Pathology of Urinary Tract Infection Flashcards
what is the typical presentation of a UTI?
- Dysuria (pain on micturition)
- Frequency
- Smelly urine
But:
- very young – unwell, failure to thrive
- very old – incontinence, off their feet
How much renal blood flow is there?
Renal blood flow = 20 to 25 % cardiac output
how does urine output change with fluid intake?
Resorption of fluid is diminished if increase fluid intake = increased urine output
do ureters store urine?
Ureters have continuous trickle of urine – they do not store urine
how do the ureters enter the bladder?
Ureters enter bladder at angle
why does the ureter enter the bladder at an angle?
Increasing pressure from bladder, as it fills, closes off ureter and stops reflux of urine
1 way, continuous flow of urine
what are the bacteriostatic properties of the normal urinary tract?
- Free flow of urine through normal anatomy - assumes drinking enough fluids
- Low pH, high osmolality, and high ammonia (NH3) content of normal urine
- prostatic secretions are bacteriostatic
- anti-bacterial antibodies
is the normal urinary tract sterile?
Urinary tract, except for terminal urethra, is sterile
are urinated specimens sterile?
Initial voiding will _____ ___ many terminal urethral floral bacteria
flush out
how do you take a urine specimen for culture?
intial urine is heavily contaminated, collect after initial void
Patient voids and stops mid-stream, discarding urine, then collects next volume of urine = MSSU (mid-stream specimen of urine)
In a Mid Stream Specimen Urine, MSSU, ar ethere any bacteria?
urethral flora diminshed but always present
what do you do with the MSSU
culture it
Got a problem on how to interoperate it as always a few bacterial colonies
urethral flora will always grow in culture
how to tell contamination from real infectionwhen culturing a MSSU?
- MSSU - microbiology for culture under set conditions
- Bacteria multiply in log phase growth
what levels usually indicate an infection?
105 usually = infection
105 per ml - <1:100 chance of contamination if asymptomatic – ie 99 times out of 100, 105 bacteria per ml represents infection – if specimen = MSSU
what does 103 - 104 indicate?
infection sometimes
probable infection if have symptoms
50% chance of infection if no symptoms
What does <103 represent on a MSSU culture?
usually no infection
MSSU are more difficult to collect in what people?
Difficult to collect in young children and elderly
what are problems with interpritation of urine cultures?
Some bacterial species are not normally present in terminal urethra/rectal flora and may be pathogenic at low colony numbers
What micro-organisms cause UTI?
- Bacteria mostly = gut flora, especially E.coli
- Viral infection rare
what is the route of infection?
always ascending?
how does an infection in the kidneys come about anf what is it classed as?
- Infection in kidneys: usually infection has spread up from bladder infection
- Upper urinary tract infection = more serious
infection of bladder is called?
cystitis
infection of the kidney is called?
acute pyelonephritis
if recurrent/prolonged infection = chronic pyelonephritis
what happens if there is an obstruction at the level of the urethra?
Upper urethral and bladder dilatation
Bilateral hydroureter (dilation of ureter)
Bladder dilatation, bilateral hydroureter and bilateral hydronephrosis (kidney swells due to urine failing to properly drain from the kidney to the bladder) - chronic renal failure
What happens if there is an obstruction at level of renal pelvis on 1 side only?
Unilateral hydroureter
Unilateral hydroureter and unilateral hydronephrosis
what are the consequences of obstruction?
- Proximal dilatation
- Slowed urine flow - Cannot flush out bacteria - infection
- Slowed urine flow - sediments form - calculous (stone) formation - obstruction
obstruction leads to more dilation, increased calculous formation and more infections
• Some bacterial infections predispose to calculous formation
causes the triad seen below:
what is vesicoureteric reflux
decreased angulation
a condition in which urine flows backward from the bladder into the ureters/kidneys
what does vesicoureteric reflux cause?
backflow of urine
hydroureter - dilation of the ureter
much worse if it is bilateral but usually unilateral
what are the common causes of obstruction in adults?
- Men – Benign Prostatic Hyperplasia (not a tumour) of prostate – functional and anatomical obstruction
- Women – uterine prolapse
- Both sexes – tumours and calculi
picture showing the normal emptying of the bladder
Get rid of any bacteria that happen to of come up the urethra
how does decreased sensation due to spinal cord/brain injury affect the emptying of the bladder?
Decreased sensation - no sense of when to micturate and do not know to empty bladder completely - leave urine in bladder (high residual volume) - stasis of urine
Hypothetical graph of urinary tract infection incidence with age
In children due to things like Vesicoureteric reflux infection
How does sexual activity in females cause UTI
In females sexual activity tends to move lower urethral flora up the tract (back wall of urethra is just in front of vagina)
How does Catheterisation (and other urological procedures) cause UTI?
Any instrumentation of urinary tract tends to move lower urethral flora up the tract
summary of various predisposing factors causing a UTI
