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Lecture 17: Vascular System Review 3 paired veins drain into the tubular heart of a 4-week embryo o Vitelline vein Return poorly oxygenated blood from the umbilical vessel Become portal system Left vitelline vein regresses Right vitelline vein forms: most of hepatic portal vein and portion of inferior vena cava o Umbilical vein Carry well-oxygenated blood from the chorion Form caval system Run on each side of liver and carry well oxygenated blood from placenta to sinus venosus As liver develops, umbilical veins lose their connection with heart and empty into liver Right umbilical vein- disappears during 7th week Left umbilical vein- only vessel carrying well-oxygenated blood from placenta to embryo o Common cardinal veins Return poorly oxygenated blood from the body of the embryo Involute after birth Large venous shunt develops within liver connects umbilical vein with IVC o Ductus venosus Forms a bypass through liver Enables most blood from placenta to pass directly to heart without passing through liver capillary networks Cardinal veins constitute main venous drainage system of embryo o Anterior cardinal veins Drain cranial part of embryo o Posterior cardinal veings Drain caudal part of embryo o Anterior & posterior cardinal veins join common cardinal veins that enter sinus venosus Pharyngeal arches form during 4th and 5th weeks and are supplied by pharyngeal arch arteries o Pharyngeal arch arteries arise from aortic sac Terminate in the dorsal aorta on ipsilateral side o Initially, paired dorsal aortas run entire length of embryo o Later, caudal portions of dorsal aortas fuse to form a single lower thoracic/abdominal aorta o Of remaining paired dorsal aortas Right regresses Left becomes primordial aorta Six pairs of pharyngeal arch arteries usually develop o Not all present at same time o By the time 6th pair of pharyngeal arch arteries has formed, 1st two pairs and fifth pair have disappeared o During 8th week, primordial pharyngeal arch arterial pattern is transformed into final fetal arterial arrangement Derivatives of the 3rd pair of pharyngeal arch arteries o Proximal parts of these arteries form common carotid arteries- supply structures in the head o Distal parts join dorsal aortas to form internal carotid arteries- supply middle ears, orbits, brain and its meninges, and pituitary gland Derivatives of the 4th pair of pharyngeal arch arteries o Left 4th pharyngeal arch artery forms part of the arch of aorta Proximal part develops from aortic sac Distal part is derived from left dorsal aorta o Right 4th pharyngeal arch artery becomes proximal part of right subclavian artery Distal part forms from right dorsal aorta and right 7th intersegmental artery Derivatives of the 6th pair of pharyngeal arch arteries o Left sixth pharyngeal arch artery develops as follows Proximal part persists as proximal part of left pulmonary artery Distal part passes from left pulmonary artery to dorsal aorta Forms a prenatal shunt called ductus arteriosus Postnatally becomes ligamentum arteriosus Transformation of the 6th pair of pharyngeal arch arteries explains why course of recurrent laryngeal nerves differs on the two sides o Recurrent laryngeal nerves supply: sixth pair of pharyngeal arches hook around sixth pair of pharyngeal arch arteries on their way to developing larynx o On the right, because distal part of right sixth artery degenerates: right recurrent laryngeal nerve moves superiorly and hooks around proximal part of right subclavian artery: derivative of fourth pharyngeal arch artery o On the left: left recurrent laryngeal nerve hooks around DA: formed by distal part of sixth pharyngeal arch artery o DA (arterial shunt) involutes after birth: left recurrent laryngeal nerve remains around ligamentum arteriosum (remnant of DA) and aortic arch Intersegmental arteries represent about 30 branches from dorsal aorta o Pass between and carry blood to somites and their derivatives o Neck intersegmental arteries join to form: vertebral arteries o Thorax intersegmental arteries persist as: intercostal arteries o Abdomen intersegmental arteries become: lumbar arteries fifth pair of lumbar intersegmental arteries remains as common iliac arteries o Sacral intersegmental arteries form: lateral sacral arteries o Caudal end of dorsal aorta becomes: median sacral artery Fate of the Vitelline Arteries o Vitelline arteries pass to umbilical vesicle and later the primordial gut: forms from incorporated part of umbilical vesicle o Only three vitelline arteries remain: celiac arterial trunk to foregut (broken circle) superior mesenteric artery to midgut inferior mesenteric artery to hindgut Fate of the Umbilical Arteries o Umbilical arteries pass through connecting stalk (primordial umbilical cord): become continuous with chorion vessels (chorion is embryonic part of placenta) o Umbilical arteries carry poorly oxygenated blood to the placenta o Proximal parts of umbilical arteries become Internal iliac arteries Superior vesical arteries o Distal parts of umbilical arteries obliterate after birth and become Medial umbilical ligaments Coarctation (constriction) of the aorta o Occurs in approximately 10% of children and adults with congenital heart defects (CHDs) o Characterized by an aortic constriction of varying length o Most coarctations occur distal to the origin of the left subclavian artery at the entrance of the DA (juxtaductal coarctation) o Classification into preductal and postductal coarctations is commonly used: however, in 90% of instances, the coarctation is directly opposite the DA o Occurs twice as often in males as in females and is associated with a bicuspid aortic valve in 70% of cases Fetal circulation o The colors indicate the oxygen saturation of the blood, and the arrows show the course of the blood from the placenta to the heart o Observe that three shunts permit most of the blood to bypass the liver and lungs: ductus venosus (becomes ligamentum venosum) oval foramen ductus arteriosus (becomes ligamentum arteriosus) o The poorly oxygenated blood returns to the placenta for oxygen and nutrients through the umbilical arteries. Neonatal circulation o The adult derivatives of the fetal vessels and structures that become nonfunctional at birth are shown o The arrows indicate the course of the blood in the infant o After birth, the three shunts that short-circuited the blood during fetal life cease to function, and the pulmonary and systemic circulations become separated Lecture Summary o What are the three systems of paired veins that drain into the primordial heart? Vitelline system, which becomes the portal system; cardinal veins, which form the caval system; and the umbilical system, which involutes after birth o As the pharyngeal arches form during the fourth and fifth weeks, they are penetrated by pharyngeal arteries that arise from? The aortic sac o During the sixth to eighth weeks, the pharyngeal arch arteries are transformed into? o The adult arterial arrangement of the carotid, subclavian, and pulmonary arteries Some congenital anomalies result from? Abnormal transformation of the pharyngeal arch arteries into the adult arterial pattern (e.g., the right sixth pharyngeal arch artery)