Embryology Flashcards
Cloaca
terminal portion of the hindgut, an endoderm lines cavity that is in direct contact with surface ectoderm. divides into two canals: one for solid and one for liquid waste
formation of greater omentum
dorsal mesogastrium buldge down over colon and SI to form a double layer sac greater omentum is the fusion between the two sheet.
what are the linings of the lungs?
endoderm lined splanchinic lateral plate mesoderm on outside
umbilical or vitelline fistula
vitelline duct remains patent over its entire length, connects umbilicus to intestinal tract. fecal discharge at umbilicus
Fixation of midgut
As intestines sit in final positions, mesenteries press against back wall of abdominal cavity. Ascending colon, duodenum become retroperitoneal The rest of the midgut (jejunum and ileum, cecum, appendix) are interperitoneal
Mesenteric changes of midgut
Descending and ascending get into position, they press against peritonum and become retroperitoneal. appendix, cecum and sigmoid are intermesternic.
Formation of perineal body
At week, fusion of urorectal spetum with cloacal membrane to divide into anal membrane and urogential membrane.
testicular migration
develop in lumbar region on dorsal abdominal wall as pelvis enlarges and trunk enlarges, gubernaculum does not grow and testes descend through inguinal canal during week 28 and takes 2-3 days move beneath peritoneum and behind processus vaginalis
what does the umbilical vein form?
Round ligament
Mesonephric duct
what drains urine in the mesonphric state. participate in the formation of the male genetical system by forming the ductus deferens and epididymis.
Mesentary proper
grows into jejunal and ileum SM a midgut region
what does foramen ovale form?
fossa ovalis
primary intestinal loop
forms during midgut physiological herniation. Part of the intestines that projects into the umbilical cord Upper arm is small intestines lower arm is terminal ileum, cecum, appendix and asecneding and part of transverse colon
anterior urorectal sinus
forms the primitive urogenital singus
Gonad development stepwise
1) primordial germ cells migrate to site of future gonadal ridge from near allontis to lumbar region 2) PGC induces thickening of gonadal ridge 3) week 6: PGC invade genital ridge and becomes enveloped by sex cords. 4) through reciprocal induction of PGC and cords, the gonad begins to develop.
pseudoglandular
first stage developing tissues resemble glands, but no gas exchange
Development of stomach
Due to differing growth rate foregut caudal to diaphragm grows faster and causes stomach to rotate right and caudal end to swing cranially thus what was left is anterior, and what is anterior is the lesser curvature
Cloacal membrane
composed of endoderm of the cloaca and ectoderm of anal pit.
Renal agenesis
failure to form kidneys because there was never a pronephric kidney. could be one side or both sides (both sides is not conducive to life)
what layer in the urinary system derived from
intermediate mesoderm - plate lying between paraxial mesoderm and lateral plate mesoderm and the cloaca`
Dorsal mesoduodenum
grows into duodenum CT
Cardiac looping
Cardiac loop bends at heart lengthens cranial goes ventrally, caudally to the right caudal, goes dorsal cranially and to the left Begins day 23 ends day 28
mesentary
double layers of peritoneum that enclose an organ or connect to body wall derived from splanchnic lateral plate mesoderm both dorsal and ventral mesentary
Dorsal mesocolon
grows into colon IM a Hindgut region
pronephric duct
formed during pronephro stage formed by union of mephrotomal vesicles that progress toward cloaca. The pronephros are though to induce mesonephric duct formation
formation of pancreatic duct
merging of vetnral and dorsal pancreatic buds. incomplete fusion can lead to accessory ducts
Formation of sex cords
in week six, primodridal germ cells invade genital ridge and become incorporated into sex cords. These proliferate and grow from coelmic epithilium into underlying mesenchyme. sex cords become the seminiferous tubules in males and medullary cords in females
Urorectal septum
ridge of mesenchye between the allontiois and hindgut. As is grows caudally to cloacal membrane, divides cloaca into anterior and posterior part.
Ductus venosus
To avoid umbilical blood through liver sinusoids bypasses heptaic portal from umbilical vein to IVC
Hepatic diverticulum
connects proximal 1/3 of duodenum with the stomach grows into ventral mesogastrium gives rise to gall bladder and bile ducts
what does ventral mesentary form?
lesser omentum falciform ligament
splanchinic mesoderm lining
forms smooth muscles, connective tissues and mesentary
parietal mesothilium
parietal peritoneal lining, on anterior body wall
Cranial folding for the heart development
Folding brings right and left endocardiotubes together Day 18-22
Dorsal mesogatrium
Dorsal mesentary that gives rise to the greater omentum Branches of Celiac trunk
Meckels diverticulum
condition where connection to yolk sack via vitellie duct persists for longer than usual and a remnant of the vitelline duct remains. Causes vitelline cysts (enteroceystoma) that contain gastric of pancreatic mucosa leads to bleeding and perforation
Basic development of urinary system
three kidney system; metanephros is preceded by 2 transitionary kidneys 1) pronephros 2) mesonephros 3) metanephros
allantois
connection between urinary bladder and amniotic space becomes a fibrous cord after birth called the urachus.
gubernaculum
a ligamentthat descends on each side of the lower poles of the testis/ovaries and passes obliquely down abdominal wall and attaches to labioscrotal swellings
Endoderm lining
forms lining of glands and gut tubes
terminal sac
third stage of lung development increased number of terminla sac, and alveoli can perform gas exchange
Reduction of midgut hernia
Intestines return to abdomen week 10 Jejunum returns first and settling behind SMa. The rest undergoes at 180 counterclockwise rotation to place cecum and appendix near right lobe of liver where they descend into right fossa. Total rotation is 270° it returns due to decrease in relative size of liver and mesophrenic kidneys, as well as abdominal enlargement and expansion
Pancreas development
ventral pancreatic bud in the ventral mesogastrium dorsal pancreatic bud int he dorsal mesogastrium as the dorsal bud grows, it rotates left and it retroperitoneal. Ventral bud (uncinate process) grows and rotates left 270° to fuse with dorsal bud
cord cells of ovary
forms follicular cells that surround oocyte
uteric bud
an outgrow of the mesonephric duct also called metanephric diverticulum branches to produce factors that produce the metanephric blastoma gives rise to ureter, renal plevis, renal calyces, collecting tubes and ducts.
Pronephros
primitive and non-functional kidey Begins at beginning of 4th week and ends at end of 4th week At level c5-c7
primordial germ cells
from indifferent genital stage originate in epiblast and migrate to wall of yolk sac near origin of allantois.
mesencyme cells of ovary from
stromal cells - supportive cells of ovary
Development of testis
due to XY composition 1) Y chromosome releases a SRY (transduction factor on Y chromosome) 2) that signals the release of the TDF (testis determination factor) 3) directly causes cord cells to transform into sertoli cells that support spermatogenesis and make up furture efferent ductules. 4) the Sertoli cells release a mullarian inhibitory factor that triggers the aponeurosis of the mullarian ducts. 5) TDF also indirectly gives rise of leydig cells from mesencyme. 6) leydig cells release testosterone to promoe external genetalia and male genital ducts
rotation in umbilical cord of proximal intestinal loop
fortates 90° around axis of superior mestenteric artery so that the proximal limb is on the right and distal limb is on the left. This is when branching of the SMa occurs.
posterior urorectal sinus
forms the anocrectal canal
ventral mesentary
exists only in foregut (esophagus, stomach and upper duo) due to extension of septum transversum associated with liver, bilary tree, ventral pancreas grow into it
Compartmentalization of intraembyonic coelom
Pleuropericarinal exens anteriorly to close the pericardioperitoneal canal. This is moving towards the septum transversum.
lower arm of midgut loop
terminal ileum, cecum, appendix, colon
Respiratory diverticulum
ventral out-pocketing of the foregut
What happens to dorsal mesentary in 5th week?
extends from esophagus to cloacal region and forms: dorsal mesogastrium dorsal mesoduodenum dorsal mesocolon mesentary proper
somatic lateral plate mesoderm
Mesoderm in contact with ectoderm
ascent of the kidney
metanephric kidneys ascent from pelvic region to the thoracolumbar level as embryo elongates and grows caudally. during ascent, kidney gets vascularized by continually higher levels of aortic branches.
what is formed as a result of cranial folding?
1) septum transversus 2) pleuroperitoneal membranes 3) dorsal mesentary of esophagus 4) body wall mesoderm
At the anus
the surface of skin is contiuous with the perineum and surrounding tissue is derived from splanchnic mesencyme Supplied by inferior rectal a and internal pudendal n.
Umbilical vein
delivers O2, nutrient rich blood from placent to fetus to enter ductus venosus
Foramen Ovale
bypasses pulmonary circulation, left atrium to right atrium
what forms the prostate
at 3 months, epithelium of cranial part of urethra prolifates and forms a outbudding of mesenchyme.
order of the cariac tube
most cranial is right ventricle, then left ventricle, then aortas are separated at the most caudal end.
Formation of anal canal
upper 2/3 are from hind gut and lower 1/3 from proctoderm ectoderm (or the area around the cocoal membrane)
splanchnic lateral plate mesoderm
mesoderm in contact with endoderm
what does the ductus arteriosus form?
ligamentum arteriosum
development of female external genetalia
due to the absence of androgens 1) genital tubercle elongates slightly to form clitoris glans 2) urogential sinus remains open with urethra and vaginal openings separated 3) urogential folds form labia minora 4) labioscoral swellings remain unfused except for most anterior and posterior sites to form labia majora
Metanephros period
permanent and function kidney develops in pelvic region starts Week5, functions week 9-10 develops from uteric bud and metanephric blastema
Hindgut gives rise to….
left 1/3 to transverse colon, descending colon, sigmoid, rectum, upper portion of anal canal, and lining of bladder and urethra.
Visceral mesothilium
is the visceral peritoneal lining that forms around gut tubes and posterior body wall
how are uterine tubes formed
from unfused mullarian ducts at cranial end
Congenital diaphragmatic hernia
when pleuroperitoneal folds do not fuse completely with septum trasnversum organs fill the open space
Mesonephric diverticulum/trigone formation
formation of the uteric bud on the posterior wall of urogenital sinus at sight of bladder. Thus the mesonephric ducts and ureters are side by side on posterior bladder. as bladder grows, mesonephric ducts get pulled down and incorporated into posterior wall. uterine bud gains independent opening on cranial and lateral side. mesonphric ducts open caudally to bladder in urethra (in males). female mesonephric ducts deteriorate trigone formed
Fixation of hindgut
mesentery fuses with peritoneum in the descending colon to make it retroperitoneal. But the mesentery of sigmoid colon persists - intraperitoneal
Development of ovaries
1) no Y chromosome means no SRY o 2) no SRY means no TDF 3) no TDF means no Mullarian Inhibiting factor, thus mullarian ducts grow and differentiate. 4) no TDF means low testosterone inhibits/regresses the formation of mesonephric ducts –> female genetalia.
Alveolar stage
final stage in lung development drastic increase in the number of alveoli
Male external genetalia
antrogens from testis induce the: growth of the genital tubercle to form the penis extension of the urogential folds to cover the shaft of the penis and fuse at the urogential groove. and the swellings and fusion of the labiosacral folds to from the scrotum. closes the urthetra plate inside, so that the ureter is internal
at what day do primary bronchials form?
28
Umbilical artery
delivers fetal blood that is deoxygenated to placenta from internal iliac a.
Mesonephros
temporary and function Week 4 - Week 10 (functional between 5-10) During pronephro regression, mesonephros appear from intermediate mesoderm to form function nephrons that filter embryonic blood and generate urine.
superficial ring
opening of inguinal canal in external oblique aponeurosis
Deep inguinal ring
opening in transversalis fascia
how are urogential ridges formed?
the nephrogenic cords producte bilateral longitudinal bulges on the dorsal wall of the coelomic cavity. (just outside the umbilicus)
Upper arm of midgut loop
Small intestines
After cranial folding:
cardiogenic field is more cranial than septum transversum intraembryonic coelom is folded inferiorly
Indifferent gential stage
formed by two types of cells: primordial germ cells and nutrient supportive cells (follicular (w) or sertolid (men)
what does umbilical artery form
medial ligaments
esophageal atresia
abnormal separation of esophagus and trachea inability to swallow
Metanephric blastema
caudal most portion of intermediate mesoderm stimulates uterine bud to continue to branch and grow stimulated by uteric buds to form nephrons (proximal and distal convoluted tube, loop of henle, bowman’s capsule)
Innervation of the diaphragm
Phrenic n. C3-5
Wolffian vs mullarian ducts
wolffian are from the mesonphric ducts created during the mesonephric stage mullaraian are from the paramesonephric ducts which develop due to longitudinal invagination of the epithelium at anterior surface of urogential ridge.
Formation of bile duct
grows in ventral mesogastrium rotates left 270° to enter duodenum from posterior and left
Formation of anal opening
Mesenchyme around anal membrane (region around cloaca) raises the surrounding ectoderm to form an anal pit. The swellings are called anal folds. the anal membrane ruptures to establish the orifice of the anal canal that opens to the amniotic cavity.
Vitelline duct in midgut looping
distal tip of midgut loop is still attached to yolk sac via vitelline duct that connects to the yold sac
urogential sinus division
urinary zone (region above mesonphric ducts continuous with allantois) middle or pelvic zone genital zone: region below mesonephric ducts close by urogenital membrane.
tracheoesophageal fistula
incomplete separation of esophagus and trachea aspirating stomach acid into lungs
Pectinate line
where the anal pit ectoderm and hindgut endoderm meet at the level of the semilunar valves. Former site of anal membrane. Epithelium changes frol columnar to stratified squamous
Endocardial tube
vasculogenic cell clusters line this area above oropharyngeal membrane in splanchinic lateral plate mesoderm.
vasculature of developing heart
3 paris of veins drain into primitive heart 1 artery (aortic sac) leaves it.
Omephalocele
When intestinal loops are not pushed back into the stomach after physiological herniation. Herniated loops are covered in amnion instead of skin.
Midgut formation
Rapid elongation of the yolk sac, leaving abdominal cavity to small and must hernaiate out of umbilical cord during week 6. Week 10 it returns.
What is the septum transversum?
forms the central tendon of the diaphgram
how is omental bursa formed?
stomach rotation causes dorsal mesogastrium to pull greater curvature to left and pulls visceral mesogastrium to the right.
Hirschsprung disease
congential anglionic megacolon due to absence of parasympathetic ganglia from neural crest cells on bowel wall (usually distal colon) can’t participate in peristaltic movement, fecal matter accumulates
Steps of lung development
1) lung bud pinches off foregut below future larynx to separate from esophagus. 2) repeated limb bud branching 3) repeated branching of respiratory diverticulum 4) Terminal branches differentiate into alveoli
what day does secondary bronchials form?
30
Ducts to the hingut
allantois ventrally and mesonphefric laterally
ovarian migration
uterine tubes were initially verticle, but during development of uterus move toward interior abdominal cavity and become horizontal Ovary is temporarily found cranial to UT on posterior body, but moves to posterior and inferior of UT
What forms the right ventricle
bulbus cordis
Umbilical herniation (physiological herniation)
process by which midgut forms by protruding intestines outside body cavity in a u-shaped umbilical loop (space of extraembryonic coelom. From weeks 6-10
Hindgut portion of anal canal
supplied by inferior mesenteric artery and made of endoderm from yolk sac
urthral plate in males
becomes the penile urethra with invagination by the urgential folds. does not reach tip of penis, needs ectodermal thickening ot extend out.
Reciprocal induction of metanerphric blastema and uteric bud
they both induce each other to create their determined factors. metanehoric blastema is the nephron uteric bud is the renal pelvis
what does vaginal process become
tunica vaginalis
tracheoesophageal ridge/septum
ridge between lung bud and esophagus during lung formation
Stages of lung development
1) pseudoglandular 2) canailcular 3) terminal sac 4) alveolar stage
Cecum development
due to cecum diverticulum in week 6 on the caudal limb of the midgut just beyond apex of loop.
processus vaginalis
from peritoneal sac develops ventral to gubernaculum and herniates through lower abdominal wall carries extensions of abdominal wall before it, and there for forms the walls of the inguinal canal (which forms coverings of testis and speramatic cord)
how is uterus formed
fusion of caudal ends of mullarian ducts. (caudal to cranial)
male vs vemal sex differentiation
all due to Y chromosome Male: mesophrenic duct proliferates to form DD; mullarian degenerates female: mullarian duct proliferates to form uterus, uterine tubes and vagina, mesonephric duct degenerates
formation of gonadal ridge
during week 5 primordial germ cells mifrate along dorsal mesentery of hindgut to lumbar region of developing embryo, causing the coelomic epithelium (lining of mesonephric duct) to thicken and form the gonadal ridge.
Coelom formation
cranial folding to change what is caudal and cranial
what forms the bladder?
The urogentical sinus that formed to the growing of the urogential septum mesencyme to divide the cloaca into two parts.
how is vagina formed?
caudal end of fused mullarian duct contacts bladder and lengthens through proliferation. Fuses with urogential sinus posteiror wall of urogenital sinus thickens to form a vaginal epithelial plate that curves to form a canal.
Before cranial folding:
spetum transversum (most cranial) cardiogeneic field (more caudal) intraembryonic coeolm is flat
what does the ductus venosum form?
ligamentum venosum
what do the mesonephric ducts form?
epididymis and ductus deferens
Ductus arteriosus
bypasses pulmonary circle from pulmonary artery to aorta
canailcular
second stage of lung development terminal sacs begin to form, but not enough for 02 exchange
how are urinary system and genital system related
very closely! both develop from common mesodermal ridge along post. ab. wall excretory ducts initially both enter cloaca cavity.
what day does tertiary bronchials form?
38
when is genetic sex determined
fertilization, but gonads do not acquire male or female morphological changes until 5-6 week of development.
