The ureter anlage and the formation of the evacuating urinary tract
The ureter anlage (stage 14) is an epithelial diverticulum which arises from the caudal portion of the mesonephric duct (Wolffian duct) at the level of the first sacral vertebra. Its enlarged end grows in the dorso-cranial direction and projects into the metanephric blastema.
It is the origin of the intra- and extrarenal excretory passages:
- Ureter
- Renal pelvis
- Major and minor calices
- Collecting ducts
- Ureter
- Major calix
- Minor calix
- Renal pelvis
- Collecting duct
- Metanephric vesicle
- Kidney lobe
- 8
- Distal tubule
- 9
- Proximal tubule
- 10
- Glomerulus
- 11
- Connecting tubule
- 13
- Intermediate tubule
The branching of the collecting ducts and calices from the renal pelvis is shown. The enlargement in B shows the collecting duct and the various elements that form the nephron.
Histological picture of the vessel architecture of the renal cortex.
Fig. 11
The cranial end of the ureter anlage subdivides dichotomically many times due to the inductive effect of the metanephric blastema.
- 1
- Cloaca
- 2
- Ureter anlage
- 3
- Metanephric blastema
- 2+3
- Metanephros
- 4
- Mesonephric duct
(Wolffian duct) - 5
- Nephrogenic cord
- 4+5
- Mesonephros
The renal excretory passages develop from the ureter anlage. This development is described in greater detail in an interactive diagram of region C (see below)
The renal pelvis arises from the swollen end of the ureteric bud (stage 16) that subdivides 4 times over the course of the 4th to 6th weeks. 16 branches arise from this that partially then coalesce again in order to finally form 2 to 4 major calices.
At around the 7th week the minor calices start to develop. They discharge into the major calices. Further dichotomic branching follow - up to the 15th generation (roughly 32 weeks). Thereby the caliber of the tubules is reduced more and more so that finally 1-3 millions collecting ducts are formed in the periphery of the metanephric blastema (stage 18).
In this interactive diagram you can study the development of the extra and intra-renal urine excretory system, especially of the ureter, of the renal pelvis, of the major and minor calices, as well as of the collecting ducts over the course of stages 14 to 20 (ca. 33 to 46 days).
Synoptic view of the illustrations presented in the interactive diagram.
- 1
- Ureter
- 2
- Metanephric blastema
- 3
- Minor calix
- 4
- Major calix
- 5
- Renal pelvis
- 6
- Collecting duct
- 7
- Papillary duct
- a
- 1st dichotomous partition
(2 branches) - b
- 2nd dichotomous partition
(4 branches) - c
- 3rd dichotomous partition
(8 branches) - d
- 4th dichotomous partition
(16 branches) - e
- Atrophy of the previous partitions
(16 branches) - D
- Enlarged image of the collecting duct system
In stage 14 (ca. 33 days) the ureter anlage develops from the caudal part of the mesonephric duct (Wolffian duct) and grows in the dorso-cranial direction into the metanephric blastema. It subdivides dichotomically into 2, then into 4 branches.
From its originally enlarged end arises the renal pelvis; the stem forms the ureter.
- 1
- Ureter
- 2
- Metanephric blastema
- 3
- Minor calix
- 4
- Major calix
- 5
- Renal pelvis
- 6
- Collecting duct
- 7
- Papillary duct
- a
- 1st dichotomous partition
(2 branches) - b
- 2nd dichotomous partition
(4 branches) - c
- 3rd dichotomous partition
(8 branches) - d
- 4th dichotomous partition
(16 branches) - e
- Atrophy of the previous partitions
(16 branches) - D
- Enlarged image of the collecting duct system
From stage 18 (ca. 44 days) the original enlargement divides itself four times and 16 branches are so engendered. These merge again and form the 2 - 4 major calices, which finally form the continuation of the renal pelvis.
- 1
- Ureter
- 2
- Metanephric blastema
- 3
- Minor calix
- 4
- Major calix
- 5
- Renal pelvis
- 6
- Collecting duct
- 7
- Papillary duct
- a
- 1st dichotomous partition
(2 branches) - b
- 2nd dichotomous partition
(4 branches) - c
- 3rd dichotomous partition
(8 branches) - d
- 4th dichotomous partition
(16 branches) - e
- Atrophy of the previous partitions
(16 branches) - D
- Enlarged image of the collecting duct system
From stage 18 (ca. 44 days) the original enlargement divides itself four times and 16 branches are so engendered.
These merge again and form the 2 - 4 major calices, which finally form the continuation of the renal pelvis.
- 1
- Ureter
- 2
- Metanephric blastema
- 3
- Minor calix
- 4
- Major calix
- 5
- Renal pelvis
- 6
- Collecting duct
- 7
- Papillary duct
- a
- 1st dichotomous partition
(2 branches) - b
- 2nd dichotomous partition
(4 branches) - c
- 3rd dichotomous partition
(8 branches) - d
- 4th dichotomous partition
(16 branches) - e
- Atrophy of the previous partitions
(16 branches) - D
- Enlarged image of the collecting duct system
During the stages 18-20 (ca. 44-46 days) the following 4 division generations atrophy again and form themselves thereby into the minor calices, which for their part have their openings in the major calices.
The collecting ducts, which also divide in a dichotomic way, drain into the minor calices.
- 1
- Ureter
- 2
- Metanephric blastema
- 3
- Minor calix
- 4
- Major calix
- 5
- Renal pelvis
- 6
- Collecting duct
- 7
- Papillary duct
- a
- 1st dichotomous partition
(2 branches) - b
- 2nd dichotomous partition
(4 branches) - c
- 3rd dichotomous partition
(8 branches) - d
- 4th dichotomous partition
(16 branches) - e
- Atrophy of the previous partitions
(16 branches) - D
- Enlarged image of the collecting duct system
From stage 18 (ca. 44 days) the 5th generation and higher differentiate themselves from the tubules of the definitive collecting ducts, which finally form a complex system of forked branches that are smaller as they extend towards the periphery.
In the 32nd week the collecting ducts have divided up to the 15th generation.