Embryology CVS 1 Flashcards by Anna Coull

what happens in the first major stage of heart development?

primitive heart tube is formed

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what happens in the second major stage of heart development?

heart looping

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what happens in the third major stage of heart development?

atrial and ventricular septation

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what happens in the fourth major stage of heart development?

outflow tract septation

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what happens during week 3 of development (not same as stage 3)

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

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which is the first major system to function in the embryo

cardiovascular system

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when does the primordial heart start to function? why?

at the beginning of week 4

rapidly growing embryo - nutrition diffusion is not enough to satisfy the growing embryo

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where do blood vessels first appear?

in the wall of the yolk sac, allantois, connecting stalk and chorion

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what do angioblastic cords canalize to form?

heart tubes

Angioblastic cords arrange themselves side by side to form the primordia of the endocardial tubes.

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what is the pericardium derived from

intra-embyronic coelem

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what is the visceral layer of serous pericardium derived from?

splanchnic mesoderm

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what is the parietal layer of serous pericardium formed from?

somatic mesoderm

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the tubular heart joins blood vessels in other areas to form what?

primordial cardiovascular system

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where do aortic arches arise from?

aortic sac

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where does the right ventricle and parts of the outflow tracts arise from?

bulbus cordis

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where does the left ventricle arise from

primitive ventricle

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where do parts of the right and left atria arise from

primitive atrium

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where does the superior vena cave and right atrium arise from

sinus venosus

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describe the sinus venosus in the primitive heart tube

it has two horns R and L

each horn gets venous blood from - yolk sac, placenta and body of the embryo

where do the aortic arches terminate

in the dorsal aorta

the bulbus cordis (in the primitive heart tube) and ventricle grow faster than other regions forming what?

a U-shaped bulboventricular loop

Clinical:-

Dextrocardio

congenital disease where the heart tube loops to the right (instead of to the left)

most frequent positional abnormality of the heart

what happens around 27th and 37th days (towards end of 4th week) of embryonic development?

endocardial cushion formation - separates R atrium and ventricle from L atrium and ventricle to form L and R AV canals

septum formation - separates right atrium from left atrium and right ventricle from left ventricle

which 2 septum and 2 foramen form at the end of the 4th week

septum primum
septum secundum

foramen primum
foramen secundum

stage 1 of L and R atria separation

septum primum growth generates foramen primum as it protrudes downwards from top of atrium

stage 2 of L and R atria separation

foramen secundum is formed on the upper end of septum primum (due to cell death)

stage 3 of L and R atria separation

septum secundum grows on the right of septum primum

stage 4 of L and R atria separation

septum secundum grows down and overlaps the foramen secundum. But septum secundum is incomplete - perforated by foramen ovale

where does the foramen secundum open in

the septum primum

where does the foramen ovale open in

septum secundum

role of oval foramen 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

role of oval foramen after birth?

Normally closes (increased pulmonary blood flow and shift of pressure to the left atrium) 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 Non closure results in Atrial Septal Defect (ASD) – “Hole in the heart”

Atrial Septal Defect (ASD)

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

what are 2 most common types of ASD

Foramen secundum defect Endocardial cushion defect with foramen primum defect

3 stages of partitioning of primitive ventricle

1. Muscular ventricular septum forms. Opening is called interventricular foramen 2. 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) 3. Growth of endocardial cushions also contributes to membranous portion of the interventricular septum.

what happens during the 5th week of embryonic development?

aorticopulmonary septum divides BC and TA into aorta and pulmonary trunk

Ventricular Septal Defect (VSD)

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

development of the conducting system of the heart

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

how does cot death or sudden infant death syndrome come about?

abnormalities of conducting tissue

transposition of great vessels - what is it?

abnormal positioning of the great vessels ie aorta coming from left ventricle instead of right etc Associated with ASD and VSD Permit exchange of systemic and pulmonary circulation

cause of transposition of great vessels?

Failure of aorticopulmonary septum to take a spiral course Defective migration of neural crest cells eg. Tetralogy of Fallot

what is tetralogy of Fallot

A combo of 4 cardiac defects: Pulmonary stenosis (obstruction of right ventricular outflow) Ventricular septal defect (VSD) Dextroposition of aorta (“overriding” aorta) Right ventricular hypertrophy

cause of Tetralogy of Fallot

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

causes of congenital heart disease? (5)

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)