MICTURITION
B. O. Adele
Applied and Environmental Physiology
Department of Physiology,
Faculty of Basic Medical Sciences, COMUI
OBJECTIVES
• Know anatomy of the bladder
• Know mechanism of filling and emptying
of the bladder
• Micturition reflex
• Cystometogram
OUTLINE
•
•
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•
•
Introduction
Anatomy of the Urinary bladder
Bladder nerve supply and innervation
Micturition reflex
Cystometogram
INTRODUCTION
Micturition
• Is the process by which urine is voided from the
urinary bladder.
• It is a reflex process, with some level of
voluntary control in grown-up children and adults.
• It is regulated by both:
– nervous and
• ANS
• Somatic system
– muscular systems
THE URINARY BLADDER
A smooth muscle chamber that holds urine,
and composed of two main parts:
• The body : The main part of the bladder in
which urine collects
– Has 4 surfaces –
• Base (posterior surface)
• Apex, • Superior surface and
• 2 infrolateral surfaces
• The neck: A funnel-shaped extension of the
body passing inferiorly and anteriorly to collect
with the urethra.
ANATOMY OF THE BLADDER
• Location:
– Located in the pelvic
cavity
• Shape
– pyramidal
• Expands superiorly
when it is full
ANATOMY OF THE BLADDER
Anatomy
• Uretrovesical Junction
• Ureteral orifice
(opening) – site where
the ureters terminate
on piercing the
bladder wall obliquely
ANATOMY OF THE BLADDER
• Mucosa
(transitional
epithelium)
• Ragae
– the mucosa foldings of
the bladder when it is
empty,
– flattens out during
filling.
– This mechanism
results in bladder filling
ANATOMY OF THE BLADDER
• Bladder neck:
• Is a funnel-like
shape
• Is an extension of
the bladder to the
urinogenital tract to
join the external
urethra
THE TRIGONE
• The trigone is a small triangular area on the
posterior wall, lying above the neck of the
bladder.
• At the uppermost part of the trigone, the
ureters enter the bladder and at the
lowermost part, the bladder opens into the
urethra.
• Each ureter passes obliquely into the
detrusor muscle, passes another 1-2cm
beneath the mucosa before it empties its
content.
THE MUSCLE LAYER
• The smooth muscle is called
detrusor muscle.
•
Is arranged in spiral, longitudinal
and circular bundles.
• The smooth muscle cells fuse with
one another and allow existence
of electrical pathway from one cell
to another.
• Contraction of the muscle can
increase pressure between 40 and
60 mmHg in the bladder
THE URETHRA
• Extends from the urinary bladder to the
exterior of the body
• Surrounded by 3 muscular layers
– Inner longitudinal, middle circular and outer
longitudinal
• The lower 2 or 3 cm of the bladder is the
internal urethra (posterior urethra)
• Differs in length and function in males and
females
THE SPHINCTERS
• The bladder has two sphincters:
-The internal sphincter : Made up of smooth
muscle and located where the bladder neck
has large amount of elastic tissue.
-The external sphincter: Made up of skeletal
muscle and located at the urogenital
diaphragm.
Sympathetic
supply
NERVE SUPPLY TO URINARY
nerve
BLADDER
Parasympathetic nerve
supply
S
L1
2
S3
L2
Pelvic nerve
L3
S4
Sympathetic
chain
_
Somatic
nerve
supply S
+
Hypogastric
+
ganglion
2
+
Hypogastric
nerve
Urethra
External sphincter
_
+
Pudendal nerve
S3
S4
BLADDER NERVE SUPPLY
• Sympathetic (T10-L2)
– Hypogastric nerves
– Inhibitory to bladder body, excitatory to the internal
sphincter
• Parasympathetic (S2-S4)
– Pelvic nerves
• Excitatory to bladder, relaxes the internal sphincter.
• Somatic (S2-S4)
– Pudendal nerves
• Excitatory to external sphincter
HIGHER CENTRES
• Spinal centres of micturition which are present in sacral
and lumbar segments are regulated by higher centres in the
brain.
These are :
• Facilitatory area in the pontine region
• Inhibitory area in the mid brain.
• Facilitatory and inhibitory areas in the cerebral cortex
BLADDER INNERVATION
• Detrusor muscle has two receptors:
– M3 receptor –
• innervated by the pelvic nerve (parasympathetic
S2-S4).
• Its stimulation results in contraction of the muscle
to initiate micturition
– Β3-receptor –
• Innervated by the hypogastric nerve (sympathetic
T10-L2)
• Its stimulation opposes the effect of pelvic nerve
and relaxes the bladder wall
BLADDER INNERVATION
• Internal urethra sphincter has α1-receptor
– innervated by hypogastric nerve, to
contract the sphincter
• External urethra sphincter has a nicotinic
receptor – innervated by pudendal nerve
(Somatic S2-S4), to relax the sphincter
permitting voiding
PROCESSES INVOLVED IN
MICTURITION
• Two processes are involved in micturition
– Progressive filling of the bladder
– Micturition reflex (empties the bladder)
FILLING OF THE BLADDER
• When the urinary bladder is empty, the
intravesical pressure is zero.
• When about 50 mL of urine is collected, the
pressure rises sharply to about 5cm H2O (Ia in
the cystometrogram). There is a small additional
pressure in the bladder with further addition of
about 200-300 mL of urine (Ib) in an adult.
• As the bladder tension increases as the urine
fills it, the radius also increases due to relaxation
of the detrusor muscle. Because of this, the
pressure rise is almost nil.
FILLING OF THE BLADDER
• When, urine of about 400 mL is collected, the
contraction of detrusor muscle becomes
intense, increasing the consciousness and
the urge for micturition.
• At this point also voluntary control is
possible, but beyond 600 – 700 mL of urine,
voluntary control starts failing and
micturition occurs.
CYSTOMETOGRAM
Intravesical pressure
(centimeters of water)
Micturition
contractions
la
lb
Basal cystometrogram
Volume (milliliters)
I
I
Is a plot of
intravesica
l pressure
against the
volume
fluid in the
bladder
MICTURITION REFLEX
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
MICTURITION REFLEX
MICTURITION REFLEX
• When bladder is full, the stretch receptors
on the bladder wall send afferent signals
through the pelvic nerve
– Contains:
• myelinated A-δ fibers with activation
threshold of 5-25 mmHg, and
• unmyelinated C fibers with high mechanical
threshold which transmits signals of
discomfort and pains)
• Activation of the spinal micturition center
MICTURITION
• Starts with:
– Increase in abdominal pressure by descent of
diaphragm and
– contraction of abdominal muscles,
– relaxation of perineal muscles,
– the detrusor muscle contracts,
– internal and external urethral sphincter are
relaxed,
• And ends as urine passes out through the
urethra.
VOLUNTARY MICTURITION
• During voluntary micturition:
• the flow of urine is facilitated by
increase in the abdominal pressure due
to voluntary contractions of abdominal
muscles which allows extra volume of
urine to enter the bladder and increase
bladder pressure. This stimulates the
stretch receptors that initiates
micturition reflex when the condition is
favorable