Session 2: Development of the Urinary System Flashcards
Embryological precursors to the kidneys.
Pronephros Mesonephros Metanephros In that order.
When does the pronephros develop?
Start of week 4 and will regress at the end of week 4.
When does the mesonephros develop?
End of week 4 and will regress at the end of week 8.
When does the metanephros develop?
At around week 5 and will not regress.
Functionality of the pronephros.
It has no function but it provides useful data on kidney development and it is a duct and structurally complete. The pronephric duct extends from cervical region to cloaca.
Functionality of the mesonephros.
It is functional but has no way of conserving water so it needs to develop further.
Functionality of the metanephros.
From end of first trimester the metanephros will be fully functional.
Subparts of the mesonephros.
Mesonephric tubules developing caudal to the pronephric region and mesonephric duct which becomes the mesonephros aka embryonic kidney.
What important role does the mesonephric duct have other than development of the male reproductive system?
It also sprouts the ureteric bud.
What is the ureteric bud?
The primoridum of the collecting system of the definitive kidney.
What does the collecting system of the kidneys develop from?
What about the excretory system?
Collecting system develops from the ureteric bud.
It will develop from the metanephric tissue cap from the metanephros aka the metanephric blastema under the influence of the ureteric bud.
The excretory system is the parenchyma aka the medulla and the cortex.
Which germ layer do the kidneys and the ureter arise from?
Intermediate mesoderm at the urogenital ridge.
Where do the kidneys develop?
In the pelvic region since that is where the urogenital ridge can be found.
Briefly explain the ascent of the kidneys from the pelvic region to the abdomen.
During the development of the kidneys they will ascend to the abdomen due to migration and expansion of the caudal region of the foetus.
The migration includes cranio-caudal shift from L4 to L1/T12.
Lateral displacement where the kidneys will meet up with the adrenal glands in their process.
A 90 degree rotation so the renal pelvis will face the midline.
What does the bladder derive from?
The hindgut aka the caudal portion of the primitive gut tube formed during embryonic folding in the fourth week of development.
What is the caudal portion of the hindgut which is a blind pouch?
The cloaca
What is the allantois?
A superoventral diverticulum of the hindgut which extends into the umbilical cord.
What happens to the lumen of the allantois?
It will regress and become the urachus.
What is the urachus?
The median umbilical ligament in adults.
What happens to the cloaca in urinary development?
The urorectal septum divides the urogenital sinus (future bladder and urethra) and the anorectal canal (future rectum and anal canal).
What does the superior part of the urogenital sinus do?
It is part of the allantois which will connect the umbilicus (median umbilical ligament).
What happens to the majority (middle) part of the urogenital sinus?
It will become the bladder
What happens to the lower part (also called the pelvic part) of the urogenital sinus in females?
It will develop into the urethra.
What is the pre-prostatic urethra, prostatic urethra, and membranous urethra derived from?
The narrowed lower segment of the urogenital sinus.
What is the spongy urethra derived from?
Phallic portion enclosed by the urethral folds.
Common ways of how things can go wrong in the development of the urinary system.
Non-development of the kidneys
Migration problems of the kidneys
Duplication of kidneys
Cystic disease
What is renal agenesis?
When the ureteric bud fails to interact with the intermediate mesoderm and therefore won’t form a kidney and ureter.
Is renal agenesis suitable for life?
Yes.
However bilateral renal agenesis is not.
Give examples of structural anomalies due to problems with migration.
Pelvic kidney where one of the kidneys don’t ascend properly.
Horseshoe kidney where the kidneys fuse.
Explain duplex kidney/ureter.
It can happen due to duplex ureteric buds leading to duplex kidneys and duplex ureters.
It can also be two ureters and one kidney.
This can be due to the splitting of the ureter.
It can be partial or complete. It is usually asymptomatic but can cause problems if there is an ectopic ureteral opening.
Where does the pronephros develop?
In the cervical region.
Where doe the mesonephric tubules develop?
Caudal to the pronephric region.
What is the ureteric bud?
Undifferentiated intermediate mesoderm that is caudal to the mesonephros.
What are the precursors of the kidneys?
The ureteric bud contacts the metanephric blastema and the bud will start to expand and branch.
The ureteric bud will be the renal pelvis and its major and minor calyx.
The metanephric blastema will be the parenchyma of the kidney (medulla and cortex).
The collecting system is derived from the ureteric bud, the excretory component is derived from intermediate mesoderm under the influence of the ureteric bud.
What is hypospadias?
When there is a defect in the fusion of the urethral folds which is supposed to form the spongy urethra by the influence of androgens (dihydrotestosterone).
This means that the urethra will be open to the ventral surface of the penis rather than at the end of the glans.
