Flashcards in Embryology Deck (53):
When does organogenesis usually take place?
During weeks 3-8 mainly
What other system is the urinary system related to?
Reproductive and urinary systems have close embryological links and some of these associations carried into adulthood both in relation to the normal individual and in some anomalies of the urogenital system
Urinary system forms template for reproductive system development
What are the constituents of the adult kidney?
What are the constituents of the adult urinary system?
Urethra - male and female
Blood supply- L1 Aorta
What components make up the nephron?
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
What makes up the uriniferous tubule?
When does gastrulation occur?
What is gastrulation?
Bilaminar to trilaminar disc
Three primary "germ" layers of all body tissues develop from these:
What does the mesoderm divide into early on?
Lateral plate mesoderm
The urinary system develops from?
-Kidney and ureter
-Urinary bladder and urethra
What does the urogenital ridge form from?
Intermediate mesoderm forms longitudinal ridge along the embryo called the urogenital ridge/cord
What does the urogenital ridge/cord form?
Partitions into a nephrogenic ridge/cord and a gonadal ridge/cord
Why is the entire urinary system retroperitoneal in the adult?
Urogenital ridge covered in front with coelomic epithelium (peritoneum)
What structures make up the nephrogenic ridge?
What does the paramesonephric duct form?
Forms uterus and uterine tubes
What does the mesonephric duct form?
Drains primitive kidney but later forms ductus deferens
What does the mesonephros form?
Is early embryonic functioning kidney
Are excretory tubules that largely disappear
Function taken over by metanephros (caudal to mesonephros)
What does the gonad form?
The gonads (testes/ovary)
What 3 sets of kidneys develop in the embryo?
What does the mesonephric duct open into?
What does it give off?
Mesonephric duct opens into the cloaca
Gives off the uteric bud
Does the urinary system or the reproductive system develop first?
What is the pronephros?
Rudimentary and non functional
-left over from evolutionary development
Appear early in week 4
Few cell clusters and tubular structures - neck region
Their ducts open into cloaca
What is the mesonephros?
Well developed and functions briefly during early foetal period
Appear late in week 4
Functions as interim kidney for 4 weeks
10-50 glomeruli and tubules
What is the metanephros?
Primordia of permanent kidneys
-forms the definitive adult kidney
Develops in the 5th week
This will ascend to the upper part of the abdomen
It will be drained by the uteric bud which forms as a diverticulum from the mesonephric duct, and which will become the definitive adult ureter
The perminant kidney develops from which 2 sources?
What is the uteric bud?
Outgrowth (diverticulum) from mesonephric duct
As it elongates it penetrates metanephric blastema
Stalk of the bud becomes the ureter
What does the cranial part of the ureteric bud form?
The cranial part endergoes branching -> collecting tubules
First 4 generations of tubules -> major calyces
Second 4 generations of tubules -> minor calyces
What does the metanephric blastema derive from?
Derived from caudal part of the nephrogenic cord
A uriniferous tubule is made up of 2 developmentally different parts.
What are they?
-from metanephric blastema
-from ureteric bud
How is ureteric bud and metanephric mesoderm growth related?
Reciprocally induce each other to form kidney components
Perturbations in any aspect of these inductive events may cause inhibition of ureteric bud grwoth and renal hypoplasia or agenesis
Conversely, duplication or overproliferation of structures can occur if there is a gain of function of the inductive factors
Describe the process of kidneys ascention?
Mainly due to differential growth of the lover body inferiorly away from kidneys (kidneys appear to "ascend")
Kidneys lie retroperitoneally in upper abdomen between T12-L3
Hilum rotates from ventral to medial (about 90 degrees)
Ascent stops when contact with adrenal (suprarenal) glands
Vascular buds from the kidneys grow toward and invade the common illiac arteries
Segmental breakdown and reform of vascular supply during ascent
Accessory renal arteries may persist at inferior pole
What is the fate of the metanephros?
The metanephros (pelvic region) will form the definitive adult kidney.
This will ascend to the upper part of the abdomen (T12-L3)
What is the fate of the mesonephric duct?
Connets with the gonad and becomes the ductus deferent in the male but regresses in the female (though may persist as cysts)
Also gives rise to the ureteric bud as a diverticulum
What is the fate of the ureteric bud?
Ureteric bud forms as diverticulum from the mesonephric duct and becomes the definitive adult ureter (and epididymis and seminal vesicle)
What does the urorectal septum do?
Divides the cloaca into the urogenital sinus and the rectal canal
How is the urogenital sinus divided?
Cranial (vesical) part)
Pelvic (urethral) part
Caudal (phallic) part
What does the cranial (vesical) part of the urogenital sinus form?
What attaches the bladder to the umbilicus?
Attached to the umbilicus through the median umbilical ligament
What is the median umbilical ligament derived from?
Fibrosed allantois = urachus
What does the pelvic (urethral) part of the urogenital sinus form?
Prostatic and membranous urethra in males and entire urethra in females
What does the caudal (phallic) part of the urogenital sinus form?
Penile urethra in males
Vaginal vestibule in females
How does the trigone of the bladder form?
Incorporation of inferior parts of mesonephric ducts
Mesonephric duct opens into primitive urogenital sinus.
As the sinus grows the proximal parts of mesonephric ducts are absorbed so that the mesonephric ducts and ureters now open separately
The openings are at first close together
Further absorption of ureters causes their opening to shift upwards and laterally.
Where is the epithelium of the male urethra derived from?
Most of the epithelium of the male urethre is derived from the endoderm of the phallic part of the urogenital sinus.
The epithelium of the terminal part of the urethra is derived from the surface ectoderm
Where is the epithelium of the female urethra derived from?
the entire female urethra is derived from endoderm of the urogenital sinus
Give some urinary system anomalies
Duplication of the urinary tract
Nephroblastoma (Wilm's tumour)
Polycystic kidney disease
Abnormal attachment of the ureters
Urachal fistulas, sinuses and cysts
What is duplication of the urinary tract?
Occurs when the ureteric bud prematurely divides before penetrating the metanephric blastema
Results in wither a double kidney and/or a duplicated ureter and renal pelvis
What is polycystic kidney disease?
Polycystic kidney disease (PKD or PCKD, also known as polycystic kidney syndrome) is a genetic disorder in which abnormal cysts develop and grow in the kidneys.
What is a pelvic kidney?
One or both kidneys stays in the pelvis rather than ascending
What is a horseshoe kidney?
The two developing kidneys fuse ventrally into a single, horseshoe shape that gets trapped in the abdomen by the inferior mesenteric artery
What is supernumeracy arteries?
Can ofetn have more than one renal artery per kidney, which is often assymptomatic but can sometimes compress the ureter causing a backup of fluid into the renal pelvis and kidney tubules (hydronephrosis)
What is trigonitis?
As a MESONEPHRIC DUCT derivative the trigone is sensitive to sex hormones and can undergo hormone- induced epithelial metaplasia (usually transformation from a transitional type to squamous type epithelium which can overproliferate and leade to urinary blockages)
What is abnormal attachment of the ureters?
The ureters can sometimes be attached to either the urethra or parts of the reproductuve tracts