The Cardiovascular Circulatory System
The Layers of the Heart Wall
- The outermost layer is called the epicardium or
visceral pericardium. It consists of serous tissue
and mesothelium.^
- A space called the pericardial cavity separates the
epicardium of the heart from the serous pericar-
dium of the pericardial sac.^
- The second layer of the heart is the myocardium.
This makes up the bulk of the heart and consists of
cardiac muscle tissue.^
- The innermost third layer of the heart is the endo-
cardium. It is the endothelial lining of the heart.
The Chambers of the Heart
- The heart is divided into four chambers: two upper
and two lower.^
- The upper chambers are the right atrium and the left
atrium separated internally by an interatrial septum.^
- Each atrium has an external appendage called an
auricle, whose rough appearance is caused by the
musculi pectinati.^
- The lower chambers are the right ventricle and the
left ventricle, which are separated internally from
one another by the interventricular septum.^
- Externally, the coronary sulcus, a groove, separates
the atria from the ventricles.^
- The anterior and posterior interventricular sulci sep-
arate the ventricles from one another externally.
The Great Vessels of the Heart
- The superior or anterior vena cava receives blood
from the upper parts of the body.^
- The inferior or posterior vena cava receives blood
from the lower parts of the body.^
3.^ The coronary sinus drains blood from the heart.^
4. The pulmonary trunk splits into the right and left
pulmonary arteries, which carry deoxygenated
blood to the lungs.^
- The four pulmonary veins return oxygenated blood to
the heart.^
- The ascending aorta carries oxygenated blood away
from the heart to all parts of the body. It is divided
into the arch of the aorta, the descending thoracic
aorta, and the abdominal aorta.^
- Atrial walls are thin, while ventricle walls are
thick. Of the two ventricles, the left ventricle has
the thickest- walls of cardiac muscle because of
the great distance it must transport blood.
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The Valves of the Heart- Valves prevent blood from backflowing. The heart has
two atrioventricular valves and two semilunar valves.^ - The tricuspid valve is found between the right
atrium and the right ventricle. It is made of three
cusps or flaps.^ - The bicuspid or mitral valve is found between the
left atrium and the left ventricle. It is made of two
cusps or flaps.^ - The cusps of the valves project into the ventricles by
the chordae tendineae, which connect to papillary
muscles in the ventricles, thus ensuring a one-way
blood flow.^ - The pulmonary semilunar valve is found in the right
ventricle where the pulmonary trunk exits the heart.^ - The aortic semilunar valve is found in the left ven-
tricle where the ascending aorta leaves the heart.^ - The semilunar valves are made of three cusps
or flaps.
Blood Flow Through the Heart- Deoxygenated blood returns to the heart from all
parts of the body via the superior (anterior) and in-
ferior (posterior) venae cavae to the right atrium of
the heart.^ - The blood is then squeezed through the tricuspid
valve into the right ventricle.^ - From the right ventricle the blood is pumped through
the pulmonary semilunar valve to the pul-monary
trunk, which divides into the right and left pulmonary
arteries.^ - The pulmonary arteries carry the blood to the lungs
where it releases carbon dioxide gas and picks up
oxygen.^ - The oxygenated blood returns to the left atrium of
the heart through four pulmonary veins.^ - The blood is squeezed through the bicuspid or mi-
tral valve into the left ventricle.^ - The left ventricle pumps the blood through the aortic-
semilunar valve to the ascending aorta, which
distributes the blood to all organs of the body.
The Conduction System
of The Heart- The conduction system of the heart generates and
distributes electrical impulses over the heart, which
cause contraction of the heart.