The kidneys provide an important function by filtering and cleansing the blood. The urinary tract is a channel to expel urine, which contains waste products filtered out of the blood, from the body. Normally, a person has two kidneys. The rest of the urinary tract consists of two ureters (the tubes connecting each kidney to the bladder), the bladder (an expandable muscular sac that holds urine until it is released from the body), and the urethra (a tube attached to the bladder that leads to the outside of the body). Each kidney continuously produces urine, which then drains through the ureter into the bladder at a low pressure. From the bladder, urine drains through the urethra and exits the body through the penis in males and at the vulva (the area of the external female genital organs) in females. Usually, urine is free of bacteria and other infectious organisms.
Kidney and Urinary Tract Disorders
Kidney and Urinary Tract Disorders Chapters (A-Z)
Biology of the Kidneys and Urinary Tract
Normally, a person has two kidneys. The rest of the urinary tract consists of two ureters (the tubes connecting each kidney to the bladder), the bladder (an expandable muscular sac that holds urine until it is released from the body), and the urethra (a tube attached to the bladder that leads to the outside of the body). Each kidney continuously produces urine, which then drains through the ureter into the bladder at a low pressure. From the bladder, urine drains through the urethra and exits the body through the penis in males and at the vulva (the area of the external female genital organs) in females. Usually, urine is free of bacteria and other infectious organisms.
Blood Vessel Disorders of the Kidneys
The blood flow to the kidneys needs to be intact for the kidneys to function properly. Any interruption of or reduction in the blood flow can cause kidney damage or dysfunction and, if long-standing, increased blood pressure (hypertension). When blood flow in the arteries supplying the kidneys is completely blocked, the entire kidney or a portion of the kidney supplied by that artery dies (kidney infarction). Kidney infarction can lead to the inability of the kidneys to process and excrete the body's waste products (kidney failure).
Cancers of the Kidney and Genitourinary Tract
Cystic Kidney Disorders
In cystic kidney disorders, the kidneys develop fluid-filled sacs (cysts). There are many cystic kidney disorders. Some are inherited and present from birth (congenital) and others develop later in life as a result of other disorders the person has (acquired). Some congenital cystic kidney disorders occur in people who have other congenital disorders such as Von Hippel–Lindau disease and Zellweger syndrome.
Diagnosis of Kidney and Urinary Tract Disorders
Disorders of Kidney Tubules
The kidneys filter and cleanse the blood. They also maintain the body’s balance of water, dissolved salts (electrolytes, such as sodium, potassium, and calcium), and nutrients in the blood. The kidneys begin these tasks by filtering the blood as it flows through microscopic tufts of blood vessels with small pores (glomeruli). This process moves a large amount of water and electrolytes and other substances into small tubules. The cells lining these tubules reabsorb and return needed water, electrolytes, and nutrients (such as glucose and amino acids) to the blood. The cells also move waste products and drugs from the blood into the fluid (which becomes urine) as it flows through the tubules as well as add hormones that maintain blood supply ( erythropoietin ), blood pressure, and electrolyte balance.
Disorders of Urination
The kidneys constantly produce urine, which flows through two tubes (the ureters) to the bladder, where urine is stored (see Figure: Viewing the Urinary Tract). The lowest part of the bladder (the neck) is encircled by a muscle (the urinary sphincter) that remains contracted to close off the channel that carries urine out of the body (the urethra), so that urine is retained in the bladder until it is full.
Kidney Filtering Disorders
Each kidney contains about 1 million filtering units (glomeruli). The glomeruli are made up of many microscopic clusters of tiny blood vessels (capillaries) with small pores. These blood vessels are designed to leak fluid from the bloodstream into a system of miniature tubules. The tubules secrete and reabsorb chemicals and substances from the fluid to cause it to become urine. The urine then drains from the tubules into larger and larger tubes until it leaves the kidney. Normally this filtering system permits fluid and small molecules (but almost no protein or blood cells) to leak into the tubules. Diseases that affect the kidneys can be divided into three categories based on the way they affect different parts of the kidneys:
Obstruction of the Urinary Tract
Stones in the Urinary Tract
Symptoms of Kidney and Urinary Tract Disorders
Urinary Tract Infections (UTI)
In healthy people, urine in the bladder is sterile—no bacteria or other infectious organisms are present. The tube that carries urine from the bladder out of the body (urethra) contains no bacteria or too few to cause an infection. However, any part of the urinary tract can become infected. An infection anywhere along the urinary tract is called a urinary tract infection (UTI).