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OBJECTIVES

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  • State 8 major functions of the kidneys.

  • Define the balance concept.

  • Define the gross structures and their interrelationships: renal pelvis, calyces, renal pyramids, renal medulla (inner and outer zones), renal cortex, and papilla.

  • Define the components of the nephron-collecting duct system and their interrelationships: renal corpuscle, glomerulus, tubule, and collecting-duct system.

  • Draw the relationship between glomerulus, Bowman's capsule, and the proximal tubule.

  • Define juxtaglomerular apparatus and describe its 3 cell types; state the function of the granular cells.

  • List the individual tubular segments in order; state the segments that comprise the proximal tubule, Henle's loop, and the collecting-duct system; define principal cells and intercalated cells.

  • Define the basic renal processes: glomerular filtration, tubular reabsorption, and tubular secretion.

  • Define renal metabolism of a substance and give examples.

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RENAL FUNCTIONS

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The kidneys are traditionally known as organs that excrete waste. Although they do indeed excrete waste, they also perform a spectrum of other functions essential for health such as assuring bone integrity and helping to maintain blood pressure. As they carry out these functions the kidneys work cooperatively and interactively with other organ systems, particularly the cardiovascular system. This chapter provides a brief account of renal functions and an overview of how the kidneys perform them, and a description of essential renal anatomy. Ensuing chapters delve into specific renal mechanisms and their interactions with other organ systems.

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Function 1: Excretion of Metabolic Waste and Foreign Substances

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Image not available. Our bodies continuously form end products of metabolic processes. In most cases, those end products are of no use to the body and are harmful at high concentrations. Therefore, they must be excreted at the same rate as they are produced. Some of these products include urea (from protein), uric acid (from nucleic acids), creatinine (from muscle creatine), urobilin (an end product of hemoglobin breakdown that gives urine much of its color), and the metabolites of various hormones. In addition, foreign substances, including many common drugs, are excreted by the kidneys. In many cases the kidneys work in partnership with the liver. The liver metabolizes many organic molecules into water-soluble forms that are more easily handled by the kidneys.

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Function 2: Regulation of Water and Electrolyte Balance

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Image not available. Water, salt, and other electrolytes enter our bodies at highly variable rates, all of which perturb the amount and concentration of those substances in the body. The kidneys vary their excretion of electrolytes and water to preserve appropriate levels in the body. In doing so they maintain balance, that is, match output to input so as to keep a constant amount in the body. As an example, consider water balance. Our input of water is sporadic and only rarely driven in response to body needs. We drink water when thirsty, but we also drink water because it is a component ...

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