Keywords
anatomy - embryology - heart - morphology - rat
Introduction
The rat, among other animals, has been used in scientific experiments since the time
before Christ, and with the intensification of research, mainly in the nineteenth
century, there has been a great increase in the number of animals used.[1] Although rats are the most used animals in researches, followed by mice, according
to the data found in the last 4 years in databases such as Medline (85%) and Lilacs
(70.5%),[2] the availability of information on the anatomy of these animals is rare and difficult
to access.
Short Communication
As articles published in periodicals are very old, they are generally not readily
available, and, moreover, there are no books with a detailed anatomical description
of the heart of these animals. Thus, the purpose of this brief communication is the
organization and description of these data in digital media for their democratization
of .
Discussion
Embryology of the Cardiovascular System
The rat does not have brachiocephalic veins. The external jugular vein of the rats
is of relatively large caliber in comparison with the internal jugular and drain portions
of the head and neck. After crossing the first ribs, the external jugular veins empty
into the subclavian veins along with the corresponding internal jugular veins on each
side. They form two previous vena cava (superior), which enter the right atrium separately.[3]
The development of the previous vena cava in rats was studied in 15 embryos of different
ages (from 12 days and 11 hours–16 days) to identify the progress of development.
The first stage has been described at 12 days and 11 hours. The cardinal veins are
short, the heart is more cephalic. At this stage, most of the segments drain into
the posterior cardinal veins, with the exception of the two first cephalic segments.
At 12 days and 23 hours, the embryo is typical, with previous mammal cardinal vessels
nourishing and draining the head (cephalic segments), and the posterior cardinal vessels
nourishing and draining the caudal region. Each corresponding cardinal vein bonds,
thus forming the common cardinal vein (or duct of Cuvier), which flows into the venous
sinus. The structure that will form the subclavian vein, for example, drains into
the posterior cardinal vein. In the later stages, there will be a gradual change because
besides the veins of the cervical segment, some veins of the upper thoracic segment
begin to drain the previous cardinal veins. In the embryo at 13 days and 11 hours,
the heart migrates caudally, and there is an increase in the number of segments linked
to the previous cardinal veins. For the first time during development, the right posterior
cardinal vein is lower than the left one. The cervical segments drain into the previous
cardinal veins, and the thoracic segment into the posterior cardinal veins. The thoracic
segments are the intercostal veins that in the adult animal drain into the azygos
vein. At 14 days and 1.5 hours, the highest thoracic segment forms an anastomosis
with the Cuvier duct immediately behind the entry of the posterior cardinal vein,
and the subclavian veins drain the preceding cardinal vein. The posterior cardinal
veins are smaller for the formation of the azygos system, and there, the posterior
cardinal veins are smaller than the anterior cardinal veins for formation of the azygos
system. At 14 days and 11 hours, the azygos system goes through the most relevant
phase of its development. The terminology of the previous portions of the caval system
can be the same as that of the adult animal. The internal jugular appears. At 16 days,
the veins are almost fully developed, as they will be when the animals reach the adult
stage. So, the appearance of the superior right and superior left vena cava is the
result of the development of the terminal segment of the anterior cardinal veins and
the Cuvier duct.[3]
Anatomy of the Cardiovascular System
The mouse has a dual blood supply system in the heart. This system is found in fish
and some mammals, but tends to disappear during the phylogenetic development. Halpern’s
studies in the 1950s concluded that the rat’s heart is nourished by coronary arteries
and an extracardiac system.[4]
[5]
The right and left coronary arteries are responsible for supplying the ventricles
and interventricular septum. The right coronary artery is also responsible for the
supply of the atrial septum. Extracardiac vessels are branches of cardiomediastinal
arteries, internal mammary or the subclavian. The arteries of the right side are responsible
for the supply of the right and left atria. The arteries of the left side supply a
small portion of the left atrium. According to the study, this system maintains a
close relationship with the right atrium and the sinoatrial node. As the mouse has
this well-developed region, there is high metabolic activity that requires adequate
blood supply. Moreover, the presence of this system favors searches requiring deviation
in the blood stream since the supply is separated from the atria and ventricles and
thus the supply of the sinoatrial node and the atrioventricular is also independent
([Fig. 1A] and [B]).[5]
Fig. 1 (A) Figure with details of the branches of the cardiomediastinal artery in right lateroventral
view responsible for the nutrition of the right and left atria. Halpern[4]. (B) Figure shows the left coronary artery and the cardiomediastinal artery and its two
branches that will assist in the nutrition of a small portion of the left ventricle.
Halpern[4].
[Fig. 1]: A- The figure with details of the branches of the cardiomediastinal artery in right
lateroventral view. These are responsible for the nutrition of the right and left
atria. Halpern[4]. B- The figure shows the left coronary artery and the cardiomediastinal artery with
its two branches that will assist in the nutrition of a small portion of the left
ventricle. Halpern[4].
Another system seen in other mammals consists of veins that start in the heart and
end in the previous vena cava. It consists of two major veins that cross the midline
and empty into the previous vena cava contralateral to its origin. They drain the
ventricular region of the right cone and the ventrocephalic region of the left ventricle.
The author uses the term “extracoronary cardiac veins” because they originate in the
heart, but have no relation to the coronary circulation ([Fig. 2]).[5]
Fig. 2 Dorsal view of an adult rat heart showing the relationship of the veins to the coronary
sinus. Halpern[5].
[Fig. 2]: Dorsal view of the heart of an adult rat showing the relationship of the veins
to the coronary sinus. Halpern[5].
Studies have occasionally described some of the structures of the rat heart. Young
and Fell described the vascular connections between the coronary circulation and the
ventricles of the rat's heart. The veins of Tebesius are probably remaining in the
adult heart, supplying made in embryonic myocardial sinusoids through vessels that
connect and form the coronary veins.[6]
Hebel & Stromberg describe the dynamic input and output of the arteries and veins
in the rat's heart in relation to the heart chambers and some peculiarities in the
macro and microscopic differences between these chambers, such as the presence of
two superior vena cava. The authors refer to them as right cranial vena cava and left
cranial vena cava, and they drain along with the caudal vena cava to the right atrium
venous sinus.[7]
Greene[8], when describing the veins of the chest, appoints the two superior vena cava in
the rat: left and right. They are formed by the confluence of the internal jugular
vein and subclavian on the first rib level, pass the ventral origin of the subclavian
arteries and run in caudal direction until they reach the right atrium. The right
vein is shorter and opens directly in the anterior portion of the atrium. The left
vein extends posteriorly across the arch of the aorta, pulmonary vessels and left
bronchi to enter the atrium above the inferior vena cava.
Since the persistence of two superior vena cava is a normal condition in rats, there
is the formation of the right and left venous brachiocephalic trunks and their consequent
fusion in the superior vena cava. The tributaries of the left vena cava are the vertebral,
internal mammary, pericardial mediastinal, bronchial, superior intercostal, superior
phrenic and azygos veins.[8]
Therefore, according to previous studies, although the rat has been used as a mammal
model in several areas, such as descriptive and experimental cardiac embryology and
experimental teratology, considerable variations and discrepancies have been found
in the literature that have resulted in various controversies and inconsistencies.
Therefore, this article aims to become an accessible and direct guide for scientific
consultation.[9]
