Kidney Infection
(Pyelonephritis)

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Kidney infection facts

  • Kidney infection is one of a number of infections that can involve the urinary tract.
  • Infection of the kidney is very common, especially in young females.
  • Prompt treatment of kidney infection with antibiotics is extremely important.
  • In people with kidney infection, it is important to drink adequate amounts of water and liquids.
  • If treated early and adequately, kidney infection generally has a good outcome.

What is the function of the kidneys?

The kidneys have a variety of important functions in the body. These functions include filtering and excreting the waste products from the blood as it circulates through capillaries within the kidneys, regulating blood pressure, maintaining steady levels of electrolytes (for example, calcium, phosphorus, sodium, potassium, and chloride), and contributing to the production of red blood cells.

Where are the kidneys located?

The kidneys are located on either side of the body underneath the diaphragm near the lower back. Each kidney is connected to the bladder in the pelvis by ureters (long tube-like structures) that drain the urine from the kidneys to the bladder. Urine stored in the bladder is excreted from the body through the urethra. Collectively, these structures make up what is called the urinary tract.

What is a kidney infection?

The main components of the urinary tract system are kidneys, ureters, bladder, and urethra. Any part of the urinary system may become infected and this is generally referred to as urinary tract infection (UTI). When a kidney becomes infected, the condition is medically referred to as pyelonephritis. Thus, kidney infection is only one of several types of infections encompassed by the term UTI. The spectrum of UTIs includes:

  • Acute uncomplicated cystitis (bladder infection)
  • Recurrent cystitis
  • Complicated UTI
  • Prostatitis (prostate infection)
  • Kidney infection (pyelonephritis)
  • Catheter-associated UTI (in individuals with indwelling urinary catheters)

A more general classification of urinary tract infection is the following:

  • Lower urinary tract infection involves the urethra, the bladder, and, in men, the prostate gland.
  • Upper urinary tract infection refers to infection of the kidneys.
Picture of the kidneys and urinary structures.
Picture of the kidneys and urinary structures.
Medically Reviewed by a Doctor on 7/5/2012

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Kidney Infection in Pregnancy

Medical Author: Melissa Conrad Stöppler, MD
Medical Editor: Charles Patrick Davis, MD, PhD

Among the many changes that take place in the body during pregnancy is an increase in the risk of developing an infection of the urinary tract. The hormonal changes as well as the physical changes exerted by the enlarging uterus can lead to a slowdown of the passage of urine through the urinary tract and even to vesicouteral reflux, a condition in which urine in the bladder backs up, or refluxes, back into the ureters (the tubes that carry urine from the kidneys to the bladder). The hormone progesterone is responsible for changes in action of the smooth muscle walls of the ureters, and the weight of the uterus itself can lead to urinary retention. There is further an expansion of blood volume and increased load on the kidneys in pregnant women, resulting in increased urine output in the face of decreased mobility of the ureters. Finally, pregnant women tend to have higher urinary levels of glucose than nonpregnant women. All of these changes predispose to infection within the urinary tract.

As in nonpregnant women, urinary infections can occur in the urethra or bladder or may spread to the kidneys (pyelonephritis). The majority of infections come from existing bacteria in the...


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