lower urinary tract Flashcards
what are the 3 structures that urine passes through from the kidneys?
- ureters
- urinary bladder
- urethra
how does urine exit the kidneys?
- tubular fluid generated within the nephron by filtration, reabsorption, secretion
- final modification of tubular fluid occurs in collecting duct under influence of ADH
- tubular fluid travels through common collecting duct deep into inner medulla of kidney
- tubular fluid exits collecting duct at tip of renal pyramid (renal papilla)
- fluid deposition into renal pelvis stretches smooth muscle
- distention triggers peristaltic contractions at hilus
- fluid moves down ureter in pulses towards bladder for storage and controlled release
what structures lead to renal pelvis?
minor an major calyces
what are the key characteristics of the mucosal later of the ureters?
- transitional epithelium
- 3-8 cells thick
- impermeable to urine
what are the 3 layers of smooth muscle used for support in the ureters?
- inner: longitudinal muscle
- outer: circular/spiral muscle
- extra outer layer of longitudinal muscle
what is the function of the ureter?
- dilation of renal pelvis generated action potential form pacemaker cells in hilum
- peristaltic waves generated: between 1 to 6 per minute
- the number of contractions can be modulated by nervous system (PNS = enhanced, SNS = inhibited)
how do peristaltic contractions work?
- consist of successive waves of contractions and relaxation of longitudinal and circular smooth muscle
- longitudinal muscle contracts first followed by circular muscle relaxation
- longitudinal muscle then starts to relax allowing a bolus to form followed by circular muscle contraction which pushes agains the bolus
- pattern of contractions is repeated resulting in slow but progressive movement of a push or urine along the ureter (PERISTALSIS)
how does urine enter the urinary bladder?
- the ureters pass through the bladder wall at oblique angle for 2-3cm into bladder
- ureteral opening are slit-like
- together this helps prevent back flow of urine up ureters during contraction of bladder
what is the structure of the urinary bladder?
- a hollow muscular organ, consisting of a fundus and neck
- outer muscle layer: consists of longitudinal, circular/spiral muscle
- inner mucosal layer: transitional epithelium, followed into ‘rugae’ when bladder empty, highly elastic
what is the trigone?
- triangular area bounded by openings of ureters and entrance to urethra
- acts as funnel to channel urine towards neck of bladder
what is the function of the urinary bladder?
- temporary storage of urine
- up to 1L capacity
- stimulated to contract by PNS
what are the 2 sphincters that guard the urinary bladder?
1) internal urethral sphincter
2) external urethral sphincter
what are the key characteristics of the internal urethral sphincter?
- loop of smooth muscle
- convergence of detrusor muscle
- under involuntary control
- normal tone keeps neck of bladder and urethra free of urine
what are the key characteristics of the external urethral sphincter?
- circular band of skeletal muscle where urethra passes through urogenital diaphragm
- acts as a valve with resting muscle tone
- under voluntary control
- voluntary relaxation permits micturition
what are the key characteristics of a female urethra?
- opens via external urethral orifice located between clitoris and vagina
- shorter urethra in females
- external sphincter not as well developed: incontinence following childbirth due to injury
what are they key characteristics of a male urethra?
- urethra passes through prostate gland and through uro-genital diaphragm and penis
- longer urethra compared to females provide some protection against UTIs
- prostate gland enlarges in 50% of males >60years
- prostate cancer
what are the 2 stages of bladder emptying?
1) bladder progressively fills until pressure within the bladder reaches a threshold
2) this elicits the ‘micturition reflex’ which provides a conscious desire to urinate or eventual emptying of the bladder
what s the micturition reflex?
an autonomic reflex which is…
1) inhibited by higher centres in the brain
2) facilitated by cortical centres in the brain
what is the function of higher centres?
keep the micturition reflex under inhibition, preventing micturition by stimulating continual tonic concentration of the external sphincter
what is the function of cortical centres?
facilitate urination by initiating the micturition reflex and relaxing the external sphincter
what is micturition inhibited by?
activity in the hypogastric and pudenal nerves
what happens during bladder filling?
- progressive bladder distention stimulates the pelvic nerve via activation of stretch receptors in the bladder wall and internal sphincter
- activation of the pelvic nerve leads to stimulation of the hypogastric nerve
what does hypogastric nerve stimulation cause?
1) relaxation and reduced excitability of the bladder detrusor muscle
2) constriction of the internal sphincter
what hold the external sphincter closed?
pudenal nerve
what promoted continence?
guarding reflexes
what happens as the bladder continues to fill?
- stretch receptors in the bladder continue to stimulate pelvic nerve
- periodic reflex micturition contractions are also stimulated above 200ml
- these micturition contractions continue to be stimulated and relax but at >300ml bladder contractions begin to predominate
- full bladder sensation conveyed to thalamus and the to cerebral cortex and desire to urinate increases
- at appropriate time, voluntary relaxation of external sphincter occurs via pudenal nerve
- micturition occurs, aided by lowering of diaphragm, contraction of abdominal muscles and opening of internal sphincter
what does stimulating the pelvic nerve cause?
1) contraction of the detrusor muscle
2) relaxation of the internal sphincter
what are the 3 neural disruptions of micturition?
- paraplegia: complete serving of nerve inputs from cerebral cortex
- partial spinal cord damage with loss of inhibitory descending signals
- crush injury of coral roots
what are the 3 problems with micturition reflex?
1) control of micturition can be lost due to stroke, Alzheimer’s, issues affecting cerebral cortex or hypothalamus
2) bladder sphincter muscles lose tone
3) urinary retention may develop in males if enlarges prostate gland compresses the urethra and restricts urine flow
what are the 2 functional classifications?
1) failure to store urine: incontinence
2) failure to empty bladder: retention
what are the 3 main types of urinary incontinence?
1) loss of sensory nerves due to injury
2) involuntary bladder contractions due to injury
3) heightened urge incontinence (sensitive bladder)
what happens with loss of sensory nerves due to injury?
- bladder fills to capacity
- no signals from stretch receptors in bladder
- overflow incontinence occurs
what are the solutions of acute urinary retention?
- catheterisation
- surgery
what are the solutions of chronic urinary retention?
- pharmacological intervention
- surgery
