L3: Fetal circulation and postnatal changes Flashcards
What Is the time of development of the truncus arteriosus?
5th week “Last thing to develop”
What are the steps of development of the truncus arteriosus?
- 2 ridges (Rt & Lt) appear in the cephalic part of TA
- Grow distally, undergo 180 spiraling, and fuse→form spiral aortico-pulmonary septum
- The septum divides TA into ascending aorta & pulmonary trunk.
What are the anomalies of truncus arteriosus?
1- Transposition of the greater vessels (TGA)
2- Persistent truncus arteriosus (PTA)
3- Fallot’s Tetralogy (FT)
What are the characteristics of TGA?
- Failure of the aortico-pulmonary septum to spiral.
- Aorta arises from the RT ventricle & the Pulmonary arises from the Lt ventricle.
- Common cyanotic heart disease.
- Associated with PDA and or, VSD, ASD, to mix oxygenated and deoxygenated blood.
What are the characteristics of PTA?
- Failure of development of the aortico-pulmonary septum.
- TA persist as single trunk overrides both ventricles→ receives mixed blood
- Accompanied by the membranous ventricular septal defect.
What are the Characteristics of FT?
- Anterior displacement of the aortico-pulmonary septum leads to unequal division of the TA.
- May be accompanied with PDA.
- Characters:
1) Pulmonary stenosis.
2) Hypertrophy of the Rt ventricle.
3) Overriding of the aorta.
4) Ventricular septal defect.
What is Fallot’s pentalogy?
FT+ASD
What are the steps of development of the aortic and pulmonary valves?
▪ 4 endocardial cushions; Rt, Lt, Ant, Post developed in the cephalic part of bulbus cordis (BC) at its junction with truncus arteriosus (TA).
▪ The Rt & Lt ridges fused dividing the orifice into anterior→pulmonary, posterior→Aortic orifices
▪ Rotation of aorta and pulmonary trunk 45-degree→ rearrangement of their cusps.
▪ The cusps are hollowed out at their upper surface.
What are the anomalies of aortic and pulmonary valves?
1- Pulmonary stenosis
2- Aortic stenosis
→Partial fusion of the valves
3- Pulmonary atresia
4- Aortic atresia
→Complete fusion of the valves
“underdevelopment of the cusps —-> blood regurgitation”
What is the definition of fetal circulation?
Circulation of the blood between fetus and mother and also through the fetus.
What does the umbilical cord contain at early embryonic life?
- Two umbilical veins: carry oxygenated blood (80%) from the placenta to the fetus (The Rt umbilical vein disappears early).
- Two umbilical arteries: carry non-oxygenated blood (60%) from fetus to placenta.
Describe the fetal circulation
- The Lt. umbilical vein carries oxygenated blood from the placenta → Lt portal vein → ductus venosus → Rt atrium → MOST BLOOD passes from foramen ovale → Lt atrium → Lt ventricle → Aorta → Upper part of the body with well-oxygenated blood.
- SMALL AMOUNT of blood in the Rt atrium (mixed) → Rt ventricle → Pulmonary trunk:
→Small amount supplies the lung
→A large amount passes through the ductus arteriosus → descending aorta → lower part of the body with mixed blood. - The umbilical arteries carry deoxygenated blood from the fetus (internal iliac arteries) to the placenta
What are the changes that happen in fetal circulation after birth?
I. Immediate Changes After Birth:
- Establishment of pulmonary circulation
- Functional closure of foramen oval
- Functional closure of ductus arteriosus
II. Late Fibrotic Changes
- Changes to The left umbilical vein
- Changes to The ductus venosus
- Changes to The ductus arteriosus
- Changes to The umbilical arteries
How is the pulmonary circulation established?
Immediately after birth, exposure to cold & anoxia occurs due to the stoppage of placental circulation → stimulating the respiratory center in the brain stem → establishment of pulmonary circulation.
How is the foreman ovale closed?
This occurs due to:
- Increase pressure in the left atrium (due to establishment of pulmonary circulation)
- Decrease pressure in the right atrium (due to stoppage of blood coming from the placenta)
- this will press the septum primum against the septum secondum leading to firm physiological closure.
