Contributions to the Ontogenetic Study Regarding the Evolution of the Primitive Cardiac Loop [602220]

Contributions to the Ontogenetic Study Regarding the Evolution of the Primitive Cardiac Loop
195Vol. X – Nr. 2 – 201 1 ORIGINAL PAPERSRevista Română de Anatomie funcțională ”i clinică, macro- ”i microscopică ”i de Antropologie
CONTRIBUTIONS TO THE ONTOGENETIC STUDY REGARDING
THE EVOLUTION OF THE PRIMITIVE CARDIAC LOOP
C. Panțu1, R. Tulin1,2, F . Filipoiu1, A. Tulin1, M. Enyedi1
1. University of Medicine and Pharmacy “Carol Davila “ Bucharest
Department of Anatomy
2. “C.I. Parhon” National Institute of Endocrinology, Bucharest
CONTRIBUTIONS TO THE STUDY REGARDING THE EVOLUTION OF THE PRIMITIVE
CADIAC LOOP (Abstract): The structural and functional organization of the heart myocardialmass is a controversial matter that cannot be resolved by anatomical studies alone. Therefore,other approaches such as investigations of the development of the primitive cardiac loop mighthelp to resolve controversies about the structural and functional organization of myocardium.Modern concepts regarding the spatial orientation of ventricular myocardium might be the mor-phological correlate of twists and torsions of the embryonic heart loop. In the present review,which only tries to be a contribution to the already well known studies, we highlight the eventsregarding the evolution of the primitive cardiac loop as one of the most important stages of cardiacdevelopment of which many mechanisms are still incompletely understood. Key words : CAR-
DIAC LOOP , SIGMOID HEART, SINUS VENOSUS, BULBUS CORDIS
INTRODUCTION
Since the cardiac tube is formed, nature
admirable start solving a problem of impres-sive difficulty: how it is possible from a rela-tively straight tube with an inflow and an out-flow pole, to achieve a four-chambered organwith six incoming blood vessels and two out-coming ones? The story of this success is stillincompletely known, situating ourselves in thestage where we hardly unravel the major me-chanisms. The determinism of these mecha-nisms is somewhere found in the biochemistry,molecular and genetic levels.
MATERIAL AND METHODS
For this study five embryonic hearts have
been used. The hearts were harvested fromabortion cases and were dissected using micro-dissection techniques under surgical magnifi-ers. Pictures were taken using a high resolutiondigital camera.
RESULTS AND DISCUSSIONS
The primitive cardiac tube is a relatively
straight tube having a superior extremity fromwich leaves the two dorsal aortas, and an infe-rior extremity-sinus venosus.
Sinus venosus presents to elongated por-
tions, the left and the right horn, in whichterminates three pairred veins: the viteline,umbillical and common cardinal veins. In thisstage of development, the cardiac tube consitsin several segments (dilated portions): the ar-terial trunk, bulbus cordis, primitive ventricle,primitive atrium and sinus venosus (1,2).
After this stage of development follows the
looping, torsion and differentiation of the pri-mitive cardiac tube. This process consits intwo major separate stages. We must point outthat the cardiac looping process is in reality acomplex modification in size and position ofdistinct segments of the primitive heart tubewhich occures in different rates for differentparts (3,4). Nevertheless, the cardiac loopingconsists in an accelerated process of cellulargrowth and differentiation.
A simple looping process would produce
similar changes on both sides of the plied tube.But inside, this could lead to the lumen’s stran-gulation. In the primitive heart loop obviouslythese things do not happen (5).
Transformation of the linear tube in a heli-

C. Panțu et al.
196Fig. 1. The cardiac loop stage
(“U” shaped heart)
Fig. 2. The sigmoid heart stage
(“cor sigmoideum”)
cal tube means that the inflow pole of the hearttube remains posterior and superior, the mid-dle region (ventricular region) forms the con-cavity in the lower loop and the outflow polereach the inflow pole, anterior and slightly tothe right of it. Between the cavities narrowedregions appears, being named bulboventricularsulcus and atrioventricular canal (this will be-come the atrioventricular junction) (6,7,8).
During this period, the growth of primitive
cardiac tube is marked by the marked dilata-tion of the ventricular segment. As a result, thegeneral disposition is that of a single loopedheart (towards right and cranial), leading tocomparisons with the appearance of the letter“U” (9,10).
The dilation process interests to both the
future sternocostal and diaphragmatic surface,but rather the future right ventricle. The sur-faces of these regions become greatly increased,especially compared to the outflow and the atrio-ventricular canal regions. The difference in sizeis reached, it is important to understand thefuture process of septum development (10,1 1,12).
Sinus venous remains fixed postero-inferior
to the transverse septum and its tributaries fromthe left decrease in size. Consequently the de-velopment of the right atrium will prevail.The primitive cardiac tube folding and the for-mation of the cardiac loop direct to the left theprimitive atrium. This way it outlines the de-velopment of an asymmetry in the atria (13).
The atrioventricular canal is placed in the
left midline continuing the future left atrium,while the sinoatrial junction is located right to
the midline, on the posterior wall of the futureright atrium. The primitive atrium appears as atransverse tube stretching between these twostructures (12,13,14).
The cardiac loop has a concave inner part
and a convex outer side. The ventricular devel-opment begins with an intense dilation of theventricular region on the convex margin.On the internal side, which remains far behindthe pace of development, the bulboventricularsulcus is better defined: this will eventuallybecome the interventricular sulcus (15).
The sinus venous, primitive atrium and its
mezocardic pedicle (which will form the primi-tive pulmonary vein), forms the inflow pole ofthe primitive cardiac tube. The bulbus cordisalong with the arterial trunk and aortic sacforms the outflow pole of the primitive cardiactube. The primitive ventricle will generate mostof the left ventricle.
The bulbus cordis will form the trabecular
part of the right ventricle and the subostialportion of the major arteries (cones or roots ofthe two major arteries). The arterial trunk gener-ates the intrapericardial part of these arteries.
At the end of the folding process:
• the outflow pole is located above the primi-
tive atrium and the atrioventricular canal
• the left ventricle is already dilated and well
structured and the right ventricle is stillhollow in aspect, attached to the anterola-

Contributions to the Ontogenetic Study Regarding the Evolution of the Primitive Cardiac Loop
197teral surface of the left ventricle (16,17,18,
19,20).
CONCLUSIONS
The growth rate difference between the two
ventricles is evident. The interventricular sul-cus and the anterior and left ventricular apexare well formed (week 6-7). On the diaphrag-matic surface, however, the posterior interven-tricular sulcus is barely evident. This differ-ence in evolution of heart on both sides, sug-
gests that the so called looping process of car-diac tube is not completed on the diaphragmaticsurface in the same intensity as in the sterno-
costal one, so it encompasses the entire diam-
eter of the cardiac tube.
Consequently, the atrial blood simultaneously
reaches both ventricles and not in succession,
first in the left then the right ventricle (21).
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