Transcript Renal Physiology 4(Micturition).ppt

(Renal Physiology 4)
Micturition
Ahmad Ahmeda
[email protected]
Cell phone: 0536313454
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Learning Objectives:
• Identify and describe the Functional Anatomy of Urinary
Bladder
• Describe the mechanism of filling and emptying of the
urinary bladder
• Cystometrogram
• Appreciate neurogenic control of the mechanism of
micturition and its disorders.
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Introduction
 Urinary bladder functions as a temporary storage
organ that can empty at appropriate time.
 Problems related to bladder are often obvious like
enuresis, incontinence or may not be apparent like
recurrent UTIs, day time urgency frequency syndrome.
 Early intervention may prevent any further renal
damage from retrograde effects of high bladder
pressures.
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Urinary Bladder Anatomy
• The bladder is situated in the pelvic cavity when
empty, but expands superiorly into the abdominal
cavity when it becomes full.
• The urinary bladder is an abdominal organ at birth,
positioned at the extraperitoneal area of the lower
abdominal wall. Around the 5th or 6th year of age the
bladder gradually descends into the area of the true
(minor) pelvis.
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Urinary Bladder Anatomy
It has 4 parts
 Apex
 Base
 Superior surface
 Inferolateral
surfaces
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Urinary Bladder Anatomy
 The mucosal lining on the
base of the bladder is
smooth and firmly attached
to the underlying smooth
muscle coat of the wall-unlike
elsewhere in the bladder
where the mucosa is folded
and loosely attached to the
wall. The smooth triangular
area between the openings of
the ureters and urethra on the
inside of the bladder is known
as the trigone.
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Urinary Bladder Anatomy
Ureterovesical Junction
As the ureter approaches the bladder, 2 to 3 cm from the
bladder, a fibro-muscular sheath (of Waldeyer) extends
longitudinally over the ureter and follows it to the trigone.
• The ureter pierces the bladder wall obliquely and
terminates at the ureteral orifice. As it passes through a
hiatus in the detrusor (intramural ureter), it is compressed
and narrows considerably.
• The intravesical portion of the ureter lies beneath the
urothelium, it is backed by a strong plate of detrusor
muscle. With bladder filling, this arrangement is thought to
result in passive occlusion of the ureter, like a flap valve
which prevent reflux.
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Urinary Bladder Anatomy
Mucosa
 The wall of UB is lined by a transitional epithelium that
is continuous with that in the ureters.
 When the bladder is empty, the mucosa has numerous
folds called rugae.
 As the bladder fills with urine these rugae flatten out and
distend with little change in intravesical pressure
 This results in high compliance of the bladder, so the
volume of the bladder can ↑ from 10 ml to 400 ml with a
pressure change of only 10 cm H2O
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Urinary Bladder Anatomy
Submucosa
 It supports the mucous membrane.
 It is composed of connective tissue with elastic fibers.
Muscle layer (Detrusor muscle):
 It is composed of smooth muscle.
 The smooth muscle fibers are interwoven in all directions
and collectively these are called the detrusor muscle.
 It consist of a mixture of spiral and longitudinal muscle
fibers
 It can increase the pressure in the bladder to 40–60
mmHg.
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Urinary Bladder Anatomy
Bladder Neck :
 It is a funnel shaped extension of the body toward the
urogenital triangle, to join the anterior urethra (external
urethra).
 The lower 2-3 cm of the bladder neck is called the
posterior or internal urethra.
 The muscle fibers in the bladder neck are arranged in 3
layers: inner longitudinal, middle circular, and outer
longitudinal.
 The tone of the bladder neck muscles, specially the middle
layer, prevents emptying of the bladder until the
appropriate time for micturition.
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Urinary Bladder Anatomy
Bladder Neck cont:
 The urethra passes through the urogenital diaphragm
where it is surrounded by the external urethral
sphincter (under voluntary control) used to prevent or
interrupt urination, specially in males, it is poorly
developed in females.
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Nerve Supply to the Bladder
Afferent supply:
A.Sympathetic nerve
It transmit impulses from the
pain receptors to the upper
lumbar segment (via the lumbar
dorsal n. roots)  resulting in the
perception of pain sensation from
the urethra & bladder e.g. severe
bladder distention & in
inflammation.
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Nerve Supply to the Bladder
B. Pelvic nerve
 It transmit impulses from the
tension (stretch) & pain
receptors present in the wall
of U.B. to the sacral region
of spinal cord (via the sacral
dorsal n. roots)  resulting
in both reflex micturition &
sensation of bladder fullness
(i.e. desire for micturition)
[The tension receptors are
stimulated when I.V.P. ]
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Nerve Supply to the Bladder
C. Pudendal
nerve
 It transmit impulses
for the sensation
of:
 Distention of the
urethra.
 Passage of urine
through the
urethra.
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Nerve Supply to the Bladder
Efferent Supply
A. Sympathetic supply
 Pregang. fibres  arise from the upper 4 L. The fibres of
both sides unite to form presacral nerve when then
divides into  The post. gang. fibres arise from
hypogastric ganglia.
 Functions of sympathetic nerves:
 Inhibitory to the bladder wall (detrusor muscle).
 Motor to the internal urethral sphincter.
 Motor to the seminal vesicle, ejaculatory duct & prostatic
musculature. It prevents the reflux of semen into the bladder.
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Nerve Supply to the Bladder
B. Parasympathetic supply
 The pregang. fibres arise from the 2nd, 3rd, 4th sacral
segments.
 They form the pelvic nerve which relays in the terminal
ganglia embedded in the wall of the U.B.
Functions of parasympathetic:
• Motor to the bladder wall (detrusor muscle).
• Inhibitory to the internal urethral sphincter.
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Nerve Supply to the Bladder
C. The somatic supply (pudendal N.)
 It arise from the 2nd, 3rd, 4th sacral segments.
 It supplies the external urethral sphincter.
Function of somatic supply:
 Motor to the external uretheral sphincter.
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The Reservoir function of U.B
 Urine enters the urinary bladder without producing
much increase in I.V.P. till the bladder becomes wellfilled.
 A plot of I.V.P. against the volume is called
“cystometrogram”.
 It is composed of three components:
1. Stage Ia:

Represent initial slight rise in I.V.P. by about 10 cm H2O when
the first increment in volume is produced by about 50 ml.
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Cystometrogram
2. Stage Ib:
 It is a long, nearly flat
segment produced by
further  in filling up to
nearly 150 ml.
3. Stage II:
 This segment is
produced by further
increment of volume
(150 – 400 ml) &
represent rise of
pressure.
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Cystometrogram
 In the urinary bladder  the tension on the wall
increases as the volume increases & also the radius
increases, so there is little change in pressure until
the organ is filled & any increase in volume beyond
this will not be accommodated & is reflected by rapid
rise of pressure.
 Superimposed on this curve, periodic acute increase
in pressure which lasts very few seconds, & called
“micturition waves” & are caused by micturition reflex.
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Sensations from the U.B at
different urine volumes:
 At a urine volume of 150 –300 ml  the first urge to void
urine.
 From 300 –400 ml  sense of fullness of the bladder.
 From 400 –600 ml  sense of discomfort.
 From 600 –700 ml  sense of pain.
 Micturition reflexes start to appear at the first stage.
They are progressively intensified in the subsequent
stages up to stage 4. Micturition reflexes can be
voluntarily suppressed.
 At about 700 ml  break point  micturition can not be
suppressed.
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Micturition
A) Unconditioned (automatic) micturition:
 In infants  urination occurs through a series of
spinal reflexes called “the micturition reflexes”
which are automatic (not under voluntary control)
because the nerve tracts are not yet myelinated in
infants.
 The stimulus that initiates these reflexes is rise of the
IVP (which stimulates stretch receptors in the
bladder wall) & they are integrated by a spinal
micturition centre in the 2nd, 3rd & 4th sacral
segments of the spinal cord.
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Micturition reflexes
The micturition reflexes can be summarized as
follows:
 Distention of the U.B. (as a result of  I.V.P. & not by
an  in the bladder volume) produces reflex
contraction of its wall & relaxation of the internal
urethral sphincter & external urethral sphincter.
 The flow of urine in urethra will produce contraction of
the U.B. wall & relaxation of both internal & external
urethral sphincters.
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Micturition reflexes
• B) Voluntary or conditioned micturition:
 In adults  the act of micturition occurs also through
the micturition reflexes, but however, it can be
voluntarily controlled by certain higher (or supraspinal) centers in the brain, which include the
following:
Facilitatory
• In pontine area.
• Posterior hypothalamus.
• Other cortical centers
Inhibitory
• In the mid
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Mechanism of voluntary control
of micturition:
 Filling of the bladder beyond 300 –400 ml causes
stretching of sensory stretch receptors.
 These sensory signals stimulate sacral segment,
which is consciously appreciated by higher centers.
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If the condition is favourable
 The cortical centers facilitate micturition by discharging
signals that leads to:
 Stimulation of sacral micturition center.
 Inhibition of pudendal nerves  relaxation of external
urethral sphincter.
 Contraction of anterior abdominal muscle &
diaphragm to increase intra-abdominal pressure 
the intra-vesical pressure is increased. This
intensifies the micturition reflex.
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If the conditions are unfavorable
 The higher centers will inhibit the micturition reflex
by:
 Inhibition of sacral micturition center.
 Stimulation of pudendal nerves  contraction of
external urethral sphincter.
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Disturbances of micturition
 Denervation of the afferent supply e.g.in tabes
dorsalis (tabetic bladder):
 Characterized by:
 Loss of the U.B. sensations & reflex micturition.
 Some intrinsic responses of the smooth muscle are
retained.
 The bladder becomes distended, thin walled &
hypotonic (a tonic bladder).
 There is retention with overflow i.e. dribbling of urine
when the bladder becomes over filled.
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Disturbances of micturition
 Denervation of the afferent & efferent supply e.g.
tumour, injury to cauda equina.
 Characterized by:
 Reflexes are abolished.
 Intrinsic responses of the smooth muscles are increased.
 The bladder is hypertonic.
 This is due to denervation hypersensitivity because:
  degradation of acetyl choline by process of reuptake.
  cholinesterase in the tissue
  number of cholinergic receptors.
 This condition is associated with uncontrolled periodic
micturition about 25 – 100 ml at a time
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Disturbances of micturition
 Spinal cord transection (above the sacral region).
1) Stage of spinal shock
 This occurs due to the sudden separation of the spinal
centers from the higher centers that control them.
 The spinal centers become functionless for 2 – 6 weeks.
So, the micturition reflex is abolished  “retention with
overflow” i.e. the bladder distends until the I.V.P.
exceeds the urethral sphincter resistance & so, urine
starts to dribble.
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Disturbances of micturition
2) Stage of recovery of the spinal centres
 “Automatic micturition” occurs as soon as the I.V.P.
rises to 15 – 20 cm water  reflex micturition occurs.
3) Stage of failure recovery
 Damage of the spinal centers by toxins of bacterial
infections  abolishes the micturition reflex 
“Retention with overflow”.
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Composition of Urine
Substance
+
Na
+
K
Ammonium (NH4+)
Concentration
50-130 mEq/L
20-70 mEq/L
30-50 mEq/L
++
5-12 mEq/L
++
2-18 mEq/L
Ca
Mg
-
Cl
50-130 mEq/L
Inorganic phosphate (Pi)
20-40 mEq/L
Urea
200-400 mM
Creatinine
6-20 mM
pH
5.0-7.0
Osmolality
500-800 mOsm/kg H2O
Glucose
0
Amino acids
0
Protein
0
Blood
0
Ketones
0
Leukocytes
0
Bilirubin
0
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Physical Characteristics of Urine
• Color and transparency
– Clear, pale to deep yellow (due to urochrome)
– Concentrated urine has a deeper yellow color
– Drugs, vitamin supplements, and diet can
change the color of urine
– Cloudy urine may indicate infection of the
urinary tract
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Physical Characteristics of Urine
• Odor
– Fresh urine is slightly aromatic
– Standing urine develops an ammonia odor
– Some drugs and vegetables (asparagus)
alter the usual odor
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Physical Characteristics of Urine
• pH
– Slightly acidic (pH 6) with a range of 4.5 to
8.0
– Diet can alter pH
• Specific gravity
– Ranges from 1.001 to 1.035
– Is dependent on solute concentration
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Chemical Composition of Urine
• Urine is 95% water and 5% solutes
• Nitrogenous wastes include urea, uric acid, and
creatinine
• Other normal solutes include:
– Sodium, potassium, phosphate, and sulfate
ions
– Calcium, magnesium, and bicarbonate ions
• Abnormally high concentrations of any urinary
constituents may indicate pathology
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