Embryology Flashcards
what layer of the embryo forms the kidneys?
the mesoderm
which part of the mesoderm are the kidneys derived from?
intermediate mesoderm
what are nephrotomes?
segments of the intermediate mesoderm
aka nephric structures
in which direction does development of the nephric structures occur?
craniocaudal
name the three nephric structures formed in the order they appear
pronephros
mesonephros
metanephros
what is another name for the pronephros?
the pronephric system
where does the pronephros form?
the cervical region of the embryo
when does the pronephros undergo segmentation?
the beginning of week four
when does the pronephros regress?
completely gone by the end of week 4
what is another name for the mesonephros?
the mesonephric system
where does the mesonephros form?
the thoracic and lumbar regions
what does the mesonephros form?
mesonephric tubules
these act as temporary excretory units
what are the mesonephric tubules in contact with?
vasculature at one end
mesonephric duct at the other
what is the mesonephric duct?
a longitudinal duct running alongside the intermediate mesoderm, connecting to the developing bladder
what is another name for the metanephros?
the metanephric system
where does the metanephros develop?
the sacral region of the embryo
how many mesonephric tubules are formed?
40
appear in a craniocaudal fashion
what happens to the mesonephric tubules at week 5?
the cranial ones regress, leaving some lumbar ones
when do the mesonephric tubules function?
weeks 6-10
then they regress
when does the metanephros appear?
week 5
what does the metanephros form?
the kidney proper
when does the metanephros begin to function?
between weeks 9-11
what two distinct structures form from the metanephros?
ureteric bud
metanephric blastema
what is the metanephric blastema?
a mass of intermediate mesoderm
what is the ureteric bud?
a outgrowth from the mesonephric duct
what do the metanephric blastema and the ureteric bud form?
the kidney proper
when does the ureteric bud develop?
around day 28
when do the ureteric bud and the metanephric blastema fuse?
day 32
how do the ureteric bud and metanephric blastema develop after fusio?
through reciprocal induction
both send signals to help the other develop
what happens if the ureteric bud and metanephric blastema fail to communicate?
agenesis
what are the two possible mechanisms leading to agenesis in development?
the ureteric bud is not long enough
the ureteric bud fails to develop
what does the ureteric bud form?
the collecting system of the kidneys
how does the ureteric bud form the collecting system?
two cycles of branching and intussusception, followed by a final branching cycle
describe the appearance of the embryonic kidney
very lobulated and lumpy
what does the metanephric blastema form?
the nephrons
what are the four parts of a nephron?
bowman’s capsule
proximal convoluted tubule
loop of henle
distal convoluted tubule
what part of the nephron interacts with the vasculature?
bowman’s capsule
what is the loop of henle divided into?
ascending and descending limbs
when do the kidneys ascend from the pelvis?
weeks 6-9
what is the initial blood supply to the kidneys in the pelvis?
common iliac arteries
what is it called when one kidney fails to ascend?
pelvic kidney
what is it called when the inferior poles of the kidney fuse?
horseshoe kidney
what issue do horseshoe kidneys run into?
cannot ascend, they get trapped under the IMA
what is the cloaca?
an expansion of hindgut endoderm
what are the two divisions of the cloaca?
rectum
primitive urogenital sinus
what divides the cloaca?
urorectal septum
what does the primitive urogenital sinus give rise to?
bladder
pelvic urethra
definitive urogenital sinus
how is the bladder in contact with the umbilical cord?
via the allantois
what is the remnant of the allantois called?
the urachus
