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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?

Renal pelvis


Uriniferous tubule
-Collecting duct


What are the constituents of the adult urinary system?

Urinary Bladder
Urethra - male and female

Blood supply- L1 Aorta


What components make up the nephron?

Renal corpuscle
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule


What makes up the uriniferous tubule?

Collecting duct


When does gastrulation occur?

3rd week


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?

Paraxial mesoderm
Intermediate mesoderm
Lateral plate mesoderm


The urinary system develops from?

Intermediate mesoderm
-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?

Paramesonephric duct
Mesonephric duct


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?

Urinary system


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?

Uteric bud
-Metanephric diverticulum

Metanephrogenic blastema
-Metanephric mesoderm


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

Collecting tubule
-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?

The bladder


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

Pelvic kidney

Horseshoe kidney

Supernumeracy arteries


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


What are urachal fistulas, sinuses and cysts

Occur when a remnant of the allantois persists and are found in the midline along the path from the umbilicus to the apex of the bladder (i.e. along the median umbilical ligament