Micturition and Urinary incontinence Flashcards
What are the 2 phases of micturition? What can damaging of these 2 phases lead to?
- Continence: damage to continence neurones can cause incontinence
- Voiding; damage to these neurones can cause urinary retention
What is unique about the trigone muscle, and what does the neck of the bladder do?
Trigone: particularly distensible smooth muscle
Neck: connects bladder to urethra
How is the detrusor muscle orientated?
What feature enables it to distend?
Muscle is orientated in 3 general directions to give it strength
Does not use peristalsis, uses transitional epithelium for expansion and dealing with toxins (tight junctions form an impermeable barrier)
What is the difference between the internal and external urethral sphincter?
Internal is involuntary and only in males
External: formed by pelvic floor muscles and is voluntary, both genders
Why is it so important that transitional epithelium forms an impermeable barrier?
The urine is hypertonic, and could draw water out of the body’s cells
What is the average capacity of the bladder and how long does it take to fill?
Averagely around 550 mL and takes 9 hours to fill (sleeping time)
How is the brain informed that the bladder is being filled/in pain?
Stretch receptors continually indicate sensation and can also sense pain from bladder irritation and temperature. They send afferent nerves to the brain
What are the 3 responses the brain can initiate, and which nerve coincides with each response?
Parasympathetic response: Pelvic N contracts the detrusor
Sympathetic response: Hypogastric N relaxes the detrusor muscle and contracts the internal sphincter
Somatic response: Pudendal N stimulates the external sphincter by communicating with the Pontine Micturition Centre and cerebral cortex - decision of whether to pee or not
Which region in the brain controls the bladder?
The pontine micturition centre
What does the lateral region of the PMC control?
What will stimulation to this area result in?
Lateral region controls continence and storage:
Stimulation will result in a contraction of the urethral sphincter to keep urine in
Name 5 things that a bilateral lesion to the PMC can lead to
- Inability to store urine
- Reduction in bladder capacity
- Excessive detrusor muscle activity
- premature voiding
- leaky bladder
What does the medial region of the PMC control?
What 3 things result from stimulation to this area?
The medial region is the micturition centre:
Stimulation results in
1. decrease of urethral pressure
2. silencing of pelvic floor muscles (EMG signal)
3. Rise in detrusor pressure
Overall leads to voiding
What does a lesion to the micturition centre lead to?
Severe urinary retention
Name a specific part of the brain that is active during voiding
Dorsomedial pontine tegmentum
What happens mechanically for the bladder to begin to fill?
Rugae flatten and the internal urethral sphincter will tighten
What is the stress-relaxation phenomenon?
As rugae continually flatten the capacity of the bladder can increase up to 700 mL
What happens once the bladder reaches about 200 mL?
Micturition Reflex
1. Stretch receptors stimulated
- Afferent fibres go to the spinal chord
- Parasympathetic responses transmitted back to the bladder
- Parasympathetic motor neurone responses are transmitted to the thalamus, PMC and cerebral cortex: decide whether you want to pee
Where is the thalamus and what is its role?
The thalamus is above the brainstem between the cerebral cortex and the midbrain.
It’s function is to relay sensory and motor signals to the cerebral cortex
What happens when you ignore the first signal to pee?
- Brain sends impulses down spinal chord to inhibit the micturition reflex: sympathetic relaxation of the detrusor muscle
- The pudendal N is stimulated and contracts the external sphincter to prevent urination
Why do children have less of an ability to control micturition?
The cortico-spinal connections haven’t been developed in the CNS
Can the bladder fully empty?
10 mL of urine is left in the bladder after normal urination
Explain how pressure increases over time in the bladder
At first, pressure only increases minorly, but as volume steadily increases the pressure will increase more rapidly
Name 5 things that could cause Incontinence:
- UTIs: chemical stimuli increases bladder activity
- Women: stress and urge incontinence
- Detrusor overactivity: common in older individuals
- Damage to the CNS might lose innervation to the PMC and control of external sphincter (pudendal N)
- Damage to pelvic nerves can abolish the micturition reflex
What’s the difference between stress and urge incontinence and how would you treat them?
Stress: Caused by a weak pelvic floor, urination may occur when someone coughs, sneezes, laughs after childbirth, elderly, etc. Need to do pelvic floor exercises
Urge: Need to urinate constantly, person must retrain their bladder
What happens over time if the micturition reflex is continually ignored?
- As the bladder continually fills: stretch receptors will produce more extreme degrees of stimulation that activate ganglionic neurones in the bladder to initiate detrusor muscle contractions until the pressure of the detrusor muscle overcomes the ability to keep the int. sphincter closed
- If bladder >500 mL int.sphincter opens
- If external sphincter doesn’t relax at this point an increase in bladder volume will re-initiate the cycle
Name 2 causes for pathological urinary retention?
- Enlarged prostate gland in men, may be due to cancer or inflammation
- Kidney stones
What replaces an internal sphincter in females?
The bladder neck and proximal urethra
