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Chapter 7: Urinary System

Sarah E. A. McConnell

OBJECTIVES

Objectives

After studying this chapter, you should be able to:

  • Trace the development of the urinary system from its origins in the tubiform embryo.

  • Compare and contrast the three sets of embryonic kidneys with respect to their temporal sequence, locations, functions, and derivatives.

  • Explain how the ureteric bud and metanephric mesoderm collaboratively give rise to the definitive kidney.

  • Relate the ascent of the kidneys to changes in their blood supply.

  • Describe the development of the urinary bladder and urethra from the urogenital sinus.

  • Describe the formation of the suprarenal cortex and medulla from the intermediate mesoderm and neural crest cells, respectively.

ORIGINS OF THE URINARY SYSTEM

  • The components of the urinary system are derived from the mesoderm and endoderm.

    • The kidneys and ureters develop from the intermediate mesoderm (Figure 7-1).

    • The epithelium of the urinary bladder and urethra develops from the endoderm of the urogenital sinus (Figure 7-2).

    • Smooth muscle and connective tissue develop from the splanchnic (visceral) mesoderm.

Figure 7-1.

Intermediate mesoderm position. (A–E) Transverse sections illustrate the process of lateral embryonic folding. (A) Prior to lateral folding, the intermediate mesoderm is located between the paraxial mesoderm and the lateral plate mesoderm. (E) At the conclusion of lateral folding, the intermediate mesoderm is located in the posterior abdominal wall.

Source: Based on Figure 7.1 in T. W. Sadler, Chapter 7, “The Gut Tube and the Body Cavities,” in Langman's Medical Embryology, 14th ed. Wolters Kluwer. 2019.

Five diagrams show lateral embryonic folding, with intermediate mesoderm moving to the posterior abdominal wall.
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Figure 7-2.

Formation of the urogenital sinus. (A–C) Midsagittal sections illustrate the descent of the urorectal septum toward the cloacal membrane, dividing the cloaca into the urogenital sinus anteriorly and the anorectal canal posteriorly. Rupture of the cloacal membrane creates the openings for the urogenital sinus and the anus. The allantois is also shown.

Source: Based on Figure 15.36 in T. W. Sadler, Chapter 15, “Digestive System,” in Langman's Medical Embryology, 14th ed. Wolters Kluwer. 2019.

A series of 3 diagrams shows the formation of the urogenital sinus and anorectal canal by the descent of the urorectal septum toward the cloacal membrane.
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KIDNEYS AND URETERS

  • A series of three developmental renal structures form from the intermediate mesoderm in a craniocaudal sequence (Figure 7-3A).

    • The pronephros is a temporary collection of cell clusters and tubules that forms bilaterally in the cervical region early in the fourth week.

      • It is a vestigial structure that never functions in humans.

      • It regresses by the end of the fourth week.

    • The mesonephros is a partially transitory structure that forms bilaterally at the thoracic and upper lumbar levels during the fourth week.

      • The mesonephros forms an elongated prominence that runs craniocaudally along the posterior abdominal wall, with the developing gonad on its medial side. Together, these structures comprise the urogenital ridge, which will form much of the urinary and genital systems (see Chapter 8...

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