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Medicine LibreTexts

22.1: Introduction to the Urinary System

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  • Chapter Learning Objectives

    • Label structures of the urinary system
    • Characterize the roles of each of the parts of the urinary system
    • Illustrate the macroscopic and microscopic structures of the kidney
    • Trace the flow of blood and urine through the kidney
    • Trace the flow of urine through the urinary tract

    This chapter will help you to understand the anatomy of the urinary system: kidneys, ureters, urinary bladder, and urethra. You will trace the blood flow through the kidney; think of the kidney as a regulator of plasma makeup rather than simply a urine producer. Knowing the anatomy will help you to understand how the urinary system maintains homeostasis and affects all the other systems of the body when you take physiology.

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    Watch this video Kidney Function from the Howard Hughes Medical Institute for an introduction to the urinary system.

    The Urinary or Renal System consists of two kidneys and the pathway, two ureters, urinary bladder, and one urethra, for urine to exit the body. The kidneys' primary function is to make urine by first filtering out many of the electrolytes, solutes, and water in the blood, forming the filtrate. As the filtrate passes through microscopic units called nephrons, certain solutes and water molecules are reabsorbed back to the blood because they are too precious to waste and other molecules are secreted because the body does not want them. As the filtrate becomes more concentrated, because water has been reabsorbed back to the blood, as it moves through the nephron, the end product is urine containing the waste products that the body can spare. Another perspective on the function of the kidneys is to monitor the level of certain solutes in the blood to maintain homeostasis. The kidneys' secondary function is to make hormones. Please review the Endocrine chapter for details.

    The two ureters will carry urine from the kidneys down to the urinary bladder by peristalsis for storage. As the urinary bladder fills with urine, nerve endings will detect the stretched bladder to signal emptying. With sphincters relaxing, urine will flow out of the urinary bladder through the urethra to be expelled.

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