Heart Development !

8/13/2019 Heart Development !

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Development of the heart 1


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Objectives:

Understand early development of blood vessels.

Basic understanding of the early stages of heartdevelopment.

Describe the formation and position of the heart

tube.Discus the development of sinus venosus.

Describe partioning by septa and chambers

formation.Discus congenital malformations.

Gain knowledge of fetal circulation.


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THE CARDIOVASCULAR SYSTEM

The cardiovascular system is the first

functional system; blood begins to

circulate by the end of the third

week of development.


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Blood vessels:

Mesenchymal cells of the splanchnic

mesoderm group together to formblood islands (angiogenic clusters).The

clusters develop a lumen.The cells on

the periphery become endothelium; the

cells in the middle become blood

cellsThe clusters spread toward oneanother and fuse to form the vessels.


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Heart Formation:

The cardiogenic area develops

cranial to the oropharyngealmembrane during the third week of

development; the cranial folding of

the embryo pushes the

cardiogenic area caudally. This

area (one on each side) developsinto the endocardial heart tubes.


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As the embryo folds, the

endocardial heart tubes

approach each other and fuseto form a single endocardial

tube.Differential growth in theheart tube causes the heart to

bend.


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Blood flow thourgh the primitive

heart:

Common cardinal viens, umbilicalveins and vitelline veins drain into

the sinus venosus--> atrium --

>atrioventricular canal--> venricle--

> bulbus cordis--> truncus

arteriosus--> aortic sac--> aorticarches--> dorsal aortae.


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Looping of heart tube (Days 23-

28): The primitive atrium loops

up behind and above theprimitive ventricle and behind

and to the left of the bulbuscordis.


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As the heart is bending and

enlarging, the internal partitioning

of the original single chamber isoccurring; this partitioning is

occuring simultaneously in the

atrium and the ventricle during

days 27-37.The atrioventricular

partition produces one atrium andone ventricle.


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The endocardial cushions (which

contain neural crest cells)

approach each other and fuse,leaving an opening on each side

which is the site where the

atrioventricular valves develop(tricuspid and bicuspid).The atrial

septum divides the primitiveatrium into two atria.


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The septum primum:

Grows toward the developing

endocardial cushions from the

superior part of the atrium.The

space between the inferior flapof the septum primum and the

endocardial cushions is theforamen primum.


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The foramen primum is a space

that is gradually getting smaller

as the septum primum extendsdownward.Eventually the

foramen primum is obliteratedBUT by the time it is

obliterated, a second foramen

has appeared in the upper part

of the septum primum .


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This second foramen is the

foramen secundum; thus, the

flow of blood from the rightatrium into the left atrium is

maintained. This is one of themechanisms to bypass the

non-functional fetal lungs.Both

the foramen primum and the

foramen secundum are in the

septum primum.


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The septum secundum:

This is a second flap that develops

and grows downward from theatrium toward the ventricle and

upward from the ventricle to the

atrium (there are two segments to

this septum); it is located just to

the right of the septumprimum.The two segments of the

septum secundum do NOT fuse

together.

Th t d l th


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The septum secundum overlaps the

foramen secundum in the septum

primum, forming an incompletepartition, the foramen ovale. Most of

the atrial septum is formed by the

septum primum.The interventricularseptum grows from the bottom of the

ventricle and fuses with the

downgrowing part of the endocardialcushion.The bottom part = the

muscular part of the septum. The top

part = membraneous part of septum.

Ri ht t i


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Right atrium:

As the heart continues to grow, the right

side of the sinus venosus isincorporated into the right side of the

primitive atrium. The primitive atrial wall

is pushed ventrally, eventually becomingthe right auricle. In the adult heart, the

right auricle contains pectinate muscle

derived from the primitive atrium,whereas the sinus venarum is derived

from the sinus venosus and therefore

smooth-walled.

L ft t i


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Left atrium:

The left side of the primitive atrium

sprouts a pulmonary vein whichbranches and sends two veins toward

each of the developing lungs. The trunk

of this pulmonary vein is incorporatedinto the left side of the primitive atrium,

forming the smooth wall of the adult left

atrium. The left side of the primitiveatrium is pushed forward and eventually

becomes the trabeculated left auricle.


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What embryonic structures are incorporated into the

adult right atrium?


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Thank You


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Heart Development !

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