Urn kidney
As mesonephros ( mesonephros ), also Wolff shear body is called the second generation kidney in the development of vertebrates . In the embryo, they are formed with the regression of the front kidney ( pronephros ). While the urnal kidney in fish and amphibians is also the place where urine is formed in adult animals , the urnal kidney in amniotes (animals with an amnion , i.e. reptiles , birds and mammals ) regresses in the embryo and is formed by a third generation of kidneys, the post-kidney ( Metanephros , the actual kidney ), replaced.
introduction
The urinary organs develop in the human embryo at the age of 21 days from the transition area between the parietal and the visceral mesoderm , the so-called intermediate mesoderm. From the 25th day, the intermediate mesoderm becomes a segmented intermediate mesoderm near the head, and from this the fore-kidney with the first excretory units, the glomeruli . Caudally (towards the foot) of this, the unsegmented mesoderm becomes the urnal kidney. From the 5th week onwards, the gonads appear medial to the urnal kidney and the urnal duct ( Wolff's duct ) lateral to the urnal kidney .
Structure of the urn kidney
The excretory units arise from the tissue of the urn kidney. These are S-shaped canals, at one end of which the glomerulus arises and the other end of which leads into the urinary duct. The glomerular end of the excretory unit is covered by a capillary ball and thus forms the Bowman capsule . The tubules of the kidney with what is known as Henle's loop arise from the other end of the tubules .
From the second month the urnal kidney appears in the human embryo as an elongated organ lying in the lumbar region. This is connected to the posterior abdominal wall via a fabric handle. These tissue stalks are called mesenteries . The unit made up of the urinary duct located on the side, the urinary kidney following the middle and the gonadal gland to the middle of the body (medial) is called the urogenital ridge .
In animal embryos, the functionality of the urn kidney has been proven experimentally. In the course of the second month, the urnal kidney changes in such a way that the cranial (headward) parts degenerate and some of the caudal (footward) urnal tubules form close connections with the gonads. Depending on the gender, these parts form the ovaries and testicles .
Urniate descendants
In males, the mesonephric tubules develop in the caudal portion of the primitive kidney for so-called Epigenitalis and Paragenitalis . On the one hand, these give rise to the excretory ducts from the testes ( ductuli efferentes ) to the epididymis ( epididymis ). The most caudal part of the urinary tubules develops in males into the ductus deferens , the vas deferens.
In female individuals, vesicular remnants of the urnal kidney can remain in the mesentery of the ovaries or fallopian tubes as epoophoron and paroophoron .
literature
- Jan Langman: Medical Embryology. Thieme, Stuttgart 1980, ISBN 3-13-446606-6 .
- Werner Kahle, Helmut Leonhardt , Werner Platzer: Pocket Atlas of Anatomy. Volume II, Thieme, Stuttgart 1979, ISBN 3-13-492103-0 .
Individual evidence
- ^ Jan Langman: Medical Embryology , 5th edition, Georg Thieme Verlag, Stuttgart 1977, ISBN 3-13-446605-8 , page 193.