Cellular function produces waste products that accumulate in the blood. Some waste products are toxic and can hinder normal cellular function. To rid the body of excessive substances and toxic waste products, the body contains an efficient excretory system, including organs such as the skin, intestine, lungs and kidneys. The body contains two kidneys located just behind the lower two ribs in the back. They primarily function to filter the blood and produce urine, according to the University of Maryland Medical Center, or UMMC.
Cellular Waste
The cells of the body produce energy and fulfill specific functions by converting nutrients from food to smaller usable substances. As the cells break down sugar, fat and protein into nitrogen, sulfur and phosphorus, metabolic waste products quickly accumulate in the blood. Metabolic waste products include water, urea, bilirubin, creatinine and uric acid. An excessive amount of water causes severe swelling and increased blood pressure. Other waste products act as neurotoxins or poisons, according to the National Kidney and Urologic Diseases Information Clearinghouse.
Blood Filtration
Detailed in the "Introduction to the Human Body," the kidneys consist of thousands of structures called nephrons. Blood enters the nephron through tiny arteries called capillaries. At the center of the nephron is a tightly packed cluster of capillaries, called the glomerulus. Toxic waste products and excess water, ions, hormones and salts are filtered from the blood within the glomerulus and from other capillaries in the area. A vessel called the renal tubule collects the filtered fluid. As the filtered fluid travels within the renal tubule, some substances are sent back to the blood. For example, water, sodium, potassium, calcium, hormones and other usable substances are sent back to the blood for the body to use once more.
Other Kidney Functions
In addition to filtering the blood of harmful substances, the kidneys also regulate ion levels in the blood. Ions are substances such as sodium, potassium, calcium and chloride. The kidneys also regulate blood volume and blood pressure by balancing the water content in the blood. The kidneys also maintain pH by adjusting the hydrogen and bicarbonate concentration in the blood. The pH level determines if the blood is too acidic or too alkaline. Lastly, the kidneys produce hormones such as calcitrol, which is the active form of vitamin D that regulates calcium levels and red blood cell production, according to "Introduction to the Human Body."
Urine Content
The fluid collected by the renal tubules eventually collects within the urinary bladder. The average person eliminates approximately one to two liters of urine per day. Water accounts for 95 percent of the volume; the remaining 5 percent consists of urea, creatinine, potassium, ammonia, uric acid, sodium, chloride, magnesium, sulfate, phosphate and calcium, according to the "Introduction to the Human Body."
Kidney Disease
With kidney disease, other substances not normally found in the urine begin to appear. Abnormal substances include albumin, glucose, red blood cells, white blood cells, urobilinigon, microbes and casts, which are clumps of tissue, according to the "Introduction to the Human Body."
References
- University of Maryland Medical Center: Kidney Disease
- National Kidney and Urologic Diseases Information Clearinghouse: Your Urinary System and How it Works
- "Introduction to the Human Body"; Gerard Tortora and Bryan Derrickson; 2010
