Embryology 2 Flashcards
Septation
Septum present in Interatrial septum
Septum present in Interventicular septum
Septation of ventricular outflow tract (where the ductus Arteriosus was present as fetus)
pulmonary trunk
aorta
Septum present t
The inter-atrial septum - separation - Step 1
First thing to appear is the Endocardium cushions - developing in the AV region
Divides the developing heart into right and left channels within the primitive heart
Atrial septation
Division of the common atrium involves formation of two septa with
Atria summary
Both left & right atria have components derived from the primitive atrium (i.e. auricles)
The right atrium absorbs the sinus venosus
The left atrium sprouts the pulmonary vein then grows to absorb it and its first 4 branches
Interatrial septum forms to divide the chamber into left and right chambers
The fossa ovalis is the adult remnant of the shunt used in uteroto by- pass the lungs
Left side of heart atria is smooth as its developed from a vein not from heart material
When first breath is taken and pressure in LA is greater than pressure in RA, the septum primum is pushed against the septum secundum closing this gap - as the two holes dont align - no blood passes through
Atrial septal defect
Ostium secundum defect
Could be due to the septum primum being resorbed or too short
Or the septum secundum being too small
Essentially blood flows from LA to RA
Hypoplastic left heart syndrome
Exact cause not known
Some embryological speculation……..
could be a defect in development of mitral and aortic valves which results in atresia and Limited flow
could be that the Ostium secundum is too small
Either one of the theories would lead to there being = right to left flow inadequate in utero
And seeing as in Utero the use it or loose it rule applies - the left heart becomes underdeveloped
Development of the ventricles
Ventricular septation:
Starting with a single ventricular chamber
Ventricular septum forms, which has 2 components
Muscular
Membranous,
Muscular portion forms most of the septum and grows upwards
towards the fused endocardial cushionss
Primary interventricular foramen
Muscular portions grows upwards towards the endocardial cushions leaving a small gap, the 1st interventricular foramen
Membranous portion of the interventricular septum formed by connective tissue derived from endocaridal cushions to “fill the gap”
Ventricular septal defect
(Most commonly) - membranous portion of interventricular septum involved - the portion of ventricular septum coming from the atrial cardiac cushions
If this occurs deoxygenated blood from the right and oxygenated blood from the left mix and a mixture of the 2 enter both the pulmonary artery and the aorta
If this occurs then Dividing the outflow is key - getting the plumbing right - routing oxygenated and deoxygenate blood appropriately
Separation of the outflow tract
Endocaridal cushions also appear in the truncus arteriosus
As they grow towards each other they twist around each other
Which forms a spiral septum
Ventral wall of RV and Truncus Arteriosus removed
Eventually the aorticopulmonary septum forms - separating the aorta and the pulmonary artery - these two twist around each other
Congenital birth defects
Can be - structural abnormalities or complete absence of a structure
Result from interference with / interruption of normal developmental processes
Causes can be
genetic
exposure to chemicals / drugs (warfarin) / infectious agents (e.g. rubella)
unexplained
Congenital heart defects
The developing heart is subject to the same vulnerabilities as all other systems
Occur when there is:
a structural defect - of the chambers or of the vasculature
There is an obstruction There is communication between pulmonary and systemic circulations because - additional complexity due to the differing circulatory needs of the fetus as compared to the newborn (mature)
Overview of congenital heart defects
Congenital heart defects are the most common birth defect
Worldwide incidence 1%
90% survive to adulthood
Compared to just 20% in the 1950s - large increase in ability to manage these symptoms
What are the implications of this?
135000 young people and adults living with congenital heart defects in England
e.g. pregnancy
Most common cause of indirect maternal death
Medications used to manage heart disease highly teratogenic - therefore need to be aware that drugs given to mum will affect baby and vice versa
Transposition of great arteries
This occurs when aorta comes from RV and pulmonary artery comes from LV
Which leads to -
1) Due to no pressure change the foramen ovale stays open - therefore presenting an atrial septal defect
2) Aorta sends blood from RV to body
3) Due to no pressure change the ductus Arteriosus stays open a as well
4) Pulmonary trunk arises from left ventricle
Without the septal defect and patent ductus Arteriosus - life isn’t viable as heart would have 2 systems - oxygenated blood circulating around just the lungs and deoxygenated blood just circulating around the body - at least with the defects some oxygenated blood leaks into systemic circulation
What will happen?
Cyanosis (bluish cast to skin and mucous membranes)
Depending on what other if any defects are present
Likely to relate to the development of the aortic and pulmonary values which need to be carefully positioned to ensure normal
Tetralogy of fallot
4) Large ventricular septal defect - due to overriding aorta the mucosal membranous part of the ventricular septum and the muscular part of the ventricular septum dont fuse causing a ventricular septal defect
3) Overriding aorta - could be congenital which leads to (1)
1) Right ventricular outflow tract obstruction - due to pulmonary stenosis or aortic overgrowth during fetal development
2) Right ventricular hypertrophy - due to the build up of pressure present in the RV due to lack of blood flow through the pulmonary artery
Overall this means that deOx and Ox blood mix going into systemic circulation - therefore lethargy and blood problems could present
Conotruncal septum formation defective
• Importance of neural crest cells
