Embryology of the CVS 1 - Heart Flashcards by Michael Alcorn

What are the 4 main stages of heart devolopment

1) Formation of heart tube
2) Looping of the heart tube
3) Atrial & Ventricular septation
4) Development of the outflow tract

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What structure forms before the heart tube?

Bilateral heart primordia

Two tubes with 4 smaller bridge tubes linking them

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Which mesoderm gives rise to the cardiovascualr system?

Lateral plate splanchnic mesoderm

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In the 3rd week, all the mesoderms etc have formed and the CVS can begin development

Describe how the embryo forms the 2 primitive heart tubes

Angiogenic cells collect in the splanchnic mesoderm

They then move towards to midline

Once at the midline, they coalesce and form the 2 primitive heart tubes

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Why does the CVS develop & start working so early on?

Embryo is growing

Can not satisfy nutritional needs through diffusion

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Creation of the cardiogenic field is a key precursor step to the formation of the cvs

What is the cardiogenic field?

Primitive heart + blood vessels in the embryo

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In the formation of the cardiogenic field:

What areas first develop blood vessels?

The walls of the yolk sac, allantois, connecting stalk and the chorion

Initially, these are not actually linked to the heart

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In formation of the cardiogenic field:

How are the newly formed blood vessels ‘linked’ to the tubular heart?

1) Angioblastic cords form in the cardiogenic mesoderm (3rd week)
2) The cords fold into a tube (canalize) to form heart tubes
3) Heart tubes link up with the blood vessels to form ‘primordial CVS’

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The pericardium forms alongside the primitive heart

What is the pericardium derived from?

Intra-embryonic coelom

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Initially, the pericardium does not contain the heart tube, but is instead the Pericardial cavity

Describe how the 2 structures join each other

Cephalic/cranial folding of the embryo kind of shoves the 2 together

PC moves from dorsal to ventral

Cardiac tube moves from ventral to dorsal

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The pericardium is multilayered

How does each layer form?

Fibrous pericardium + Parietal layer of serous pericardium = SOMATIC mesoderm

Visceral (inner) layer of serous pericardium = SPLANCHNIC mesoderm

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2 important events happen on the 22nd day

What are they?

1) Cranial/cephalic folding begins

2) The 2 Heart tubes start fusing

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The fused primitive heart has 2 ends

What are they?

Cranial end (arterial)

Caudal end (venous)

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Describe the parts of the fused primitive heart

Truncus arteriosus (L&R horns)

Bulbus cordis

Ventricle

Atrium

Sinus venosus (L&R horns)

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Describe the structure & function of the sinus venosus

2 horns

Each horn has 3 veins, receiving venous blood from:

Common cardinal vein
(body of embryo)
Umbilical vein
(placenta)
Vitelline vein
(yolk sac)

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The truncus arteriosus leads into what blood vessels?

Left and right dorsal aortae

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Describe the structure thing that leaves the Truncus arteriosus

Aortic sac with left and right horns

Each horn splits into 6 arches (the top being the 1st)

Aortic arches terminate in left or right dorsal aorta

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Describe the formation of the cardiac (bulboventricular) loop?

Day 22:
- Bulbus cordis & Ventricle expand rapidly and bulge out

Day 23:
- Heart tube droops and loops to the right side

Day 24:
- BC & Ventricle are have sunk down past the atrium

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Abnormal cardiac looping causes ______

Dextrocardia

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Describe how abnormal cardiac looping happens?

Heart tube loops to the left instead of the right

This means it ends up lying facing the right (= dextro)

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Dextrocardia can be associated with what major positional abnormality?

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Situs transversus

all your viscera face the wrong way

When does partitioning of the heart occur?

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27th & 37th days

What are the 2 stages of heart partitioning?

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27th = Endocardial cushion formation

37th = septum formation

What does endocardial cushion formation do?

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Separates the atrium and ventricle

Forms L&R atrioventricular canals

What does septum formation do?

Separates right atrium from the left atrium Separates the left Vent from the right Vent (Forms the two sides of the heart)

Problems with heart partitioning can cause what health problems?

atrial septal defect (ASD) | & ventricular septal defect (VSD)

Describe the process of endocardial cushion formation

Superior & inferior endocardial cushions grow across the common atrioventricular canal Meet & fuse in the middle leave 2 gaps, which are the L&R AV canals

Describe the process of atrial partitioning

Starts at end of 4th week 1) Septum primum grows down from top of atrium. Gap between SP and endocardial cushion = foramen primum 2) Cell death in the SP creates a hole at the top = foramen secundum 3) Foramen primum fuses shut & Septum Secundum begins to grow in the right atrium 4) Septum secundum grows down, Septum primum grows up. The gap between them = Foramen Ovale 5) Top part of SP and bottom part of SS degenerate. Foramen ovale becomes small

Why does the foramen ovale remain open until after birth?

1) When in utero, the baby does not use it's lungs ∴ no pulmonary circulation Oval foramen allows blood flow from right atrium to left atrium ∴ skips pulmonary circulation Once born, baby begins to breathe ∴ hole closes 2) Also prevents blood flow in wrong direction

What is the name given to the opening between the septum primum and the endocardial cushion?

Ostium primum

What changes occur in the atrium post birth?

Foramen ovale closes: - Sept. primum and Sept. secundum fuse together^ - OVAL FOSSA remnant of Foramen Ovale (fossil = fossa)

What is the epidemiology of Atrial Septal defect (ASD)?

One of the most common congenital heart anomalies More common in females Common form - patent foramen ovale

What are the 4 clinically significant types of ASD?

Atrial septal defect: 1) Foramen secundum defect 2) Endocardial cushion defect with foramen primum defect 3) Sinus venosus defect 4) Common atrium The first two types are more common

What happens after the atria have split?

Ventricles split | probably overlaps but hey ho

Describe the process of ventricular septation

Muscular ventricular septum forms. Opening is called interventricular foramen Bottom of spiral aorticopulmonary septum fuses with MVS 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*

Describe how the bulbis cordis and truncus arteriosus are split

During 5th week of development... Aorticopulmonary septum (mad spiral thing) goes up the middle of the BC & TA and creates two sections Two sections: - Aorta - Pulmonary trunk As time goes on, these sort of separate and form two distinct shaped tubes

What congenital heart condition is causes by ventricular septation not reading the textbook

Ventricular septal defect (VSD)

What type of VSD is most common?

Membranous type is most common

Initially, the heart does not have any nodes n shit What acts as the primitive pacemakers?

primitive atrium and then sinus venosus

How does the conducting system of the heart develop?

SA node (pacemaker) develops during 5th week AV node and bundle (bundle of His) develops from cells of AV canal and sinus venosus

What conditions are linked to abnormalities in the development of the conducting system?

Cot death or sudden infant death syndrome (SIDS) Cause – abnormalities of conducting tissue

Overall, what is the fate of the Aortic sac in the primitive heart tube?

Aortic arches

Overall, what is the fate of the Bulbis cordis in the primitive heart tube?

Right ventricle Part of the outflow tract

Overall, what is the fate of the primitive ventricle in the primitive heart tube?

Left ventricle

Overall, what is the fate of the primitive atrium in the heart tube?

Forms parts of the right and left atria

What is the fate of the sinus venosus on the primitive heart tube?

Superior vena cava Right atrium

What are the main causes of 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) *It is multifactorial though*

What is the link between ASD/VSD and congenital heart disease?

VSD and ASD account for ~ 30% of congenital heart disease: VSD for 20% and ASD for 10%.

What are the causes of transposition of great vessels?

1) Failure of aorticopulmonary septum to take a spiral course 2) Defective migration of neural crest cells

Why is transposition of great vessels dangerous?

Permits exchange of pulmonary and systemic blood (oxygenated & deoxygenated blood mixes up) Common cause of cyanotic disease in newborns Associated with ASD & VSD

What is Fallot?

Congenital heart condition made up of several heart defects: - Pulmonary stenosis (obstruction of right ventricular outflow) - Ventricular septal defect (VSD) - Dextroposition of aorta (“overriding” aorta) - Right ventricular hypertrophy

What causes Fallot

Unequal division of the conus due to anterior displacement of aorticopulmonary septum

Embryology of the CVS 1 - Heart Flashcards

(52 cards)