embryo Flashcards
urinary system develops from
intermediate mesenchyme (primordial embryonic connective tissue consisting of mesenchymal cells)
during horizontal folding of embryo, mesenchyme is carried
ventrally + loses connection with the somites
longitudinal elevation of mesoderm is called the
urogenital ridge
urogenital ridge forms
on both sides of the dorsal aorta
part of urogenital ridge that gives rise to urinary system is called
the nephrogenic cord
urinary system develops (before or after?) the genital system
before
urinary system consists of the
kidneys, ureters, urinary bladder and urethra
what are the 3 sets of successive overlapping kidney systems developing in embryos
pronephroi, metanephroi and mesonephroi
the pronephroi are
the first set and rudimentary
end of 3 weeks - 6.5 weeks (3.5 weeks total)
the mesonephroi are
the second set and function briefly after the early fetal period
late in 4th week - 8th week (function for 4 weeks)
the metanephroi
are the 3rd set and form the perma kidneys
begin to develop at 5 weeks and become functional at 9 weeks
kidneys develop from 2 sources
- ureteric bud = metanephric diverticulum
2. metanephrogenic blastema = metanephric mass of mesenchyme
ureteric bud is an outgrowth from
the mesonephric duct
outgrowth = diverticulum
metanephrogenic blastema is derived from
caudal part or nephrogenic cord
the blastema is a
metanephric mass of mesenchyme
mesonephric kidneys consist of
glomeruli (10-50 per kidney) and mesonephric tubules
mesonephric tubules open into
bilateral mesonephric ducts (originally pronephric ducts)
mesonephric ducts open into
the cloaca
mesonephric ducts degenerate towards
the end of the 12th week
even though mesonephric ducts degenerate, metanephric tubules become
the efferent ductules of the testes
mesonephric ducts have several adult derivatives in males
stalk of ureteric bud becomes
the ureter
what part of the ureteric bud undergoes repetitive branching to become collecting tubules
the cranial part of the bud
first 4 generations of collection tubules do what to form the major calices
they enlarge and become confluent
what forms the major calices
the enlargement and confluence of the first 4 generations of collecting tubules
the second 4 generations coalesce to form
the minor calices
what forms the minor calices
the coalescence of the second 4 generations of the collecting tubules (aka the major calices)
what does the end of each arched collecting tubule do
induces growth of clusters of mesenchyme cells in the metanephrogenic blastema
what do clusters of mesenchyme cells in the metanephrogenic blastema form
small metanephric vesicles
what do the metanephric vesicles become
metanephric tubules
how do the small metanephric vesicles become metanephric tubules
they elongate
as branching continues, some metanephric mesenchyme cells condense and form
cap mesenchyme cells
what happens to cap mesenchyme cells
they undergo mesenchymal to epithelial transition
what do the cap mesenchyme cells become
majority of the nephron’s epithelium
what invaginates the proximal ends of the tubules
glomeruli
tubules differentiate into
proximal and distal convoluted tubules
what constitutes a nephron
the nephron loop (loop of henle)
the glomerulus
the glomerular capsule
what does a urineferous tubule consist of
- a nephron = derived from metanephrogenic blastema
2. a collecting tubule = derived from ureteric bud
number of glomeruli grows gradually during the
10 - 18th weeks
number of glomeruli grows rapidly when
from 18 - 36th week (upper limit is reached)
nephron formation is completed when
at birth (in non premature births)
fetal kidneys are subdivided into
lobes
lobulation of fetal kidneys disappears when
usually at end of 1st year of infancy
why does lobulation of fetal/ infant children disappear
nephrons increase and grow
what causes increase in kidney size after birth
elongation of the proximal convoluted tubules + increase in interstitial tissue
when does functional maturation of kidneys + increasing rates of filtration occur
after birth
when does glomerular filtration begin
at approx 9th fetal week
what is the branching of ureteric bud dependent on
induction by the metanephric mesenchyme
what does the metanephric mesenchyme induce
the branching of the ureteric bud
differentiation of nephrons depends on
induction by the collecting tubules
what do the collecting tubules induce
the differentiation of the nephrons
what two structures are involved in reciprocal induction
the ureteric bud and metanephrogenic blastema
what process are the metanephrogenic blastema and the ureteric bud involved in
reciprocal induction = interact and induce each other
to form the perma kidneys
nephrogenesis begins
around the beginning of 8th week
metanephric tubules connect with the collecting tubules to form
the uriniferous tubules
suprrarenal glands are usually (large/small) compared to the kidneys at a fetus
large: they will become smaller during first year of infancy
why do kidneys gradually relocate to the abdomen and move farther apart
because the abdomen and pelvis begin to grow so there is space
the ascent of the kidneys during development results from
growth of the embryo’s body, caudal to the kidneys
what initially faces ventrally during the positional changes of the kidneys
the hilum
what is the hilum of the kidneys
the entry and exit site for blood vessels, ureter and nerves of the kidneys
what happens to the position of the hilum as the kidneys relocate
the hilum rotates medially 90 degrees
how does the hilum rotate during kidney relocation
rotates medially 90 degrees
when are the hila (plural of hilum) directed anteromedially (final position)
by the 9th week
kidneys are (sub/retro/pre/intra) peritoneal structures
retroperitoneal: located outside and behind the peritoneal space
shape of left suprrarenal gland
crescent shape
shape of right suprrarenal gland
pyramidal
renal arteries initially grow from the
common iliac artery
as kidneys ascend, the stop receiving blood from common iliac arteries and begin receiving it from
the distal end of the abdominal aorta
when kidneys are located at a high level, they receive new arterial branches from the
aorta
what happens to caudal branches of the renal vessels after kidney ascension
caudal branches of renal vessels undergo involution (shrinkage) and disappear
when do the positions of the kidneys become fixed
once the kidneys meet the suprrarenal glands
when do the kidneys meet the suprrarenal glands
in the 9th week
the (right/left) renal artery is longer and more superior
right
percentage of adult kidneys with 2 - 4 renal arteries
25%
from where do accessory renal arteries arise
the aorta (superior or inferior to main renal artery)
accessory renal arteries arise (superior/inferior) to the main renal artery
either superior or inferior, can vary
accessory renal arteries are also known as
supernumerary renal arteries
accessory renal arteries
a) follow the main renal artery through the hilum into the kidneys
or
b) enter the kidneys directly through superior or inferior pole
both A and B are correct
supernumerary renal arteries enter the kidney through the (superior/inferior) pole
can enter through either pole
hydronephrosis is caused by
an accessory renal artery entering through the inferior pole (polar renal artery) and crossing anterior to the ureter = obstructing ureter
in hydronephrosis, the supernumerary renal artery crosses (anterior/posterior) to the ureter
anterior = obstructs the ureter
hydronephrosis causes
swelling of the kidney as the urine cannot be drained out
swelling of the kidney is caused by
hydronephrosis
distension of the renal pelvis and calices by urine is associated with
hydronephrosis (swelling of kidney bc urine cant be drained)
accessory renal arteries are
end arteries
what happens if an accessory renal artery is damaged/ ligated
part of kidney supplied by it will become ischemic (blood flow AKA oxygen flow is reduced/ restricted)
accessory arteries are (more/less) common than accessory veins
more: approx 2 times more common
suprrarenal glands can be divided into 2 parts
cortex and medulla
origin of cortex of suprrarenal glands
develops from mesenchyme
origin of medulla of suprrarenal glands
derived from an adjacent sympathetic ganglion
how does the cortex of suprrarenal gland begin developing
begins as an aggregation of mesenchyme cells on each side of embryo (between root of dorsal mesentery and developing gonad)
when are the suprrarenal glands simply aggregations of mesenchyme cells
during the 6th week
when do the neural crest cells differentiate into secretory cells of the suprrarenal medulla
as they are surrounded by the cortex
how is the cortex enclosed
mesenchymal cells arise from mesothelium and enclose it
where do neural crest cells form a mass to create the medulla of suprrarenal gland
on the medial side of the embryonic suprrarenal cortex
when do the neural crest cells form a mass on the suprrarenal cortex
at 7 weeks
what are the 3 layers of the suprrarenal cortex
from most inwards to outwards:
- zona glomerulosa
- zona reticularis
- zona fasciculata
what is the zone between the permanent cortex and fetal cortex of suprrarenal glands called
transitional zone
indentified by immunohistochemical studies
from what is the zone/ layer is the zona fasciculata derived
the transitional zone
what 2 layers of suprrarenal gland cortex are present at birth
zona glomerulosa and zona reticularis
what layer of suprrarenal gland cortex is not present at birth
zona fasciculata
when is the zona fasciculata recognizable in the suprrarenal gland cortex
at the end of the 3rd year of infancy
relative to body weight, suprrarenal glands are … times (smaller/larger) than in adult glands
10 - 20 times larger
why are the suprrarenal glands so large compared to the kidneys during development
bc of extensive size of fetal suprrarenal cortex = cortex produces steroid precursors
what are the steroid precursors secreted by fetal suprrarenal glands used for
used by placenta to synthesize estrogen
medulla is relatively (small/large) during development
small: will grow after birth
why will the suprrarenal glands rapidly become smaller
bc the fetal cortex will regress during 1st year of infancy
when will the fetal suprrarenal cortex regress
during the 1st year of infancy
glands lose approx … of their weight during the 2-3 weeks post birth
1/3 (one third)
when do suprrarenal glands lose approx 1/3 of their mass
during the 2-3 weeks post birth
when do the suprrarenal glands regain the 1/3 mass lost during 2-3 weeks post birth
end of 2nd year of infancy
what happens at the end of the 2nd year of infancy
the suprrarenal glands have regained the mass lost during 2-3 weeks post birth
urogenital sinus has 3 parts
vesical part
pelvic part
phallic part
what does the vesical part of urogenital sinus do
vesical part: forms urinary bladder and is continuous with the allantois
what is continuous with the allantois
the vesical part of the urogenital sinus
what does the pelvic part of the urogenital sinus do
pelvic part: becomes urethra in neck of bladder
- in males = prostatic part of urethra
- in females = entire urethra
what does the phallic part of the urogenital sinus do
phallic part: grows towards the genital tubercule
- primordium of the penis OR clitoris
from what does the bladder develop
the vesical part of the urogenital sinus
entire epithelium of bladder is derived from
endoderm of the vesical part of urogenital sinus
endoderm of vesical part of urogenital sinus forms
the epithelium of the bladder
endoderm of vesical part also known as
ventral part of cloaca
other layers of wall (not epithelium) of bladder develop from
the adjacent splanchnic mesenchyme
adjacent splanchnic mesenchyme forms
the other layers (not epithelium) of the bladder wall
allantois is
a fetal membrane developed from the hindgut
initially bladder is continuous with
allantois
allantois will constrict and become a thick fibrous cord called
the urachus
the urachus is formed by
the allantois (after it constricts and forms a fibrous cord)
the urachus extends from … to the …
from the apex of the bladder to the umbilicus
in adults, the urachus is represented by
median umbilical ligament
what used to be the median umbilical ligament
the urachus
why are distal parts of the mesonephric ducts incorporated into dorsal wall of bladder
bc the bladder begins enlarging
what happens when the bladder begins growing in size
distal parts of mesonephric ducts begin incorporating into the dorsal wall of bladder
connective tissue in the trigone of bladder is formed by
the absorption of the mesonephric ducts which were incorporated into the dorsal wall of the bladder
when do the ureters open separately into the bladder
as the mesonephric ducts incorporated into dorsal wall of bladder are absorbed
the orifices of the ureters move … and enter … through bladder base
move superolaterally and enter obliquely through bladder base
why do orifices of ureters move superolaterally and enter obliquely through bladder base
partly bc of traction exerted by kidneys as they ascend
in males, what happens to the orifices of the ureter ducts
orifices move closer + enter prostatic part of urethra + caudal ends of ducts develop into ejaculatory ducts
in females, what happens to the distal end of the mesonephric ducts
they degenerate
where is the bladder in infants and children
in the abdomen (even when empty)
when does the bladder begin to enter the greater pelvis
at 6 years old
when does the pelvis enter the lesser pelvis (and become a pelvic organ)
after puberty
the apex of the bladder in adults is continuous with what structure
the median umbilical ligament
the median umbilical ligament is continuous with what structure
in adults
the apex of the bladder
where does the median umbilical ligament extend in adults
posteriorly along the posterior surface of the anterior abdominal wall
what extends posteriorly along the posterior surface of the anterior abdominal wall in adults
the median umbilical ligament
from what is the epithelium of most of the male and the entire female urethra derived
endoderm of the urogenital sinus
the endoderm of the urogenital sinus derives what structure
- most of the male urethra
- the entire female urethra
distal part of urethra in glans penis is derived from
a solid cord of ectodermal cells (which grow inwards from the tip and joins rest of spongy urethra)
solid cord of ectodermal cells forms what structure
the distal part of the urethra in the glans penis (which grows inwards from tip of glans penis to rest of spongy urethra)
how does the solid cord of ectodermal cells that forms distal part of urethra in the glans penis grow
grows inwards from tip of glans penis to rest of spongy urethra
what grows inwards from tip of glans penis to rest of spongy urethra
a solid cord of ectodermal cells which forms the distal part of urethra in the glans penis
from what is the terminal part of the urethra derived
from surface ectoderm
surface ectoderm will form
the epithelium of the terminal part of the urethra
connective tissue and smooth muscle of urethra for both sexes is derived from
splanchnic mesenchyme
splanchnic mesenchyme will form the
connective tissue and smooth muscle of the urethra for both sexes
