organ systems: embryology of the urinary systems

[picture courtesy of erika yosefah william shortbread zelfand]













this lecture is the last in the series of the kidney and looks at renal embryology. kidney development can be roughly divided into three phases: pronephros, mesonephros, and metanephros. pronephros is both the early evolutionary form of the renal filtering system and also the first stage in human kidney development. mesonephros has nephrons with glomeruli and s-shaped tubules, which filter blood from the aorta and drain it into the gut tube via the mesonephric duct. the formation of the last stage, metanephros, begins with signalling factors from the metanephrogenic mesenchyme that stimulate the growth of the "uretic bud" from the lower part of the mesonephric duct. the uretic bud branches out and anastomoses to form the renal tubules and framework for the kidney. one additional note regarding early development: the urorectal septum divides the gut tube into the anorectal canal and the urogenital sinus, which form the urinary and GI tracts.

some pathologies of kidney development: if kidney fails to "ascend" (a misnomer because the kidney stays in place while the body grows downwards) to its position deep to the 12th rib, this is called pelvic kidney. horseshoe kidney is the fusion of the kidneys below the inferior mesenteric artery, and a failure to ascend. duplications of a kidney / supernumerary kidney can occur if the uretic bud divides prior to the development of the metanephric mesoderm. agenesis is the lack of development of uretic bud, leading to inadequate contact between mesoderm and uretic bud, leading to lack of a kidney.

questions
1. urogenital and reproductive systems develop from..
2. early nephrons develop in...
3. what are the three stage is kidney development?
4. what are the characteristics of the mesonephros stage?
5. urine formation begins...
6. describe the excretion of metabolic waste in the embryo.
7. uretic bud branches out from...
8. what are the renal tubules formed by?
9. metanephrogenic mesenchyme initiates growth of uretic bud via...
10. what are the collecting ducts formed by?
11. what is the "ascent of the kidney"?

12. what is the urorectal septum's role in renal development?
13. what is pelvic kidney?
14. what is horseshoe kidney?
15. what is duplications of the kidney?
16. what is agenesis of the kidney?
answers
1. urogenital ridges of intermediate mesoderm.
2. lateral part of urogenital ridge.
3. pronephros, mesonephros, metanephros
4. nephrons consisting of glomeruli and S-shaped tubules, which filter blood from the aorta, and a duct that drains into the gut tube.
5. ~9 weeks
6. metabolic wastes are dumped into the gut via the mesonephric duct, absorbed into blood and transported across placental wall for removal.
7. mesonephric duct
8. repeated dichotomous branching of the developing metanephron.
9. signalling factors
10. uretic bud
11. the apparent ascent due to the growth of the embryo caudal to the kidneys.

12. the urorectal septum divdes the gut tube into the GI tube and the urinary system.
13. no ascent of kidney
14. kidneys fuse below inferior mesenteric artery and do not ascend
15. double kidneys develop because ureteric bud divides prior to development of metanephric mesoderm
16. lack of development of uretic bud leading to inadequate contact between bud and mesoderm.