Embryological Source of the Urinary System
During the third week of gestation, gastrulation takes place. Gastrulation is a process during which three germ layers are formed. These germ layers arise from the epiblast (layer of high columnar cells which lie adjacent to the amniotic cavity). These germ layers are divided into
1. Ectoderm - the outer layer.
2. Mesoderm - the middle layer.
3. Endoderm - the innermost layer.
During the third week of gestation, gastrulation takes place. Gastrulation is a process during which three germ layers are formed. These germ layers arise from the epiblast (layer of high columnar cells which lie adjacent to the amniotic cavity). These germ layers are divided into
1. Ectoderm - the outer layer.
2. Mesoderm - the middle layer.
3. Endoderm - the innermost layer.
Gastrulation, the three embryonic layers, available at: http://scienceblogs.com/pharyngula/2007/02/19/basics-gastrulation/
On the 17th day of fertilization, the cells lying close to the midline proliferate and form a thickened plate, called the paraxial mesoderm. Towards the lateral side, the mesodermal layer remains thin and is termed as the lateral plate mesoderm. Both the paraxial and lateral plate mesoderm are connected together by the intermediate mesoderm.
Intermediate mesoderm, available at: http://www.ultratwistersgym.com/Resources/Urogenital/Urinary.html
The urinary or renal system develops from the intermediate mesoderm, one of the three mesodermal layers. During 4th week of development, the intermediate mesoderm forms a longitudinal elevation on each side of the dorsal aorta called the urogenital ridge. A portion of the urogenital ridge forms the nephrogenic cord, which gives rise to the urinary system.