Foetal circulation

30.3.06

Cardiovascular system
• Vasculogenesis.
• Early circulation.
• Foetal circulation.

Vasculogenesis
• Day 17.
• Wall of yolk sac.
• Splanchopleuric mesoderm form aggregations of cells.
• Blood islands.
-Core of haemoblasts.
-Surround of endothelial cells.
-Haemoblasts - embryonic blood cells.
-Endothelial cells - blood vessel endothelium.
-Blood vessel endothelia elongate.
-Interconnected mesh.
-End week 3: vascular network around yolk sac, connecting stalk and chorionic villi.
• Angioblastic cords - throughout germ disc.
• Angioblastic plexuses.

Growth of circulatory system
• Continued formation and fusion of angiocysts.
• Angiogenesis - budding and sprouts of new vessels.

Cardiogenic area

Heart development
• Two tubes.
• Fusion.
• Single chamber.
-Sinus venosus.
-Atrium.
-Ventricle.
-Bulbus cordis.
-Truncus arteriosus.
• Chamber elongates - restricted by volume of primitive pericardial cavity.
• Develops kink.

Circulation
• Blood from placenta → primitive heart → dorsal aortae → umbilical arteries → tertiary villus → umbilical veins → sinus venosus → primitive heart.
• Vitelline vessels give rise to portal vein.

Placental structure
• Blood pumped in spurts into intervillous space.
• Vessels on maternal side separate entities that pump maternal blood to placenta.
• Branches increase surface area - each branch contains mesh of capillaries.
• Embryonic tissue forms septa - strengthen placenta (cotyledons) - seen on maternal side.

Foetal haemoglobin - hypoxia countered by
• γ chains in haem.
• Carry more O2 - greater affinity for O2.
• 180gl-1.
• Greater cardiac output.

Umbilical cord
• Begins as connecting stalk.
• 2 arteries, 1 vein (right umbilical artery disappears).
• Set in gelatinous substrate - mucoid connective tissue.
• → ductus venosus.
• Bowels herniated into umbilical cord, then come back into abdomen later in development.
• Umbilical vein → north towards liver → shortcut: ductus venosus → inferior vena cava.

Veins

Portal vein

Bilateral symmetry and regressions
• Arterial system - regresses on right.
• Venous system - regresses on left.

Limb vessels
• Primary - axial artery.
• Axial artery rearranged into minor vessels.
• Secondary vessels form major vessels - new development from primary vessels.

Arch arteries
• Trucus arteriosus → 6 arch arteries (number 5 doesn't develop in humans) → aortic trunk → divides into 2 flows.
• Give rise to adult vessels.
-IV and VI important.
-I = maxillary artery.
-IV = arch of aorta on left, subclavian on right.
-VI = ductus arteriosus on left (shunt between pulmonary circulation and systemic circulation).

Foetal circulation
• IVC.
• Right atrium.
• Foramen ovale (shunt between right and left atria).
• Left side.
• Head and brain.
• Right side.
• Pulmonary trunk.
• Ductus arteriosus.

Infant circulation.

Auscultation.