Embryology Flashcards
What is the first organ in the body to develop?
The heart (functions at 4th week) as the rapidly growing embryo requires more nutrition that placenta can provide
What week does the heart tube begin to form?
3rd week
How does the heart tube form?
- Angiogenic cell (blood) islands collect in the lateral plate mesoderm (splanchnic)
- Moves towards midline of the body and coalesce to form two endocardial heart tubes
- After lateral folding, fusion of the endocardial tubes to form the primitive heart tube
- Cranial folding brings the heart tube dorsal to the pericardial cavity
How does the pericardium form?
Serous pericardium (parietal layer) formed from the somatic mesoderm Serous pericardium (visceral layer) formed from the splanchnic mesoderm Pericardial cavity formed from intra-embryonic coelom
What is the pericardial cavity derived from?
Into-embryonic coelom
What occurs at 21 days?
Fused primitive heart tube divides into primitive chambers separated by grooves
What are the 5 sections to the primitive heart tube?
Truncus arteriosus Bulbis cordis Ventricle Atrium Sinus venous
What does the trunchus arterioles divide into?
Two pairs of aortic arches
Describe the structure trunchus arteriosus
Continues cranially with the aortic sac (where aortic arches arise) and terminates in the dorsal aorta and terminates in the dorsal aorta
What 3 veins drain into the horns of the sinus venosus?
Vitelline vv.
Umbilical vv.
Common cardinal vv.
Where does the vitelline vein drain blood from?
Poorly oxygenated blood from the yolk sac
Where does the umbilical vv. drain blood from?
Well oxygenated blood from the placenta
Where does the common cardinal vv. drain blood from?
Returns poorly oxygenated blood from the body of the embryo
Main venous drainage of embryo
Anterior, poster and common cardinal veins drain into the sinus venosus of heart tube
Explain the formation of the cardiac loop
Bubus cordis and ventricle grow faster than other regions from a U-shaped bulboventricular loop - the differential growth rates causes folding to the right
What is the abnormality in Dextrocardia?
Heart tube loops to the left instead of right, so it faces the right instead of the left, so apex beat is on the right
Usually occurs in situs inverses (when all organs reversed)
Describe the steps in the positioning of the primordial heart
- Endocardial cushion formation - separates R and L atrioventricular opening -> R and L AV canals
- Septum formation: separated R + L atria and ventricles
How does the partitioning or the primordial atria occur?
- Septum primum grows from the atria roof and forms Foramen Primum with end. cushion
- Part of septum primum moves down and fuses with endo. cushion between the septum - forms foramen secundum
- Septum secundum forms on the right for septum primum, and overlaps the foramen secundum as it grows towards the endo. cushion
- Foramen ovale formed
Where is the foramen secundum found?
Between septum primum
Where is the foramen ovale found?
Between septum secundum and endocushion
What happens to the foramen ovale after birth?
Close as there is increased pulmonary flow and there is a shift of pressure to the LV
Septum primum and secundum fuse
Becomes fossa ovalis
What is the role of the foramen ovale in the embryo?
Blood bypasses the lungs and moves straight from the RA to the LA as the lungs are not functioning
Prevents back flow of blood
What does the bulbis cordis become in the adult?
Aorta
What does the truncus arterioles become in the adults?
Pulmonary trunk
What does partitioning of the BC and TA occur?
5th week
What are the stages in partitioning of the BC and TA?
- Proliferation of mesenchymal cells (neural crest) in the walls of BC and TA
- Bulbar ridges and truncal ridges form
- They undergo 180 spiralling in formation of aorticopulmonary septum
This septum divides BC and TA into aorta and pulmonary trunk
When does the SA node (pacemaker) develop
During 5th week
What do the AV node and the bundle of His develop from?
Cells in the AV canal and sinus venosus
What causes SIDS?
Sudden infant death syndrome due to abnormal conduction in the heart
What are the more common congenital heart diseases in females?
Atrial septal defect
Patent ductus arterioles
What are teratogens that cause congenital heart disease?
Rubella -> PDA Alcohol -> septal defects Drugs Radiation Genetic (8%) Chromosomal (2%)
How does situs inverses occur?
Autosomal recessive inheritance
What is transposition of great vessels?
I.e. Aorta from RV and pulmonary trunk from LV
Common cause of cyanotic disease in children
Permit exchange of systemic and pulmonary circulation
What causes transposition of great vessels?
Failure of aorticopulmonary septum to take a spiral course
Defective migration of neural crest cells
What is teratology of fallot?
Term used to describe when 4 specific defects are present:
Pulmonary stenosis
Ventricular septal defect
Dextroposition of aorta (overriding aorta)
RV hypertrophy
What causes teratology of fallot?
Unequal division of the conus due to anterior displacement of aorticopulmonary septum
What are the two different methods of blood vessel development?
Vasculogenesis (new formation of a primitive vascular network)
Angiogenesis (growth of new vessels from pre-existing blood vessels)
Describe the formation of the aortic sac
Each endocardial tube has a ventral and dorsal aorta, and when they fuse to form the primitive heart tube, the ventral aorta partially fuse to form the aortic sac (gives rise to aortic arches)
What form the aortic arches from the aortic sac?
Pharyngeal arteries join the aortic branches to form 6 pairs of aortic arches that terminate at the dorsal aorta
What are the fates of aortic arches 1 and 2?
Disappear early, but remnants of the 1st arch form the maxillary artery
What is the fate of aortic arches 3?
Commencement of the internal carotid artery - carotid arch
What is the fate of aortic arches 4?
R - subclavian artery
L - distal part of aortic arch
What is the fate of aortic arches 5?
Either never forms, or forms incomplete and regresses
What is the fat of aortic arches 6?
R - R pulmonary artery of pul. trunk
L - L pulmonary artery and form ductus arteriosus
What is the fate of ductus arteriosus after birth?
Becomes ligamentum arteriosum
What is a common reason for defects with the great arteries occur?
Due to arches that should disappear not regressing, or one that should not regress, disappear
How does the aberrant subclavian artery occur?
When the R subclavian (should come form first branch of arch of aorta, but this defect means it arises from the L side and goes behind trachea and oesophagus (can constrict them)
Regression of the R aortic arch 4 and R dorsal aorta
How does a double aortic arch arise?
Development of abnormal R aortic arch as well as the L aortic arch, surrounding the trachea and oesophagus causing difficulty breathing and swallowing
What is the effect of a patent ductus arteriosus?
Fails to close after brith
First year work of breathing harder and poor weight gain
If uncorrected, can cause heart failure
What is coarctation of the aorta?
Aorta is narrowed around the D. arteriosum inserts - post or pre ductal
What do the umbilical arteries develop form?
Paired branches of the dorsal aorta
What is the fate of umbilical arteries after birth?
Proximal: internal iliac and superior vesical branches (to urinary bladder)
Distal: degenerates and becomes medial umbilical ligaments
Where does the umbilical vein arise from and why does is carry oxygenated blood?
Chorionic villi of placenta and carries oxygenated blood to the RA (to bypass hepatic circulation) -> LA due to foramen ovale (to bypass lungs) then arteries deliver it to body and carry deoxygenated blood to placenta
What is the fate of vitelline veins?
Portal veins
Hepatocardiac channels (liver to heart as part of IVC)
Liver sinusoids
Superior mesenteric vein
What is the fate of umbilical veins?
R vein: generate completely
L vein: obliterates and forms ligamentum teres hepatic (round ligament) of adult liver
What is the function of ductus venosus in the embryo?
Shunts portion of blood of the L umbilical vein blood flow directly to the IVC, this allows oxygenated blood to bypass the liver
What is the fate of the ductus vensosus?
Obliterate and form ligamentum venosum
What is the fair of cardinal veins?
Form vena caval system (SVC and IVC) by anastomosis among the veins
Name 4 venous system abnormalities
Double IVC
Absence of IVC
L SVC
Double SVC
What develops at the end of the 6th week?
Six primary lymph sacs develop at the end of the sixth week around the main veins - end of embryonic period
Describe development of the lymphatic system
Form lymph sac initially and will canalise to form the two main lymphatic channels; thoracic duct and lymphatic duct
What is the function of the ductus arteriosus
Allows blood that escapes the RV (does not pass through the foramen ovale) to bypass the lungs and travel from the pulmonary trunk to the aorta
State the different vessels from LA to the placenta
Aorta Descending aorta Abdominal sorta Common iliac aa. Umbilical aa. - Placenta - Umbilical vv.
What is the effect of patent ductus arteriosus?
Failure of muscular walls to contract
Respiratory distress syndrome (low O2)
Lack of surfactant
What causes coarctation of the aorta?
Incorporation of muscle tissue of DA into arch of aorta (during development), so when DA contracts after birth, part of aorta also constricts
Genetic/environmental factors
