Micturition Flashcards
How often do peristaltic waves occur in the ureter and what is the effect?
Occurs at frequency of approx 1-6 contractions/minute
Ureters squeeze urine to pressure of 10-20mmHg
Why do the ureters open obliquely into the bladder?
Prevents reflux of urine back into ureters by passive flap-valve effect
What volume can the bladder hold up to w/out much increase in pressure? What structural feature causes this?
400ml
Spherical structure evens out pressure as it fills
Female/Male bladder/urethra comparison
Female:
- Short urethra
-External sphincter poorly developed
-More prone to incontinence esp after childbirth
Male:
- Caries urine+semen
-Urine elimination aided by contraction of bulbocavernosus muscles
What muscle is the internal sphincter controlled by?
Detrusor muscle ( involuntary control )
What muscle is the external sphincter controlled by?
Two striated muscles
(compressor urethrae/bulbocavernosus)
Muscles responsible for continence
(voluntary control)
Bladder lining?
Transitional epithelium
Is the bladder impermeable to salt or water?
yes
Is the bladder permeable to lipophlipophillic molecules?
Yes
What are kidney stones?
- Renal calculi
- Develop from crystals that precipitate from urine
-Calcium is present in nearly all stones (80%) - Others made of uric acid/struvite/cysteine
How does normal urine prevent kidney stones?
Contains inhibitors (citrate)
Why are kidney stones more common in men that women?
Due to testosterone
Causes of kidney stones?
- Excess dietary intake of stone forming substances
- Poor urine output/obstruction
- Altered urinary pH
- Low conc of inhibitors
- Infection
What is ureterolithiasis?
Kidney stone disease
Symptoms of KDS:
- Dysuria
- Haematuria
- Reduced urine flow
- Urinary tract obstruction
Where can kidney stones form?
Kidney/ureter/bladder
anywhere in the urinary tract
What is strangury?
intense urethral pain - can inhibit micturition
* can be caused by kidney stone that reaches top of the urethra
* can be caused by urethritis
Which three nerves are involved in bladder function?
- Hypogastric nerve
- Pelvic nerve
- Pudendal nerve
Hypogastric nerve?
Stems from T11, T12, L1, L2
Attatches to stretch receptors
Monitors fullness of bladder
Pelvic nerve?
Stems from S2-S4
Attatches to stretch receptors
Monitors fullness of bladder
Pudendal nerve?
Stems from S2-S4
Afferent attatches to flow receptors
Detects flow of urine
What nervous system to each of the nerves belong to?
Hypogastric = sympathetic
Pelvic = parasympathetic
Pudendal nerve = somatic
NO and ACh cause what?
Relaxation of internal sphincter
Parasympathetic neurons (Efferent)
- Contract detrusor via ACh (muscarinic R) & ATP (purigenic R)
- Relax internal sphincter via NO (cGMP) & ACh (nicotinic R?)
ENCOURAGES MICTURITION
Noreadrenaline causes what?
Contraction of internal sphincter
How is the external sphincter kept closed?
Tonic activity of ACh
Efferent nerves connect to ?
Muscles!
Sympathetic neurons (Efferent)
- Relax detrusor
- indirectly via NA (α-R)
- Directly via NA (β-R)
- Contract internal sphincter via NA (α-R)
Inhibits micturition
Somatic neurons (Efferent)
Contract external sphincter via ACh (nicotinic R)
Inhibits micturition
What are the types of afferent (sensory) nerve fibres?
“A fibres”: sense tension in detrusor:
*Filling of bladder
*Detrusor contraction
*bladder fullness, discomfort
“C fibres”: respond to damage & inflammatory mediators
* PAIN (urgent desire to micturate)
What causes UTIs?
bacteria im retained urine seeds fresh urine (urine is normally sterile)
retained urine-> clinical infection
Name of UTIs depending on location:
*Bladder – cystitis or a bladder infection
- Kidneys – pyelonephritis
- Ureters – rarely the site of infection
- Urethra – urethritis
UTI risk factors?
Diabetes mellitus; long-term catheterisation; pregnancy; enlarged
prostate; prolonged immobility; kidney stones; bowel incontinence;
advanced age
How does BPH (benign prostatic hyperplasia) increase risk of UTI?
Slow urine stream → incomplete emptying → infection
Treatments for incontinence?
Anti-muscarinics relax smooth muscle & ↓ detrusor contraction
Bladder retraining (used for stress & urge incontinence) (KEGEL exercises:)
Surgery
Explain the process of micturition
Initially – bladder empty
* Sphincters closed
* (tonic activity sympathetic & somatic nerves)
* Bladder pressure low
- Arrival of urine
- Detrusor relaxes progressively
- (sympathetic activity inhibiting parasympathetic transmission)
- Little increase in pressure
- Sphincters still closed
