L28- vascular development (arterial system) (1).pdf

L28 VASCULAR DEVELOPMENT (Arterial System) ILOs By the end of this lecture, students will be able to 1. Describe the development, fate and derivatives of the aortic arches. 2. Correlate between the developmental basis of the aortic arches and different congenital anomalies of these great vessels. Ao...

L28 VASCULAR DEVELOPMENT (Arterial System) ILOs By the end of this lecture, students will be able to 1. Describe the development, fate and derivatives of the aortic arches. 2. Correlate between the developmental basis of the aortic arches and different congenital anomalies of these great vessels. Aortic Arches Development : 1- Two dorsal aortae are present dorsal and other two are present ventral to the embryo. 2- The two ventral aortae fuse forming a single sac, called aortic sac. 3- When pharyngeal arches are formed each arch receives its own artery. These arteries, the aortic arches, arise from the aortic sac (the most distal part of the truncus arteriosus). These arches connect the aortic sac ventrally, to the dorsal aortae dorsally. 4- The aortic arches are embedded in the pharyngeal arches and terminate in the right and left dorsal aortae. (In the region of the arches, the dorsal aortae remain paired, but caudal to the sixth arch, they fuse to form a single vessel). 5- The aortic sac contributes a branch to each new arch as it forms, giving rise to a total of five pairs of arteries. (The fifth arch either never forms or forms incompletely and then regresses). Consequently, the five arches are numbered I, II, III, IV, and VI. 6- During further development, this arterial pattern becomes modified, and some vessels regress completely. 7- Division of the truncus arteriosus by the aorticopulmonary septum divides the outflow channel of the heart into the ventral aorta and the pulmonary trunk. The aortic sac then forms right and left horns, which give rise to the brachiocephalic artery (innominate artery) and the proximal segment of the aortic arch, respectively. Fig 1: Aortic arches development Page 1 of 6 The following changes occur: 1- The first aortic arch has disappeared, although a small portion persists to form the maxillary artery. 2- The second aortic arch soon disappears. The remaining portion of this arch is the stapedial artery. 3- The third aortic arch forms the common carotid artery (proximal part )and the first part of the internal carotid artery (distal part ). The remainder of the internal carotid is formed by the cranial portion of the dorsal aorta. The external carotid artery is a bud of the third aortic arch. 4- The fourth aortic arch its ultimate fate is different on the right and left sides. On the left, it forms part of the arch of the aorta, between the left common carotid and the left subclavian arteries. On the right, it forms the most proximal segment of the right subclavian artery, the distal part of which is formed by a portion of the right dorsal aorta and the right seventh intersegmental artery. 5- The fifth aortic arch either never forms or forms incompletely and then regresses. 6- The sixth aortic arch is known as the pulmonary arch. The proximal part on each side and the bud becomes the pulmonary arteries. On the right side, the distal portion of this arch loses its connection with the dorsal aorta and disappears. On the left, the distal part persists during intrauterine life as the ductus arteriosus. 7- The seventh intersegmental arteries (right and left) migrate to the level of the fourth arch. These arteries will give all the subclavian artery on the left, and a part of subclavian artery on the right. Derivatives of the aortic arches. Arch Arterial derivatives 1st 2nd 3rd Maxillary artery Stapedial artery Common carotid and 1st part of internal carotid arteries External carotid formed as a bud from it Arch of aorta from left common carotid to left subclavian Right subclavian artery (proximal part) Left pulmonary artery and ductus arteriosus Right pulmonary artery 4th Left side Right side 6th Left side Right side Page 2 of 6 Fig 2: Derivatives of the aortic arch system. Notice that: *The right subclavian artery is formed from: a. Right fourth aortic arch. b. Right seventh intersegmental artery. c. Part of dorsal aorta that lies between the right forth aortic arch and right seventh intersegmental artery. *The left subclavian artery is formed only from the left seventh intersegmental artery. *Aortic sac is divided into two parts: a. Left horn forms the arch of the aorta caudal to the fourth arch. b. Right horn forms the innominate artery. *Arch of the aorta is formed from: a. Left horn of aortic sac. b. Left forth arch. c. Dorsal aorta distal to the forth arch. Page 3 of 6 Other changes occur in the aortic arch system: ⮚ The dorsal aorta between the entrance of the third and fourth arches is obliterated. ⮚ The right dorsal aorta disappears between the origin of the seventh intersegmental artery and the junction with the left dorsal aorta. ⮚ Relation to recurrent laryngeal nerves: The course of the recurrent laryngeal nerves becomes different on the right and left sides. Initially, these nerves, branches of the vagus nerve, supply the larynx. When the heart descends, they hook around the sixth aortic arches and ascend again to the larynx, which accounts for their recurrent course. On the right, when the distal part of the sixth aortic arch and the fifth aortic arch disappear, the recurrent laryngeal nerve moves up and hooks around the right subclavian artery(4th arch). On the left, the nerve does not move up, since the distal part of the sixth aortic arch persists as the ductus arteriosus, which later forms the ligamentum arteriosum. A. Aortic arches and dorsal aortae before transformation into the definitive vascular pattern. B. Aortic arches and dorsal aortae after the transformation. Broken lines, obliterated components. Note the patent ductus arteriosus and position of the seventh intersegmental artery on the left. C. The great arteries in the adult. After disappearance of the distal part of the sixth aortic arch (the fi fth arches never form completely), the right recurrent laryngeal nerve hooks around the right subclavian artery. On the left, the nerve remains in place and hooks around the ligamentum arteriosum Page 4 of 6 Arteria system defects: 1- Patent ductus arteriosus: one of the most frequently occurring abnormalities of the great vessels especially in premature infants. 2- Coarctation of the aorta: the aortic lumen below the origin of the left subclavian artery is significantly narrowed, classical clinical sign include hypertension in the arms concomitant with lowered blood pressure in the legs. 3- Double aortic arch: the right dorsal aorta persists between the origin of the seventh intersegmental artery and its junction with the left dorsal aorta. Page 5 of 6 4- Right sided aortic arch: the left fourth arch and left dorsal aorta are obliterated and replaced by the corresponding vessels on the right side. 5- Transposition of the great vessels. Page 6 of 6