Embryology of the Kidney Flashcards
How does the mesoderm become highly organised at day 17?
It is split into
- paraxial mesoderm (innermost)
- intermediate mesoderm
- lateral plate mesoderm
What does the paraxial mesoderm go on to form?
The majority of the skeleton, skeletal muscles and dermis of the skin
What does the intermediate mesoderm go on to form?
The gonads, internal reproductive tracts and the kidneys
What does the lateral plate mesoderm go on to form?
The lining of body cavities
This includes the peritoneum of the abdomen
What is the urogenital system?
This comprises the urinary system and the reproductive system
They are closely related in development
What are the components of the urinary system?
- kidneys
- ureters
- urinary bladder
- urethra
What are the components of the reproductive system?
Internal and external genitalia
What is the first of three nephric structures that forms?
When does it form?
The pronephros
It forms during the 4th week of development
What does the pronephros form from?
Intermediate mesoderm in the cervical region condenses and reorganises
What is the role of the pronephros?
It develops and regresses without doing anything in humans
Development of the pronephros starts a cascade, leading to development of the 2nd nephric structure
What forms from the pronephros?
When does it disappear?
It forms are number of epithelial buds
It disappears around day 25
What forms lateral to the condensements (pronephroi)?
The mesonephric duct
At this stage, it is a solid cord of mesoderm and only starts to develop
In which direction does the mesonephric duct develop?
When does it fuse?
It forms from intermediate mesoderm in the lower cervical region
It develops caudally
It fuses with the walls of the cloaca on day 26
What is the cloaca?
It is a common point at which the GI system and the urinary system are emptied in to
What happens once the mesonephric duct has fused with the cloaca?
Canalisation commences from the caudal end
Apoptosis turns the solid cord into a hollow tube
What does canalisation of the mesonephric duct induce?
Formation of mesonephric buds from mesenchyme
During which week does the mesonephros form?
Week 4
What is the mesonephros derived from?
Intermediate mesoderm in the upper thoracic to the upper lumbar regions
How does development of the mesonephric duct affect the formation of the mesonephros?
It induces formation of mesonephric buds from the mesenchyme
In what fashion are mesonephric tubules formed?
Craniocaudal fashion
As the more caudal tubules differentiate, the cranial tubules regress
What happens to the mesonephric ducts in the thorax and the lumbar region?
In the thorax, the buds begin to regress and are broken down
In the lumbar region, the buds develop into mesonephric tubules
What will the mesonephric tubules differentiate into?
They differentiate rapidly and lengthen rapidly to form an S-shape and Bowman’s capsule
What forms the glomerulus?
The tuft of capillaries that form at the medial end of the tubule
What is the renal corpuscle?
It consists of the Bowman’s capsule and the glomerulus
This is the first functional unit in the human urinary system
What happens to the cranial-most mesonephric tubules that fuse with the mesonephric duct?
They function between weeks 6-10 to produce a small amount of urine
This is excreted into the amniotic fluid
What happens to the mesonephric ducts after week 10?
In the male, they will develop into reproductive structures
In the female, they will regress
What is the function of the mesonephric duct?
It acts as a primitive collecting system until is regresses of develops another function
How does gonadal development relate to the mesonephric ridge?
Gonadal development takes place on the medial aspect of the mesonephric ridge
Why is the mesonephric ridge referred to as the urogenital ridge?
This includes the mesonephric ridge and the genital ridge
What is significant about the metanephros?
It will go on to form the definitive adult kidney
It has a dual origin
What does the metanephros begin as?
What does it form from?
It begins as a specialised bit of mesoderm around the pelvic region
This is the metanephric mesenchyme
it contains undifferentiated cells
What does the metanephric mesenchyme fo on to form?
EXCRETORY PORTION
- Bowman’s capsule
- proximal convoluted tubule
- loop of henle
- distal convoluted tubule
What is the role of the mesonephric duct in development of the metanephros?
The ureteric bud sprouts from the caudal region of the mesonephric duct
What does the ureteric bud go on to form?
COLLECTING PORTION
- collecting ducts
- minor and major calyces
- renal pelvis
- ureter
What happens to the metanephros at day 32 of development?
The ureteric buds penetrate the metanephric mesenchyme
What happens to the ureteric bud as it penetrates the metanephric mesenchyme?
The ureteric bud bifurcates in a specific pattern
This leads to formation of the collecting system
What are the stages in bifurcation of the ureteric buds which lead to formation of the collecting ducts?
- renal ampulla
- renal pelvis
- major calyces
- minor calyces
- collecting ducts
What is each collecting tubule formed from the metanephric mesenchyme covered with?
A metanephric tissue cap
This contains cell clusters
What does interaction between the tubule and the metanephric tissue cap cause?
- specific branching of the tubule
2. differentiation of cells in the metanephric cap to form a renal vesicle
What happens to the renal vesicle?
It expands to form an S-shaped tubule (nephron) and Bowman’s capsule
What happens at the proximal end of the excretory tubule?
Capillaries develop in the proximal end of the tubule to form the glomerulus
The proximal end forms the Bowman’s capsule
When and why does tissue breakdown occur during development of the metanephros?
Tissue breakdown occurs between the 2 embryological origins of the metanephros
This is the excretory and collecting systems
What actually forms the definitive nephron?
The renal corpuscle, tubule and collecting tubule
What causes duplication of the ureter?
Premature bifurcation of the ureteric bud
Bifurcation can be partial or complete
What is meant by premature bifurcation of the ureteric bud?
The ureteric bud pierces the mesenchyme and then it splits
If it splits before it enters the mesenchyme, an extra collecting system may develop
What can duplication of the ureter lead to?
- ectopic ureter (takes a different course and attaches to structures that it shouldn’t)
- bifid ureter
What causes renal agenesis?
Early degeneration of the ureteric bud
OR
failed interaction between the ureteric bud and the metanephric tissue cap
What does unilateral agenesis lead to?
This is failure of one kidney to form
It is usually asymptomatic
It leads to hypertrophy of the remaining kidney
What does bilateral agenesis lead to?
It is usually incompatible with life
If not, it leads to Potter sequence
This is a flattened head and failure of limbs to form correctly as they don’t have enough space
What is oligohydramnios?
Decreased volume of amniotic fluid reduces the space for the developing foetus
This causes the foetus to present with Potter sequence
Why does bilateral agenesis lead to a reduced volume of amniotic fluid?
Usually the foetus swallows amniotic fluid, and the foetal kidney excretes urine into the amniotic sac
If no urine is secreted, this reduces the volume
What are the 2 types of polycystic kidney disease?
- autosomal dominant
(adult PKD)
- autosomal recessive
(congenital PKD)
Where do cysts form from in autosomal dominant PKD?
What age group does it affect?
How many births does it affect?
Cysts form from all parts of the nephron
Affects 30-50 years of age
Affects 1 in 1000 births
It is not as progressive as recessive PKD
Where do cysts form from in autosomal recessive PKD?
What age group does it affect?
How many births does it affect?
Cysts form from the collecting ducts
It presents in childhood
It occurs in 1 in 5000 births
What happens to the size of the kidneys in polycystic kidney disease?
The kidney tries to heal itself and make more structures when the cysts form
This leads to enlargement of the kidneys
What mutations are involved in PKD?
Mutations in genes of cilia
How do the kidneys relocate during development?
- the metanephric mesenchyme is in the sacral region (pelvis)
- growth and elongation of the foetus causes the kidneys to ascend
- they reside in a more cranial position in the adult
What happens the the blood supply of the kidney as it ascends?
As the kidney ascends, it develops a new blood supply more cranially
The original lower vessels degenerate
How may someone have more than one renal artery?
If the kidney does not lose its blood supply as it ascends
It still develops a new blood supply
By which week are the kidneys in their adult position?
week 9
What causes a horseshoe kidney?
Where does it reside?
As the kidneys ascend, the inferior poles fuse together
It resides lower in the lumbar region
What are the symptoms of horseshoe kidney?
How many people does it affect?
It is usually asymptomatic
It occurs in 1 in 600 people
What happens to the cloaca in weeks 4 - 7?
The cloaca divides into the:
- urogenital sinus (cranial)
- anal canal (anorectal region) (caudal)
How is the cloaca divided?
The urorectal septum grows towards the midline and separates the cloaca
The urorectal septum is a mesoderm derivative
What are the 3 distinguishable parts of the urogenital sinus?
- upper part - presumptive urinary bladder
- pelvic part - urethra
- phallic part - penile urethra/vestibule
What is the bladder initially continuous with?
Why?
The allantois
This allows excretions to leave the placenta and enter the mother’s circulation
What is formed when the allantois obliterates?
The urachus
This connects the apex of the bladder with the umbilicus in the adult
