The Lower Urinary Tract Flashcards
What organs make up the urinary tract?
- The Kidney
- Ureters
- Urinary Bladder
- Urethra
Explain how urine moves from the kidney o the ureter
- Tubular fluid exits collecting duct at the tip of renal pyramid - also known as the renal papilla
- Minor and major calyces lead to the renal pelvis
- Fluid deposition into renal pelvis stretches the smooth muscle
- Distension triggers peristaltic contractions at the hilus (ext of the kidney entrance to the ureter)
- Fluid moves down ureter in pulses towards bladder for storage and controlled release
Describe the structure of the ureter
- Tubes approximately 30 cm long
- Mucosal layer: transitional epithelium
-3-8 cells thick, impermeable to urine
• Supported by layers of smooth muscle:
- inner: longitudinal muscle (L)
- outer: circular/spiral muscle (C)
- extra outer layer of longitudinal muscle
What is the function of the Ureters?
- Dilation of renal pelvis generates action potential from pacemaker cells in hilum
- Peristaltic waves generated – between
1 to 6 per minutes
- no. of contractions can be modulated by the nervous system:
- PNS: enhanced
- SNS: inhibited
How is urine moved down the ureter?
- through peristaltic movements as seen in the GI tract
- longitudinal muscles contracts first followed by circular muscle relaxation
- The longitudinal muscle then starts to relax allowing a bolus to form followed by circular muscle contraction which pushes against the bolus
How does the ureter attach to the urinary bladder?
- Ureters attach to the posterior wall of the urinary bladder
- Pass-through bladder wall at an oblique angle for 2-3 cm into the bladder: ureteral openings are slit-like rather than rounded
- this prevents backflow of urine up ureters during contraction of the bladder
Describe the structure of the Urinary Bladder
- A hollow muscular organ, consisting of fundus (body) and neck
- Outer “Detrusor” Muscle layer: consists of longitudinal, circular/spiral muscles
- Inner Mucosal layer:
- transitional epithelium
- folded into “rugae” when bladder empty
- highly elastic – expands as the bladder fills
The Trigone
- the triangular area bounded by openings of ureters and the entrance to the urethra: acts as a funnel to channel urine to the neck of the bladder
What is the function of the urinary bladder?
- temporary store of urine up to 1 litre
- contraction stimulated by the PNS
What are the two sphincters that guard the exit of urine from the urinary bladder and how do they work?
Internal Urethral Sphincter
- Loop of smooth muscle
- Convergence of detrusor muscle
- Under involuntary control
normal tone keeps the neck of the bladder and urethra free of urine
External Urethral Sphincter
- Circular band of skeletal muscle where urethra passes through the urogenital diaphragm
- Acts as a valve with a resting muscle tone
- Under voluntary control
Explain the elimination of Urine in women.
- give two possible complications
- Opens via external urethral orifice located between clitoris and vagina
- A shorter urethra in females -> more susceptible to UTIs
- If the external sphincter is not as well developed -> incontinence following childbirth due to injury
Explain the elimination of urine in men.
give two possible complications
- The urethra passes through the prostate gland and through urogenital diaphragm and penis
- Longer urethra compared to females provide some protection against UTIs
- Prostate gland enlarges in 50% of males >60 yrs (along with hypertrophy of detrusor muscle)
- may require surgical or hormone treatment
- Prostate cancer – one of the commonest cancers affecting older men (death rate ~ 3%)
How is Micturition controlled?
it is an autonomic reflex
Inhibited by: Higher centres in the brain
- stimulate continual tonic contraction of the external sphincter
Facilitated by: Cortical centres in the brain
- intimates the micturition reflex and relaxing the external sphincter
- the internal sphincter relaxes at the same time and urination occurs*
What does this graph tell you about bladder filling?
Red solid lines: normal intrinsic tone of the bladder wall
Red broken lines: pressure peaks (micturition contractions/waves)
- In a partially full bladder: contractions relax spontaneously after a few seconds
- In an Increasingly full bladder: contractions are more frequents, intense and last longer
What innervates the bladder and the sphincter?
- the Hypogastric Nerve (sympathetic invol. from L2) and Paudendal Nerves (Somatic vol. from S2+3) inhibit micturition
- the Pelvic nerves (parasympathetic invol. from S2+3) facilitate micturition
How does the Guarding Reflex promote continence
- Progressive bladder distension stimulates the pelvic nerve via activation of stretch receptors in the bladder wall and the internal sphincter (1)
- Activation of the pelvic nerve leads to stimulation of the hypogastric nerve
- Hypogastric nerve stimulation causes:
(i) relaxation and reduced excitability of the bladder detrusor muscle(2)
(ii) constriction of the internal sphincter (3)
• Also, the external sphincter is held closed by the pudendal nerve(4)
What does the stimulation of the Pelvic Nerve also result in when stretch receptors in the bladder stimulate it during continues filling of urine?
- contraction of the detrusor muscle
- relaxation of the internal sphincter
Explain 3 major ways Micturition can be neurally disrupted.
Paraplegia: the complete severing of nerve inputs from the cerebral cortex (1)
– Mictuiation reflexes return, but without cortical control
– Periodic but unannounced bladder emptying – “Automatic bladder”
Partial spinal cord damage with loss of inhibitory descending signals(2)
– Frequent urination as excitatory impulses from cerebral cortex remain unopposed
– aka “Uninhibited bladder”
• Crush injury of dorsal roots (3)
– Afferent nerve destruction - micturition reflexes lost despite having a complete efferent system
– Bladder fills to capacity and overflows dropwise - “overflow incontinence”
– aka “Atonic bladder”
Infants lack voluntary control over urination until corticospinal connections are established
What are the 3 main types of Urinary Incontinence?
Loss of sensory nerves due to injury:
- the bladder fills to capacity
- no signals from stretch receptors in the bladder
- overflow incontinence occurs (atonic bladder)
Involuntary bladder contractions due to injury:
- urge incontinence or increased frequency
Heightened urge incontinence- sensitive bladder:
- Spicy food (capsaicin)
- Caffeine/ chocolate (xanthines)
- Citrus fruits (citric acid)
- Carbonated beverages
- Excitement or even laughter
What does the Pelic Nerve release to promote Micturition?
- ACh
- this causes detrusor muscle to contract
- and involuntary internal sphincter relaxation
What drugs are used to prevent Micturition?
Anticholinergics (muscarinic ACh receptor antagonists):
- Action: inhibit bladder contractions, facilitates involuntary contraction of internal bladder sphincter
- Examples: Oxynitinin, Tolterodine, Flavooxate (fewer side effects, less effective)
Tricyclic antidepressants
- Action: anticholinergic, direct muscle relaxant effects on the bladder but also inhibits the reuptake of noradrenaline and serotonin increasing their levels
- Examples: Impipramine (children), Duloxetine, Desmopressin (children), Mirabegron
What are some unwanted effects of Anticholinergics used for continence treatment?
- Dry mouth,
- Blurred vision,
- Palpitations,
- Drowsiness,
- Facial flushing (Atropine-like)
What is the treatment for acute and chronic urinary retention?
Acute
- Catheterisation
- Surgery
Chronic
- Pharmacological intervention
- Surgery
What is the effect of Noradrenaline on the bladder?
- released by the Hypogastric Nerve
- reduces micturation
What are alpha-adrenergic blocking drug? give the following:
- Actions
- Examples
- Unwanted effects
Drugs used to prevent urinary retention
Action
- Antagonist action at alpha-1A adrenoceptors in the bladder neck
- Relaxes smooth muscle at the bladder neck and increases the urine flow rate
Examples
- Alfuzosin, Doxazosin, Indoramin, Prazosin, Tamsulosin, Terazosin
Unwanted effects
- hypotension
- drowsiness
- depression
- headaches
- dry mouth
- GI disturbances
What are Parasympahteomimetics?
Choline Esters to prevent urinary retention
Actions:
- Agonist action at muscarinic ACh receptors
- Increases contraction of the bladder detrusor muscle
- Limited role in the relief of urinary retention – now superseded by catheterisation
Examples:
- BETHANECOL
Cautions:
- Use with care or avoid using in patients with the cardiac disorder (e.g. arrhythmias)
- Avoid in cases involving GI ulceration, asthma, hypotension, epilepsy, Parkinsonism, pregnancy
Unwanted effects:
- Nausea, vomiting, intestinal colic, bradycardia, blurred vision,
sweating
How do UTI pathogens evade destruction in the bladder?
- Type 1 pilus binds to host cell.
- This induces actin rearrangement within the host cell and causes uptake of the bacteria
- Inside the cell, the bacteria is protected from many antibiotics and host defences.
- Toll-like receptor 4 recognises LPS released by UPEC and activates pathways (via cAMP production) to push the bacteria out (exocytosis).
- BUT the UPEC escapes this by escaping into the cytoplasm, where it multiplies up into intracellular bacterial communities (IBC).
- These can then go on to invade more host cells; or to invade the transitional cells below and establish a quiescent intracellular reservoir – where they can survive for months
How do UTI pathogens invade the bladder?
- UPEC secretes factors to enable nutrients acquisition
- Hemolysin A forms pores in the host cell which promotes host cell lysis, releasing iron and other nutrients.
- UPEC also expresses siderophores which scavenge iron, which the bacteria depend on.
- Hemolysin A also triggers epithelial exfoliation which helps the UPEC spread. Other colonised cells have their apoptotic pathways blocked, allowing the UPEC to survive.
- Some extracellular UPEC adopts a filamentous morphology which makes it harder for the neutrophils to kill them.
What are the stages of CKD using the eGFR?
