The Aortic Arches

Objectives

Describe the formation of the aortic arches. Enlist the derivatives of aortic arches. Discuss the development of venous system

of the heart. Differentiate between fetal and neonatal

circulation. Discuss the congenital anomalies of the

aortic arches.

Aortic Arches The aortic arches are a series of

paired arterial channels encircling the embryonic pharynx

They: Develop in the 4th week Supply the developing

pharyngeal arches Arise from the aortic sac Run dorsally, embedded in the

mesenchyme of the pharyngeal arches and

Terminate in the right and left dorsal aortae

Develop in a craniocaudal sequence

There are potentially six pairs, but the fifth pair is poorly developed and disappears soon after formation

Not all the 6 pairs present at the same time. By the time the 6th aortic arches are formed, the 1st & 2nd have disappeared

In the region of aortic arches, the dorsal aortae remain paired, but caudal to this region they fuse to form a single median vessel

Aortic --sac

During week 6 to 8, the primitive aortic arch pattern is transformed into the adult arterial arrangement of carotid, subclavian, and pulmonary arteries

Derivatives of Aortic Arches

First Pair Largely disappear Dorsal part persists

as the maxillary arteries which supply the ear, teeth and muscles of the eyes and face

May give rise to the external carotid artery The first arch is obliterated before

the 6th arch is formed

Second Pair

Largely disappear Dorsal part persists

as the hyoid and stapedial arteries

Third Pair

Proximal part: forms the common carotid arteries

Distal part: joins the dorsal aortae to form the internal carotid arteries

Fifth Pair

Disappears completely with NO vascular derivatives

The fate of 4 & 6th pairs of aortic arches differs on the right and left

side

Fourth Pair

RIGHT: Becomes the proximal part of the right subclavian artery

LEFT: Forms part of the arch of aorta

Arch of Aorta

Derived as: Proximal segment

from aortic sac Middle segment from

the left 4th aortic arch Distal segment from

the left dorsal aorta

Subclavian Artery

The right subclavian artery formed from the: Right 4th aortic arch Right dorsal aorta & Right 7th

intersegmental artery The left subclavian

artery formed from the left 7th intersegmental artery

Sixth Pair RIGHT:

• Proximal part: persists as the proximal part of the right pulmonary artery

• Distal part: degenerates LEFT:

• Proximal part: persists as the proximal part of the left pulmonary artery

• Distal part: forms ductus arteriosus, a shunt between pulmonary artery and dorsal aorta

Changes in the original aortic arch system

Obliteration of:

1. Most of the 1st & 2nd arches

2. 5th arches completely

3. Distal part of the right sixth arch

4. The segment of both aortae lying between the 3rd & 4th arches

5. The segment of right aorta lying between the 7th intersegmental artery & the fused dorsal aortae

Relation of recurrent laryngeal nerves to the aortic arches

Anomalies of the Aortic Arches

Coarctation of Aorta Characterized by narrowing of aorta More common in males Classified as Preductal & Postductal

types, but mostly the constriction lies distal to the origin of subclavian artery opposite the ductus arteriosus (Juxtaductal)

Preductal type: Less common. The narrowing is proximal to the

ductus arteriosus. If severe, blood flow to the aorta

distal to the narrowing (supplying lower body) depends on a patent ductus arteriosus, and hence its closure can be life-threatening.

Postductal type Most common. The narrowing is distal to the ductus

arteriosus. The ductus usually remains open to

communicate pulmonary artery with the descending aorta

Even with an open ductus arteriosus blood flow to the lower body can be impaired.

Allows development of collateral circulation during the fetal period. The collateral circulation will develop mainly by branches from both subdavian arteries, scapular, internal thoracic and intercostal arteries.

It is associated with notching of the ribs, hypertension in the upper extremities, and weak pulses in the lower extremities.

Right Arch of Aorta Occurs when the entire right aortic arch persists &the segment of left dorsal aorta distal to the 7th intersegmental artery involutes

TYPES: Without retropharyngeal component: The DA passes from right pulmonary artery to right arch of aorta. No effect on the trachea & esophagus

With retropharyngeal component: The right arch lies posterior to esophagus. The attachment of DA to distal part of the arch of aorta forms a ring around the trachea & esophagus and may lead to their compression

Double Arch of Aorta Characterized by a vascular

ring encircling the trachea and esophagus, usually causing compression of both structures.

The degree of compression varies

Usually the right arch is larger and passes posterior to the esophagus

The right common carotid and subclavian arteries arise separately from right arch

RSA LSA

LCCRCC

Patent Ductus Arteriosus Before birth, the aorta and

the pulmonary artery are normally connected by a blood vessel called the ductus arteriosus, which is an essential part of the fetal circulation.

After birth, the vessel is supposed to close within a few days. The obliterated vessel forms the ligamentum arteriosum.

In some babies, the ductus arteriosus remains open (patent).

This allows blood to flow directly from the aorta into the pulmonary artery, which can put a strain on the heart and increase pressure in the pulmonary circulation

Abnormal Right Subclavian Artery

May arise from the distal part of arch of aorta

In some cases, the right subclavian artery arises from the descending aorta and runs behind the trachea and the esophagus to supply the right upper limb

Thank You

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Good Luck