embryology Flashcards
week that gastrulation occurs
week 3
week that heart development begins
week 3
what is the first organ that begins to function
heart
define gastrulation
process of transforming a bilaminar disc (hypoblast and epiblast) into a trilaminar disc (ectoderm, mesoderm, and endoderm)
describe the migration of cells during gastrulation
ectoderm: epiblast cells that do not migrate
epiblast cells that migrate move towards the primitive streak where they invaginate and pass the epiblast layer to become mesoderm or continue downward and replace hypoblast to become endoderm
some epiblast cells migrate through the primitive node to become the notochord
define primitive streak
on the surface of the epiblast layer and is the site for invaginating epiblasts that give rise to the mesoderm and endoderm layers
define primitive node
raised area that surrounds the primitive pit and is located at the cephalic end of the primitive streak
list areas of mesoderm
paraxial, intermediate, and lateral plate (which has somatic and splanchnic layers)
from which area does the cardiovascular system arise
splanchnic lateral plate mesoderm and neuroectoderm (neurocrest cells)
how are neural crest cells important to the cardiovascular development
important in development of the outflow tract of the heart (aorta and pulmonary trunk)
how is the primary heart field developed
cardiac progenitor cells emerge from the primitive streak and migrate bilaterally to the cranial end of the embryo wherere they reside in the splanchnic layer of the lateral plate mesoderm at the most cranial end
how is secondary heart field formed
derives from splanchnic mesoderm of the pharynx and is regulated by neural crest cells (secondary heart field is responsible for lengthening the outflow tract)
two types of body folding, what week does it occur
week 4
cephalocaudal folding: displaces primitive heart inferiorly into thorax
lateral folding: closes anterior wall and endocardial heart tubes become single heart tube
precursor of heart tube
blood islands
ectopia cordis
lateral folding defect
lateral folds do not meet to close ventral (anterior) wall of thorax, heart is outside of body
may be combinded with lateral folding defects of the ventral abdomen
what day does the heart spontaneously beat
day 22
list 5 major dilations cranial to caudal
truncus arteriosus bulbus cordis primitive ventricle primitive atrium sinus venosus (l. and r. sinus horn)
left sinus horn gives rise to:
coronary sinus and oblique vein
right sinus horn gives rise to:
siuns venarum and valves of the coronary sinus and IVC
primitive atrium gives rise to:
trabeculated, muscular components of atria (pectinate muscle)
primitive ventricle gives rise to:
trabeculated, muscular components of the ventricle
bulbus cordis gives rise to:
smooth portions of the ventricles (conus arteriosus, aortic vestibule)
truncus arteriosus gives rise to:
pulmonary trunk and aorta
describe process of cardiac looping
cranial end: folds caudally, anteriorly, and right
caudal end: folds cranially, posteriorly, and left
*apex ultimately points to the left
dextocardia
cardiac looping abnormality
apex of heart points to the right side
describe shunting of sinus venosus
originally: left and right horn each have common cardinal vein, umbilical vein, and vitelline vein
eventually left to right shunting occurs so that venous drainage into to left and right sinus horn is not symmetrical
left horn becomes cornonary sinus and oblique vein
right horn becomes valves of the inferior vena cava and coronary sinus and the sinus venarum
where does the umbilical vein carry blood from
placenta
where does vitelline vein carry blood from
yolk sac and G.I.
how is sinus venosus incorporated into heart
it becomes the smooth wall of the right atrium or the sinus venarum which is between the superior and inferior vena cava
how are pulmonary veins incorporated into the heart
first a single vein branches off of left atrium which divides and divides again resulting in 4 veins and gives rise to smooth wall of right atrium
list all of the pieces that must come tofether for proper separation and alignment of the chambers and outflow tract to occur
endocardial cushions of the atrioventricular region septum primum septum secundum conotruncal ridges of the outflow tract muscular ventricular septum membranous ventricular septum neural crest cells
endocardial cushions
located in atrioventricular and conotruncal regions
required for complete septation of the atria, atrioventricular canal, ventricles, and outflow tract
describe septation of atria
septum primum grows from roof inferiorly towards cushions (ostium primum is opening between cushions and growing septum premum)
ostium secundum forms by cell death in upper portion of septum primum (allows blood to bypass lungs)
septum secundum grows to the right of septum primum and is crescent shaped, leaving foramen ovale to allow blood flow
septum primum is valve of foramen ovale and closes to become fossa ovalis after birth
list causes for atrial septal defect
ostium secundum defect: 70%, most common, escessive cell death of septum prmum or lack of septum secundum
ostium primum defect: 20%, failure of septum primum and endocardial cushions to fuse
sinus venosous defect: 10%, usually associated with partial anamalous pulmonary venous return
soronary sinus defect: 1%
patent foramen ovale
no structural development, the foramen ovale just doesnt close at birth
atrroventricular septum formation
fusion of endocardial cushions
persistent common atrioventricular canal
atrioventricular septum is not formed causing both an ASD and VSD, cushions do not close
tricuspid atresia
right atrioventricular canal does not develop
always accompanied with: foramen ovale patency, VSD, underdeveloped right ventricle, left ventricular hypetrophy
septation of outflow tract
two endocardial cushions are formed and invaded by neural crest cells
grow toward eachother and spiral to form aorticopulmonary septum dividing the truncus arteriosus into aortic and pulmonary trunks
ventricular septation
muscular septum: grows upward from floor but does not separate completely
membranous septum: formed from the prolliferation of endocardial cushions
muscular part, membranous part, and aorticopulmonary septum all fuse creating the entire septum
Ventricular septal defect
most common congenital heart defect
hole can occur anywhere on the septum but most commonly occurs in the membranous portion
eisenmenger syndrome
uncorrected left to right shunt as result of VSD, ASD, or PDA causes pulmonary hypertention and right ventricular hypertrophy
the shunt reverses and deoxygenated blood gets pushed through systemic
what are the 5 terrible Ts
blue babies/ early cyanosis
- tricuspid atresia
- truncus arteriorsus (persistent)
- transposition of great vessels
- tetralogy of Fallot
- total anomalous pulmonary venous return
persistent truncus arteriosus
aorticopulmonary septum does not form to divide the truncus arteriosus into the aortic and pulmonary trunks
transposition of great vessels
aorticopulmonary septum does not spiral
creates 2 separate tracts that never merge
right ventricle empties to body and body returns to right atria
left ventricle empties to lungs which empties to left atria
administer prostaglandins to keep ductous arteriosus open (connection of pulmonary trunk to aorta)
tetralogy of fallot
unequal separation of the conotruncal region
really big aorta and small pulmonary arteries
pulmonary stenosis
right ventricular hypertrophy
overriding aorta
ventricular septal defect
total anomalous pulmonary venous return
pulmonary veins drain into the right atrium or superior vena cava
where do the aortic arches develop
within the mesenchyme of the pharyngeal arches
what week does the development of the aortic arches begin
week 4 and 5
aortic arches branch off of what and end where?
aortic arches branch off of aortic sac and connect posterioly with the dorsal aorta
ductus arteriosus
a fetal shint that connects the pulmonary trunk and arch of the aorta as a route to bypass the lungs
this closes after birth and becomes the ligamentum arteriosum
what nerve wraps around the ligamentum arteriosum and aortic arch
left recurrent laryngeal nerve
what nerve wraps around the right subclavian artery
right recurrent laryngeal nerve
derivatives of 3rd aortic arch
common carotid and first poart of the internal carotid arteries
derivatives of left 4th aortic arch
arch of the aorta from the left common carotid to the left subclavian arteries
derivatives of right 4th aortic arch
right subclavian artery (proximal portion)
derivatives of left 6th aortic arch
left pulmonary artery and ductus arteriosus
derivatives of right 6th aortic arch
right pulmonary artery
coarction of the aorta
stenosis (narrowing) of the aorta proximal or distal to the ductus arteriosus
preductal coarctation
stenosis occurs proximal to ductus ateriosous
difference in blood pressure between upper and lower extremities (higher in upper extremities)
patent ductus arteriosus
differential cyanosis
postductal coarctation
stenosis occurs distal to ductus arteriosus
difference in blood pressure between upper and lower extremities (higher in upper)
collateral circulation to the lower extremities occurs via an anastomosis between anterior intercostals and posterior arteries (rib notching is seen on imaging due to enlarged intercostals)
what would happen if the 4th aortic arch were obliterated
the right subclavian would develop from the right dorsal aorta and with descent of the heart, the right subclavian artery resides nect to the left subclavian and therefore must cross the midline (dysphagia lusoria)
double aortic arch
persistence of the right dorsal aorta which results in a vascular ring around the esophagus
vitelline veins
drain the G.I.
form a plexus around the developing duodenum which then gives rise to the portal vein and its main substituents, liver disrupts the plexus and forms the hepatic sinusoids
enlarges and gives rise to part of the IVC
umbilical veins
form connections with the hepatic sinusoids and lose connection with sinus venosous, the rest of the left umbilical vein is maintained while the right completely regresses
ductus venosous
fetal shunt within liver used to bypass sinusoids
oxygenated blood from placenta –> left umbilical vein -> ductus venosous –> IVC
obliterated after birth, becoming ligamentum venosum
left umbilical vein after birth
obliterated and becomes ligamentum teres hepatis
anterior cardinal veins (derivatives)
drain head and neck
left braciocephalic arises from an anastomosis between left and right anterior cardinal vein
superior vena cava arises from right common cardinal and small portion of the right anterior cardinal vein
internal jugular vein arises from the anterior cardinal veins
saturated blood from the placenta is carried by
umbilical vein
desturated blood returns to the placenta via
two umbilical arteries
list the changes to circulation after birth
closure of distal umbilical arteries –> medial umbilical ligaments
closure of umbilical vein –> ligamentum teres hepatis
closure of ductus venosous –> ligamentum venosum
closure of ductus arteriosus –> ligamentum arteriosum
closure of foramen ovale –> fossa ovalis
which region/layer gives rise to the respiratory system
endoderm and lateral plate mesoderm (both splachnic and somatic)
the lung diverticulum buds off the ______
ventral foregut (at week 4)
which part of the respiratory system is derived from endoderm
lining of the larynx, trachea, bronchi, and lungs
which part of the respiratory system is derived from splanchnic mesoderm
cartilaginous, muscular, blood vessels, and connective tissue elements of the trachea and lungs
describe how trachea and esophagus devide
initially, the trachea and esophagus are in open communication with one another
transesophageal ridges form and grow towards one anotherand fuse to separate trachea and esophagus
upper esophageal atresia and tracheoesophageal fistula
most common deffect of trachea and esophagus separation
a portion of the esophagus is absent (atresia), this results in a blind-ending upper esophagus. the distal esophagus forms an abnormal connection (fistula) with the trachea
air can pass from trachea nto esophagus and stomach (air bubble present on imaging)
swallowing not possible –> polyhydraminos (excessive amount of amniotic fluid)
gastric contents pass into trachea due to fistula which can cause pneumonitis and pneumonia
isolated esophageal atresia
blind-ending upper esophagus
nasoenteric tube coils
swallowing not possible –> polyhydramnios
no connection to the trachea
h-type of tracheoesophageal fistula
esophagus forms an abnormal connection (fistula) with trachea
no esophagel atresia, so continuity through esophagus maintained–> swallowing possible
air can pass from trachea into the esophagus and stomach –> air bubbles
gastic contents can pass into trachea and lungs –> pneumonitis and pneumonia
proximal tracheoesophageal fistula and lower lower esophageal atrasia
esophagus forms an abnormal connection (fistula) to the trachea
swallowing not possible–> polyhydramnios
upper and lower tracheoesophageal fistulas
esophagus forms two abnormal connections (fistulas) with the trachea
air can pass from the trachea into the esophagus and stomach (air bubbles on imaging)
gastric contents can pass into the trachea and lungs –> pneumonitis and pneumonia
no continuity of the esophagus
swallowing not possible –> polyhydramnios
tracheoesophagel partitioning defects are associated with what other birth defects
Vertebral anomoalies anal atresia cardiac defects tracheoesophageal fistula esophageal atresia renal anomalies limb defects
(VACTERL are mesoderm defects)
embryonic period occurs at what week and what occurs during it
week 4- week 6
development of lung bud - formation of segmental bronchi
how many tertiary bronchi in each lung
10 tertiary in right
8 tertiary in left
pericardioperitoneal canals
lateral, longitudinal spaces on either side of the foregut that connect the thorax and abdominal (peritoneal) cavities, tentatively
what are the visceral and parietal pleura derived from
splanchnic mesoderm
pseudoglandular period: when and what happens
weeks 6-16
terminal bronchioles present but not canalized
rspiratory bronchioles and alveoli have not formed
respiration not possible, not compatible with life, no type 1 or type 2 cells present
canalicular period- when and what happens
16-26
terminal bronchioles are canalized (have lumen) and have divided into respiratory bronchioles and the respiratory bronchioles have divided into alveolar ducts
cuboidal epithelium
type 2 cells are present and just enough surfactant is produced around 24-26 weeks so that the earliest premature babies may survive at this time
terminal saccule period: when and what happens
week 26-36
primitive alveoli (terminal saccules) have formed
epithelium has changed from cuboidal to thin, flat cells (type 1 alveolar epithelial cells)
proximity of capillaries has increased
alveolar period (week 36- childhood)
blood-air-barrier is well established (endothelium of blood capillary and thin squamous epithelium)
mature alveoli are formed (increase in type 1 cells)
appropriate amounts of surfactant should be present
the number of alveoli continues to increase years after birth
respiratory distress syndrome
deficiency in surfactant causing alveolar collapse
rapid breathing, grunting
can be treated with artificial surfactant
cause of 20% of newborn deaths
intraembryonic cavity
the space between the visceral (spanchnic) and parietal (somatic) layers of the mesoderm
it is closed when lateral body folds meet to form the anterior body wall
gives rise to pleural, pericardial, and peritoneal cavities
what divides the pleural and ppericardial cavities when lung buds are forming in pericardioperitoneal
pleuropericardial folds
septum transversum
thick, transverse wedge of splanchnic mesoderm that forms to assist in the septation of the intrembryonic cavity into the thoracic and peritoneal (abdominal) cavities
gives rise to part of the diaphragm, specifically the central tendon of the diaphragm
initially forms in cervical region and descends, bringing with it the phrenic nerves (C3-5)
pericardioperitoneal canals
posterior, longitudinal canals connecting the thoracic cavity and peritoneal cavity, left open by septum transversum not fully separating thoracic and peritoneal cavities
what structures make up the diaphragm
septum transversum
pleuroperitoneal folds
a layer of muscular ingrowth from the body wall
connective tissue around esophagus
congenital diaphragmatic hernia
incomplete formation of the diaphragm usually caused by failure of ones pleuroparitoneal membranes to close the pericardioperitoneal canals
GI structures herniate into the thorax and typically impinge upon lung, stunting lung growth: pulmonary hypoplasia (under development of lung)
