The Cardiovascular system
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The cardiovascular system
 The cardiovascular system includes:
- heart
- blood vessels
 Performs the function of pumping and
carrying blood to the rest of the body.
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The Heart
-The heart is the central organ of the thorax
- In the dog, the heart lies caudoventrally between the
third and seventh ribs and slightly to the left.
- In the horse, the heart lies dorsalventraly between
the third and sixth ribs and slightly to the left.
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Pericardiumthe fibroserous sac enclosing
the heart, composed of:
A. fibrous pericardium
B. serous pericardium
- and covered by the
pericardial mediastinal pleura
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A. Fibrous pericardium- tough, fibrous sac
surrounding the serous pericardium, the heart
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and
pericardial cavity
B. Serous pericardium
- a serous membrane forming
a closed cavity, composed of :
1. Parietal layer of Serous pericardium 6
lines the inner surface of the fibrous
pericardium
B. Serous pericardium- cont.
2. Visceral layer of Serous pericardium -
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covers the myocardium of heart
also called: epicardium
C. pericardial cavity: potential space between
the visceral and parietal layers of serous pericardium
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contains
~ 1 ml of serous fluid that acts as a lubricant
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the pericardial mediastinal pleura covers the
fibrous pericardium
Structure
 The heart is
roughly conical with
the base being
dorsal and the apex
close to the sternum
opposite the sixth
costal cartilage.
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Structure
- The base is formed by
the thin walled atria
which are clearly
separated from the
ventricles by an
encircling coronary
groove
- coronary groove
contains the main
coronary vessels.
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General anatomy of the heart
In the adult it consists of four chambers:
1. Right atrium
2. Left atrium
3. Right ventricle
4. Left ventricle
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Structure
- The ventricles constitute a much larger part of
the heart which is much firmer than the atria
due to muscular walls
- The left being much thicker than the right.
- The right ventricle lies as much cranially as to
the right of the left ventricle.
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Right atrium
The caudal vena cava
enters the chamber above
the opening of the coronary
sinus.
The cranial vena cava opens
at the terminal crest.
The intervenous tubercle
separates the two caval
openings preventing
confrontation between the
15 two streams.
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Right atrium
Caudal to the tubercle lies the fossa ovalis which
corresponds to the foramen ovale of fetal life.
The right auricle is a blind-ended sac extending to
the cranial face of the pulmonary trunk.
Pectinate muscles within the auricle branch from
the terminal crest which marks the boundary
between the auricle and the main atrium.
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Left atrium
Similar form to the right atrium.
Receives pulmonary veins which enter at
two or three sites.
Auricle similar to right.
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Right ventricle
Receives blood from right atrium through right
atrioventricular valve (tricuspid).
Cusps are joined by fibrous Chordae Tendinae
which attach to papillary muscles on ventricular
wall.
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Right ventricle

Lumen of ventricle crossed by septomarginalis
trabecula (muscle band extend from septum to
lateral wall).

Blood flows through semilunar pulmonary valve
to pulmonary trunk.
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Left ventricle
 Left atrioventricular valve is bicuspid and
much larger and stronger than the right.
 The ventricular wall is much thicker than
on the right due to high resistance of the
systemic circulation.
 Blood leaves the ventricle via the
semilunar aortic valve into the aorta.
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Cardiac vessels
• The heart tissue receives 15% of the
cardiac output from the left ventricle.
•
• This travels in two arteries from sinuses
just above the aortic valve.
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Dog Heart
arteries and veins contrasted
The Heart
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The coronary veins
– Blood returns to the heart via the cardiac vein.
– This opens into the the right atrium via the
coronary sinus just below the entrance of the
caudal vena cava.
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Systemic circulation
• The systemic arteries:
• The aortic arch
• The origin of the aorta is similar to that of
the pulmonary trunk but is from the left
ventricle.
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Arteries and Veins Cranial to the Heart
dog-dorsal view
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3
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4 8
5
1
7
3
5
6
2
6
4
8
4
3
5
7
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Cow
Horse
heart
heart
I. Arteries- Branches of the Aortic Arch
A. Dog
heart
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1. Brachiocephalic trunk- 1st branch from the aortic arch,
gives rise to: (2) left common carotid artery and
terminates as the (3)right common carotid artery
and (4) right subclavian artery
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4
1
5. left subclavian artery- originates from aortic arch
beyond the brachiocephalic trunk
B. Horse and Ruminant:
1. Brachiocephalic trunk- only branch from the aortic
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arch.
(2) left and (3) right common carotid arteries
do not arise separately as in dog, but from a (6)common
bicarotid trunk
Dog-ventral view
 The common carotid arteries supply structures
of the head.
 The subclavian artery supplies blood to the
forelimb and to structures of the neck and
cerviocothoracic junction .
 It winds around the cranial border of the first
rib to enter the limb through the axilla ,it
changes its name to axillary at this point.
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The subclavin detaches four branches
in its intrathoracic course:
1. The vertebral artery
1. The costocervical trunk
1. The internal thoracic artery
1. The superficial cervical artery
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The thoracic aorta
•
The thoracic aorta runs caudally
below the roof of the thorax to enter the
abdomen by the aortic hiatus of the
diaphragm .
• It continues as the abdominal aorta
in company with the azygous vein and
thoracic duct.
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The systemic veins
 The systemic veins return blood to the
heart through the cranial vena cava ,
caudal vena cava and coronary sinus.
 The cranial vena cava :
- is formed close to the entrance to the
chest by the union of the external jugular
and subclavian veins.
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The systemic veins

The caudal vena cava:
- is formed on the abdomen near the pelvic inlet ,
by the union of right and left common iliac veins.
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Diaphragm
Diaphragm consists
of contractile
skeletal
muscle, innervated
by phrenic nerve
Openings in Diaphragm:
1. Aortic hiatus-(hiatus- term for gap, cleft, or opening)dorsal part of diaphragm, passage of aorta, azygos, and
thoracic duct
2. Esophageal hiatus- centrally located and ventral to
aortic hiatus,
passage of esophagus
3. Caval foramen- to right\ventral of esophageal
hiatus, passage of caudal vena cava
dog