Academic journal article Alcohol Health & Research World

Kidney Structure and Function

Academic journal article Alcohol Health & Research World

Kidney Structure and Function

Article excerpt

Cushioned in fatty tissue near the base of the spinal column, the kidneys are efficiently designed organs that perform two primary tasks in the body: excretion of metabolic end products and precise regulation of body fluid constituents. As they accomplish these tasks, the kidneys form and collect urine, which exits through the ureters to the bladder.

Each of the 2 million functional units (i.e., nephrons) in a pair of normal kidneys forms urine as it filters blood plasma of substances not needed by the body. Within each nephron, blood plasma enters a tiny ball of unusually permeable capillaries (i.e., the glomerulus), filters into a capsule that surrounds the glomerulus, then flows through a long, looping conduit called the nephron tubule.

As the plasma filtrate passes along this channel, the substances the body needs to conserve are reabsorbed into an extensive network of capillaries that wrap the nephron tubule. Many electrolytes and 99 percent of the water in the filtrate are reabsorbed, while waste products, such as urea (an end product of protein metabolism formed chiefly in the liver) and creatinine (an end product of muscle metabolism), as well as excess electrolytes (particularly sodium, potassium, chloride, and hydrogen ions), continue to journey along the tubule. Small amounts of unwanted substances also are secreted directly into the nephron tubules. Together, the filtered and secreted substances form urine (see figure) and eventually trickle into a series of progressively larger collecting ducts. Each 4.5inch-long kidney contains about 250 of the largest collecting ducts, each duct transmitting urine from approximately 4,000 nephrons.

Of the 48 gallons of filtrate processed through the nephrons of the kidneys each day, only about 1 to 1.5 quarts exit as urine. During this filtering process, substances are reabsorbed or secreted to varying degrees as the filtrate passes through the distinct segments of the nephron tubule. …

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