The kidneys play key roles in body function, not only by filtering the blood and getting rid of waste products, but also by balancing the electrolyte levels 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 on 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 ofelectrolytes 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 usually are measured; 1) blood urea nitrogen (BUN), and 2) creatinine (Cr)
When blood flows to the kidney, sensors within specialized kidney cells regulate how much water to excrete as urine, along with whatconcentration 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.
Urine that is made by each kidney flows through the ureter, a tube that connects the kidney to the bladder. Urine is stored within the bladder, and when urination occurs, the bladder empties urine through a tube called the urethra.
Kidney failure may occur from an acute situation that injures the kidneys or from chronic diseases that gradually cause the kidneys to stop functioning.
In acute renal failure, kidney function is lost rapidly and can occur from a variety of insults to the body. Since most people have two kidneys, both kidneys must be damaged for complete kidney failure to occur. Fortunately, if only one kidney fails or is diseased it can be removed, and the remaining kidney may continue to have normal kidney (renal) function. If a both patient’s kidneys are injured or diseased, a donor kidney(s) may transplanted.
The list of causes of kidney failure 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 of kidney failure are:
- Hypovolemia (low blood volume) due to blood loss
- Dehydration from loss of body fluid (for example, vomiting, diarrhea,sweating, fever)
- Poor intake of fluids
- Medication, for example, diuretics (“water pills”) may cause excessive water loss
- Abnormal blood flow to and from the kidney due to obstruction of the renal artery or vein
- Renal causes of kidney failure (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 simple urinary tract infections.
Some medications are also toxic to the kidney including:
- Nonsteroidal anti-inflammatory drugs(NSAIDs) like ibuprofen (Advil, Motrin, and others), and naproxen (Aleve, Naprosyn)
- Antibiotics like aminoglycosides gentamicin (Garamycin), tobramycin
- lithium (Eskalith, Lithobid)
- Iodine-containing medications such as those injected for radiology dye studies
Initially, kidney failure may be not produce any symptoms (asymptomatic). As kidney function decreases, the symptoms are related to the inability to regulate water and electrolyte balances, clear waste products from the body, and promote red blood cell production.
If unrecognized or untreated, the following symptoms of kidney failure may develop into life-threatening circumstances.
- Lethargy
- Weakness
- Shortness of breath
- Generalized swelling (edema)
- Generalized weakness due to anemia
- Loss of appetite
Diet is an important consideration for those with impaired kidney function. Consultation with a dietician may be helpful to understand what foods may or may not be appropriate.
In this state of impaired kidney function, the kidneys cannot easily remove excess water, salt, or potassium from the blood, so foods high in potassium salt substitutes may need to be consumed in limited quantities. Examples of potassium rich foods include:
- Bananas
- Apricots
- Cantaloupe
- Sweet potatoes
- Yogurt
- Spinach
- Avocados
Phosphorus is a forgotten chemical that is associated with calcium metabolism and may be elevated in the body in kidney failure. Too much phosphorus can leech calcium from the bones and cause osteoporosisand fractures. Examples of foods and beverages high in phosphorus include:
- Milk
- Cheese
- Nuts
- Dark cola drinks
- Canned iced teas
- Yogurt
- Organ meets
- Sardines
- Oysters
- Baked beans
- Black beans
- Lentils
- Kidney beans
- Soy beans
- Bran cereals
- Caramels
- Whole grain products
Different classes of medications may be used to help control some of the issues associated with kidney failure including:
- Phosphorus-lowering medications, for example, calcium carbonate (Caltrate),calcitriol (Rocaltrol), and sevelamer (Renagel)
- Red blood cell production stimulation, for example, erythropoietin, darbepoetin (Aranesp)
- Red blood cell production (iron supplements)
- Blood pressure medications
- Vitamins
Once the kidneys fail completely, the treatment options are limited to dialysis or kidney replacement by transplantation.
Dialysis cleanses the body of waste products in the body by use of filter systems. There are two types of dialysis; 1) hemodialysis, and 2) peritoneal dialysis.
Hemodialysis uses a machine filter called a dialyzer or artificial kidney to remove excess water and salt, to balance the other electrolytes in the body, and to remove waste products of metabolism. Blood is removed from the body and flows through tubing into the machine, where it passes next to a filter membrane. A specialized chemical solution (dialysate) flows on the other side of the membrane. The dialysate is formulated to draw impurities from the blood through the filter membrane. Blood and dialysate never touch in the artificial kidney machine.
For this type of dialysis, access to the blood vessels needs to be surgically created so that large amounts of blood can flow into the machine and back to the body. Surgeons can build a fistula, a connection between a large artery and vein in the body, usually in the arm, that allows a large amount of blood flow into the vein. This makes the vein swell or dilate, and its walls become thicker so that it can tolerate repeated needle sticks to attach tubing from the body to the machine. Since it takes many weeks or months for a fistula to mature enough to be used, significant planning is required if hemodialysis is to be considered as an option.
If the kidney failure happens acutely and there is no time to build a fistula, special catheters may be inserted into the larger blood vessels of the arm, leg, or chest. These catheters may be left in place for weeks. In some diseases, the need for dialysis will be temporary, but if the expectation is that dialysis will continue for a prolonged period of time, these catheters act as a bridge until a fistula can be planned, placed, and matured.
Dialysis treatments normally occur three times a week and last a few hours at a time. Most commonly, patients travel to an outpatient center to have dialysis, but home dialysis therapy is becoming an option for some.
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