2. The Aortic Arches
Dr. Zeenat Zaidi

3. 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

4. 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.

5. 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

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

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

8. 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).

9. 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

10. 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

11. 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

12. 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

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

14. Derivatives of Aortic Arches

15. 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

16. Second Pair Largely disappear
Dorsal part persists as the hyoid and stapedial arteries

17. Third Pair Proximal part: forms the common carotid arteries
Distal part: joins the dorsal aortae to form the internal carotid arteries

18. Fifth Pair
Disappears completely with NO vascular derivatives

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

20. Fourth Pair
RIGHT: Becomes the proximal part of the right subclavian artery
LEFT: Forms part of the arch of aorta

21. 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

22. 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

23. 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

24. 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

25. Relation of recurrent laryngeal nerves to the aortic arches

26. Anomalies of the Aortic Arches

27. 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.

28. 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.

29. 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

30. 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

31. 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.

32. 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

33. 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

34. Thank You
&
Good Luck