The Renal System

The body's filtering abilities tie in to many other functions.

By Joy Keller
Oct 18, 2018

When the body’s systems are running smoothly, we’re a walking, talking cellular symphony. When something goes “off note,” we become more cognizant of how vital interconnections affect our functionality. More commonly, though, we take the actions of some body parts for granted. Consider, for example, the renal, or urinary, system.

This system produces, stores and eliminates fluid waste, which travels from the kidneys through the ureters and fills the bladder. The kidneys make urine by filtering waste and extra water from blood (Zimmermann 2018). The renal system regulates the amount of water in the body, particularly in the blood, and controls electrolyte (e.g., sodium and potassium) concentrations. It also removes toxins, metabolic byproducts and other foreign substances. Here are some trivia points on the renal system:

  • The human bladder holds about 400 milliliters of urine (Warjri 2018).
  • Can exercise benefit people who have kidney disease? Yes, “by improving muscle function, lowering blood pressure, lowering cholesterol, keeping a healthy body weight, and improving sleep” (Sutton-Kerchner 2018).
  • Each kidney has approximately 1,000,000 nephrons, or filtering units (American Physiological Society 2017).
  • Adults eliminate about 27–68 fluid ounces per day, based on a 68-fluid-ounce intake (Zimmermann 2018).
  • The body’s blood is filtered through the kidneys 400 times daily (Warjri 2018).
  • In Charles Tipton’s Exercise Physiology (Springer 2003), chapter authors Jacques Poortmans and Edward Zambraski note that “historically, sports medicine textbooks have given little attention to the kidney and exercise.” They point out that exercise “alters renal hemodynamics, excretory function, and hormone release,” which, according to the authors, “has implications for total-body homeostasis” (Poortmans & Zambraski 2003).
  • Proteinuria—an excess of protein in the urine—occurs in 18%–100% of people during exercise, depending on the type and intensity of the activity (Bellinghieri, Savica & Santoro 2008). This effect can be considered transient, however (German 2018).
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Joy Keller

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