1. Dr Rania Gabr

2.  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.

3. Aortic Arches  During 4th and 5th weeks of development, aortic arches arise from aortic sac

4.  During folding:  The primitive aorta is divided into 3 segments: 1) Ventral aorta 2) First aortic arch 3) 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.

5.  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

6.  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 definitive vascular pattern. aortic sac The fifth pair is rudimentary and disappears at a very early stage

7.  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.

8.  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

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

10.  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.

11. 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)

12.  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.

13. 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.

14. 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 4 th aortic arch  3) Distal Part: From the dorsal aorta between the left fourth and 6 th arches

15. 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.

16. 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.

17. 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.

18.  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.

19.  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

21.  In a 4 weeks embryo, three paired veins open into the tubular heart:  Vitelline veins, returning deoxygenated blood from the yolk sac  Umbilical veins, bringing oxygenated blood from the placenta.  Common cardinal veins, returning deoxygenated blood from the body of the embryo

22.  Pass through the septum transversum and drain into the sinus venosus  In relation to the liver developing within the septum transversum, the vitelline veins are divided into:  Pre-hapatic part: forms anastomosis around the duodenum which later on gives rise to the portal vein  Hepatic part: interrupted by the liver cords, forms an extensive vascular network called the hepatic sinusoides  Post-hepatic part:  Left vein disappears  Right vein forms the:  Hepatic veins &  Hepatic segment of inferior vena cava

23.  Bring oxygenated blood from the placenta  Initially run on each side of the developing liver and drain into the sinus venosus  As the liver grows, the umbilical veins loose their connection with heart and open into the liver  The right vein disappears by the end of the embryonic period. The left vein persists

24.  A wide channel, the ductus venosus, appears through the substance of liver to connect the left umbilical vein with the inferior vena cava After birth: - The left umbilical vein obliterates to form the ligamentum teres of the liver - The ductus venosus obliterate to form the ligamentum venosum

25.  Are responsible to drain the body of the embryo  The cranial part of the embryo is drained by paired anterior cardinal veins  The caudal part of the embryo is drained by paired posterior cardinal veins  The anterior & posterior cardinal veins join to form common cardinal veins, which drain into the sinus venosus

26.  Become connected by an oblique anastomosis which shunts blood from left to right  This anastomosing channel becomes the left brachiocephalic vein  Left anterior cardinal vein  Cranial part: becomes the left internal jugular vein  Caudal part: degenerates

27.  Right anterior cardinal vein  Cranial part: (cranial to the 7 th intersegmental vein) becomes the right internal jugular vein  Middle part: gives rise to the right brachiocephalic vein  Caudal part of right anterior cardinal vein and the right common cardinal vein form the superior vena cava

28.  Drain the caudal part of the body of embryo including the developing mesonephros and largely disappear with this transitory kidneys.  Caudally the two veins get connected by an anastomosing channel that directs the blood from the left to the right vein

29.  Gradually the posterior cardinal veins are replaced by two new veins: subcardinal & supracardinal The adult derivatives of the posterior cardinal veins are the:   Root of the azygos vein &   Common iliac veins

30.  SVC is derived from the:  Caudal part of the right anterior cardinal vein &  Right common cardinal vein

31.  Azygos vein is derived from the:  Cranial part of the right supracardinal vein &  Terminal part of the right posterior cardinal vein  Hemiazygos vein is derived from the cranial part of the left supra-cardinal vein

32.  The IVC develops during a series of changes in the primordial veins  Composed of: Hepatic segment derived from the right vitelline vein Prerenal segment derived from the right subcardinal vein Renal segment derived from the subcardinal- supracardinal anastomosis Postrenal segment derived from the right supracardinal vein

33.  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.

35.  Pair of umbilical arteries carry deoxygenated blood & wastes to placenta.  Umbilical vein carries oxygenated blood and nutrients from the placenta.

36.  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

37.  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.

38.  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.

39.  The change from fetal to postnatal circulation happens very quickly.  Changes are initiated by baby’s first breath.

40. 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