File:Girgis09.jpg

Fig. 9. The Nephric System

Links: Fig 1 | Fig 2 | Fig 3 | Fig 4 | Fig 5 | Fig 6 | Fig 7 | Fig 8 | Fig 9 | Plate 1 | Girgis 1926 | Carnegie stage 12

Reference

Girgis A. Description of a human embryo of twenty-two paired somites. (1926) J Anat. 60(4): 382-410.1. PMID 17104111

Cite this page: Hill, M.A. (2024, April 25) Embryology Girgis09.jpg. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/File:Girgis09.jpg

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© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G | Renal System Development

Legend

• C.W. - Coelomic Wall
• Ect. - Ectoderm
• Mes. - Mesonephros
• P.E.D. - Primary excretory duct
• Pro. - Pronephros
• 9-22 - Somites

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The nephric system (fig. 9) consists of pronephros, mesonephros and a primary excretory duct on either side. The pronephros is more in the form of vesicles than tubules and the mesonephros is in the form of a segmented cord.

The arrangement differs slightly on the two sides. On the right side there are six pronephric vesicles; the 1st is at a level between the 8th and 9th somites. The cranial three-quarter of the 2nd vesicle lies at the level of the 10th somite. The caudal quarter of the 2nd, the whole 3rd and the cranial half of the 4th vesicle lie at the level of the 11th somite. The caudal half of the 4th, the whole of the 5th, and cranial half of the 6th lie at the level of the 12th somite. The caudal half of the 6th lies at the level of the 13th somite. Each of the six vesicles has a lumen, and each is connected with the coelomic wall by a solid strand of cels.This connection is thicker in some than in others. In none of these strands (which represent remains of the nephrostomes) is a lumen seen. There is a gap between the 1st and 2nd vesicles of about 11 somites.

Caudal to the last vesicle, the mesonephros appears as a cord running to the end of the embryo, where it ends in the coelomic wall near the undifferentiated mesodermic mass of the tail. It has an interrupted lumen, and its cranial part is segmented, showing three segments separated by three constrictions, and there is a lumen in each of these segments. The mesonephros is also connected with the wall of the coelomic cavity by the remains of the nephrostomes.

The primary excretory duct begins with the 2nd pronephric tubule and 10 ends in contact with the ectoderm at the level of the last somite. It is interrupted between the 2nd and 3rd pro-nephric vesicles, but from the 3rd to 1 its end it runs as a continuous duct. It has an interrupted lumen but this does not communicate with the lumen of the pronephros; its connection is 12 only by its wall. The duct is entirely separated from the mesonephros and is situated very close to the ectoderm.

On the left side there are also six pronephric vesicles but they differ in 14 their arrangement from the right side. The 1st, 2nd and cranial half of the 15 3rd are at the level of the 11th somite.

The caudal half of the 3rd, the whole of the 4th and cranial half of the 5th vesicles are at the level of the 12th somite. The caudal half of the 5th and the whole of the 6th vesicles are at the level of the 13th somite. they al possess a lumen. The meso- nephros and the primary excretory duct With the exception of the 1st vesicle, are like those on the right side, except that there appear to be six mesonephric segments instead of three, and the duct is interrupted between the 4th and 5th vesicles, instead of between the 2nd and 3rd on the right side.

The above description differs in one important respect from that given by Felix, and that is the asymmetry and entire absence of metameric arrangement in the pronephric vesicles of the two sides. According to Felix the pronephric duct is formed by the union of the caudal ends of the pronephric tubules, and its subsequent growth caudally. In this embryo the duct has almost become an independent structure, the connection of the pronephric vesicles with the duct being none too complete and in some being only one cell thick.

Reference

<pubmed>17104111</pubmed>| PMC1249865