Q.53 The perforation between left and right atria of a fetal heart is known as
1. Foramen ovale
2. Ductus arteriosus
3. Fossa ovalis
4. Ligamentum arteriosum
The perforation between the left and right atria in a fetal heart is the foramen ovale, enabling oxygenated blood to bypass the lungs. It typically closes post-birth, forming the fossa ovalis.
Fetal Circulation Shunts
Fetal heart has three shunts bypassing non-functional lungs: foramen ovale (atria), ductus arteriosus (pulmonary artery-aorta), ductus venosus (vena cava-portal).
Foramen ovale shunts oxygen-rich placental blood from right to left atrium via septum primum/secundum flap valve.
Birth pressure changes seal it functionally; anatomical fusion later.
Correct Answer: 1. Foramen ovale
Foramen ovale is the interatrial opening allowing ~30% right-to-left shunt during gestation.
Postnatally becomes fossa ovalis; patent foramen ovale (PFO) occurs if unfused (~25% adults).
Option Breakdown
| Option | Description & Role | Correct? |
|---|---|---|
| 1. Foramen ovale | Interatrial fetal shunt; oval flap between septa. | Yes |
| 2. Ductus arteriosus | Connects pulmonary artery to aorta; shunts to systemic circulation. | No |
| 3. Fossa ovalis | Postnatal remnant/scar of closed foramen ovale. | No |
| 4. Ligamentum arteriosum | Fibrous remnant of closed ductus arteriosus. | No |
Postnatal Changes
Lung expansion drops pulmonary resistance; left atrial pressure rises, pressing septum primum against secundum to close foramen ovale.
Failure causes PFO (stroke risk); ductus closes via O₂/smooth muscle constriction.
