2. • The heart is the pump of the
cardiovascular system.
• The heart's contractions continually
propel the blood through hollow blood
vessels.
• The blood vessels transport blood to the
body's tissues and back to the heart
again.
3. LOCATION & SIZE OF THE HEART:
• The heart is
a hollow
organ that is
about the
size of a
person's
fist. The
heart weighs
about 300
grams
(about 10
oz). The
heart is
about 12 cm
(5 inches)
long.
4. • The heart is snugly enclosed within the region between the lungs
called the MEDIASTINUM.
• In other words, the heart lies anterior to the vertebral column,
posterior to the sternum and medial to the overlapping lungs.
• The heart tips slightly to the left.
• About 2/3's of its mass can be seen to the left of the body's
midline.
• Its broad superior
portion (called the
BASE) is about 9 cm
(3.5 inches) wide and is
directed toward the
right shoulder.
• Its more pointed APEX
is directed inferiorly
toward the left hip and
rests on the
DIAPHRAGM.
5. COVERINGS OF THE HEART:
• The heart is enclosed within a thin double-layered sac of SEROUS
MEMBRANE called the PERICARDIUM. The PARIETAL PERICARDIUM
lines the internal wall of the PERICARDIAL CAVITY.
• At the superior part of the heart (the heart's BASE), the parietal
pericardium turns downward and continues over the heart surface as
the VISCERAL PERICARDIUM. The VISCERAL PERICARDIUM is the
outer layer of the heart wall and often contains fat, particularly in
older people.
6. • Between the VISCERAL PERICARDIUM and the PARIETAL
PERICARDIUM is a potential space, called the PERICARDIAL
CAVITY, which contains a small amount of thin serous fluid,
called PERICARDIAL FLUID.
• The pericardial fluid lubricates the serous membranes so they
glide smoothly against one another during the heart beat,
allowing the heart to beat in a relatively friction-free
environment.
7. HEART WALL:
• The heart wall is composed of 3 layers: the outermost EPICARDIUM,
the middle MYOCARDIUM, and the innermost ENDOCARDIUM.
• The EPICARDIUM is another name for the VISCERAL PERICARDIUM
surrounding the outside of the heart.
• The MYOCARDIUM is composed mainly of cardiac muscle tissue with
some connective tissue. It is the thickest layer of the heart wall. This is
the layer that actually contracts and beats the heart.
• Note the
INTERCALATED
DISCS between the
cardiac muscle
fibers.
• INTERCALATED
DISCS contain GAP
(COMMUNICATING
) JUNCTIONS
through which
electrical impulses
can travel from cell
to cell.
8. • The ENDOCARDIUM is a glistening white sheet of
ENDOTHELIUM overlying a thin connective tissue
layer.
• ENDOTHELIUM is a layer of simple squamous
epithelium that lines the walls of the heart and blood
vessels.
• The endocardium lines the heart chambers and covers
the heart valves.
• The endocardium is continuous with the endothelial
linings of the blood vessels entering and leaving the
heart.
9. CHAMBERS OF THE HEART AND ASSOCIATED GREAT
VESSELS:
• The heart has 4 chambers: the superior LEFT and RIGHT ATRIA and
the inferior LEFT and RIGHT VENTRICLES.
• Note that the LEFT VENTRICLE forms the APEX of the heart. The 2
atria are separated by the INTERATRIAL SEPTUM and the 2
ventricles are separated by the INTERVENTRICULAR SEPTUM.
10. • An external groove in the heart called the CORONARY SULCUS
separates the atria from the ventricles.
• The ANTERIOR INTERVENTRICULAR SULCUS is an external groove
that separates the right and left ventricles.
• The POSTERIOR INTERVENTRICULAR SULCUS separates the right and
left ventricles on the posterior side of the heart. The sulci are grooves
that contain coronary blood vessels and some fat.
11. • Functionally, the ATRIA are receiving chambers for blood
returning to the heart from circulation.
• Because they need to contract only minimally to push blood into the
ventricles, the atria are relatively small, thin-walled chambers.
They contribute little to the propulsive pumping activity of the
heart.
12. • The VENTRICLES are the discharging chambers or actual pumps of the
heart; when they contract, blood is pushed out of the heart into
arteries to be circulated to other parts of the body.
• The ventricle walls are more muscular, and therefore thicker, than the
atrial walls, because the ventricles have to pump blood out of the heart.
13. PATHWAY OF
BLOOD
THROUGH THE
HEART:
The heart actually
consists of 2 side-by-
side pumps, each
serving a separate
blood circuit: the
pulmonary circuit
and the systemic
circuit. The
pulmonary circuit
receives low oxygen
blood returning from
the body and sends it
to the lungs for
oxygenation. The
oxygenated blood
then returns to the
heart. The systemic
circuit supplies the
entire body with
oxygenated blood.
14. The right side of the heart is the pulmonary
circuit pump.
Blood returning from the body, which is relatively
OXYGEN-POOR and CARBON DIOXIDE-RICH,
enters the RIGHT ATRIUM from the superior
vena cava, inferior vena cava & coronary sinus.
The SUPERIOR VENA CAVA returns blood from
body regions superior to the heart.
The INFERIOR VENA CAVA returns blood from
body areas inferior to the heart.
The CORONARY SINUS collects blood from veins
in the heart wall. The blood passes from the
RIGHT ATRIUM into the RIGHT VENTRICLE,
which pumps the blood into the PULMONARY
TRUNK. The pulmonary trunk divides into the
RIGHT and LEFT PULMONARY ARTERIES, each
of which carries blood to each lung. In the lungs,
the pulmonary arteries divide into CAPILLARIES,
that are closely associated with the AIR SACS of
the lungs. Gas exchange takes place here between
the capillaries and air sacs: the blood releases
carbon dioxide to the air sacs and oxygen moves
from the air sacs into the blood. The capillaries
merge into the four PULMONARY VEINS which
return the oxygenated blood to the LEFT
ATRIUM.
15. • The left side of the heart is the
systemic circuit pump.
• Blood in the LEFT ATRIUM passes
from the left atrium into the LEFT
VENTRICLE.
• The left ventricle pumps the blood into
the AORTA.
• The aorta branches into smaller
SYSTEMIC ARTERIES that carry
blood to the body tissues, where
exchange of gases and nutrients occurs
across the capillary walls.
• The capillaries empty the oxygen-
depleted blood into systemic veins.
• The systemic veins merge together,
eventually emptying into the
SUPERIOR or INFERIOR VENA CAVA.
The SUPERIOR and INFERIOR VENA
CAVAE deliver the blood to the RIGHT
ATRIUM. And now the pulmonary
circuit begins again.
