Embryology of Kidney Flashcards
What does the mesoderm become highly organised into?
- Paraxial mesoderm
- Intermediate mesoderm
- Lateral plate mesoderm
What does the paraxial mesoderm develop into?
Majority of skeleton, skeletal muscles and dermis of skin
What does the intermediate mesoderm develop into?
Gonads, internal reproductive tracts, kidneys
What does the lateral plate mesoderm develop into?
Lining of body cavities
What makes up the urinary system?
- Kidneys
- Ureteres
- Urinary bladder
- Urethra
What are the pronephros?
Pronephros is the most basic of the three excretory organs that develop in vertebrates, corresponding to the first stage of kidney development
When does the pronephros form?
4th week
What does the pronephros form from? Where do they develop?
Intermediate mesoderm in the cervical region condenses an reorganises to form a number of epithelial buds
Development begins in the cervical region of the embryo
When do pronephros disappear?
Around day 25
They develop and regress in humans, with no function except kicking off cascade of kidney development
What begins to form lateral to pronephros in the lower cervical region?
A solid duct - mesonephric duct
Where does mesonephric duct form from?
Intermediate mesoderm
What is the 2nd kidney structure to form? Where does it develop?
Mesonephros
Develops caudally to the prenephros
How does the mesonephric duct develop?
Develops caudally and fuses with the walls of the cloaca
When does the mesonephric duct fuse with the cloaca?
Day 26
What is the cloaca?
Common point of emptying of GI and urinary system
After fusion with the cloaca, what happens to the mesonephric duct?
Starts to form a lumen inside of it –> canalisation commences from caudal end and moves cranially
When does the mesonephros develop?
As pronephros is regressing (overlapping process)
Where is the mesonephros derived from?
Intermediate mesoderm in the upper thoracic to the upper lumbar regions
What does the development of the mesonephric duct induce?
Formation of mesonephric buds from mesenchyme
I.e. pronephros stimulates mesonephric duct to form which stimulates mesonephros to form
What do the mesonephric buds elongate to form?
Mesonephric tubules (tubules formed in a craniocaudal direction)
As the caudal tubules differentiate, the cranial tubules regress (mesonephros is transient)
I.e. ones in lumbar (caudal) region develop more than those in cranial region that regress
As the mesonephric tubules differentiate and lengthen rapidly, what forms?
An S-shape and Bowman’s capsule
How does the mesonephros form the 1ary excretory system?
Lateral edges of mesonephros joins to mesonephric duct
Forms collecting system –> joins with amniotic fluid
What forms at medial surface of tubule?
Tuft of capillaries –> Glomerulus
Grown into Bowman’s capsule
What is the renal corpuscle?
- Bowman’s capsule
- Glomerulus
Primitive excretory system
What happens to mesonephric duct after week 10?
Male –> develop into reproductive structures
Female –> regress
What is the mesonephric ridge (urogenital ridge)?
Formed from development of mesonephros
What takes place on medial aspect of mesonephric ridge?
Gonadal development
When the mesonephros regresses, what then forms?
Metanephros
Goes on to form definitive (adult) kidney
Where does the excretory portion of the kidney form from?
Specialised mesoderm around pelvic region –> is undifferentiated (mesenchyme)
Metanephric mesenchyme
What forms at caudal end of mesonephric duct?
A ureteric bud is formed
What does the ureteric bud then form?
The collecting portion of the kidney
What makes up the excretory portion of the kidney?
- Bowman’s Capsule
- Proximal convoluted tubule
- Loop of Henle
- Distal convoluted tubule
What makes up the collecting portion of the kidney?
- Collecting ducts
- Major and minor calyces
- Renal pelvis
- Ureter
How does the ureteric duct grow?
Penetrates the metanephric mesenchyme (forms communication between the 2)
What is important of connection between ureteric duct and metanephric mesenchyme?
Signal to each other and induce each other to grow
How does the ureteric bud bifurcates (sprouting pattern) as it penetrates the mesonephric mesenchyme?
Renal ampulla –> renal pelvis –> major calyces –> minor calyces –> collecting ducts
These collecting ducts are all connected
What are the 2 structures that the definitive kidney comes from?
- Ureteric bud (collecting)
- Metanephric mesenchyme (excretory)
What forms in the mesenchyme at the end of the collecting ducts (in the metanephric caps)?
Condensements of cells (of mesenchyme)
Called renal vesicles
What then happens to the renal vesicles?
Elongate (due to signals from collecting system)
Elongate and form the nephron (excretory portion) –> forms S-shape tubule and Bowman’s capsule
What forms in the proximal end of this tubule?
Capillaries to form the glomerulus
Proximal end of the tubule then forms the Bowman’s capsule
How do the collecting and excretory parts of the kidney connect?
Distal end of tubule connects with collecting tubule. Tissue breakdown between 2 embryological origins
What can cause duplication of the ureter?
Premature bifurcation of ureteric bud (before piercing mesenchyme)
Bifurcation can be partial or complete
What can result from duplication of ureter?
- Bifid ureter
- Ectopic ureter
What are the potential options for a bifid ureter?
- Only proximal part of ureter has 2 parts
2. 2 separate ureters coming from kidney (if bifurcation happens very early)
What is an ectopic ureter?
Takes a different course to normal ureter and attaches to structures that it shouldn’t
What is renal agenesis?
A newborn is missing one or both kidneys (unilateral or bilateral)
What is renal agenesis caused by?
Caused by early degeneration of ureteric bud or failed interaction between ureteric bud and metanephric tissue cap
What are symptoms of unilateral renal agenesis?
- Generally asymptomatic
- Remaining kidney grows a little bigger
What are symptoms of bilateral renal agenesis?
Usually incompatible with life
What are dangers of a deficient volume of amniotic fluid?
Baby swallows amniotic fluid to help with development of muscles. Kidneys filter this out and excretes it into amniotic cavity.
A deficiency in amniotic fluid leads to Oligohydraminos (usually due to bilateral renal agenesis)
What are symptoms of Oligohydraminos?
Potter sequence
What is the autosomal dominant version of polycystic kidney disease?
Cysts form in kidneys from all parts of nephron
Presents in adulthood
What is the autosomal recessive version of congenital polycystic kidney disease?
Congenital
Cysts form from the collecting ducts
What are dangers of congenital polycystic kidney disease?
Kidneys enlarge and renal failure occurs in childhood
How do kidneys relocate? What happens to the blood supply?
Develop in pelvic region but reside in more cranial position in adults
As the kidney ascends it establishes a new blood supply more cranially. The original lower vessels normally degenerate
What is the ascent of the kidney caused by?
Growth and elongation of developing foetus
When is the adult position of the kidneys attained?
By week 9
What is a horseshoe kidney? When does this occur?
As kidneys ascend, inferior poles of kidneys fuse. Therefore, cannot ascend past IMA and resides lower in lumbar region.
Occurs if kidneys become too close together during their ascent, and they become fused.
Usually asymptomatic, may be prone to obstruction
What does the cloaca divide into? When does this happen? What causes this division?
- Urogenital sinus (anterior)
- Anal canal (posterior)
Weeks 4-7
Separated by urorectal septum (mesoderm derivative)
What can the urogenital sinus be separated into?
3 parts:
- Upper part
- Pelvic part
- Phallic part
Initially, what is the bladder drained by? What then happens?
The allantois
Allantois is obliterated to form the urachus (fibrous cord) that connects the apex of the bladder with the umbilicus in the adult
What does the caudal mesonephric duct grow into? What does this become? What is purpose of this?
The wall of the bladder (i.e. the bladder absorbs the caudal parts of the duct)
Becomes the trigone of the bladder
Ureteric bud now has opening into bladder
Does the cranial or caudal end of the mesonephric duct grow quicker?
What is result of this?
Cranial
Differential growth means it looks like it migrates caudally
What is the pronephric duct?
A duct that extends from the cervical region to the cloaca of the embryo (appears and regresses before the mesonephric duct)
This early system is non-functional and regresses completely by the end of week 4
Describe the development of the mesonephros
The mesonephros develops caudally to the pronephros. First, the presence of the pronephric duct induces nearby intermediate mesoderm to form mesonephric tubules.
What do the mesonephric tubules receive?
A tuft of capillaries from the dorsal aorta, allowing for the filtration of blood
Where do the mesonephric tubules drain into? What does this system act as?
The mesonephric duct (a continuation of the pronephric duct)
They act as a primitive excretory system in the embryo, with most tubules regressing by the end of the 2nd month
What does the mesonephric duct spout caudally?
The ureteric bud (which induces development of the definitive kidney)
Where is the collecting system derived from?
The ureteric bud
What does the ureteric bud form?
It dilates to create the ureter, renal pelvis, major and minor calyces and collecting tubules – terminating at the distal convoluted tubule.
What can an early splitting of the ureteric bud cause?
Two ureters or two renal pelvices connected to one ureter
What is the excretory system derived from?
Metanephric mesenchyme
What is each collecting tubule from the collecting system covered by?
A metanephric tissue cap which gives rise to the excretory tubules
What do the excretory tubules form?
Along with the developing glomeruli, they form the kidneys functional units –> the nephron
What does the proximal and distal end of the excretory tubule form?
Proximal end forms the Bowman’s capsule around a glomerulus
Distal end elongates to form the proximal convoluted tubule, loop of Henle and distal convoluted tubule
While the kidney is initially developing in the pelvic region, what is it supplied by?
Receives its blood supply from a pelvic branch of the abdominal aorta and as it ascends, new arteries from the abdominal aorta supply the kidney
What happens to the pelvic vessels supplying the kidneys?
The pelvic vessels usually regress, but can persist as accessory renal arteries.
What does the upper part of the urogenital sinus form?
Forms the bladder
What does the pelvic part of the urogenital sinus form?
Forms the entire urethra and some of the reproductive tract in females, and the prostatic and membranous parts of the urethra
What does the phallic/caudal part of the urogenital sinus form?
Forms the penile (spongy) urethra in males, vestibule in females
What is a remnant of the urachus in adults?
The median umbilical ligament, which connects the apex of the bladder to the umbilicus
What do the ureters form as?
Outgrowths of the mesonephric duct
Where do the ureters enter the bladder?
At the base of the trigone
What happens to the ureteric openings as the kidneys ascend?
They move cranially
What happens to the mesonephric ducts in males?
Move caudally and closer together, entering the prostatic urethra to become the ejaculatory ducts
What happens to the mesonephric ducts in females?
Degenerate due to a lack of testicular androgens
How is the urethra formed in females?
Formed from the pelvic part of the urogenital sinus
How is the urethra formed in males?
The pre-prostatic, prostatic and membranous urethra is formed from the pelvic part of the urogenital sinus.
The spongy urethra is formed from the phallic part of the urogenital sinus.
