Urinary Session 2 Flashcards
Where does the urinary system derive from?
Hindgut region of primitive gut tube
What are nephrotomes?
Segmental cell clusters of intermediate mesoderm which are functional basic units
How do nephrotomes change as the pronephros disappears?
Regress and are replaced by more caudal ones
What do nephrotomes contain?
Glomerulus Bowman's capsule PCT DCT Collecting duct
Which is the first and most cranial kidney system to develop?
Pronephros
Is the pronephros functional in humans?
No
Where is the duct in the pronephros located?
Extends from cervical region to cloaca
Why does the primary nephric duct have no function?
It doesn’t reach the cloaca
Where does the pronephros fit into the timeline of embryonic development?
Develops and regresses in the fourth week
In what order (both sequentially and from cranial to caudal) do the kidney systems arise?
Pronephros
Mesonephros
Metanephros
What is the urogenital ridge?
Area of intermediate mesoderm surrounding the mesonephric duct which gives rise to both the embryonic kidney and gonad from primitive nephrotomes
When does the mesonephros appear?
4th week
Describe the development of mesonephric tubules.
Develop caudal to pronephric region early in the 4th week as the pronephros system regresses. Lengthen rapidly –> S shape and acquire capillary tuft
What do the mesonephric tubules and mesonephric duct form?
Embryonic kidney
Does the embryonic kidney function?
May for a short time during the early foetal period
Why is the mesonephric duct essential?
Sprouts the ureteric bud which induces development of the definitive kidney
What does the mesonephric duct make contact with?
Cloaca
What part of the mesonephros has an important role in the male reproductive system?
Mesonephric duct
What is the final outcome for kidney development?
Paired retroperitoneal organs either side of vertebral column at T12-L3
Arterial supply from direct branch of abdominal aorta
Produces urine that drains to bladder via ureter
Describe the development of the metanephros.
Ureteric bud releases differentiating factors –> factors act on surrounding intermediate mesoderm of caudal region –> metanephric blastema which the ureteric bud expands to meet –> ureteric bud expands and branches
What does ureteric bud expansion and branching form?
Widened renal pelvis and future major calyces
When does the metanephros appear during development?
5th week
In which region of the developing kidney does the renal functional unit develop?
Metanephros
What does the ureteric bud form in the renal functional unit?
Collecting system: urethral, calyces and collecting tubules
What does the intermediate mesoderm under ureteric bud influence form in the renal functional unit?
Excretory component: nephron from Bowman’s capsule to DCT
Where does the metanephric kidney first appear in the body?
Pelvic region
Why does the metanephric kidney first appear in the pelvic region?
Ureteric bud sprouts very caudal, close to the cloaca
What is most of the ‘ascent’ of the kidney due to?
Relative elongation of the embryo
How does the vascular supply of the kidneys change as they ascend?
Pick up new arterial supply as they cross the arterial fork formed by vessels returning blood from the foetus to the placenta
Early in development where do the GI, urinary and repro tracts end?
Cloaca
What basic components of the male and female external genitalia are common to both?
Genital tubercle
Genital folds
Genital swellings
At 9 weeks, how does genital fold fusion differ in males and females?
Males: steroidal testicular hormones drive genital fold fusion to form spongy urethra
Females: no genital fold fusion
Other than genital fold fusion, what do steroidal testicular hormones drive in the male embryo?
Genital tube to move cranially
What separates the cloaca during embryonic development?
Urogenital septum
What will develop if the median umbilical ligament remains patent?
Urachal cyst
What does formation of the urogenital septum create?
Urogenital sinus
What separates the pelvic parts of the urogenital sinus from the future bladder?
Rough level of peritoneum
Which parts of the urogenital sinus will form the future urethra?
Phallic and pelvic
Is the cloacal membrane complete when the urogenital sinus forms?
Yes, doesn’t rupture until ~6.5 weeks
What happens when the mesonephric ducts each the urogenital sinus in males?
Ureteric bud sprouts from them –> smooth musculature begins to appear –> UGS begins expansion –> ureteric buds and mesonephric ducts make independent openings as UGS increases –> male androgens cause mesonephric duct to become vas deferens and prostate and prostatic urethra formation
Which section of the male urethra is most similar to the female urethra and why?
Membranous as it passes through the peritoneum
What happens when the mesonephric ducts reach the UGS in a female?
Ureteric bud sprouts from mesonephric duct –> UGS increases and mesonephric duct regresses –> ureteric bud opens into UGS
Why does the mesonephric duct regress and no prostate form in female urinary bladder and urethra development?
No tropic androgens
What forms the female urethra?
Pelvic part of the UGS as it passes through the peritoneum
What happens if the ureteric bud fails to interact with the intermediate mesoderm?
Renal agenesis
What will the ascending kidneys get caught on in pelvic kidneys?
Umbilical arteries
How does horseshoe kidney arise?
Lower poles of kidney touch as they are pushed through the arterial fork
How do accessory renal arteries form?
Embryonic vessels, usually from aorta to superior/inferior poles, persist
What is Wilm’s tumour?
Genetic mutation causing malignant tumour of metanephric blastema
Is the prognosis of Wilm’s tumour good or bad?
Good
What happens if the ureteric bud splits into two or two buds are formed during kidney development?
Two induction events happen so there are two ureters and an additional lobe on the affected kidney
When might supplication defects be symptomatic?
If there is an ectopic ureteral orifice which bypasses the urinary sphincters thus causing incontinence
What is the pathogenesis of multicystic kidney disease?
Atresia of ureter leads to cysts forming in kidney
How is renal function maintained in multicystic kidney disease?
Unaffected kidney takes over function
Is multicystic kidney disease heritable?
No
Compare the two inheritance patters of polycystic kidney disease.
Autosomal recessive: more progressive
Autosomal dominant: more common
Why does polycystic kidney disease have a poor prognosis?
Due to effects of ciliopathies
What is exstrophy of the bladder?
Where it opens onto the anterior abdominal wall
Where might you find an ectopic urethral orifice?
Vagina
What is the pathogenesis of hypospadia?
Lack of response/level of androgen causes defect in urethral fold fusion so urethra opens onto ventral surface instead of the glans
Is hypospadia a major or minor defect?
Minor
Describe the flow of filtrate in the kidney.
Renal corpuscles –> tubule system –> medullary Ray’s –> ducts of Bellini –> renal papillae –> minor calyx
What are medullary rays created by?
Tubules of increasing diameter
What converges to form renal papillae?
Ducts of Bellini
What does a renal corpuscle consist of?
Vascular pole
Urinary pole
Bowman’s space
What is the function of the renal corpuscle?
Produce ultrafiltrate
What forms the filtration barrier in Bowman’s capsule?
Visceral layer of capsule and capillary endothelium
How is the visceral layer of Bowman’s capsule organised with respect to the capillaries?
Wraps around them
What is the function of the parietal layer of Bowman’s capsule?
Simple squamous epithelium creates funnel to collect ultrafiltrate and direct it to the urinary pole
Where is the urinary pole located?
Start of the PCT
How is the primitive renal tubule derived?
From the ureteric bud as a blind ending tube
How is the double layer seen in the Bowman’s capsule formed?
Primitive renal tube grows into primordium of true kidney and envelopes a developing glomerulus
Which part of the trilaminar layer do glomeruli develop from?
Mesoderm
Describe the capillary endothelium in the filtration barrier.
Fenestrated
Describe how podocytes contribute to the filtration barrier.
Invest capillary endothelium allowing filtration slits as spaces between pedicels overlap with capillary fenestrations
What shares a basement membrane in the filtration barrier?
Endothelium and podocytes
Which creates a finer mesh, the fenestrated capillary or the interdigitation of podocyte foot processes?
Interdigitation of podocyte foot processes
Which is the longest section of the tubule in the nephron?
PCT
What epithelium makes up the PCT?
Simple cuboidal with microvilli brush border
What in the nephron consists of 4 parts described by their epithelial lining?
Loop of Henle
What epithelium is found in the ascending and descending limbs of the Loop of Henle?
Simple squamous
How is the epithelium of the thin limbs of the loop of Henle adapted to its function?
No active transport takes place here
Which part of the loop of Henle has simple cuboidal epithelium and why?
Thick ascending limb for active transport
Where are the thick ascending limbs of the loop of Henle Sen on the kidney?
Medulla interspersed with thin limbs, vasa recta and collecting ducts
Does the epithelium of the thick ascending limb have a brush border?
No
What are pars recta?
Straight tubules in the loop of Henle
What does the DCT make contact with in the cortex?
‘Parent’ glomerulus
How can the DCT be distinguished from the PCT on histology?
More mitochondria
No brush border
Larger lumen
What forms the juxtaglomerular apparatus?
Macula densa of DCT
Juxtaglomerular cells of afferent arteriole
Extraglomerular mesangial cells
Where are mesangial cells located?
Inside corpuscle but outside glomerulus near macula densa bound by afferent and efferent arterioles
What does the collecting duct have a similar histological appearance to?
Thick limbs of Henle’s loop
How can collecting ducts be distinguished from other tubules on histology?
Larger lumen
Irregular shape
How many layers of smooth muscle does the ureter have?
Two
Where is there greater muscle mass in the ureter due to a third layer of muscle appearing?
Lower 1/3
What is fasciculation?
Contraction in one direction
What epithelium lines the ureter?
Transitional epithelium (urothelium)
Describe the structure of the bladder wall.
3 muscle layers, transitional epithelium and add outer adventitia
How does transitional epithelium remain impermeable when distended?
Surface layer of ‘umbrella cells’ stretch out and overlap
