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Lecture_15_Comparative Anatomy_The Urogenital System

It should be noted here that although this structure

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Unformatted text preview: e coelom via a peritoneal funnel. • In summary, the fundamental plan underlying the excretory system is envisioned to consist of paired and segmented uriniferous tubules that open on one end to the coelom and on the other end to the nephric duct, with a glomerulus in between. The ciliated peritoneal funnel seems to drive fluid from the coelom into the tubule, the associated glomerulus adds fluids from the blood, and the tubule itself modifies this collected fluid before it flows into the nephric duct. It should be noted here that although this structure represents the primitive or fundamental plan of excretory tubule organization, tubules opening to the coelom are rarely found in the kidneys of adult vertebrates because they fuse early in development with the nephric ridge.  Tripartite Concept of Kidney Organization • Theory o The tripartite concept envisions formation of the nephric tubules in one of three locations (anterior or pronephros, middle or mesonephros, posterior or metnephros) within the nephrogenic nephric ridge with the subsequent loss, merger, or replacement of these tubules constituting the developmental basis for the definitive adult kidneys. o In addition to positional differences, the three regions vary with respect to their connections to the coelom.  Tubules retain their connections to the coelom through the peritoneal funnel in the pronephros.  Tubules arising within the middle or posterior regions are not connected to the coelom. • Pronephros o Usually only a transient embryonic developmental stage in all vertebrates. o Pronephric tubules – tubules that appear within the anterior portion of the nephric ridge which join to form a common pronephric duct. o The pronephric duct grows posteriorly...
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