Urology - Congenital abnormalities of the urogenital tract Flashcards
What cell type does the renal and genital system develop from?
The renal and genital systems both develop from intermediate mesoderm, this is a collection of cells on the dorsal aspect of the fetal abdominal cavity. Both systems initially drain into the same space, the fetal cloaca.
What are the 3 components of the developing kidney formed by intermediate mesoderm?
These are the pronephros, the mesonephros and the metanephros. The intermediate mesoderm first forms the pronephros in the cervical region, followed by the mesonephros and last the metanephros in the pelvic region. The pronephros and mesonephros regress and do not form part of the adult kidney. The metanephros forms the final adult kidney and only becomes active in the second half of pregnancy.
What structure removes fetal waste?
Although the fetus swallows amniotic fluid, digests it and secretes urine into it, it is the placenta that actually removes fetal waste products for excretion by the mothers kidneys.
What is required for the development of all 3 kidney systems?
For the pronephros, mesonephros and metanephros to develop mesenchyme needs to be induced to become epithelium. In the metanephros, the ureteric bud induces the mesenchyme around its tips to form nephrons. This metanephric mesenchyme forms the tubular system from the glomerulus to the distal nephron. The ureteric bud forms the collecting duct and drainage system.
When do the kidneys start developing?
The kidneys start developing around week 4 of gestation. Clusters of cells in the intermediate mesoderm form very primitive glomeruli in the cervical region. Together, these form the non functional pronephros which later regresses.
How does the pronephros form the mesonephros?
The pronephros is formed from clusters of cells composed of intermediate mesoderm in the cervical region. The lateral portions of these cell clusters fuse at each level to form the mesonephric (or Wolfian) duct which grows down and enters the cloaca. As the pronephros regresses, the intermediate mesoderm below it forms the mesonephros. This may function briefly, draining into the mesonephric duct, but it regresses by the end of the second month.
When does the metanephros form?
Remember that the metanephros is the only primitive kidney system that is present in the adult kidney. From week 5 onwards, the metanephros forms from the intermediate mesoderm cells in the pelvis.
What is the ureteric bud?
The metanephros forms the future nephron, including the glomerulus to the distal nephron. The collecting ducts, calices, and ureters develop from the ureteric bud. The ureteric bud is an outgrowth of the mesonephric duct and invades the metanephric tissue mass. The bud dilates to form the renal pelvis, splits progressively to form the calices and then small branches elongate to form the collecting ducts. As the ureteric bud invades the metanephric tissue, it induces it to become epithelium.
Where do the gonads develop in relation to the kidney?
The testes or ovaries are medial to the developing kidney.
How does the developing kidney receive its blood supply?
In the pelvis, the metanephric kidney receives its blood supply from the pelvic branches of the aorta. As the kidneys move upwards to their final posterior abdominal position, these original arteries regress and the kidneys are vascularised by the renal arteries, which come off the aorta at a higher level.
How does the bladder and urethra form?
The ureteric bud forms the ureters which drain into the mesonephric ducts. These in turn drain into the urogenital sinus. The lower part of the mesonephric ducts becomes absorbed into the wall of the urogenital sinus to form the trigone area of the bladder. As the kidneys ascend, the openings of the ureters move up the urogenital sinus into the zone that they will occupy when that part of the urogenital sinus becomes the bladder. The lower part of the urogenital sinus forms part of the urethra in both sexes.
What is a duplex system?
Early division of the ureteric bud can lead to various varieties of double, or Y shaped ureter.
What is renal ectopia?
Failure of the kidney to ascend results in a pelvic kidney. Occasionally, one or another kidney, usually the left, crosses the midline and fuses with the other kidney at its lower pole.
Why do aberrant renal arteries cause problems for potential surgery?
Aberrant renal arteries are persistences of one or more of the lateral branches of the aorta. If they are present they usually enter the lower pole of the kidney and they may make transplantation of such a kidney difficult or impossible. Such arteries are end arteries supplying a segment of the kidney, and their ligation will cause death of that part of the kidney.
What is horseshoe kidney?
This is where the lower ends of the fuse, so that when they ascend the isthmus of the combined kidneys meets at the inferior mesenteric artery (this prevents further ascent). The 2 ureters cross the isthmus which may give rise to ureteric obstruction.
