Embryology of the Urinary System Flashcards
When does the development of the urinary system begin?
During week 4
Where does the urinary system develop from?
The urogenital ridges in the intermediate mesoderm on either side of the primitive aorta
What are the three overlapping systems that the kidneys develop from?
The pronephros, mesonephros and metanephros
Where does development of the pronephros begin?
The cervical region of the embryo
What system do the nephrotomes belong to?
The pronephros
What are the nephrotomes?
Segmented divisions of intermediate mesoderm = between 6 and 10 pairs are formed in total
What structure do the nephrotomes join with?
Join into the pronephric duct
What is the pronephric duct?
Duct that extends from the cervical region to the cloaca of the embryo
What is the fate of the pronephros?
Non-functional and regresses completely by the end of week 4
Where does the mesonephros develop?
Caudally to the pronephros
What does the presence of the pronephric duct induce in the mesonephros?
Induces the nearby intermediate mesoderm in the thoracolumbar region to form mesonephric tubules
How is filtration of blood by the mesonephros facilitated?
Mesonephric tubules receive a tuft of capillaries from the dorsal aorta
Where do the capillaries that supply the mesonephric tubules drain into?
The mesonephric duct = continuation of the pronephrotic duct
What do the mesonephric tubules act as?
A primitive excretory system = most tubules regress by end of month 2
What structure does the mesonephric duct give rise to?
Sprouts the ureteric bud caudally, which induces the development of the definitive kidney
What does the metanephros form?
The definitive kidney
When does the metanephros begin to develop?
Appears in week 5 and becomes functional around weeks 9-11
What are the components of the metanephros?
Ureteric bud and the metanephric blastema = consists of a collecting system and an excretory system
Where is the collecting system of the metanephros derived from?
The ureteric bud
What does the collecting system of the metanephros go on to form?
Dilates to create the ureter, renal pelvis, major and minor calyces, and collecting tubules
Where does the collecting system of the metanephros terminate?
At the distal convoluted tubule
What happens if the ureteric bud splits too early?
May cause two ureters, or two renal pelvices connecting to one ureter
Where is the excretory system of the metanephros derived from?
The metanephric blastema
What is each collecting tubule from the collecting system of the metanephros covered by?
A metanephric tissue cap = gives rise to the excretory tubules
What structures go on to form the nephrons?
The excretory tubules of the metanephros along with the developing glomeruli
What does the proximal end of the excretory tubule form?
The Bowman’s capsule around the glomerulus
What does the distal end of the excretory tubule form?
Elongates to form the proximal convoluted tubule, loop of Henle and distal convoluted tubule
Where does the definitive kidney develop?
Initially develops in the pelvic region before ascending in to the abdomen to L1 level during weeks 6-9
Where does the kidney receive blood from when it’s in the pelvis?
From a pelvic branch of the abdominal aorta
What happens to the blood supply to the kidney as it ascends?
New arteries from the abdominal aorta supply the kidney
What happens to the pelvic vessels that used to supply the kidney once it has ascended?
Pelvic vessels usually regress but can persist as accessory renal arteries
What causes a horseshoe kidney?
Inferior poles of the metanephroi meet and fuse before ascent = kidney becomes trapped beneath the IVC
Where are the bladder and the urethra derived from?
The cloaca
When does the urorectal septum divide the cloaca into two parts?
During weeks 4-7
What are the two part that the cloaca is divided into by the urorectal septum?
Anal canal (posterior) and the urogenital sinus (anterior)
What are the three parts of the urogenital sinus?
Upper part = forms bladder
Pelvic part and phallic/caudal part
What does the pelvic part of the urogenital sinus form?
Entire urethra and some of the reproductive tract in females
Prostatic and membranous urethras in males
What does the phallic/caudal part of the urogenital sinus form?
Part of the reproductive tract in females
Spongy urethra in males
What initially drains the bladder?
The allantois = obliterated during foetal development and become the urachus
What does the urachus become in adults?
Remnant exists as the median umbilical ligament = connects apex of bladder to umbilicus
What happens as the bladder develops from the urogenital sinus?
It absorbs the Wolffian ducts to become the trigone of the bladder
What are the Wolffian ducts?
Caudal parts of the mesonephric ducts
Where do the ureters enter the bladder?
At the base of the trigone
Where do the ureters form from?
Form as outgrowths of the mesonephric ducts
How do the bladder and urethra develop in males?
As kidneys ascend the ureteric openings move cranially
Wolffian ducts move caudally and closer together and enter the prostatic urethra
What do the Wolffian ducts form in men?
The ejaculatory ducts
How do the bladder and urethra develop in women?
As kidneys ascend the ureteric openings move cranially
What happens to the mesonephric ducts in women?
They degenerate due to a lack of testicular androgens
What are some defects that can occur in the bladder?
Urachal fistula, urachal cysts, urachal sinus
What happens to the ureteric buds at 28 days of development?
They sprout from the distal mesonephric ducts
When do the ureteric buds penetrate the metanephric blastema?
At 32 days of development
