9.1 Embryology And The Development Of The Urinary System Flashcards
What is the functional unit of the kidney
Nephron
How does urine drain into the bladder?
Ureter
Where does arterial blood supply to the kidneys stem from?
Abdominal aorta
How many kidney systems form in early embryological life?
3 - pronephros, mesonephros, metanephros
Where do kidney systems develop from?
Intermediate mesoderm
What is the 1st kidney system that develops?
The pronephros
Where does the pronephros develop?
In the cervical region
What is the clinical significance of the pronephros?
Provides useful data on kidney development
What is the function of the pronephros?
Has no clinical function
Forms the duct of the next developmental stage
What is the urogenital ridge?
Region of intermediate mesoderm that gives rise to both the embryonic kidney and gonad
What structures form the embryonic kidney?
Mesonephric tubules
Mesonephric duct
Why does the kidney need to upgrade from the embryonic kidney?
As the embryonic kidney cannot conserve water
What are the important functions of the mesonephros?
• Mesonephric duct has important role in the development of the reproductive system in the male mesonephros
• Mesonephric duct sprouts the ureteric bud which induces
development of the definitive kidney
What is the ureteric bud?
It’s a sprout from the mesonephric duct.
Undifferentiated intermediate mesoderm caudal to the mesonephros
What is the importance of the ureteric bud?
Later forms the ureter
Induces development of undifferentiated mesoderm close by into the true kidney, which can conserve water. Metanephros develops
Why does the maintenance of the mesonephros vary?
Is maintained in males by androgens secreted by developing testis. Degrades in females
What structure is derived from the metanephric blastema?
Kidney
What structure forms the collecting aspects of the kidney?
The ureteric bud of the mesonephric duct
What structures does the ureteric bud form in a developed kidney?
Minor calyx
Major calyx
Renal pelvis
Ureter
What primitive structure forms the excretory part of the kidney?
Metanephric blastema
Where does the metanephric kidney first appear?
In the pelvic region, near the cloaca
Describe the movement of the kidneys during development
Caudal to cranial shift (ascent)
Crosses the arterial fork formed by vessels returning blood from the foetus into the placenta
Why are secondary/ additional renal arteries retained in some individuals?
As the kidney changes position in the abdomen there is usually resolution and appearance of a new artery branch. In 25% of people the early renal artery does not resolve and maintains past birth
What developmental issues can arise in development of the urinary system?
- Ureteric bud fails to interact with intermediate mesoderm (renal agenesis)
- Migration goes awry
- Duplication defects
- Ectopic ureter
- Cystic disease
What is renal agenesis?
Unilateral renal agenesis - cervical defect when a kidney does not develop
Bilateral renal agenesis - both kidneys did not develop, incompatible with life
What structural anomalies occur due to a flaw in migration?
Pelvic kidney - problem with kidney ascent
Horseshoe kidney - during ascent the caudal poles of the 2 true kidneys come into contact and fuse. Has limited functional implications but stops migration of the kidney as it gets stuck on the 1st unpaired branch of the abdominal aorta
What causes duplication defects?
Splitting of the ureteric bud
Multiple ureteric buds
What is an ectopic ureter?
A ureter that doesn’t empty into the bladder, opens into another structure
What is a duplication defect?
When an extra kidney or extra kidney lobe is formed
What other defect is associated with duplication defect?
Ectopic urethral orifices
Ureter can open into vagina/urethra
Why can ectopic urethral orifices impact on quality of life?
As not subject to normal control of micturition.
Open distal to normal continence sphincter mechanisms and result in incontinency
What is the cloaca?
A blind ended dilated structure that the hind gut, reproductive tract and urinary tract share
How does the urogenital sinus develop?
Cloaca is split by development of the urogenital septum. This separates the urogenital sinus from the hind gut.
Where is the urogenital sinus?
Anterior to the hind gut, at the caudal end of the embryo.
Urogenital sinus is continuous with the umbilicus via the urachus
What happens to the urachus during development?
Closes to become the median umbilical ligament
What develops from the urogenital sinus?
The bladder and urethra
What can be seen emerging through the umbilicus in a patient with a patent urachus?
Urine
Describe the development of the female urinary system
Mesonephric ducts reach urogenital sinus
Ureteric bud sprout from MD
Urogenital sinus begins to expand and connect to ureteric buds
MD regresses or genital sinuses expand and fuse together
Describe the development of the urinary system in males
MD reach urogenital sinus
Ureteric bud sprouts from MD
Smooth musculature begins to appear and UGS expands
Androgens produced by testis stop the MD regressing
UBS and MD make independent openings into the urogenital sinus
Ureters enter into bladder via trigone and mesonephric ducts drain into prostate and from the prostatic urethra
What forms the female urethra?
The pelvic part of the urogenital sinus below the peritoneum
What forms the male urethra?
Pre-prostatic = from the urogenital sinus, before it passes into prostate gland Prostatic = formed from the urogenital sinus and receives contribution from the MD, passes through prostate Membranous = as urethra passes through peritoneum, formed from the urogenital sinus Spongy = formed by the extension and fusion of the genital fold
What influence doe dihydrotestosterone have on external genitalia?
Released by testis to cause elongation of the genital tubercle and genital folds fuse to form the spongy urethra a
What determines the differentiation of the external genitalia?
Presence of androgens
Ability of tissue to respond to these hormones
What is hypospadias?
A defect in the fusion of the genital folds
Results in the urethra opening onto the ventral surface of the penis rather than at the end of the glans penis
Where does the bladder and urethra develop from?
From the urogenital sinus, which is endoderm origin
What are the 3 divisions of the mesoderm?
Paraxial mesoderm
Intermediate mesoderm
Lateral mesoderm
What doe the different divisions of the mesoderm form?
Paraxial = vertebral column
Intermediate = kidneys and gonads
Lateral plate = body wall linings and dermis
What is the urogenital ridge?
A downwards projection of the intermediate mesoderm. Goes on the form nephrogenic cord
What is a mesonephros?
A functioning unit of the mesonephric duct. Can filter blood as produce urine but cannot control water absorption
What form the trigone region of the bladder in males?
The absorption of the mesonephric duct by the bladder
What stimulates the formation of the ureteric bud from the mesonephric duct?
Stimulated at the caudal end of the mesonephric duct by the growth factors released from the metanephric blastema
Where do we see reciprocal induction in the development of the urinary system?
During the development of the true kidney.
Metanephric blastema releases GF to stimulate growth of ureteric bus into ureteric stalk and the into the renal pelvis, minor and major calyx and millions of collecting tubules.
Uterovaginal stalk releases GF to stimulate the metanephric blastema to develop into the nephron
At what spinal level do the kidneys ordinarily ascend to?
L1
What structures are formed from the lower part of the urogenital sinus?
Clitoris in females
Penis in men
What structures are formed from the mid part of the urogenital sinus?
Urethra in females
Membranous and prostatic urethra in males
When is the kidney functional and able to excrete urine?
By 10 weeks
