Embryology 1 Flashcards
What are the stages of heart development?
Bilateral heart primordia
Primitive heart tube
Heart loobing
Atrial and ventricular septation
Outflow tract and septation
What happens in the 3rd week in cardiovascular development?
Lateral plate splanchnic mesoderm forms circulatory system (and other viscera)
Angiogenic cell islands collect in the lateral plate splanchnic mesoderm, move towards the midline and coalesce to form the two primitive heart tubes
What is the first major system to function in the embryo?
Cardiovascular system
When does the heart start to function?
Beginning of week 4
Why does the embryo need a functioning cardiovascular system at an early stage?
Rapidly growing embryo –
Nutrition by diffusion is not
Enough to satisfy the growing embryo
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Where do blood vessels first appear?
Wall of yolk sac, allantois, connecting stalk and chorion
Where and when do angioblastic cords form?
In the cardiogenic mesoderm in the 3rd week
What do angioblastic cords canalize to form?
Heart tubes
What happens does tubular heart join to?
Blood vessels in other areas to form primordial cardiovascular system
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What does cranial folding of the embryo do?
Reorientates the heart tube dorsal to pericardial cavity
What is the pericardium dervied from?
Intra-embryonic coelom
What is dervied from the somatic mesoderm in the cardiovascular system
The parietal layer of serous pericardium and fibrous pericardium
What happens to the perocardial cavity?
Dorsal to ventral
What happens to the cardiac tube?
Goes from ventral to dorsal
What is derived from splachnic mesoderm?
Visceral layer of serous pericardium
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How many horns are there?
2- left and right
Where does each horn get venous blood from?
Yolk sac
Placenta
Body of the embryo
Where does the yolk sac get blood from?
Vitelline vein
Where does the placenta get blood from?
Umbilical vein
Where does the body of the embryo get blood from?
The common cardinal vein
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Where does the aortic arches arise from?
Aortic sac
Where do the aortic arches terminate?
The dorsal aorta
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What grows the fastest in the growing heart?
Bulbis cordis and ventricle grow faster than other regions forming a U-shaped bulboventricular loop
When does the cardiac crescent occur?
Day 15
When does the linear heart tube form?
Day 21
When does the looped heart tube form?
Day 28
When does the mature heart form?
Day 50
What happens in dextrocardia?
Heart tube loops to the left side (instead of right), thus coming to lie facing the right (= dextro)
Most frequent positional abnormality of the heart
Dextrocardia can be associated with situs inversus (transposition of viscera)
When does the partitioning of the primordial heart form?
Seen around 27th and 37th days of embryonic development.
Involves one or two actively growing masses of tissues.
What happens during endocardial cushion formation?
Separates right atrium + ventricle from left atrium +ventricle to form L&R AV canals
What happens during septum formation?
Separates right atrium from left atrium + right ventricle from left ventricle
What are many cardiac malformations associated with?
Defective formation of endocardial cushion and septum formation, e.g. atrial septal defect (ASD) & ventricular septal defect (VSD)
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What are the stages in the partitioning of primitive atrium into left and right atrium
How does the septum primum form?
End of 4th week
Sickle shaped crest grows from roof of atrium
What is the ostium primum?
Opening between septum primum and enocardial cushion
When is foramen secundum formed?
Formed at the upper end of septum primum
Forms on the right side of the septum primum
Septum secundum grows down and overlaps the foramen secundum.
What is the septum secundum perforated by?
Oval foramen
What is the role of foramen ovale before birth?
Allows most of the blood to pass from the right atrium to the left atrium (non functioning lung)
Prevents the passage of blood in the opposite direction
What is the role of foramen after birth?
Normally closes (increased pressure in the left atrium due to increased pulmonary circulation)
Septum primum (= valve of oval foramen) fuses with the septum secundum
Oval fossa (fossa ovalis) of adult heart is a remnant of foetal oval foramen
What happens if foramen ovale does not close?
Patent Foramen Ovale = Atrial Septal Defect (ASD) – “Hole in the heart”
What is an atrial septal defect?
Common congenital heart anomaly
More common in females than in males
Common form – patent foramen ovale
What are the 4 clinically significant types of ASD?
Foramen secundum defect
Endocardial cushion defect with foramen primum defect
Sinus venosus defect
Common atrium
The first two types are more common
What are the steps in partitioning of the primitive ventricle?
Muscular ventricular septum forms. Opening is called interventricular foramen.
Bottom of spiral aorticopulmonary septum fuses with muscular ventricular septum to form membranous interventricular septum, closing interventricular foramen. (Aorticopulmonary septum divides bulbis cordis and truncus arteriosus into aorta and pulmonary trunk).
Growth of endocardial cushions also contributes to membranous portion of the interventricular septum.
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When does the aorticopulmonary septum develop?
5th week
What does the aorticopulmonary septum divide the bulbus cordis and truncus arterios into?
Aorta and pulmonary trunk
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What is a ventricular septal defect?
Most common type of CHD (congenital heart disease) – 25% of defects
Common in males
Can appear in any part of septum
Small VSDs close spontaneously (30 -50%)
Membranous type of VSD is most common
How does the conducting system of the heart work?
Early pacemakers - primitive atrium and then sinus venosus
SA node (pacemaker) develops during 5th week
Adult location of SA node – High in the right atrium near the entrance of the SVC
AV node and bundle (bundle of His) develops from cells of AV canal and sinus venosus
What is the clinical syndrome of the conducting system of the heart?
Cot death or sudden infant distress syndrome
What are the causes of the conducting system abnormality
Abnormalities of conducting tissue
What does the truncus arteriosus form?
Aorta
Pulmonary trunk
What is the bulbis cordis?
Smooth part of the right ventricle (conus arteriosus)
Smooth part of left ventricle (aortic vestibule)
What is the primitive ventricle?
Trabeculated part of right ventricle
Trabeculated part of left ventricle
What does the primitive atrium form
Trabeculated part of right atrium
Trabeculated part of left atrium
What does the sinus venosus form?
Smooth part of right atrium
Coronary sinus
Olique vein of left atrium
What is aetiological factors in congenital heart disease?
Rubella infection in pregnancy (PDA)
Maternal alcohol abuse (septal defects)
Maternal drug treatment and radiation
Genetic - 8%
Chromosomal – 2% (Down’s and Turner’s syndrome)
What percentage of congenital heart disease are accounted for by VSDs and ASDs
30% of congenital heart disease: VSD for 20% and ASD for 10%.
Girls have ASDs twice as often as boys
VSDs are also slightly more commonin female patients than in male patients
What is transposition of great vessels?
Common cause of cyanotic disease in newborn infants
Associated with ASD and VSD
Permit exchange of systemic and pulmonary circulation
What are the causes of transposition of great vessels?
Failure of aorticopulmonary septum to take a spiral course
Defective migration of neural crest cells
What are the 4 cardiac defects of the teratology of fallot?
Pulmonary stenosis (obstruction of right ventricular outflow)
Ventricular septal defect (VSD)
Dextroposition of aorta (“overriding” aorta)
Right ventricular hypertrophy
What are the causes of the teratology of fallot?
Unequal division of the conus due to anterior displacement of aorticopulmonary septum
