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  • State seven major functions of the kidneys.

  • Define the balance concept and give examples.

  • Define the gross structures and their interrelationships: renal pelvis, calyces, renal pyramids, renal medulla (inner and outer zones), renal cortex, 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 three 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 distal nephron including the collecting-duct system; define principal cells and intercalated cells.

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

  • Define renal metabolism of a substance and give examples.


The kidneys are fascinating biological machines. They are multifunction organs that carry out essential tasks far beyond the well-known excretion of waste. Among the most important of these tasks are preservation of blood volume, total body salt and water composition, maintenance of acid-base balance, and assuring bone integrity. The kidneys work cooperatively and interactively with many other organ systems to maintain body function using a coordinated array of cellular mechanisms. This chapter provides a brief account of renal functions and an overview of how the kidneys perform these functions, plus a description of essential renal anatomy. Subsequent chapters delve into the specific renal mechanisms that mediate these functions and how the kidneys interact with other organ systems.

Function 1: Regulation of Water and Electrolyte Balance

imageWater, salt, and other electrolytes enter our bodies at variable rates, which perturb the amount and concentration of these 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. We should think of the body as an open system in steady state. In a steady state there are no net changes (of anything) inside the body. Therefore, intake must equal output. As an example, consider water in the body. Our input of water is sporadic and often not driven in response to body needs. We drink water when thirsty, but we also drink water because it is a component of beverages that we consume for reasons other than hydration. In addition, solid food often contains large amounts of water. The kidneys respond to increases in water content by increasing the output of water in the urine, thereby restoring body water to normal levels. The same principles apply to many electrolytes and other substances that have variable inputs.

We have discussed the importance of balance for water and electrolytes, but another major aspect of water and electrolyte balance is ...

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