development of the heart - session 3 Flashcards
congenital birth defects
- can be
- strucutural abnormalities
- complete absence of a structure
- Result from interference with/ interruption of normal developmental processes
- causes can be
- genetic
- Exposure to chemicals/ drugs/ infectious agents
- unexplainable
congenital heart defects
congenital heartdefects = most common birth defect
Developing heart is subject to same vulnerabilities as all other systems, occurs when there is:
- a structural defect of chambers or vasculature
- there is an obstruction
- communication between pulmonary + circulatory systems
These occur due to additional complexity due to differing circulatory needs of foetus compared to a newborn
cardiogenic field and cardiovascular system (CVS)
- embryo folds in 4th week - cardiogenic field appears -> zone within mesoderm - has capacity to differentiate into cvs in its entirety - heart, vessels, cells etc.
primitive heart tube
- heart develops from precursor= primitive heart tube
- it’s a modified blood vessel with an inlet and outlet
- must be divided into 4 chambers
- blood enters through sinus venosus + moves through without being pumped
cardiac looping
- primitve heart tube undergoes looping as it elongates in order to fit into space of pericardial sac
- twists + folds up which places inflowand outlow tubes in correct orientation with respect to each other
- atrium pushed superiorly and posteriorly
development of the atria
- RA develops mainly from primitve atrium + sinus venosus - RA has rough surface
- recieves venous blood from body (vena cava) + the heart (coronary sinus)
- LA develops mainly from proximal parts of pulmonary vein + a small portion from primitive atrium
- recieves oxygenated blood from lungs + has a smooth surface
conflicting circulatory requirements 1
in mature circulation:
- deoxygenated blood collected frombody - pumped to lungs for reoxygenation +removal of CO2
- reoxygenated blood returned from lungs to heart - pumped around body
but in foetus:
- lungs dont work - oxygenation + CO2 removal occur at placenta - shunts required to maintain foetal life
- these must be reversible at birth
conflicting circulatory requirements 2
- blood enters via umbilical vein- passes through liver
- then shunted into inferior vena cava leading blood to RA
- blood needs to be in LV to be pumped around body so shunted into LV
- some blood shunted to RV for development
fetal circulatory shunts
- Ductus venosus shunts blood from placenta to IVC then into RA
- Foramen ovale shunts blood from RA to LA
- Ductus arteriosus shunts blood from Pulmonary trunk to aorta
At birth, respiration begins increasing left atrial pressure + causing foramen ovale to close. Ductus aretriosus also closes. As the placental support is removed, the ductus venosus closes
aortic arches - aortic development
- early arterial system begins as bilaterally symmetrical system of arched vessels
- undergo extensive remodelling to create the major arteries of the heart
4th arch develops into - left side into arch of aorta
- right side into proximal part of right subclavian artery
6th arch = pulmonary artery - right into right pulmonary artery
- L into L pulmonary artery + ductus arteriosus
Patent Ductus Arteriosus (PDA)
- congenital condition where DA doesn’t close after birth
- means there is persistent cimmunication between aorta + pulmonary artery/ pulmonary trunk
- blood flows from aorta to PA leading to increased vol. + pressure inside the PA
The Foramen Ovale
- 2 walls form between atria; septum … primum + septum secundum - each wall has ostiums (holes) -these don’t line up - allows blood to flow from RA into LA - this is the foramen ovale
- at birth pressure in LA rises above pressure in RA- causes septum primum to push against septum secundum - thus closing flow of blood
atrial septal defect
- There can be a defect in the ostium secundum caused by either the septum primum being too short or resorbed.
- The septum secundum can be too small causing the defect.
Hypoplastic Left Heart Syndrome
- exact cause unknown
- could be from defect in development of mitral + aortic valves which leads o atresia leading to limited flow
- Could be that the ostium secundum Is too small so there’s inadequate flow from right to left in utero – left heart is underdeveloped
the ventricles
- muscular component of ventricular wall grows upwards towards endocardial cushions but leaves small hole called 1º interventricular foramen
- connective tissue from endocardial cushions fills gap
- in ventricular septal defect the CT portion doesn’t form leavinggap in septum
in diagram - endocardial cushions in red
dividing the outflow tract - routing oxygenated and deoxygenated blood appropriately
- blood pumped out of truncus arteriosus (TA) - need to be separated into 2 vessels
- endocardial cushions also appear in TA
- as they grow towards eachother they twist around each other - forming a spiral septum
transposition of great arteries and ventricular septal defect
ventricular septal defect - most commonly membranous portion of intraventricular septum involved
transposition of great arteries
- aorta comes out of the RV and pulmonary artery comes out of the LV.
- blood that goes to the lungs returns and goes back into the lungs again.
- blood that goes to the body comes back and then is returned to the body. The blood isn’t oxygenated.
tetralogy of fallot
- overriding aorta means that the blood doesn’t leave through the pulmonary artery causing an obstruction.
- Other defects seen are ventricular septal defect, right ventricular hypertrophy or pulmonary stenosis
the recurrent laryngeal nerves
- each aortic arch has corresponding nerve
- nerve corresponding to 6th is laryngeal nerve
- right descends to T1-T2, + left descends to T4-T5
- 2 factors influence course of nerve on L + R sides
- caudal shift of developing heart + expansion of the developing neck region
- need for a fetal shunt between pulmonary trunk + aorta
understanding congenital heart defects
aetiology
Aetiology (the causes of a disease) of Congenital Heart Defects::
- Genetic (Down’s, Marfan’s, Turner’s, etc. syndromes)
- Environmental – teratogenicity from drugs, alcohol etc
- Maternal infections – Rubella, Toxoplasmosis etc
A teratogen is an agent that can disturb the development of the embryo or fetus. Teratogens halt the pregnancy or produce a congenital malformation (a birth defect).
Pathophysiology
Pathophysiology – when physiology goes wrong in injury/illness. By understanding normal anatomy physiology, pathological findings become logical
considerations of congenital heart defect pathophysiology:
- RV pumps deoxygenated blood to lungs
- Pulmonary circulation has low resistance
- LV pumps oxygenated blood at systemic blood pressure to Aorta
- Each ventricle is morphologically adapted for its task
Cyanosis
cyanosis - bluish discoloration of skin due to poor circulation or inadequate oxygenation of the blood
- presence of deoxygenated haemoglobin in arterial circulation
- Cardiac cyanosis – deoxygenated blood bypasses lung
- Respiratory cyanosis – inadequate oxygenation of blood
acyanotic heart defects
- blood shunted from left to right
- This can also refer to obstructive lesions such as; aortic, pulmonary, mitral stenosis.
- requires hole, blood from left heart returned to lungs instead of body
- Increased lung blood flow by itself is not damaging but increased pulmonary artery or pulmonary venous pressure is
cyanotic heart defects
right to left shunts - much more complex
- requires hike + distal hole + obstruction
- deoxygenated blood bypasses lungs
examples of both acyanotic and cyanotic in image
atrial and ventricular septal defects
atrial
can be Acyanotic. leads to increased pulmonary blood flow - more blood in the RV. can lead to LV hypertrophy + failure or sometimes pulmonary hypertension.
ventricular
can be Acyanotic. leads to LV overload - increases the pressure in the pulmonary venous system. This eventually leads to pulmonary hypertension.
tetralogy of fallot
As heart is forming, LV + RV separate from each other + the arteries rotate around each other. In tetralogy of Fallot, they haven’t gone quite far enough so pulmonary artery is still slightly over to the right and the aorta is sitting above the ventricular septum which doesn’t close. Thus, the upper part of the heart is rotated to the right a bit
effects; pulmonary stenosis, ventricular septal defect, RV hypertrophy, over-riding aorta
tricuspid atresia
form of congenital heart disease where there is a complete absence of the tricuspid valve –there is an absence of right atrioventricular connection. This leads to a Hypoplastic (undersized) or absent right ventricle
- No RV inlet
- R to L atrial shunt of entire venous return
- Blood flows to the lung via Ventricular septal defect or Patent Ductal Arteriosus
hypoplastic left heart
left heart under-formed
- LV underdeveloped
- Ascending aorta very small
- RV supports systemic circulation
- Obligatory R to L shunt
pulmonary atresia
- no pulmonary valve - no RV outlet
- R to L shunt of entire venous return
- blood flows to lungs via PDA
Natural History of Common Congenital Heart Diseases
see image
