Download Extraembryonic blood vessels form during the early 3rd week

Cardiovascular Development:
1. Development of the Heart
2. Development of the Vasculature
Pamela Knapp, Ph.D.
Professor, Dept. Anatomy & Neurobiology
MSB1 - Rm. 411
6-7570
[email protected]
Early Vessel Formation
A.
Blood islands are first formed by proliferating yolk sac,
connecting stalk, and chorion. These unite to form
plexi of capillaries, some of which enlarge forming
extraembryonic veins and arteries.
Embryonic blood islands are formed by proliferation of
visceral (splanchnic) mesoderm during mid-3rd week
(~day 18).
Blood islands migrate to surround the neural plate in a
horse shoe-shaped cardiogenic area.
Chorion
(fetal placenta)
Blood islands – Cardiogenic region
B.
Blood cells are supplied at first by the yolk sac.
Starting at ~5 wks, they are supplied by a sequence of
embryonic organs - liver, spleen, thymus, and, finally
bone marrow.
Yolk Sac
ARTERIAL SYSTEM
Derived from 2 structures – Aortic arches & Dorsal aortae
Primitive pattern established early in 4th week
Aortic arches are the arteries that supply the embryonic pharyngeal arches
5 arches
(#5 is rudimentary
in humans)
Paired – initially identical
Form in craniocaudal manner
Blood flows from primitive
heart, through aortic sac, and
out to dorsal aortae through
aortic arches
Major contributions to adult
arterial system made by
arches 3, 4, and 6.
Restructuring
of
aortic
arches
EXT. CAROTID
BRACHEOCEPHALIC Art.
Asc.
Aorta
Pulm.
Trunk
RIGHT
1st
and
2nd
LEFT
arches largely regress.
Critical to restructuring is breakdown of left and right DA between arches 3 and 4.
3rd arches - same fate right and left sides
-remain connected at ends to aortic sac & DA
-proximal parts form common carotid arteries; distal parts form portion of internal carotid artery (rest from
dorsal aorta); ext carotids sprout later from 3rd arch also
4th arches - different fates on right and left side.
-Left 4th arch forms midportion of the arch of the aorta. Retains connections to derivatives of aortic sac and
dorsal aorta, which form proximal and distal portions of the arch of the aorta.
-Right 4th arch also retains connections to derivatives of aortic sac and dorsal aorta. Forms proximal
segment of right subclavian artery, (leads to more distal section formed by dorsal aorta). Aortic sac
here is restructured into the bracheocephalic artery.
6th arches – different fates on right and left side.
- Left proximal portion forms proximal part of left pulmonary artery. Distal left forms transient ductus
arteriosus.
- Right proximal forms proximal portion fo right pulmonary artery. Distal right regresses.
Aortic arch restructuring affects
course of recurrent laryngeal
nerves
Branches of vagus.
Originally hook under the 6th aortic arch on both
sides.
Left 6th arch persists as ductus arteriosus, and
then as ligamentum arteriosum.
Right 6th duct regresses at distal end. 5th arches
degenerate. Nerve ends up hooking under the
right subclavian artery, the 4th arch derivative
on the right side. In position superior to same
nerve on left side.
More derivatives of dorsal aortae
Initial right and left dorsal aorta run the length of the
embryo. They fuse just below the pharyngeal arches,
creating a single dorsal aorta.
Right dorsal aorta degenerates below origin of 7th
intersegmental artery (branch of dorsal aorta that
becomes far distal portion of right subclavian artery).
Cranial paired dorsal aortae remain, forming a large
part of the internal carotid arteries. The portion of the
dorsal aorta located between 3rd and 4th arches is
obliterated (carotid duct).
The left 7th intersegmental artery becomes the left
subclavian artery. It’s origin shifts cranially due to
overgrowth of cephalic regions.
Segmental &
Intersegmental arteries
These are paired, dorsal aorta derivatives that supply
derivatives of the somites. Many lose their original
physical connections to the aorta.
Segmental arteries:
Ventral: Vitelline (yolk sac) arteries fuse as the ventral
dorsal aortae fuse. These will form the arteries of the
dorsal mesentery of the GI tract (celiac, sup & inf
mesenteric)
Umbilical arteries contribute to common iliacs
Lateral – give rise to renals, gonadals, and phrenics, etc.
Dorsal intersegmental arteries (30+ pairs!):
Cervical intersegmentals anastomose to form vertebrals
7th cervical intersegmentals contribute to subclavians
Thoracic intersegmentals form the posterior intercostals
Abdominal intersegmentals form lumbars
Ventral segmental arteries
5th lumbar intersegments contribute to common iliacs
(along with umbilical arts)
Arterial Anomalies
*
**
VI arch
derivatives
Pulm.
Trunk
Patent ductus arteriosus*
Common anomaly – often associated with hypoxia
Failure of the ductus arteriosus to close after birth.
DA closure is related to increased PO2 at birth. Low P02 and
other factors cause production of prostaglandins that inhibit
ductus muscular contraction, keeping the opening patent.
Higher left side pressure after birth shunts blood through the patent
DA, back to the pulmonary arteries.
May respond to PG inhibitors.
Coarctation of the aorta**
A localized narrowing of aorta in region of DA
Can be above the DA (preductal) (shown here) or below the DA
(postductal).
Etiology uncertain.
One theory is that PO2 sensitive muscle from wall of DA is
incorporated into aortic wall … contracting as PO2 rises.
Double Aortic Arch:
Uncommon
Abnormal persistence of the
right dorsal aorta between
the origin of the 7th
intersegmental artery and
the junction with the left
dorsal aorta. Result is that
the trachea and
esophagus are trapped
inside a vascular ring.
This
connection
should
break down
to form normal
structures
shown below
EXT. CAROTID
NORMAL
BRACHEOCEPHALIC Art.
Asc.
Aorta
Pulm.
Trunk
RIGHT
LEFT
VENOUS SYSTEM
Posterior cardinal v.
Anterior cardinal v.
Umbilical v.
Time: 4 weeks
3 sets of veins are returning blood
to the primitive heart (rt and left
horns of sinus venosus)
Common
cardinal v.
Vitelline v.
Umbilical – paired; highly
oxygenated blood from fetal
placenta (chorion)
Vitelline – paired; originally drain
the yolk sac, then its derivatives in
the GI tract
Cardinal – 3 pairs carry blood from
the embryo proper. Anterior and
posterior cardinals drain into the
common cardinals.
Developmen
t
of the
Vitelline
Veins
Vitelline veins form a
plexus of vessels
around the gut before
passing through the
septum transversum.
Right
Left
Yolk
Sac
Hepatic IVC
Muscular
interventricular
septum
The growing plexus
invades the liver
tissues.
Blood from the left side of the abdomen drains through the plexus to the right side. Parts of the plexus form the ductus
venosus – a transient structure important in shunting relatively oxygenated blood centrally and bypassing the liver tissue.
Inferior portions of the right vitelline vein (below the liver) form the portal and superior mesenteric veins. Portions of the plexus
contribute to the portal vein system. The midportion of the right vitelline vein forms the hepatic vein. The superior portion
becomes the terminal (hepatic) part of the inferior vena cava (IVC).
RIGHT
LEFT
Developmen
t of the
Umbilical
Veins
Both umbilical
veins initially
bypass the liver.
They eventually
make
connections
with hepatic
sinusoids (like
vitelline veins).
Placenta
Proximal portions of both umbilical veins, and entire RIGHT umbilical vein degenerate.
The caudal, LEFT umbilical vein is the only remaining path from placenta to liver.
The left umbilical vein forms an anastomosis with the ductus venosus (a transient shunt that develops in the liver, channeling
blood into the nascent inferior vena cava … formerly part of the right vitelline vein).
The ductus venosus is critical during fetal life. It shunts about half of the oxygenated blood from the umbilical vein directly to
the right atrium via the IVC.
The ductus venosus and left umbilical vein degenerate after birth to form the ligamentum venosum and ligamentum teres
hepatis.
Development of the Cardinal Veins
Anterior and common cardinal veins:
An anastomosis between anterior cardinal veins creates the
left bracheocephalic vein.
Cranial portions of right and left anterior cardinal veins form
internal jugular veins. (External jugular veins from facial
capillary plexi that connect with the internal jugular veins).
The right common cardinal vein and caudal portion of the
right anterior cardinal vein form the superior vena cava.
Posterior cardinal veins
Both are largely obliterated and replaced by 3 other venous
systems:
a. Subcardinal
b. Sacrocardinal
c. Supracardinal
These venous systems form large anastomoses.
Large portions degenerate during embryonic period.
Subcardinal remnants include the renal, suprarenal and
gonadal veins.
Portions of the subcardinal, supracardinal, and
sacrocardinal venous anastomoses contribute to the
inferior vena cava, as well as azygous veins that drain the
body wall.
Venous Anomalies
Largely due to persistence of structures
that normally degenerate.
Double Superior Vena Cava:
Common defect
Left anterior cardinal vein persists
Result is inefficient anastomosis between
left and right anterior cardinals AND
persistance of a vessel that drains the
coronary sinus on the left side.
RIGHT
LEFT
Fetal and Postnatal Cirulatory Systems
Be able to compare
-structures that differ (ex. ductus arteriosus, ligamentum arteriosum)
-bloodflow pathways
Be able to explain the basis of these differences