Notes

Development of the Upper Urinary System:
Early Embryogenesis:
The site of fertilisation is the ampulla. Sperm migrate to the oocyte. DNA of sperm merges with oocyte forming a zygote. After fertilisation, every single day a division occurs. 2 cells --> 4 cells --> 8 cells --> 16 cells.
At 4 cells, there is totipotency where each cell can develop into a full organism. At 8 cells, there is pluripotency where each cell can develop into a specific tissue. Cells then become compact and form a morula. On day 6 or 7, a blastocyst is formed, which is divided between the inner cell mass from which the embryo develops and the trophoblast which provides nourishment. Embryo transitions into the uterus.
Implantation: formation of epiblast and hypoblast:
Trophoblast (outer layer) either invades endometrium or surrounding the blastocoel. Epiblast and hypoblast layers are derived from inner cell mass and start to surround blastocoel as well.
Gastrulation: Formation of ectoderm, mesoderm, endoderm from which different organs are derived.
Formation of neural groove and notocord by the ectoderm.
Differentiation of the mesoderm:
-mesoderm divides into different layers
-intermediate mesoderm: urinary tract, paraxial: somites (precursor of vertebrae), and lateral: abdominal wall and peritoneum.
- paraxial --> intermediate --> lateral
In the Embryo there are three sets of kidneys: pronephros, mesonephros, and metanephros. The Allantois collects urine in the embryo. In the embryo urine, feces, and genital tract go the same exit.
Pronephros: form tubules that are non-functional and then degraded. Appear in the fourth week in the developing neck region
Mesonephros: very large, elongated, excretory organs. Appear late in the 4th week. Contain glomerula and mesonephronic tubules. Functional, produces urine and opens into cloaca. Mesonephric tubules develop into efferent ductules of testis. Mesonephric duct is the main duct of the kidney will develop into epididymis, dutctus deferens, ejaculatory duct, and seminal gland.
Metanephros: primordia of the permanent kidneys, develop in the 5th week, urine formation continues throughout fetal life. Kidneys develop from the ureteric bud (collecting system) and metanephrogenic blastoma (nephrons).
The ureteric bud dilates and eventually forms the ureter, renal pelvis, major and minor calyxes, and collecting ducts. 1st four generations of tubules enlarge to form major calyxes and 2nd four generation tubules coalesce to form minor calyxes.
Initially the kidneys are pelvic, they ascend to the adult position by week 9, where they are supplied by the aorta. They rotate medially. Nephrons develop by week 36.
Kidneys have lobes at first that disappear as well as very large adrenal glands.
Clinical considerations:
- Renal agenesis: lack of kidney caused by mutation in gonadal derived neurotrophic factor
- Wilm's tumor: developed in 5 year olds due to mutation WT1 gene
- Multicystic dysplastic kidney: failure of nephrons to develop resulting in potter sequence, ureteric bud fails to branch.
- Multiple ureters
- Horseshoe kidney: blood vessels block ascent of the kidney