DEVELOPMENT OF THE AORTIC

ARCHESDr Rania Gabr

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.

VASCULAR DEVELOPMENT——ARTERIAL SYSTEM

Aortic Arches During 4th and 5th weeks of development,

aortic arches arise from aortic sac

During folding: The primitive aorta is divided into 3

segments:1) Ventral aorta2) First aortic arch3) Dorsal aorta

The 2 ventral aortae fuse to form the heart tube.

Now the heart tube is connected to the dorsal aorta by the first aortic arch on each side.

The aortic arches terminate in right and left dorsal aortae. (In the region of the arches the dorsal aortae remain paired, but caudal to this region they fuse to form a single vessel.)

Only the vessels on the left side of the embryo are shown.

Ventral view of the embryo

The aortic aches appear in a cranial to caudal sequence gradually.

The aortic sac gives rise to a total of six pairs

of arteries. During further development, some vessels regress completely.

A. Aortic arches and dorsal aortae before transformation into the definitivevascular pattern.

aortic sac

The fifth pair is rudimentary and disappears at a very early stage

Arch I:

By day 27, most of 1st aortic arch has disappeared on both sides, a small portion persists to form maxillary artery.

Arch II: 2nd aortic arch soon

disappears.

The remaining portions are hyoid and stapedial arteries.

Arch III: CAROTID ARCH – Persists becomes part of carotid arteries.

1- Common carotid artery 2-Proximal part of internal carotid artery 3-External carotid artery

The remainder of internal carotid artery is formed by the cranial portion of the dorsal aorta

Arch IV: AORTIC ARCH -Right side: Rt subclavian -Left side : Main Part of the ARCH OF AORTA.

Arch V: DISAPPEARS

The aortic sac then forms right and left horns, which subsequently give rise to brachiocephalic artery and proximal segment of aortic arch, respectively.

B. Aortic arches and dorsal aortae after the transformation. Broken lines, obliterated components. C. The great arteries in the adult.

Arch VI: PULMONARY ARCH –On the left side: Ventral part: Left pulmonary artery Dorsal part: Ductus arteriosus

On the rt side:Ventral part: Right Pulmonary artery Dorsal part: Disappears

( No ductus arteriosus on the right side)

The left recurrent laryngeal nerve, recurs on the ductus arteriosus.

Absence of the ductus on the rt side allows the rt recurrent laryngeal nerve to recur on the rt subclavian artery

Persistence of the Ductus arteriosus and later Ligamentum arteriosum is the cause of presence of the left recurrent laryngeal nerve in the thorax , while the rt remains in the neck due to absence of ductus on the rt side.

A number of other changes occur: (a) dorsal aorta between entrance of 3rd and 4th

arches, known as carotid duct, is obliterated.

(b) right dorsal aorta disappears between origin of the 7th intersegmental artery and junction with the left dorsal aorta.

So , the Arch of Aorta develops from 3 parts:

1) Proximal part : from the left part of the aortic sac

2) Middle part: from the left 4th aortic arch

3) Distal Part: From the dorsal aorta between the left fourth and 6th arches

Vitelline Arteries vitelline arteries, supplying yolk sac, gradually

fuse and form arteries in dorsal mesentery of gut, celiac, superior mesenteric, and inferior mesenteric arteries.

These vessels supply derivatives of foregut, midgut, and hindgut respectively.

Umbilical arteries The umbilical arteries are paired ventral branches of

dorsal aorta During the 4th week, each artery acquires a secondary

connection with dorsal branch of aorta, common iliac artery, and loses its earliest origin.

After birth the proximal portions of umbilical arteries persist as internal iliac and superior vesical arteries, and distal parts are obliterated to form medial umbilical ligaments.

CLINICAL CORRELATES---Arterial System Defects

Under normal conditions the ductus arteriosus is functionally closed through contraction of its muscular wall shortly after birth to form the ligamentum arteriosum.

A patent ductus arteriosus either may be an isolated abnormality or may accompany other heart defects. In particular, defects that cause large differences between aortic and pulmonary pressures may cause increased blood flow through the ductus arteriosus, preventing its normal closure.

Coarctation of aorta

It is a Local narrowing of the lumen of the aorta just distal to the origin of the Left Subclavian Artery ,above or below the entrance of ductus arteriosus.

2 types:In preductal type, ductus arteriosus persists

In postductal type, ductus arteriosus is obliterated.

Abnormal origin of the right subclavian artery(ABERRANT) Right subclavian artery is formed by distal portion of the

right dorsal aorta and the 7th intersegmental artery. The right 4th aortic arch and proximal part of right dorsal aorta are obliterated.

With shortening of aortic arch, origin of abnormal right subclavian artery finally settles just below left subclavian artery.

Since its stem is derived from right dorsal aorta, it must cross midline behind esophagus to reach the right arm. This location does not usually cause problems with swallowing or breathing, since neither esophagus nor trachea is severely compressed.

Double aortic arch right dorsal aorta persists between origin of

7th intersegmental artery and its junction with left dorsal aorta.

A vascular ring surrounds the trachea and esophagus and commonly compresses these structures, causing difficulties in breathing and swallowing.

7th intersegmental artery

Right aortic archleft 4th arch and left dorsal aorta are obliterated and replaced by corresponding vessels on right side.

Occasionally, when ligamentum arteriosum lies on left side and passes behind the esophagus, it causes complaints with swallowing.

Interrupted aortic arch It is caused by obliteration of 4th aortic arch on left

side. It is frequently combined with an abnormal origin of

right subclavian artery. Ductus arteriosus remains open. Descending aorta and subclavian arteries are supplied

with blood of low oxygen content. Aortic trunk supplies two common carotid arteries.

common carotid arteries

DEVELOPMENT OF VENOUS SYSTEM In 5th week of development 3 major pairs

Vitelline veins Portal vein and superior mesenteric from

right VVUmbilical veins

Left umbilical vein connects to right hepatocardiac channel via ductus venosus (bypass liver sinusoids)

After birthDuctus venosus closes ligamentum

venosumLeft umbilical vein is obliterated

ligamentum teres hepatisCardinal veins main venous drainage of

fetus

CARDINAL VEINS (CV) Ant. cardinal veins drain anterior region

Anatomose btw ant CV left brachiocephalic V Post. cardinal V drain the rest During 5th – 7th weeks more veins formed

Subcardinal V Mainly drains the kidneys Anatomose left renal vein

Supracardinal V Drains the body wall by way of intercostal veins

Superior vena cava From rt. common & proximal part of rt. ant. CV

VENA CAVA, AZYGOUS, HEMIZYGOUS Superior vena cava

Formed by the right common CV & proximal part of right anterior CV

Inferior vena cavaFormed from right subcardinal vein

AzygousFormed from right supracardinal veins

HemizygousFormed from part of left supracardinal veins

FETAL CIRCULATION By the third month of development, all

major blood vessels are present and functioning.

Fetus must have blood flow to placenta.

Resistance to blood flow is high in the lungs.

UMBILICAL CIRCULATION

Pair of umbilical arteries carry deoxygenated blood & wastes to placenta.

Umbilical vein carries oxygenated blood and nutrients from the placenta.

UMBILICAL VEIN TO PORTAL CIRCULATION Some blood from the

umbilical vein enters the portal circulation allowing the liver to process nutrients.

The majority of the blood enters the ductus venosus, a shunt which bypasses the liver and puts blood into the hepatic veins .Then to Inferior vena cava

FORAMEN OVALE Blood is shunted

from right atrium to left atrium, skipping the lungs.

More than one-third of blood takes this route.

Is a valve with two flaps that prevent back-flow.

DUCTUS ARTERIOUSUS The blood pumped

from the right ventricle enters the pulmonary trunk.

Most of this blood is shunted into the aortic arch through the ductus arteriousus.

WHAT HAPPENS AT BIRTH? The change from fetal to postnatal

circulation happens very quickly. Changes are initiated by baby’s first

breath.

Foramen ovale Closes shortly after birth, fuses completely in first year.

Ductus arteriousus Closes soon after birth, becomes ligamentum arteriousum in about 3 months.

Ductus venosus Ligamentum venosum

Umbilical arteries Medial umbilical ligaments

Umbilical vein Ligamentum teres

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