Learning aims

At the end of this module you should be able to:

• Describe the sequence of transitory and definitive anlagen of the upper urinary tract as well as their functions over the course of their development.
• Describe how the lower urinary tract forms from the cloaca.
• Explain some of the basic mechanisms that can lead to pathological development of the urinary system.

What you should already know

• Embryonic disk
• Embryonic period

Introduction

In the module in which the placenta was treated, we saw that during the intrauterine period, this transitory organ is responsible for the water and electrolyte households, and not the kidneys. The fetal kidneys only begin to produce urine in the 12th week. This is then excreted into the amniotic cavity and is responsible for producing up to 80% of the amniotic fluid. Although it is closely connected with that of the genital system, the development of the urinary system starts somewhat earlier (after the 3rd week).

It begins with the formation of the nephrogenic cord (arises out of the intermediate mesoderm) and the urogenital sinus and proceeds, as quite often occurs during embryonic development, in a cranio-caudal gradient.

Delving deeper

• What relationship exists between the urinary and genital systems during development?
• How can one gauge the importance of the reciprocal induction between the urinary and genital systems?
• How can one explain the fact that anomalies in the urinary system often appear only on one side (asymmetrically)?
• How can anomalies in the urinary system be discovered and what can be done against them?