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What are the three divisions of organised mesoderm?
1) paraxial
2) intermediate
3) lateral plate
What structures does the paraxial mesoderm form?
majority of the skeleton, skeletal muscles and the dermis of the skin
What structures does the intermediate mesoderm form?
gonads, internal reproductive tract and kidneys
What structures does the lateral plate mesoderm form?
lining of the body cavities
Where is the intermediate mesoderm located?
Between paraxial and lateral mesoderm
During which week of development do the nephric structures begin to form?
week 4
What are the 3 nephric structures?
1) pronephros
2) mesonephros
3) metanephros
True or false: the development of the nephric structures is progressive and overlaps
true
Where are all the nephric structures derived from?
intermediate mesoderm
On what day of development does the pronephros disappear?
day 25
Describe the formation of the pronephros and its function:
the intermediate mesoderm in the cervical region condenses, it is non-functional but forms epithelial buds called nephrotomes
Where is the mesonephros derived from?
the intermediate mesoderm in the upper thoracic to lumbar region
Which vertebral levels are the kidneys found?
T12-L3
In which direction does condensation of the nephric structures take place?
cranial to caudal
Describe the formation of the mesonephric ducts:
the intermediate mesoderm in the lower cervical region is induced to epithelise, forming a solid mesonephric duct which develops caudally until it fuses with the cloaca followed by canalisation
On what day do the mesonephric ducts fuse with the cloaca?
day 26
What is the cloaca?
Common opening for excretory, digestive, and reproductive products
What process induces the formation of mesonephric ducts?
formation of the mesonephric ducts
Describe how renal corpuscles are formed from the mesonephros:
mesonephric tubules from the mesonephric duct differentiate and lengthen rapidly to form an S-shape and Bowman's capsule which is filled with a tuft of capillaries at the medial end, forming the glomerulus
What is a renal corpuscle?
glomerulus and bowman's capsule
Where do renal corpuscles empty into?
the cloaca via the mesonephric duct
What range of weeks do the mesonephric renal corpuscles function, producing small amounts of urine?
week 6 to 10
What does the mesonephric duct regress to in males?
vans deferens
What does the mesonephric duct regress to in females?
nothing
Where does gonadal development take place?
urogenital ridge
What is the urogenital ridge?
longitudinal elevation of intermediate mesoderm on the medial aspect of the mesonephric ridge
On what day does the metanephros form?
day 28
Which of the nephric structures forms the definitive kidney?
metanephros
What is the name of the structure that forms the collecting portion of the kidneys?
ureteric buds
What is the name of the tissue that forms the excretory portion of the kidneys?
metanephric mesenchyme
What makes up the collecting portion of the kidneys? (4)
1) collecting ducts
2) ureter
3) major and minor calyces
4) renal pelvis
What makes up the excretory portion of the kidneys? (4)
1) Bowman's capsule
2) proximal convoluted tubule
3) loop of Henle
4) distal convoluted tubule
On what day do the ureteric buds penetrate the metanephric mesenchyme?
day 32
What three things are stimulated by the signalling between the ureteric buds and metanephric mesenchyme?
1) specific branching of the tubule
2) differentiation of the cells in the metanephric cap to form renal vesicles
3) the renal vesicle expanding to form the S-shaped tubule and Bowman's capsule
What are metanephric tissue caps?
coverings on newly formed collecting tubules that form renal vesicles
What causes duplication of the ureter?
premature bifurcation of the ureteric bud
What are the two types of ureter duplication?
partial or complete
What is meant by an ectopic ureter?
a ureter that doesn't end up at the bladder but somewhere else like the urethra or vagina
What is renal agenesis?
failed development of one or more kidneys and their associated collecting components
What causes renal agenesis? (2)
1) early degeneration of the ureteric buds
2) failed interaction between the ureteric bud and metanephric tissue cap
True or false: renal agenesis affecting one kidney is usually asymptomatic other than hypertrophy of one of the kidneys
true
True or false: complete renal agenesis (absence of both kidneys) is compatible with life
false
What is oligohydramnios?
too little amniotic fluid
Why is their oligohydramnios in renal agenesis?
urine is excreted into amniotic fluid
What effect does oligohydramnios have on the foetus?
causes Potter sequence (flattened head and poorly developed hands)
Describe recessive congenital cystic kidney disease:
severe cysts on the collecting ducts
Describe the dominant congenital cystic kidney disease:
cysts form on all parts of the nephron
What is a horseshoe kidney?
inferior poles of both kidneys fuse- during the ascent from the pelvis in development, the horseshoe kidney gets trapped under the inferior mesenteric artery
At what vertebral level do horseshoe kidneys reside?
L3
True or false: horseshoe kidneys are usually asymptomatic
true
What enables the relocation and ascent of the kidneys?
growth and elongation of the developing foetus
During what week of development do the kidneys reach their adult positon?
week 9
During what weeks does the cloaca divide?
weeks 4 to 7
What two structures are formed by the division of the cloaca?
1) urogenital sinus
2) anal canal
What structure separates the cloaca into the urogenital sinus and anal canal?
urorectal septum
Where is the allantois found?
superiorly extended from the cloaca
What does the upper part of the urogenital sinus form?
urinary bladder
What does the pelvic part of the urogenital sinus form?
urethra
What does the phallic part of the urogenital sinus form? (2)
1) penile urethra in men
2) vestibule in women
What forms when the allantois is obliterated?
urachus
Where is the urachus located?
between the apex of the bladder and the umbilicus