Normal transformation of arterial aortic arches
During individual development (ontogenesis), the arterial aortic arches formed in the embryo undergo drastic changes. Their transformation is strictly programmed and asymmetric in nature.
- I, II, and V pairs: completely regress and disappear in the postnatal period.
- III pair: persists and transforms into the carotid arteries (Carotid arteries), which supply blood to the head.
- IV pair: develops asymmetrically. The right part regresses, while the left part transforms into the main artery of the body—the left aortic arch.
- VI pair: gives rise to the pulmonary arteries (Pulmonary arteries).
As a result of these complex transformations, normal adult mammalian anatomy is established: only two major blood vessels (the pulmonary trunk and the left aortic arch) originate from the heart.
Malformations as recapitulation of ancestral forms
Disruption of the genetic program of vascular development often leads to anomalies that, from an evolutionary perspective, represent recapitulation—the repetition of traits of ancestral classes (specifically, reptiles).
1. Right aortic arch Normally, the right arch of the fourth pair should regress, but in this pathology, the left one disappears instead. As a result, a right aortic arch is formed, which completely corresponds to the normal structure of the reptilian circulatory system.
2. Double Aortic Arch Occurs when both arches of the IV pair (both right and left) persist and develop. This malformation has significant clinical importance: the vascular ring tightly compresses the trachea and esophagus, which are anatomically trapped between the ascending and descending aorta. From a phylogenetic standpoint, this is also a recapitulation of the reptilian circulatory system.
3. Persistence of embryonic ducts (heterochrony)
- Patent ductus arteriosus (Botallo's duct): the commissure between the IV and VI pairs of arches persists (connection of the left aortic arch with the pulmonary artery). This causes a pathological blood shunt and increases pulmonary blood flow. A similar structure is characteristic of turtles.
- Patent ductus caroticus: persistence of the connection between the III and IV pairs of arches (carotid artery and aorta). The hemodynamic consequence is an excessive increase in cerebral blood flow. It is a recapitulation of the lizard circulatory system.
Ontogenetic vascular developmental disorders
Some severe congenital heart and vascular malformations have no evolutionary basis and do not replicate the anatomy of other animal classes. They represent pure ontogenetic disruptions.
Truncus Arteriosus (Truncus Arteriosus) In this malformation, only a single common arterial trunk emerges from the heart, having failed to divide into the aorta and pulmonary trunk during development.
Transposition of the great arteries This pathology is associated with a disruption of the spatial arrangement of structures—heterotopia. As a result of this defect, the great vessels switch places: the aortic arch originates from the right ventricle (instead of the left), and the pulmonary arteries arise from the left ventricle (instead of the right). This malformation is a fatal ontogenetic defect requiring immediate surgical intervention.
Briefly: answers to topical questions
What specific teratogenic factors cause malformations of the arterial arches?
Sources do not specify exact teratogenic factors specifically for arterial arch malformations. It is noted that they occur when the genetic program of arterial arch development is disrupted in combination with the impact of external and internal teratogenic factors.
What hemodynamic disturbances occur in patent ductus arteriosus?
In patent ductus arteriosus, communication between the aorta and the pulmonary artery persists, causing a continuous left-to-right blood shunt. The main hemodynamic disturbances include:
- Pulmonary hypervolemia — blood flow in the lungs increases due to a constant pressure gradient and blood shunting from the systemic to the pulmonary circulation.
- Heart overload — increased workload develops on all chambers of the heart (predominantly the left ones), as well as volume overload of the right chambers with their compensatory hypertrophy.
- Reversal of blood flow — upon exhaustion of compensatory mechanisms, a change in the direction of the shunt (right-to-left) is possible, leading to total heart failure.
To remember the fate of the arches, use the rhyme: "1, 2, and 5 disappear and don't survive. 3 feeds the brain (carotids), left 4 feeds the body (aorta), and 6 goes to the lungs."
Class and exam questions
What happens to the fourth pair of arterial arches normally?
It develops asymmetrically: the left arch forms the left aortic arch, while the right part completely regresses.
Why is the formation of an aortic arch ring dangerous?
If both arches of the fourth pair persist, a ring is formed that physically compresses the esophagus and trachea passing between them.
Which malformation is a recapitulation of the vascular structure of turtles?
Patent ductus arteriosus (Botallo's duct). It arises due to heterochrony and the persistence of the connection between the IV and VI pairs of arterial arches.
What else to study on this topic
- Hemodynamic consequences of patent ductus caroticus
- Heterotopia in transposition of the great arteries
- Comparative characteristics of the reptilian circulatory system and human anomalies
- The influence of internal and external teratogenic factors on the embryogenesis of the aortic sac
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