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OBJECTIVES

OBJECTIVES

  • 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, 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 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.

RENAL FUNCTIONS

The kidneys are multifunction biological machines that accomplish far more than their popularly known function, excretion of soluble waste. The kidneys do indeed excrete waste, for example, the end products of protein metabolism, and of course water, which constitutes almost the entire urinary volume. However, the kidneys are far from just physiological trash chutes leading to the bladder. Virtually everything that goes into the bladder is regulated by processes within the kidneys that add or subtract material, thereby controlling what is conserved or what is lost from the body.

The kidneys work cooperatively and interactively with many other organ systems to maintain body function. 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. The actual mechanics of renal function is relatively straightforward. Regulation of those mechanics is more complicated.

Function 1: Regulation of Water and Electrolyte Balance

imageAn important physiological concept is balance. Balance starts at a single-cell level: a single cell is an open system that tries to maintain an unchanging internal composition; balance means that for an individual cell all substances that enter or that are produced by the cell must be exactly equal to the same substances which leave or are metabolized by the cell. If this criterion is met the cell will maintain an unchanging internal environment; if it is not met the cell will die usually because of uncontrolled volume changes. When a cell is in balance, the intracellular composition is in an unchanging, steady state; that is, because inputs and outputs are exactly equal, there is no change in the composition of the cell interior even though the intracellular composition may be quite different from the extracellular composition. Maintaining balance involves large movements of material into and out of a cell. Maintaining the steady state requires energetic input; this is ...

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