上部尿路と下部尿路の発生学的な違い

上部尿路と下部尿路の発生学的な違い

上部尿路と下部尿路は、発生学的（ものが作られる過程）な由来が異なります。上部尿路（腎臓・尿管）は主に中胚葉から、下部尿路（膀胱・尿道）は主に内胚葉から発生します。

由来の違い

  • 上部尿路 (腎臓・尿管): 中胚葉由来
    • 腎臓は、中間中胚葉と呼ばれる部分から発生します。具体的には、前腎、中腎、後腎という3つの段階を経て、最終的に永久腎となる後腎が作られます。
    • 尿管は、中腎管から芽のように出てくる尿管芽が伸びて作られます。
  • 下部尿路 (膀胱・尿道): 内胚葉由来
    • 膀胱の大部分と尿道の上部は、原始的な腸管の末端部分である総排泄腔が分割してできる尿生殖洞という部分（内胚葉由来）から発生します。
    • ただし、膀胱の一部（膀胱三角）は中胚葉由来の尿管が開口部として取り込まれるため、完全に内胚葉のみでできているわけではありません。

このように、上部尿路と下部尿路は、全く異なる胚葉から発生するため、構造や機能、そして病気の種類にも違いが見られます。

（Gemini 2.5 Pro）

Embryological Differences Between the Upper and Lower Urinary Tracts

The upper and lower urinary tracts have different embryological origins. The upper urinary tract (kidneys and ureters) is primarily derived from the mesoderm, while the lower urinary tract (bladder and urethra) is primarily derived from the endoderm.

Differences in Origin

  • Upper Urinary Tract (Kidneys, Ureters): Mesodermal Origin
    • The kidneys develop from a part of the mesoderm called the intermediate mesoderm. Specifically, they form through three successive stages: the pronephros, mesonephros, and finally the metanephros, which becomes the permanent kidney.
    • The ureters develop from the ureteric bud, which branches off from the mesonephric duct.
  • Lower Urinary Tract (Bladder, Urethra): Endodermal Origin
    • The majority of the bladder and the upper part of the urethra develop from the urogenital sinus, which is formed when the cloaca (the terminal end of the primitive gut, derived from the endoderm) is divided.
    • However, a part of the bladder, known as the bladder trigone, is formed by the incorporation of the mesoderm-derived ureters into its wall. Therefore, it is not composed entirely of endoderm.

Thus, the upper and lower urinary tracts originate from completely different germ layers, which contributes to differences in their structure, function, and the types of diseases that affect them.

（Gemini 2.5 Pro）

参考

  1. https://www.lecturio.com/concepts/development-of-the-urogenital-system/
  2. Development of the Urogenital System – Urinary System and Kidney Development by John McLachlan, PhD　https://app.lecturio.com/#/lecture/s/8188/36586