The Aortic Arches Dr. Zeenat Zaidi

Embryonic Blood Vessels By the beginning of the 4th week, an extensive network of blood vessels is formed throughout the embryonic body The heart begins to beat on 21st or 22nd day, and blood begins to circulate. This makes the CVS to be the first system in the body to reach the functional state The embryonic heartbeat can be detected ultrasono-graphically during the 5th week

The main embryonic vessels are the paired dorsal aortae, which receive blood from the heart and distribute it to body tissues The dorsal aortae fuse caudally during the fourth week, forming a single median vessel, the descending aorta.

The descending aorta gives the following branches: Lateral segmental Ventral segmental Dorsal intersegmental The caudal end of the descending aorta becomes the median sacral artery

Lateral Segmental Arteries: Supply the: Diaphragm Kidneys Adrenal glands Gonads These vessels become the phrenic, renal, middle suprarenal, and gonadal arteries of the adult.

Ventral Segmental Arteries: Supply the: Yolk sac (Vitelline arteries) Allantois (Umbilical arteries) Embryonic part of placenta (Chorionic arteries)

Vitelline arteries: Supply the yolk sac and the primitive gut Three major arteries remain as the: Celiac trunk (artery of foregut) Superior mesenteric artery (artery of midgut) Inferior mesenteric artery (artery of hindgut).

Umbilical arteries: Pass through the connecting stalk in close association with the allantois Become continuous with the chorionic blood vessels. Carry poorly oxygented blood to the placenta Derivatives: Proximal parts: persist as the superior vesical arteries, which supply the urinary bladder Distal parts: obliterate after birth and become the median umbilical ligaments

Dorsal intersegmental arteries: Somatic branches About thirty or more pairs arise at serial segmental levels, run between the somites Supply the body wall, limbs, brain and spinal cord. Derivatives: In cervical region: join to form the vertebral artery. The 7th pair contributes to the subclavian arteries. In thoracic region: become the posterior intercostal arteries In abdominal region: become the lumbar arteries. The 5th pair remains as the common iliac artery In sacral region: form the lateral sacral arteries

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

The first arch is obliterated before the 6th arch is formed 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: LEFT: 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: Most of the 1st & 2nd arches 5th arches completely Distal part of the right sixth arch The segment of both aortae lying between the 3rd & 4th arches 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 RCC LCC RSA LSA

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

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