Kidney Failure
Medical Author: Benjamin C. Wedro, MD, FAAEM
Medical Editor: Melissa Conrad Stöppler, MD
What are the kidneys?
The kidneys play key roles in body function, not only by filtering the blood
and getting rid of waste products, but also by balancing levels of
electrolytes in the body, controlling blood pressure, and stimulating the
production of red blood cells.
The kidneys are located in the abdomen toward the back, normally one of each
side of the spine. They get their blood supply through the renal arteries
directly from the aorta and send blood back to the heart via the renal veins to
the vena cava. (The term "renal" is derived from the Latin name for kidney.)
The kidneys have the ability to monitor the amount of body fluid, the
concentrations of electrolytes like sodium and potassium, and the acid-base
balance of the body. They filter waste products of body metabolism, like urea
from protein metabolism and uric acid from DNA breakdown. Two waste products in
the blood can be measured: blood urea nitrogen (BUN) and
creatinine (Cr).
When blood flows to the kidney, sensors within the kidney decide how much
water to excrete as urine, along with what concentration of electrolytes. For
example, if a person is dehydrated from
exercise or from an illness, the kidneys
will hold onto as much water as possible and the urine becomes very
concentrated. When adequate water is present in the body, the urine is much more
dilute, and the urine becomes clear. This system is controlled by renin, a
hormone produced in the kidney that is part of the fluid and blood pressure
regulation systems of the body.
Kidneys are also the source of erythropoietin in the body, a hormone that
stimulates the bone marrow to make red blood cells. Special cells in the kidney
monitor the oxygen concentration in blood. If oxygen levels fall, erythropoietin
levels rise and the body starts to manufacture more red blood cells.
After the kidneys filter blood, the urine is excreted through the ureter, a
thin tube that connects it to the bladder. It is then stored in the bladder
awaiting urination, when the bladder sends the urine out of the body through the
urethra.
What causes kidney failure?
Kidney failure can occur from an acute situation or from chronic problems.
In acute renal failure, kidney function is lost rapidly and can occur from a
variety of insults to the body. The list of causes is often categorized based on
where the injury has occurred.
Prerenal causes (pre=before + renal=kidney) causes are due to decreased
blood supply to the kidney. Examples of prerenal causes are:
- Hypovolemia (low blood volume) due to blood loss
- Dehydration from loss of body fluid (vomiting, diarrhea, sweating, fever )
- Poor intake of fluids
- Medication, for example, diuretics ("water pills") may cause excessive water loss.
- Loss of blood supply to the kidney due to obstruction of the renal artery
or vein.
Renal causes (damage directly to the kidney itself) include:
- Sepsis: The body's immune system is overwhelmed from infection and
causes inflammation and shutdown of the kidneys. This usually does not occur
with urinary tract infections.
- Medications: Some medications are toxic to the kidney, including
nonsteroidal
anti-inflammatory drugs like ibuprofen and
naproxen. Others are
antibiotics like aminoglycosides [gentamicin
(Garamycin), tobramycin], lithium
(Eskalith, Lithobid), iodine-containing medications
such as those injected for radiology dye studies.
- Rhabdomyolysis: This is a situation in which there is significant muscle
breakdown in the body, and the degeneration products of muscle fibers clog the
filtering system of the kidneys. Often occurring because of trauma and crush
injuries, it can also be caused by some medications used to treat high
cholesterol.
- Multiple Myeloma
- Acute glomerulonephritis or inflammation of the glomeruli, the filtering
system of the kidneys. Many diseases can cause this inflammation including
systemic lupus erythematosus,
Wegener's granulomatosis, and
Goodpasture syndrome.
Post renal causes (post=after + renal= kidney) are due to factors that affect
outflow of the urine:
- Obstruction of the bladder or the ureters can cause back pressure when
there is no place for the urine to go as the kidneys continue to work. When the
pressure increases enough, the kidneys shut down.
- Prostatic hypertrophy or prostate cancer may block the urethra and prevents
the bladder from emptying.
- Tumors in the abdomen that surround and obstruct the ureters.
- Kidney stones
Chronic renal failure develops over months and years. The most common causes
of chronic renal failure are related to:
Less common causes:
Next: What are the symptoms of kidney failure? »
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