embryology of the heart fetal

Cardiovascular Program Director at WCUI, Los Angeles

  • Dr. Gehan Youssef, MBBCh, RDCS, RCCS (Gigi)

Part 1: Embryology of The Heart

## Overview

  • Topics covered:

    • Basic embryology of the heart.

    • Fetal circulation.

    • Changes at birth.

    Basic Embryology of the Heart

  • Fetal Growth Stages:

    • 3 Weeks:

      • Embryo, known as blastocyst, implants into the uterus.

      • Represents one-sixth of an inch long but rapidly developing.

      • Early formation of backbone, spinal column, and nervous system.

      • Kidneys, liver, and intestines start to take shape.

      • The yolk sac produces blood cells during initial weeks.

    • 7 Weeks:

      • Development of facial features including mouth and tongue.

      • Eyes develop retinal and lens structures.

      • Major muscle systems have developed; fetus begins practicing movements.

      • Fetus has its own distinct blood type, shifting blood cell production from yolk sac to liver.

  • Heart Development Timeline:

    • 18 Days:

      • Formation of the cardiogenic area and primitive blood vessels.

      • Endocardial tubes begin to fuse into a primitive heart tube.

    • 20 Days:

      • Initial structures include truncus arteriosus, bulbus cordis, primitive ventricle, and atrium.

    • Week 4:

      • Looping of the heart occurs leading to further complex chamber formation.

    • Days 21-35:

      • Formation of aortic arches and partitioning of the heart into four chambers: septum primum, right/left atrium and ventricles, tricuspid and mitral valves.

    Septation and Chambers of the Heart

  • Septation Phases:

    • Initial Phase: Endocardial cushions fuse to form medial walls between atria and ventricles.

    • Second Phase: Integration into functional structures including interventricular septum and atrioventricular canals.

    • Final Phase: Normal function established including the closure of foramen ovale, forming a complete partition between oxygenated and deoxygenated blood.

    Development Dynamics

  • Important Structures:

    • Endocardial Cushions:

      • Vital in the formation of heart valves and septa.

      • Helps segregate chambers during developmental phases.

    • Ductus Arteriosus and Foramen Ovale:

      • Critical for fetal circulation; changes post-birth.

Part 2: Fetal Circulation

## Fetal Circulation Before Birth

  • Detailed study of fetal circulatory patterns, including:

    • Oxygenation through the umbilical vein, transporting oxygen-rich blood from the placenta to the fetus.

    • Systemic circulation path from the right atrium to the left atrium through the foramen ovale, significantly mixing oxygen-rich and poor blood due to transitional physiology in fetal lungs, not immediately functional.

    • Ductus arteriosus facilitates connection between pulmonary trunk and aorta, crucial for bypassing non-ventilated lungs.

    Key Vascular Structures:

    • Umbilical Arteries: Returns deoxygenated blood to the placenta.

    • Pulmonary Arteries: Transports blood to lungs, which are not yet functional before birth; hence lower pressures are involved in fetal circulation.

    • Venous Structures: Superior and inferior vena cavas coalesce to facilitate systemic return of deoxygenated blood to the right atrium.

Part 3: Changes After Birth

## Transition to Postnatal Circulation

  • At Birth:

    • Fluid within alveoli is rapidly replaced by air as the newborn takes the first breath.

    • Immediate changes in circulation due to lung expansion and oxygenation occurs.

    • Ductus arteriosus closes, transitioning posterior blood flow and shifting the direction towards the pulmonary circulation.

    • Foramen ovale closes to separate the left and right atrium functionally.

    Major Circulatory Changes:

    • Umbilical structures collapse and seal, raising blood oxygen levels and reducing reliance on placental blood flow.

    • The lung's development is paramount to adapting the systemic and pulmonary circuits within moments after birth.

Conclusion

  • Understanding the embryological development of the heart and the dynamics of fetal circulation provides critical insights into cardiovascular physiology and pathologies. This comprehensive overview from fetal development through postnatal transition is essential for medical professionals working in neonatal care and cardiology.

Visual Aids and Further Reading

  • Videos related to the embryology of the heart and fetal circulation can be found at the links provided in the slides.