6 - Heart Embryology Flashcards
What are the main things that happen in week 3 and 4 in utero?
Week 3 - Week of 3’s, gastrulation
Week 4 - Folding and mesoderm organisation
What does the heart look like before embryonic folding?
Blood islands are two endocardial tubes in the horse shoe cardiogenic field
Why are there so many congenital heart defects?
Development and functioning of heart occurs before woman knows she is pregnant a lot of the time so a lot more chance they will expose themselves to environmental risks
How does folding form the heart?
- Lateral fold: creates a heart tube by joining two endocardial tubes
- Cephalocaudal fold: Brings tube into thoracic region
OCCURS AROUND DAY 22
What is the structure of the primitive heart tube?
Why does the heart fold?
- As embryo gets larger, so does the heart tube and it runs out of space in the pericardial cavity
- Places inflow and outflow in the correct orientation
Where does the transverse pericardial sinus appear from?
Cardiac looping, arteries sitting infront of veins
Where do the right and left atrium mainly develop from?
RA - mainly the primitive atrium and sinus venosus. recieves drainage from coronary sinus and body
LA - mainly pulmonary veins and a small bit of primitive atrium
How does the right atrium vessels form?
- Sinus horns equal
- Venous return increases to rhs so left horn regresses
- Part of right sinus horn absorbed by englarging ra
How do the vessels of the left atrium form?
Sprouting of pulmonary vein from LA that splits into four. Absorption of vessels, making atria quite smooth walled, not rough walled like RA
Where does the oblique sinus come from?
Expanding left atrium as it absorbs the pulmonary veins
How does fetal circulation occur?
Oxygenated blood flows from placenta to umbilical vein where it enters the right atrium via the IVC, blood is then shunted from right to left atrium. Higher pressure in the right atrium than left ventricle
Where are the three places in utero that blood is bypassed and what are the names of the shunts that by-pass this?
- Liver by ductus venosus
- Lungs and right ventricle by foramen ovale
- Lungs by ductus arteriosus
Does any blood flow in the right ventricles in utero?
Yes as if you don’t use the muscle you lose it, however only small amount as can damage lungs
How do the three shunts close?
- FO: Respiration starts and the increase in pressure in the left atrium forces foramen ovale closed
- DA: Ductus arteriosus contracts in response to increase in pO2 as it is smooth muscle
- DV: Ductus venosus closes when placental support removed
How do the main arteries form?
- Initially five aortic arches, 1-6 no 5. Bilaterally symmetrical system of arched vessels
4th arch:
R: proximal part of right subclavian artery
L: arch of aorta
6th arch:
R: pulmonary artery
L: left pulmonary artery and ductus arteriosus
All other arches disappear during remodelling
What happens to the nerves as the heart descends?
Nerves becomes hooked around the 6thaortic arch and turns back on itself. The left recurrent laryngeal nerve hooked on shunt between PT and aorta. If someone is hoarse throated, sign of thoracic issues
What is patent ductus arteriosus?
Where there is still communication between pulmonary trunk and descending aorta due to the failed contraction and closing of the ductus arteriosus.
Blood shunts from left to right so less oxygenated blood reaching systemic.
Mainly occurs in premature babies
How does atrial septation occur?
Step 1: Endocardial cushions develop in the atrioventricular canal, proliferation dorsal and ventrally
Step 2: Two septa and 3 holes
Septum primum grows from roof towards endocardial cushions
Ostium primum present before septum primum fuses with endocardial cushions so blood can shunt R to L
Just before ostium primum closes, ostium secundum appears in septum primum
Crescent shaped septum secundum grows and the hole in this is the foramen ovale
What happens to the foramen ovale after birth?
With the first breath, the pressure changes increase the pressure in the left atrium so that the septum primum is pushed against the septum secundum. Forms fibrous tissue eventually, sealing it shut
What are some atrial septal defects caused by?
- Ostium secundum defect
- Septum primum resorbed or too short
- Septum secundum too small
How does ventricle septation occur?
- Muscular region of ventricle grows upwards towards endocardial cushion leaving small gap, primary interventricular foramen
- Foramen filled by membranous portion from endocardial cushion
What is the most common ventricular septal defect?
Membranous part of septum involved
How does septation of the truncus arteriosus (outflow tract) occur?
Endocardial cushions stagger on the sides of the truncus arteriosus that when proliferate form a spiral septum called the aorticopulmonary septum
What is transposition of the great arteries?
Aorta arises from the right ventricle and pulmonary trunk arises from the left ventricle. Two circuits form where oxygen-poor blood circuits in right side of heart from body to the body and oxygen rich blood travels from lungs to lungs in left side.
Leads to cyanosis and if no other defect allowing mixing of blood, is fatal.
What is Tetralogy of Fallot?
Heart defects caused by:
- Large ventricular septal defect
- Overriding aorta
- Right ventricular outflow tract obstruction e.g stenosis
- Right ventricular hypertrophy
Due to defect in conotruncal septum formation so neural crest cells are defective.
Blue Tet Spells that can lead to syncope
