development of the heart and congenital heart diseases session 6
TRANSCRIPT
Development of the Heart and Congenital Heart diseases
SESSION 6
Development of the heart• Week 3• Cardiogenic region appears
– Overlying mesoderm differentiate into myoblasts and blood islands
– Horseshoe region at cephalic end
• Lateral Folding:– Brings the two endocardial tubes together in the
midline– Primitive heart tube
• Cephalocaudal folding: – Brings tube into the thoracic region
Primitive heart tube
Looping• Day 23 – day 28
• Cephalic portion• Ventrally• Caudally• Right
• Caudal portion
• Dorsally• Cranially• Left
What does looping achieve?
• Primordium of RV closest to outflow tract • Primordium of LV closest to inflow tract • Inflow is dorsal to outflow
• Forms transverse pericardial sinus
Atrial Septation• Two septums grow down
towards the endocardial cushions
• The first is the septum primum• Ostium primum (temporary
gap between septum and endocardial cushion)
• Ostium secundum (hole in the septum primum)
• The second is the septum secundum• Foramen ovale (hole in
septum secundum)
Ventricular septation• 2 components:
• Muscular portion• Membranous portion
• Muscular portion• Forms most of the septum• Grows upwards
• Membranous portion• Connective tissue • Grows down from endocardial
cushions
• They meet and fuse
• Defects usually occurs in the membranous parts.
Septation of the outflow tracts• Endocardial cushions appear in
Truncus arteriosus– Requires neurocrest cells migrating into
the heart
• Staggered appearance • They twist around each other
as they grow• Forming a spiral septum
Arches of the aorta
• Arterial systems develop from bilaterally symmetrical systems of arched vessels • 5 arches – 1,2,3,4,6 • 5th one regresses
• 4th Arch• RIGHT arch right subclavian artery• LEFT arch arch of the aorta
• 6th Arch • RIGHT arch pulmonary artery• LEFT arch pulmonary artery & ductus arteriosus
Recurrent Laryngeal Nerve • Each arch of the aorta has a corresponding nerve
• 6th arch recurrent laryngeal nerve
• Laryngeal nerve shifts caudally into thorax • Left larygneal nerve descends to T5- hooks around ductus
arteriosus • Right laryngeal nerve descends to T1/T2
• Laryngeal nerves both loop back up to innervate the larynx
Fetal Circulation
Fetus v. Baby Fetus Baby
Foramen ovale Fossa ovalis
Ductus arteriosus Ligamentum arteriosum
Ductus venosus Ligamentum venosum
Umbilical vein Ligamentum teres
Congenital Heart Diseases
Pressures in the heart
0-8mmHg
1-10mmHg
Diastole: 1-10mmHgSystole: 100-140mmHg
Diastole: 0-8mmHgSystole: 15-30mmHg
Pulmonary ArteryDiastole: 4-12mmHgSystole: 15-30mmHg
AortaDiastole: 60-90mmHgSystole: 100-140mmHg
Congenital Heart Diseases
• Atrial Septal Defects
• Ventricular Septal Defects
• Coarctation of the aorta
• Tetralogy of Fallot
• Transposition of the great vessels
Left to right shunt• Blood in left heart enters the right heart
• Requires a hole between right and left heart• The right heart is at lower pressure than left • If there is an opening blood flows from left to right
• Acyanotic
• Examples• Atrial Septal Defect• Ventricular Septal Defect• Patent Ductus Arteriosus
Atrial Septal Defect • Left to right shunt
• Hole atrial septum • Blood move from the left atria to the right atria
• Caused by failure of closure of:• foramen ovale• Ostium secundum• Ostium primum
• Leads to:• Pulmonary hypertension • Right ventricle overload • RIGHT HEART FAILURE
Ventricular Septal Defect• Left to right shunt
– Hole in intraventricular septum – Blood moves from left ventricle into
the right ventricle
• Caused by: failure of the membranous part of the ventricular septum to develop
• Leads to:– Pulmonary hypertension– Right ventricular hypertrophy– Pulmonary venous congestion– Dyspnoea – LEFT HEART FAILURE
Coarctation of the aorta
• Narrowing of the aorta usually occurring near the attachment of the ductus arteriosus
• Leads to:– volume overload in the heart – congestive heart failure
• Signs and symptoms:– Tachypnoea– Dyspnoea– RADIAL- RADIAL DELAY
Right to left shunt • Blood bypassing the lungs• This requires a Hole and a Distal Obstruction.
– The right heart is usually at a lower pressure than the left– However a distal obstruction in the right heart pressure in right heart
> left heart – Leading to blood flowing from the left to the right
• Cyanosis- Blue discolouration arising due to the presence of deoxygenated
blood in the arteries
• Examples– Tetralogy of Fallot
Tetralogy of fallot1. Overriding aorta
2. Ventricular septal defect (HOLE)
3. Pulmonary stenosis (DISTAL OBSTRUCTION)
4. Right ventricular hypertrophy
Transposition of the great vessels• The aorta and pulmonary artery
are reversed– RVaorta– LV pulmonary artery
• Not viable unless the 2 circuits communicate via: – patent ductus arteriosus– patent foramen ovale– VSD or ASD.
• Allows adequate mixing of blood to:– deliver enough oxygenated blood
to the body
• Treat– Englarging the septal defect and
increasing the mixing of blood