Urinary Tract

• Bladder (detrusor)– Stores urine at low pressure– Compresses urine for voiding

• Urethra– Conveys urine from bladder to outside world

• Sphincter(s) internal & external– Controls urine flow & maintain continence

between voidings

Transport of Urine from the Kidney through Ureters into Bladder

• Kidneys– Calyces

• Ureters• Bladder• Vesicoureteral Reflux• Pain and uerterorenal reflex

Urinary Bladder

Filling of the bladder

When urine collects in the renal pelvis, the pressure in the pelvis increases. This increase in the pressure initiates a peristaltic contraction beginning in the pelvis and spreading downward along the ureter to force urine toward the bladder.

Peristaltic waves occur

1-5 times/minute

The walls of ureters contain smooth muscle arranged in spiral, longitudinal and circular bundles.

In some people, the distance that the ureter courses through the bladder mucosa is less than normal, so that contraction of the bladder during micturition does not always lead to complete occulusion of the ureter. As a result some of the urine in the bladder is propelled backward into the ureter. This is called ‘Vesicoureteral reflux’.

Ureterorenal reflexUreterorenal reflex

The ureters are well supplied with pain nerve fibers. When a ureter is blocked eg. by a ureteral stone, there will be intense reflex constriction which is associated with very severe pain. These pain impulses cause a sympathetic reflex back to the kidney to constrict the renal arterioles, thereby decreasing urinary output from that kidney. This effect is known as ‘Ureterorenal reflex’.

INNERVATION OF BLADDER

1. PARASYMPATHETIC NERVES (PELVIC NERVE) (S2-3) a) Sensory (stretch) b) Motor (detrusor, Internal sphincter)

2. SKELETAL MOTOR FIBER (PUDENDAL NERVES) (S2-3)

a) Sensory (stretch)b) Motor (external sphincter)

3. SYMPATHETIC NERVES (HYOGASTRIC NERVES) (L2)

a) Sensory (fullness, pain)b) Motor (stimulate blood Vs)

They prevent reflux of semen into the bladder during ejaculation.

(MAIN)

L1

L2

L3

Sympathetic nerve supply

Sympathetic

chain

Hypogastric

ganglion

Hypogastric

nerve Urethra

External sphincter

Parasympathetic nerve supply S2

S3

S4

S2

S3

S4

Pelvic nerve

Pudendal nerve

Somatic nerve supply

Bladder Innervation

Regulation of the BladderMain Influence: Parasympathetic

Pelvic nerve Detrussor muscle

Hypogastric nerve

Pudendal nerve

Internal sphincter

External sphincter

Para

Sym

Vol

1. Pressure builds up in the bladder

2. This causes the contraction of the detrussor muscle, via the pelvic nerve.

3. The internal sphincter relaxes due to decreased sympathetic stimulation.

4. The external sphincter relaxes due to voluntary decrease in stimulation.

What is micturition reflex? Spinal cord reflex activity.

* facilitated or inhibited by higher centers

* voluntary facilitation or inhibition

Micturition Reflex• Micturition contractions begin• Role of sensory and motor parasympathetic

nerves• Self regenerative once begins• Complete cycle

– Rapid increase in pressure– Period of sustained pressure– Return to basal tone

Bladder Filling & Emptying Cycle

The cycle ofbladder fillingand emptying

1. Bladder fills

2. First desire tourinate (bladder

half full)

Urination 3. Urinationvoluntarily inhibiteduntil time and place

are right

Detrusor muscle

contracts

Detrusor muscle relaxes

Urethralsphinctercontracts

Urethral sphincter relaxes

Voiding Urine - Micturition

• Micturition reflex1) 300-400 ml urine in bladder, stretch receptors

send signal to spinal cord (S2, S3)2) parasympathetic reflex arc from spinal cord,

stimulates contraction of detrusor muscle 3) relaxation of internal urethral sphincter4) this reflex predominates in infants

• Infants– Spinal reflex

• Adults– Spinal reflex – Higher control

• (pelvic muscles and external urethral sphincter)

Normal Control of Urination

Cystometrogram

100 200 300 400

Intravesical volume (mL)

Intravesical pressure

(cm of

Water)

80

60

40

20

00

IaIb

Bladder filling –cystometrogram• Relation between bladder volume & pressure.• Empty bladder……P zero• 30-50 ml urine……P 5-10 cm H2O

• 50 – 300 ml urine…. P 5-10 cm H2O

• More than 400 ml…..rapid rise in P

LAW of LAPLACE

• This is in accordance with law of Laplace. In the bladder tension increases as the urine is filled. At the same time, the radius also increases due to relaxation of the detrusor muscle. Because of this, the pressure rise is almost nil.

• When bladder wall stretches during filling it will initiate a reflex contraction which has lower threshold. That does not trigger micturition reflex. When bladder is filled about 300 – 400 mL of urine, there will be sharp rise in the intravesical pressure as the micturition reflex is triggered.

• At this point also voluntary control is possible. Beyond 600 – 700 mL of urine voluntary control starts failing.

Filling of the bladder – partially filled

Reflex contractions

Acute increase in pressure

Contractions relax spontaneously

Pressure falls back to baseline

Bladder continues to fill

Reflex contractions – more frequently and powerful

Filling of the bladder ………..

Facilitation or inhibition of micturition by brain

• Pons– Facilitatory and inhibitory centers

• Cortex– Mainly inhibitory centers

Voluntary Urination

• Micturition center is located in the – Frontal lobe

• Function of micturition center – Send tonically inhibitory

signals to the detrusor muscle to prevent the bladder from emptying (contracting) until a socially acceptable time and place to urinate is available.

Next stop is the…..

Pons• The major relay center

between the brain and the bladder

• Pontine micturition center– The PMC coordinates the

urethral sphincter relaxation and detrusor contraction to facilitate urination

Pontine Micturition Center• Bladder filling detrusor

muscle stretch receptors signal to the pons brain – Perception of this signal (bladder

fullness) as a sudden desire to go to the bathroom

– Normally, the brain sends an inhibitory signal to the pons to inhibit the bladder from contracting until a bathroom is found.

• Brain deactivating signal to PMC– Urge to urinate disappears– At appropriate time, brain sends

excitatory signals to the pons, allowing voiding

Spinal cord • Function

– Long communication pathway between the brainstem and the sacral spinal cord

– Sensory information from bladder Sacral cord Pons Brain Pons Spinal cord Sacral cord Bladder

– Spinal cord acts as an important intermediary between the pons and the sacral cord

– Intact spinal cord is critical for normal micturition

Next Stop After the PMC….

Normal Micturition – Spinal Cord• Sacral spinal cord – what is the significance?

– Sacral reflex center• Responsible for bladder contractions• Primitive voiding center

– In infants, the brain is not mature enough to command the bladder

– SRC controls urination in infants and young children – When urine fills the infant bladder, an excitatory signal

sacral cord spinal reflex center detrusor contraction involuntary detrusor contractions with coordinated voiding

Adult Micturition Reflex Diagram

Cystometrogram

Abnormalities

• Atonic bladder Sensory nerve fibers from the bladder to the

spinal cord are destroyed Overflow incontinence Crush injury, syphilis,

Automatic bladder• Above the sacral region with intact sacral

cord segments• No longer controlled by the brain• Spinal shock

• contd.

TThe urinary bladder looses its tone and becomes flaccid he urinary bladder looses its tone and becomes flaccid and unresponsive. So, the bladder is completely filled, and and unresponsive. So, the bladder is completely filled, and later urine overflows by dribbling. After the spinal shock later urine overflows by dribbling. After the spinal shock has passed, the voiding reflex returns although there is no has passed, the voiding reflex returns although there is no voluntary and higher centre control. voluntary and higher centre control.

Whenever, the bladder is filled with some amount of urine, Whenever, the bladder is filled with some amount of urine, there is automatic evacuation of the bladder.there is automatic evacuation of the bladder.

(Spastic neurogenic bladder)(Spastic neurogenic bladder)

Uninhibited Neurogenic Bladder

• Partial damage in the spinal cord or the brain stem

• interrupting most of the inhibitory signals• Slight quantity of urine elicits an

uncontrollable micturition reflex

Nocturnal micturition (Bed wetting)

This is normal in infants and children below 3 years. It occurs due to incomplete myelination of motor nerve fibers of the bladder resulting loss of voluntary control of micturition .

Incontinence from impaired sphincter function

•Of lesser degree

•In response to sudden rise in intravesical pressure (coughing, sneezing)

•After multiple child births in women

•After prostatic surgery involving damage to sphincter