The foramen ovale of the foetal and neonatal foal.

The research investigates the structure and function of the foramen ovale in foetal and newborn horses. The study was conducted on the hearts of 24 foals, using electron and light microscopy to understand how the foramen ovale behaves and changes over time.

Research Methodology

• Hearts from 24 foals were analyzed; 10 of these were from foetuses at various gestation periods, and the rest from newborn and young foals up to 17 days old.
• The main research tools were scanning electron microscopy for the broad observation of the foramen ovale and its related structures, and light and transmission electron microscopy for detailed observations.

Findings and Observations

• In all samples, researchers detected a tube-like flap of tissue stretching from the opening in the caudal vena cava (a large vein carrying deoxygenated blood into the heart) to the lumen of the left atrium (a chamber on the left side of the heart).
• In younger foetuses, the end of this tube was shielded by a delicate tissue network, though this was replaced by distal fenestrations (small openings or holes) in individuals closer to term.
• Protrusions were identified on the edge of the tube’s opening as it entered the atrium.

Interpretation and Significance

• The alterations observed in the tube-like tissue, specifically the replacement of the tissue network with fenestrations as the foetus matured, indicate a changing function of the foramen ovale towards birth. In mammals, the foramen ovale allows blood to bypass the nonfunctional lungs in the foetus, and it usually closes shortly after birth when the lungs become functional.
• The presence of protrusions at the rim of the tube’s opening into the atrium as well as the existence of cardiac muscle and non-elastic connective tissue in the tube’s wall may play roles in the closing of the foramen ovale post-birth.
• This research provides significant insight into the structural and functional transformation of the foramen ovale from a foetal to a postnatal stage, which is crucial for understanding normal heart development and diagnosing diseases related to the foramen ovale’s function in horses and potentially other mammals.