[Osmosis sound logo]
With acute pyelonephritis,
"pyelo-" means pelvis and "neph-" refers to the kidney
--so in this case it's the renal pelvis,
which is the funnel-like structure of the kidney that drains urine into the ureter--
and "-itis" means inflammation.
So acute pyelonephritis describes an inflamed kidney that develops relatively quickly,
usually as a result of a bacterial infection.
Now a urinary tract infection --or UTI-- is any infection of the urinary tract,
which includes the upper portion of the tract --the kidneys and the ureters--
and the lower portion of the tract --the bladder and the urethra.
So acute pyelonephritis is a type of upper urinary tract infection.
Acute pyelonephritis is most often caused by ascending infection:
meaning bacteria start by colonizing the urethra and bladder,
--which would be a lower urinary tract infection--
and make their way up the ureter to the kidney.
Therefore, upper UTI shares a lot of the same risk factors as lower UTI:
things like female sex, sexual intercourse,
indwelling catheters,
diabetes mellitus, and urinary tract obstruction.
One major factor that increases the risk of an upper UTI [developing] from a lower UTI spreading upward
is vesicoureteral reflux --or VUR--
which is where urine is allowed to move backward --up the urinary tract--
which can happen if the vesicoureteral orifice fails.
The vesicoureteral orifice is the one-way valve that allows urine to flow from each ureter into the bladder,
but not in the reverse direction.
VUR can be the result of a primary congenital defect
or it can be caused by bladder outlet obstruction,
which increases pressure in the bladder and distorts the valve.
As kind of a double whammy,
obstruction also leads to urinary stasis
--where urine stands still--
which makes it easier for bacteria to adhere and colonize the urinary tract.
So for ascending infections that cause acute pyelonephritis,
the most common organisms are E. coli,
Proteus species, and Enterobacter species, all of which are commonly found in the bowel flora.
Now, it's also possible that the kidneys get infected via hematogenous infection,
or spread through the bloodstream,
although this is a lot less common.
Usually, pyelonephritis from hematogenous spread is a consequence of septicemia or bacteremia
--which is bacteria in the blood-- as well as infective endocarditis,
an infection of the inner layer of the heart.
In these situations, the most common organisms are Staphylococcus species and, again, E.coli.
Acute pyelonephritis is most often unilateral
--meaning it affects just one kidney--
and when bacteria mount an attack, they usually start by adhering to the renal epithelium of the tubules,
which triggers an inflammatory response.
Chemokines attract neutrophils to the renal interstitium,
but typically the glomeruli and vessels of the kidney are spared.
As neutrophils infiltrate and die off,
they make their way through the urinary tract, and are peed out;
so people with acute pyelonephritis
often have white blood cells in their urine.
Sometimes the cells and the surrounding inflammatory protein debris
is even "casted" [sic] into the shape of the tubule
which is then also peed out and is called a white blood cell cast.
Patients also can present with increased white blood cells in their blood --called leukocytosis--
and as a result of the inflammatory immune response, patients can also develop fevers, chills,
nausea and vomiting, as well as flank pain at the costovertebral angle.
These systemic symptoms are what often distinguish acute pyelonephritis
from a lower urinary tract infection.
Treatment is typically antibiotics and making sure that the individual stays well hydrated.
Like most bacterial infections, there's also a possibility of a renal abscess that can form as a complication.
Also, if there are recurrent infections
--which can be the case in people with an anatomic problem
that allows bacteria to easily cause infections--
then it can lead to chronic pyelonephritis, as well as papillary necrosis --or death of the renal papillae tissue--
which has a much worse prognosis because that can affect the kidney's overall ability to function.
All right, as a quick recap:
Acute pyelonephritis is typically a bacterial infection of the upper urinary tract,
which usually develops from a lower urinary tract infection,
especially in individuals with vesicoureteral reflux.
The infection causes systemic symptoms like fevers and flank pain at the costvertebral angle
and is treated with antibiotics.
Thanks for watching! [Osmosis closing sound logo]
You can help support us by donating on Patreon,
subscribing to our channel, or telling your friends about us on social media.