Embryology Flashcards
When does the development of kidneys start ?
In the third week of fetal development
What type of embryonic tissue does the kidney develop from ?
Intermediate mesoderm
What are the stages of kidney development ?
3 Stages : Pronephros , mesonephros and metanephros
At what directoction does the kidney develop ?
Craniocaudal direction
What stage will be the permenant stage ?
Third stage : Metanephros
What part of intermediate mesoderm does the pronephros develop from ?
Cephalic part of intermediate mesoderm
Fate of Pronephros :
Transient ; it degenerates at the 4th week
Function of Pronephros :
Functionless, but induces the formation of Mesonephros
The mesonephros ( second kidney is formed of :
1) Mesonephric duct ( Wolffian duct )
2) Mesonephric Tubules
Each Mesonephric tubule has ……………….. .
Two ends :
Medial end : invaginate by Glomerulus ( capillaries arise from dorsal or abdominal aorta )
Lateral end : Opens into Mesonephric duct
Function of mesonephros :
Urine excretion for approximately four weeks ( 4-8 weeks ) , till the permanent kidney develops
Fate of Mesonephric Tubules in Females :
1) Majority degenerate with their glomeruli
2) Some persist and give rise to ego epoophoron
Define epoophoron :
Non functional remnants and Clinically it may give rise to a local paraovarian cysts
Fate of Mesonephric tubules in Males :
1) Majority degenerate with their glomeruli
2) Some persist and give rise to efferent ductules of testes
When do Mesonephric generally disappear :
By the end of second month
Fate of Mesonephric duct in females :
Mostly degenerated, but its caudal part is often seen in histological sections along the vagina as Gartner’s ducts.
Fate of Mesonephric duct in males :
Not degenerated and gives rise to ;
a) Body & tail of epididymis
b) Vas deferens
c) Seminal vesicle
d) Ejaculatory duct
In both male& female;The caudal part of the mesonephric ducts open into ……………….
Cloaca = urogenital sinus
When does the metanephros begin to develop? And what time does it start to function ?
Time of development : fifth week
Time of functioning : four weeks later ( 9th week )
What are the sources the The permenant kidney come from ?
Mesonephric cap and ureteric bud
Metanephric cap arise from ……………………….. And form ………………….
Caudal part of intermediate mesoderm , Nephrons
Ureteric bud arise from ………………………….. and forms ……………………….
Mesonephric duct close to the cloacal opening / ureters , renal pelvis , major and minor calyces , collecting ducts
Mention the correct arrangement of nephron development beginning from the ureteric bud .
Ureteric bud touches the the metanephric cap —> division of metanephric cap into metanephric vesicles —> these vesicles elongate to form metanephric tubules
About Metanephric vesicles :
Small masses that surround the distal end of each ureteric bud division
About metanephric tubules :
Elongate from metanephric vesicles and each has two ends :
1) One end which forms bowman’s capsule THEN it is invaginate by capillaries arise from dorsal aorta forming the glomerulus
2) Other end THEN it opens into the corresponding collecting tubules
These tubules differentiate into proximal and distal convoluted tubules and Henle’s loop
Mention the position changing of the kidneys :
Lies in pelvis ( Pelvic position ) —- > ASCENDS downward AND ROTATES 90 medially ( Lumber position )
Kidneys in the pelvic position :
1) CONCAVE BORDER facing anteriorly ( Ventrally ) And CONVEX BORDER facing dorsally
2) The kidneys are lobulated
3) Its blood supply from the pelvic vessels mainly common iliac arteries
Kidneys in lumber position :
1) CONCAVE BORDER becomes medial and CONVEX BORDER becomes lateral
2) The kidneys are loses its lobulation and becomes smooth
3) Its blood supply from abdominal aorta
Why do the kidneys ascends and rotate ?
1) Elongation of ureters
2) decrease body curvature
3) Growth of lumbar and sacral regions
Why do the kidneys become smooth ?
Due to growth of nephrons
Mention the congenital renal anomalies :
1) Unilateral renal agenesis
2) Renal hypoplasia
3) Horseshoe kidney
4) Ectopic kidneys
5) Malrotated kidneys
6) Congenital polycystic kidney
Define Unilateral renal agenesis and mention the cause .
Definition : Only one kidney is developed and the other one is abscent
Causes : 1) Failure of development of metanephric cap 2) No touch between it and the ureteric bud
Define Renal hypoplasia :
Small sized kidneys
Define horseshoe kidney :
The inferior poles of the kidneys are fused together with limited ascent
Where are most ectopic kidneys located ?
Pelvis
Define malrotated kidneys :
The hilum faces anteriorly , posteriorly or laterally instead of medially
Define congenital polycystic kidneys and mention the cause :
Definition : Both kidneys contain many hundreds of small cysts which result in renal insufficiency
Cause : Failure of union between the developing convoluted tubules and collecting tubules / wide dilation of parts of the nephrons
Developmental source of ureters :
Ureteric bud
Mention the development steps of ureters :
Lower end of mesonephric duct and near its entrance in cloaca —> Ureteric bud —> touching with the cap ——> upper end of the bud dilates and divides repeatedly to form renal pelvis , major and minor calyces and collecting ducts
Mention the developmental anomalies of ureters :
1) Duplication of the ureters
2) Ectopic Ureters
Why does ureters duplication happen ?
Division of the ureteric bud
Where do ectopic ureters in males open?
1) the neck of the bladder
2) prosthetic part of the urethra
Where do ectopic ureters in females open?
Bladder neck , urethra and vagina
Define Cloaca :
The caudal part of the hindgut derived from the endoderm
What are the divisions of cloaca ? And divided by what ?
Divided into Recto-anal canal ( Posterior part ) and Urogenital sinus ( Anterior part ) by urorectal septum
About The urogenital sinus :
Receives the opening of two mesonephric ducts , and divides into Vesicourethral portion And definitive urogenital sinus then this vesicourethral portion divides into pelvic part and phallic part
Mucosal development of urinary bladder :
Endodermal source : from vesicourethral portion of the urogenital sinus ( except for the trigone and the musculosa )
Mesodermal source : caudal part of mesonephric ducts give rise to the trigone
Adjacent splanchnic Mesodermal source ( mesoderm that surround the gut tube ) : the muscular layer of the urinary bladder
About Urachus : ( Definition and fate )
Definition : unabsorbed part of Allantois
Fate : After birth , it becomes completely obliterated and forms Median umbilical ligament ( Psses from the bladder apex to the umbilicus )
Congenital anomalies of the bladder :
1) Exstrophy of the bladder ( Ectopic vesical )
2) Urethral anomalies ( Cyst , sinus , fistula )
Talk about Exstrophy of the bladder :
It happens when the mesoderm fails to develop the musculature of the infra-abdominal region of anterior abdominal wall AND the anterior wall of the bladder . It is associated with exposure of the urinary bladder mucosa to the outside
About Urachal fistula :
The entire Urachus remains patent with subsequent discharge of the urine through the umbilicus
About Urachal sinus :
The proximal or the distal parts of the Urachus remains patent and when it is distal , it opens in the umbilicus
About Urachal cyst :
Isolated part of Urachus remains patent and the lining epithelium secret fluid
Development of male urethra :
Prosthetic Urethra : A) Mesodermal source;absorped part of mesonephric duct B) Endodermal source;Vesicourethral portion and pelvic part of urogenital sinus
Mambranous Urethra : Pelvic part of urogenital sinus ( Endoderm )
Penile Urethra : Phallic portion of urogenital sinus ( Endoderm ) AND Migrating ectodermal cells ( Ectoderm )
Note : the ectoderm is for the part of urethra inside the glans penis
Steps of penile urethra development:
1) Formation of urethral plate
2) Formation of urethral groove
3) Formation of urethral canal ( Margins of the urethral groove unite to form this canal )
4) A solid cord of ectodermal cells extends from the tip of the glans till it meets the endodermal penile urethra. It is then canalized
Developmental sources of female urethra :
1) Vesico-urethral canal (mainly).
2) Definitive urogenital sinus.
Mention the congenital anomalies of the urethra :
1) Hypospadius
2) Epispadius
Why do hypospedias happen ?
These defects result in failure of canalization of the ectodermal cord in the glans and/or failure of fusion of the urethral folds.
Mention the two types of hypospedias :
1) Glanular hypospedias : The external urethral orifice is on the ventral surface of the glans of the penis
2) Penile hypospadias : The external urethral orifice is on the ventral surface of the body of the penis
