Download The chambers of the heart A- The right atrium: 1

Dr. Eman ----------------------------------------Angiology-------------------------------------First stage
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The chambers of the heart
A- The right atrium:
1-it is form the right cranial part of the base of the heart, placed dorsally to right
ventricle.
2- it is separated from the left atrium by septum which contain diverticulum called
oval fossa at the point of the entrance of the caudal vena cava, this fossa is remanent
of the opening in the septum called oval foramen, through which the two atria
communicate in the fetus.
Interatrial septum: the septum is a small flap that covers the foramen ovale on its
left side. This flap of tissue is called the valve of the foramen ovale. It opens and
closes in response to pressure gradients between the left and right atria. When the
pressure is greater in the right atrium, the valve opens; when the pressure is greater in
the left atrium, the valve closes. Because the lungs are nonfunctional in fetal life,
pressure in the pulmonary circulation is greater than that of the systemic circulation.
Consequently, the right atrium is generally under higher pressures than the left
atrium, and the valve of the foramen ovale is normally open.
At birth, there is a reversal in the pressure gradient between the atria, resulting in
functional closure of the valve of the foramen ovale. Permanent anatomical closure of
the foramen ovale occurs with time in normal infants. Inappropriate closure of the
foramen ovale results in patent foramen ovale
1-the sinus venarum cavarum: into which the veins open
2-Auricle: it is end ear shaped conical pouch, also termed auricular appendix
appearing on the left side cranially at the pulmonary artery. It is curved around right
and cranial surface of the atrium, the atrium is lined in all walls except the auricle by
glistening membrane (endocardium).
In the right atrium, behind the crest the internal surface of the atrium is smooth,
while in front of it the muscular fibers of the wall are raised into parallel ridges
resembling the teeth of a comb, and hence named the musculi pectinati (pectinate
muscles), it is ended by curved crest known as the crista terminalis of His,which is
line of union between the right atrium and the right auricle is present on the interior
of the atrium in the form of a vertical crest. On the external aspect of the right atrium,
corresponding to the crista terminalis is the sulcus terminalis .
There are five chief openings
1-The cranial (superior) vena cava: is one of the two main veins bringing deoxygenated blood from the body to the heart. Veins from the head and cranial body
feed into the superior vena cava, which empties into the right atrium of the heart
cranially .
Dr. Eman ----------------------------------------Angiology-------------------------------------First stage
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2-The caudal (inferior) vena cava: is one of the two main veins bringing deoxygenated blood from the body to the heart. Veins from the legs and caudal body
feed into the caudal vena cava, which empties into the right atrium of the heart
caudally .
Inter-venous crest : project ventral and cranial from the dorsal wall of opening of the
caudal vena cava. It tends to direct the flow of blood from the cranial vena cava to the
right atrioventricular opening.
3-The coronary sinus is a collection of veins joined together to form a large vessel
that collects blood from the myocardium. It is present in humans and other animals.
It's located in right atrium ventral to the caudal vena cava . It runs transversely in the
groove between the left atrium and ventricle on the caudal surface of the heart.
The coronary sinus orifice (opening) is just superior to the septal leaflet of the
tricuspid valve, and is guarded by the (Thebesian valve) which is a semicircular fold
of the lining membrane of the atrium, at the orifice of the coronary sinus. The valve
may vary in size, or be completely absent. It may prevent the regurgitation of blood
into the sinus during the contraction of the atrium. This valve may be double or it
may be cribriform. It is named for Adam Christian Thebesius
4-(Some small veins drain into any of the four chambers of the heart.) It drains into
the right atrium on the posterior surface, medial to the caudal vena cava opening.
5- Right atrioventricular opening is separates the right atrium from the right ventricle.
It’s guarded by Tricuspid Valve. The orifice is larger than the left atrioventricular
orifice (mitral orifice) and is triangular.
B-The left atrium :.
1- It receives oxygenated blood from the pulmonary veins, and pumps it into the left
ventricle, through the left atrioventricular orifice, which guarded by bicuspid or
mitral valve.
2-Attached to the left atrium is the left auricular appendix (auricle) extend lateral
and cranial on the left side . It is consistently narrow and long.
3-In the left atrium, the musculi pectinati, fewer and smaller than that in the right
auricula, unlike the right atrium, the left atrium has no crista terminalis. This is due
to the embryological origin of the auricles, which are the true atria . the musculi
pectinati are useful in increasing the power of contraction without increasing heart
mass substantially.
Dr. Eman ----------------------------------------Angiology-------------------------------------First stage
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There are two opening in left atrium :
1-Pulmonary Vein opening
The pulmonary vein is the vessel transporting oxygen-rich blood from the lungs to
the left atrium. (seven to eight in number in horse and five in sheep) found caudal to
auricle on the right side of atrium
2- left atrioventricular orifice(mitral orifice), which contains the bicuspid or mitral
valve . is situated ventral and cranially , it appear oval and smaller than the right one
because the contraction of the left ventricle in the dead subject
C-The right ventricle:. Consist of cranial part of the ventricular mass. It form the
cranial border of the heart,
1-It receives deoxygenated blood from the right atrium via the tricuspid valve, and
pumps it into the pulmonary artery via the pulmonary valve and pulmonary
trunk.
2-It is triangular in form, and extends from the right atrium to near the apex of the
heart .
3-The wall of the right ventricle is thinner than that of the left, the proportion
between them being as 1 to 3; it is thickest at the base, and gradually becomes thinner
toward the apex. The of right ventricle cavity equals in size that of the left ventricle.
4-The upper left corner of the right ventricle, is called the infundibulum or conus
arteriosus, is a conical pouch at the entrance of pulmonary trunk . The wall of the
infundibulum is smooth.
5-the all wall of the ventricular except in the conus arteriosus bear muscular ridge and
bands termed the trabeculae carneae.
Pulmonary trunk
The pulmonary trunk
branches into the pulmonary arterial system which
transporting de-oxygenated blood from the right ventricle to the lungs.
D-The left ventricle
1-is longer and more conical in shape than the right, and on transverse section its
concavity presents an oval or nearly circular outline. It form the left caudal part of
ventricular mass.
2-it also forms the apex of the heart.
3-The left ventricle is thicker and more muscular than the right ventricle because it
pumps blood at a higher pressure.
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Interventricular septum (IVS), is separating the lower chambers (the ventricles)
of the heart from one another.
The ventricular septum is directed obliquely backward and to the right, and is curved
with the convexity toward the right ventricle: its margins correspond with the anterior
and posterior longitudinal sulci.
Disorders A hole in the interventricular septum is termed a ventricular septal defect
(VSD).
Atrioventricular septum
The atrioventricular (AV) septum, located behind the right atrium and left ventricle,
is divided into two portions: a superior portion (membranous) and an inferior
portion (muscular). The atrioventricular (AV) node lies in the atrial septum,
juxtaposed to the membranous and muscular portions of the AV septum