Download Lecture 17: Vascular System Review 3 paired veins drain into the

Lecture 17: Vascular System Review
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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
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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
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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
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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?
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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)