Physiology Of Micturiton And Urinary Tract Flashcards Preview

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How much urine can the bladder hold?

700-800 ml


What are the three primary functions of the urinary system

1) excretion of wastes

2) elimination of water products into the environment

3) homeostatic regulation by maintaining blood balance and blood pressure


Dimensions of the adult ureter

25-30 cm long

Diameter is 3-4 nm

Begins at the L2 level and travels retroperitoneal
- if it ruptures = retroperitonal bleeding


What nerve supplies the somatic skeletal motor fibers for the bladder?

The pudendal nerve
- branches innervate the external bladder (control voluntary skeletal muscles)


Difference in sympathetic and parasympathetic afferent and efferent fibers?

Sympathetic (T9-L1)
- afferent = exteroception of the bladder
- efferent = bladder neck contraction and stimulation of sexual glands

Parasympathetic (S2-4)
- afferent = proprioception of the bladder
- efferent = contraction of the bladder

Pudendal (S2-4)
- afferent = sensations of the urethra
- efferent = external sphincter contraction and pelvic floor Innervation


Filling phase of the bladder

Controlled by sympathetics
- detrusor muscle is relaxed via B2 sympathetic innervation
- internal urethral sphincter is contracted via a1 sympathetic innervation
- external urethral sphincter is contracted via voluntary innervation and stimulation of somatic nerves (pudendal)
- pelvic floor contracts

1) relaxation of the detrussor muscle via B2 allows for accommodation of increasing volumes of urine with appropriate sensation
- **detrusor over activity (increased parasympathetics) will lead to involuntary bladder contractions

2) the bladder must remain closed at rest (internal and external sphincter is contracted)


Emptying of the bladder phase

Controlled by parasympathetics
- detrusor muscle is contracts via parasympathetic Muscarinic receptors
- internal sphincter is relaxed via parasympathetic muscarinic receptors
- external sphincter is relaxed via voluntary action and stimulation of somatic nerves

1) coordination contraction of the detrussor muscle and concomitant lowering of the sphincter resistance at the level of smooth muscles
- can be no functional obstruction or anatomical obstruction


Spinal reflex for micturation

Is a spinal reflex arc
**when the bladder is full**
- 1) stretch receptors fire
- 2) parasympathetics fire
- 3) motor neurons stop firing by inhibition of tonic discharge that occurs (allows for filling)
- 4) smooth muscles contracts and internal sphincter is passively pulled open with external sphincter relaxing consciously


Pathological causes for low and high specific

Low specific gravity (1.001-1.010)
*also called hyposthenuria*
- diabetes insipidus (#1)
- excessive drinking of liquids
- pyelonephritis
- glomerulonephritis
- use of diuretics

High specific gravity (> 1.015)
*also called hypersthenuria*
- dehydration
- diabetes mellitus
- adrenal insufficiency
- toximea of pregnancy


Postvoid residual volume

The volume of urine that remains in the bladder after voiding
- measured by ultrasound or by folly catheter


Types of urodynamic testing

Uroflowmetry = patient urinates into device and computer calculates statistics

Cytometrogram = measures response of the bladder filing

Pressure/flow studies = tests for outlet obstruction

Video-urodynamics = x-ray contrast to obtain fluoroscopic images during urodynamic testing

Catheter monitoring = used to measure pressure during bladder filling and emptying


Cystometrogram more specific

Uses a tube that is pushed into the bladder and fills the bladder. Measures the intravesical pressures and the patients desire to void while filling the bladder
- must start at empty bladder though

First sensation of filling = 150 ml
First edge to void = 250-350 ml
Normal filling capacity = 450-500 ml

**urinary incontinence should be expected if any of these values are off in a patient**


What is the value indicated for decreased compliance?

Volume/ pressure of detrusor muscle = <20 mL/cm


What are possible causes of slowing of the filling phase?

Poor compliance

Neurogenic bladder is present

Decreased capacity (numerous causes)

Excessive detrusor overactivity (parasympathetics)


Urinary incontinence facts

Affects 30-55% of all >65 yrs
- women = 33%, men is 1:14

Affects 33 million Americans worldwide


What are the seven main types of urinary incontinence?

1) transient incontinence
- result of temporary changes (UTI, medications or severe constipation)

2) stress incontinence
- bladder muscles are weakened.
- most common in women

3) overflow incontinence
- most common in men who have enlarged prostates

4) urge incontinence
- due to muscle spasms in the bladder
- people feel frequent urges to urinate

5) total incontinence
- urine leaks constantly and is almost always caused by injury

6) psychogenic incontinence
- severe fluctuations in emotional states leads to loss of urinalysis control

7) mixed incontience
- multiple factors from 1-6 are present


Common medications for urinary incontinence

Anti muscarinic agents

B-adrenergic agonists


K+ channel openers

Botulism toxin


How much does Post void residual volume have to get to to be abnormal?

>100-200 cc


What 3 things does bladder filling and urine storage require?

1) accommodation of increasing volumes of urine at a low detrusor pressure with appropriate sensation
- no hypertrophy of the detrusor

2) a bladder outlet that is closed at rest and remains so during increases in intra-abdominal pressure
- no weakened pelvic floor and no weakened internal sphincter (stress incontinence)

3) absence of involuntary bladder contractions
- urgency incontinence causes this


What 3 things are needed for bladder empyting and voiding

1) coordinated contraction of the bladder smooth musculature of adequate magnitude and duration
- no weakened parasympathetics and no neurological blocks

2) a concomitant lowering of resistance at the level of the smooth and striated sphincter
- no hyper tonic sphincter and no functional obstruction

3) no anatomical blockage


Urologic applications of botulinum toxin

1) neurogenic detrusor overactivity:
- symptoms = bladder spasms/urinary frequency/urgency and incontinence, nocturia
- inject directly into the detrusor muscle (good results)
- can also use anticholinergic therapies and augmentation cystoplasty

2) idiopathic overactive bladder:
- symptoms = same as above
- inject directly into detrusor muscle (good results)
- can also use anticholinergic therapies and augmentation cystoplasty

3) detrusor external sphincter dyssynergia
- symptoms = difficulty emptying, urinate retnetion, recurrent UTIs, VUR, elevated bladder pressure
- inject into the sphincter itself (not the greatest therapy though)
- can also use sphicterotomy, surgery and urethral stunting

4) painful bladder syndrome/interstitial cystitis
- symptoms = unpleasant sensations, pain with bladder filling and urinary frequency
- inject into the detrusor itself (not the greatest therapy though)