Micturition
Transport of urine from the kidney to the bladder, aided by peristaltic
waves in the ureter and the anatomical designs of ureter entry into the
bladder
Consequence of obstruction
Bladder anatomy along with internal and external sphincters
Diagram showing innervation of the bladder
Motor innervation of the bladder viz. parasympathetic, sympathetic and
somatic nervous systems
The role of the parasympathetic and sympathetic nervous system in
controlling contraction/relaxation of the bladder detrusor
The role of the parasympathetic and sympathetic nervous system in
controlling opening/closing of the internal and external sphincter
Sensory innervation of the bladder
Bladder stretch receptors, their activation by filling and contraction of
the bladder, their role in the sensation of bladder fullness and in
initiating reflex contraction of the bladder
Mechanisms involved in bladder filling
The relationship between bladder volume and bladder pressure, as
shown on a graph
Mechanisms involved in bladder emptying
Diagram illustrating micturition reflex
How higher centres normally modify the basic reflex which controls
bladder function
Consequences of incomplete bladder emptying
The main ways in which ageing alters bladder function
Treatments to cover bladder problems
Micturition is the act of urination (emptying the bladder). The basic process of urine is
broken down into:
Urine made in kidneys (is formed continuously at a rate of 1ml/min.)
Urine is stored in the bladder
Urine is released from the bladder
The last two steps involve function of bladder and associated sphincters
Kidney to Bladder
Urine passes from the collecting ducts of renal tubules into the renal pelvis. The renal
pelvis is the funnel like dilated proximal part of the ureter in the kidney.
Contraction of the smooth muscle of the pelvis aids movement of urine into the ureter.
Urine enters into the ureter and smooth muscle around lumen of the ureter contract
and force urine down the ureter and close off the entry to the kidney so you don’t get
backflow
Urine from collecting ducts -> Renal pelvis -> Ureter
,Peristaltic waves in the ureter occur at a frequency of 1-6 contractions/minute.
Ureters squeeze urine to pressure of 10-20mmHg.
Ureters open obliquely into the bladder and this prevents reflux of urine back into the
ureters when pressure in bladder rises, it acts as a flap valve and gets compressed.
Ureteric peristalsis is of myogenic origin (originating in the smooth muscle) and not
under CNS control (as if you denervate you still see peristalsis)
Coordination is required between peristalsis and changing urine volume.
Kidney Stones
Kidney stones (renal calculi) develop from crystals that separate from urine within the
urinary tract.
Normal urine contains inhibitors (citrate) to prevent this occurring.
Calcium is present in nearly all stones (80%), usually as calcium oxalate or less often
calcium phosphate.
Kidney stones are not the same as gallstones.
Kidney stones are more common in men than women, possibly due to testosterone.
But you also can get it caused by poor urine output/obstruction, altered urinary pH,
low concentration of inhibitors, infection or excess dietary intake of stone-forming
substances.
Kidney stones can form anywhere within the urinary tract (where there is urine!), in
the kidney, ureter or bladder (and cause blockages)
Symptoms include
-> Dysuria (painful urination)
-> Haematuria
-> Referred pain - Loin pain/back pain
-> Reduced urine flow
, -> Urinary tract obstruction (pressure reaches 50mmHg, causes considerable pain as
peristalsis continues, called renal colic)
-> If stone approaches tip of urethra, intense pain can inhibit micturition, this is called
‘strangury’
[Ureterolithiasis when stones form in ureters]
The Bladder
The bladder can be almost empty or can expand and contain up to 400ml without
much increase in pressure. This is due to its structure of being spherical so even
though tension in wall may increase as bladder fills so does the ratio.
As well as this, the mucosal lining of the bladder is transitional epithelium, which is
capable of stretching without damage, it is also impermeable to salts and water so
there is no exchange between urine and the capillaries of the bladder (composition of
urine doesn’t change in the bladder).
The mucosal layer is also generally loosely attached to the underlying muscle which
helps in it expanding, except at the base of the bladder where the entrance of the two
ureters and exit of ureter form a triangle the trigone where the mucosa is firmly
attached.
The outlet of the bladder into the urethra is guarded by two sphincters, the internal
sphincter and external sphincter.
The internal sphincter is just an extension of the detrusor muscle, the smooth muscle
just continues down to form the internal sphincter. This is not under voluntary
control.
Transport of urine from the kidney to the bladder, aided by peristaltic
waves in the ureter and the anatomical designs of ureter entry into the
bladder
Consequence of obstruction
Bladder anatomy along with internal and external sphincters
Diagram showing innervation of the bladder
Motor innervation of the bladder viz. parasympathetic, sympathetic and
somatic nervous systems
The role of the parasympathetic and sympathetic nervous system in
controlling contraction/relaxation of the bladder detrusor
The role of the parasympathetic and sympathetic nervous system in
controlling opening/closing of the internal and external sphincter
Sensory innervation of the bladder
Bladder stretch receptors, their activation by filling and contraction of
the bladder, their role in the sensation of bladder fullness and in
initiating reflex contraction of the bladder
Mechanisms involved in bladder filling
The relationship between bladder volume and bladder pressure, as
shown on a graph
Mechanisms involved in bladder emptying
Diagram illustrating micturition reflex
How higher centres normally modify the basic reflex which controls
bladder function
Consequences of incomplete bladder emptying
The main ways in which ageing alters bladder function
Treatments to cover bladder problems
Micturition is the act of urination (emptying the bladder). The basic process of urine is
broken down into:
Urine made in kidneys (is formed continuously at a rate of 1ml/min.)
Urine is stored in the bladder
Urine is released from the bladder
The last two steps involve function of bladder and associated sphincters
Kidney to Bladder
Urine passes from the collecting ducts of renal tubules into the renal pelvis. The renal
pelvis is the funnel like dilated proximal part of the ureter in the kidney.
Contraction of the smooth muscle of the pelvis aids movement of urine into the ureter.
Urine enters into the ureter and smooth muscle around lumen of the ureter contract
and force urine down the ureter and close off the entry to the kidney so you don’t get
backflow
Urine from collecting ducts -> Renal pelvis -> Ureter
,Peristaltic waves in the ureter occur at a frequency of 1-6 contractions/minute.
Ureters squeeze urine to pressure of 10-20mmHg.
Ureters open obliquely into the bladder and this prevents reflux of urine back into the
ureters when pressure in bladder rises, it acts as a flap valve and gets compressed.
Ureteric peristalsis is of myogenic origin (originating in the smooth muscle) and not
under CNS control (as if you denervate you still see peristalsis)
Coordination is required between peristalsis and changing urine volume.
Kidney Stones
Kidney stones (renal calculi) develop from crystals that separate from urine within the
urinary tract.
Normal urine contains inhibitors (citrate) to prevent this occurring.
Calcium is present in nearly all stones (80%), usually as calcium oxalate or less often
calcium phosphate.
Kidney stones are not the same as gallstones.
Kidney stones are more common in men than women, possibly due to testosterone.
But you also can get it caused by poor urine output/obstruction, altered urinary pH,
low concentration of inhibitors, infection or excess dietary intake of stone-forming
substances.
Kidney stones can form anywhere within the urinary tract (where there is urine!), in
the kidney, ureter or bladder (and cause blockages)
Symptoms include
-> Dysuria (painful urination)
-> Haematuria
-> Referred pain - Loin pain/back pain
-> Reduced urine flow
, -> Urinary tract obstruction (pressure reaches 50mmHg, causes considerable pain as
peristalsis continues, called renal colic)
-> If stone approaches tip of urethra, intense pain can inhibit micturition, this is called
‘strangury’
[Ureterolithiasis when stones form in ureters]
The Bladder
The bladder can be almost empty or can expand and contain up to 400ml without
much increase in pressure. This is due to its structure of being spherical so even
though tension in wall may increase as bladder fills so does the ratio.
As well as this, the mucosal lining of the bladder is transitional epithelium, which is
capable of stretching without damage, it is also impermeable to salts and water so
there is no exchange between urine and the capillaries of the bladder (composition of
urine doesn’t change in the bladder).
The mucosal layer is also generally loosely attached to the underlying muscle which
helps in it expanding, except at the base of the bladder where the entrance of the two
ureters and exit of ureter form a triangle the trigone where the mucosa is firmly
attached.
The outlet of the bladder into the urethra is guarded by two sphincters, the internal
sphincter and external sphincter.
The internal sphincter is just an extension of the detrusor muscle, the smooth muscle
just continues down to form the internal sphincter. This is not under voluntary
control.
