Cadriovascular system
Part 3
The arterial system
Aortic arches:
When pharyngeal arches form during 4
th
& 5
th
wks of
development, each arch receives its own cranial nerve & its
own artery.
These arteries arise from aortic sac, the most distal part of
truncus arteriosus, the aortic arches are embeded in
mesenchyme of the pharyngeal arches & terminate in ^ Rt. &
Lt. dorsal aortae.
In ^ region of the arches, the dorsal aortae remain paired, but
caudal to this region they fuse to form a single vessel.
^ pharyngeal arches & their vessels appear in a cranial-
caudal se ue ce, so that they’ e ot all p ese t si ulta eously.
• The aortic sac contributes a branch to each new
arch as it forms; giving rise to a total of 5 pairs of
arteries (^5
th
arch either never forms or forms
incompletely & then regress.
• Consequently, the 5 arches are numbered I, II, III,
IV, &VI. During further development, this arterial
pattern becomes modified & some vessels
regress completely.
• Division of the truncus arteriosus by aortico-
pulmonary septum divides the outflow channel
of the heart into ^ ventral aorta, & ^ pulmonary
trunk.
The aortic sac then forms RT. <. horns,
which subsequently give rise to the
brachiocephalic artery
& proximal segment of ^
aortic arch,
respectively.
• By day 27, most of ^ 1
st
aortic arch
has disappeared,
although a small portion persist to form ^ maxillary
artery.
• Similarly, ^ 2
nd
aortic arch disappears. The remaining
portions of this arch are ^ hyoid & stapedial arteries.
• The third arch is large; ^ 4
th
& 6
th
arches are in the
process of formation. Even though ^ 6
th
arch is not
completed, ^ primitive pulmonary artery is already
present as a major branch.
• In ^ 29-day embryo, ^ 1
st
& 2
nd
aortic arches have
disappeared. ^ 3
rd
, 4
th
& 6
th
arches are large. ^
conotruncal region has divided so that ^ 6
th
arches
are now continuous with ^ pulmonary trunk.
• ^ aortic arches lie in each of ^ five pharyngeal
arches. Four important derivatives of ^ original
aortic arch system are: (a) ^ carotid arteries (3rd
arches), (b)^ arch of ^ aorta (left 4th aortic arch),
• (c) ^ pulmonary artery (6th aortic arch), which
during fetal life is connected to ^ aorta through ^
ductus arteriosus,& (d) ^ RT. Subclavian artery
formed by ^ RT. 4th aortic arch, distal portion of ^
RT. Dorsal aorta, & ^ 7th intersegmental artery.
• ^ most common vascular aortic arch
abnormalities include: (a) open ductus
arteriosus & coarctation of ^ aorta. (b)
persistent RT. Aortic arch & abnormal RT.
Subclavian artery, both causing respiratory &
swallowing complaints.
Other arterial systems:
• ^ vitelline arteries initially supply ^ yolk sac but later
form ^ celiac, superior mesentric, & inferior mesenteric
arteries which supply ^ foregut, midgut, & hindgut
regions, respectively.
• ^ paired umbilical arteries, initially paired branches of
dorsal aorta, during 4
th
week each artery acquires a
secondary connection with dorsal branch of aorta, ^
common iliac artery &loses its earliest origin.
• After birth, ^ distal portions of these arteries are
obliterated to form ^ medial umbilical ligaments.
• ^ proximal portion persist as ^ internal iliac & vesicular
arteries.
Venous system
• Three systems can be recognized:
• (a) ^ vitelline system, which develops into ^ portal system; (b) ^ cardinal
system, which forms ^ caval system;& (c) ^ umbilical system, which
disappears after birth.
• Initially, the cardinal veins form the main venous drainage system of the
embryo, consist of anterior & posterior cardinal veins, which drain
cephalic & rest of embryo respectively. The ant. & post. Cardinal veins join
before entering sinus venosus and forming common cardinal vein.
• During 5
th
-7
th
week a no. of veins developed:1-subcardinal vein---drains
the kidney. 2-sacrocardinal vein---drain the lower exterimities. 3-
supracardinal
—drain the body wall by intercostal veins.
• ^complicated caval system is characterized by many abnormalities, such as
double inferior & superior vena cava & left superior vena cava.
Changes at birth
• During prenatal life, ^ placental circulation provides ^
fetus with its oxygen, but after birth, ^ lungs take on
gas exchange.
• In ^ circulatory system, ^ following changes take place
at birth & in ^ 1st postnatal months ; (a) ^ ductus
arteriosus closes, (b) ^ oval foramen closes (c) ^
umbilical vein & ductus venosus (which courses from
ligamentum teres to inferior vena cava) close & remain
as ^ legamentum teres hepatis & Ligamentum
venosum; & (d) ^ umbilical arteries form ^ medial
umbilical ligaments.
Lymphatic system
• ^ lymphatic system develops later than
cardiovascular system, originating from ^
endothelium of veins as six sacs ; 2 jugular, 2 iliac,
1 retroperitoneal, & 1 cisterna chyli.
• Numerous channels form to connect ^ sacs &
provide drainage from other structures.
• Ultimately, ^ thoracic duct forms from
anastomosis of ^distal part of ^ RT. Thoracic duct
& ^ cranial part of ^ LT. thoracic duct.
• ^ RT. Lymphatic duct develops from ^ cranial part
of RT. thoracic duct.