Bladder Function and Micturition (B2: W5) Flashcards
What is the function of the renal pelvis?
Renal pelvis is like a funnel that collects urine from the kidney and sends it to the ureter
The renal pelvis is the location of several kinds of kidney cancer
How is urine moved into and along the ureter?
Pyeloureteric peristalsis moves urine into the ureter
- Initiated by pacemaker cells that drive rhythmic electrical and mechanical events from the renal pelvis to the ureter
- Dominant pacemaker is at the pelvi-calyceal border
- Force of contractions is influenced by the rate of urine flow
What is a kidney stone?
- Like a small rock that forms in the kidney
- Forms when certain chemicals precipiate
- Can remain in kidney or travel through urinary tract
What are the main sites where kidney stones get stuck?
- At the ureteric junction of renal pelvis
- As the ureter passes over the iliac vessels
- At the junction of the ureter and the bladder - vesicoureteric junction
What is hydronephrosis and what are the negative effects?
Distension and dilation of the renal pelvis and calyces
- Blocking urine flow increases pressure in the kidney, and can lead to hydronephrosis
- Causes progressive atrophy of the kidney if left untreated
What are the 4 main types of kidney stones?
-
Calcium-oxalate: eating too much Ca or vitamin D, some medications, genetics, other kidney problems
- Most common
-
Struvite: having kidny infections
- Women more than men
- More harmful to kidneys
- Uric acid: eating too much animal protein, genetics
-
Cystine: Cystinuria - a genetic kidney disease
- Very rare
Describe the excitation-contraction coupling of cells in the ureter that cause peristalsis
Pacemaker cells in the most proximal part of the renal pelvis:
- Produce an electrical event - like a depolarization
- Causes activation of calcium channels
- Each event is coupled to a contractile event
What is special about the bladder in regards to filling?
- If you put a quart of water into the bladder, it expands to receive the volume
- The c_ompliance increases_ as it fills with fluid
- Through most of the filling of the bladder, there is no increase in pressure
- When pressure does go up, signal to brain tells you to void
What is released by the urothelium in response to bladder filling?
ATP
- ATP finds receptors on sensory neurons within suburothelial tissue
- ATP opens ion channels in these neurons
- Action potentials in central neurons
- Develops a signal that comes from efferent neurons and into the target organ
- Release ACh and ATP to produce contraction and micturition
Describe the neural process involved in the filling phase
- Urine comes into bladder from ureter
- Slight increase in pressure - relaxation caused by hypogastric nerve
- Release NE in the sphincter causing it to contract
- Pudendal nerve innervates skeletal mucle of external sphincter and keeps it contracted
- Sensory neurons through pelvic nerve go to spinal cord gaglia and bring information about the state of things in the bladder
- Send info to sympathetic side to cause relaxation
- Send info to CNS
Which nerve causes relaxation in the bladder in repsonse to an increase in pressure?
Hypogastric nerve
- Inhibits detrusor
Which nerve is responsible for skeletal muscle of external uretheral sphincter?
Pudendal nerve
- Conscious control from CNS helps keep sphincter closed
What causes contraction of the internal urethral sphincter, which is involuntary?
Norepinephrine
Describe the neural process involved in micturition
- Pelvic nerve senses that bladder is full
- At some point, pressure beings to rise
- Pelvic nerve goes to higher centers and initiates a signal down the spinal cord to the pudendal nerve to turn off
- Excitatory signal through pelvic nerve causes contraction of the detrusor
- NO increases and causes internal sphincter to relax
What causes relaxation of the internal uretheral sphincter?
Nitric Oxide
Which nerve senses that bladder is full?
Pelvic nerve
What causes contraction of the detrusor muscle of the bladder?
Excitatory signal through pelvic nerve
What happens when latent pacemakers are excited by noxious or irritant stimuli?
Can produce an antiperistaltic wave of contraction producing urine reflux toward the kidney
Where does the pudendal nerve come from?
Somatic nerve (skeletal muscle motor neuron)
From Sacral segments S2-S4
What efferent pathways are involved in urine storage?
- External sphincter contraction (pudendal)
- Internal sphincter contraction (hypogastric nerve) - NE
- Detrusor inhibition (hypogastric nerve)
What efferent pathways are involved in micturition?
- Inhibiton of external sphincter activity (pudendal nerve, CNS control)
- Inihibition of sympathetic outflow (inhibiting hypogastric)
- Activation of parasympathetic outflow (pelvic nerve)
- To bladder
- To urethera
What happens when urothelium is exposed to noxious side effects (chemical irritants, pH, mechanical trauma, thermal)?
- Substances other than ATP are released from the urothelium
- NO
- Prostaglandins
- Nerve growth factor (can cause remodeling)
- Acetyl choline
- Substance P
- These things activate other receptors present on sensory neurons
- TRPV1 and trkA
- Can cause hypoalgesia - receptor changes phenotype and becomes more active
- A lot of receptors present in urothelium produce other effects
- Change the amount of things being released
- Can affect sensation - A∆ and C fibers → noxious sensations
What are the neurotransmitters and receptors involved in filling and micturition?
What is the mechanism for contraction of the detrusor muscle when stimulated by pelvic nerve?
- Entry of calcium
- Release of Ca from cellular stores
- Sensitization of contractile apparatus by inhibiting myosin light chain phosphatase (MLCP)
What initiates bladder contraction?
The bladder does not begin to contract until a certain intravesical pressure is reached to initiate urination (neurogenic)
- Up to about 500 mL, there is no increase in pressure
- When it rises above, it is at the sensory threshold
What happens in the case of decreased bladder compliance?
- As volume increases, pressure increases
- Walls don’t become more compliant
- IF the sensory urge to empty bladder comes early, there is frequency of an urge to void
- Examples
- Prostate problems
- Interstitial cystitis - chronic inflammation of the urothelium
- Radiation
What happens in the case of uninhibited (overactive) bladder?
Nonvoiding contractions occur during filling
- Detrusor overactivity
Compare cystometrograms showing normal and abnormal micturition cycle in non obstructed bladder
Voiding contractions (top) correspond to urine volume (bottom)
A) Normal
B) Abnormal
Increase in frequency of voiding contractions
Tone can be elevated during filling - start to get leakage
