The Circulatory System
Circulatory System
• The Circulatory System has two major
subdivisions:
1. The cardiovascular system: The heart
1. The lymphatic system: Pumpless system of
vessels and lymphoid organs that aids the
cardiovascular system
Cardiovascular System
Location and Size
• Location and size:
- Approximately the size
of a person’s fist, the
hollow, cone-shaped
heart weighs less than a
pound
- The heart is located
within the bony thorax
and is in between the
lungs
Location and Size
• Location :
- Its more pointed apex is
directly toward the left hip
and rests on the
diaphragm, approximately
at the level of the fifth
intercostal space
- Its base, from which the
great vessels of the body
emerge, points toward the
right shoulder and lies
beneath the second rib
Coverings and wall
• The heart is enclosed by a
double sac of membrane, the
pericardium:
- The thin visceral pericardium,
or epicardium, tightly hugs
the external surface of the
heart and is actually part of
the heart wall
- The fibrous layer, parietal
pericardium, helps protect the
heart and anchors it to
surrounding structures, such
as the diaphragm and the
sternum
Coverings and wall
• A slippery lubricating fluid
is produced by the
pericardial membranes:
- This fluid allows the heart
to beat easily in a
relatively frictionless
environment as the
pericardial layers slide
smoothly across each
other
Pericarditis
• Inflammation of the
pericardium, often
results in a decrease in
the amount of fluid
• This causes the
pericardial layers to bind
and stick to each other,
forming painful
adhesions that interfere
with heart movements
Heart Wall - Myocardium
• The heart walls are composed of
three layers:
- The outer epicardium, the
myocardium, and the innermost
endocardium
• The myocardium consists of thick
bundles of cardiac muscle twisted
and whorled into ring like
arrangement
- It is the layer that actually
contracts
- It is reinforced internally by a
dense, fibrous connective tissue
network called the “ skeleton of
the heart”
Heart Wall - Endocardium
• The endocardium is a
thin, glistening sheet
of endothelium that
lines the heart
chambers
• It is continuous with
the linings of the
blood vessels leaving
and entering the heart
Our circulatory system is a double circulatory system.
This means it has two parts parts.
Pulmonary
Circulation:
Lungs
the left side of the
system: carries
oxygenated blood
away from the heart
the right side of the
to the body, and
system: carries
returns
deoxygenated blood
deoxygenated blood
away from the heart,
back to the heart
to the lungs, and
returns oxygenated
blood back to the
heart
Body cells
Systemic
Circulation
Superior
Vena
Cava
Aorta
Left pulmonary artery
right pulmonary
artery
Pulmonary
semilunar
valve
right pulmonary
veins
Right atrium
Left pulmonary
veins
Left atrium
Aortic
semilunar
valve
Tricuspid valve
Bicuspid valve
Right ventricle
Interventricular
septum Left ventricle
Inferior
Vena
Cava
Valves – AV valves
• The atrioventricular or AV valves
are located between the atrial and
ventricular chambers on each side
• The AV valves prevent backflow
into the atria when the ventricles
contract
• The left AV valve
- Bicuspid (mitral) valve: consist of 2
cusps, or flaps, of endocardium
• The right AV valve
- Tricuspid valve: has 3 cusps
• Tiny white cords, the chordae
tendineae (heart strings), anchor
the cusps to the walls of the
ventricles
Valves – semilunar valves
• The semilunar valves guards the
bases of the two large arteries
leaving the ventricular chambers
• Thus, they are known as the
pulmonary and aortic semilunar
valves
• Each semilunar valve has 3
cusps that fit tightly together
when the valves are closed
• When the ventricles are
contracting and forcing blood
out of the heart, the cusps are
forced open and flattened
against the walls of the arteries
Stage 1
Blood enters the heart through a
vein known as the vena cava. The
blood is low in oxygen. The first
chamber it goes into is the right
atrium.
Stage 4
The blood returns from the lungs with
lots of oxygen and re-enters the heart
through the left atrium.
Stage 2
The heart pumps the blood
from the right atrium into the
right ventricle.
Stage 5
The heart pumps the blood
from the left atrium into the
left
Stage 3
The heart pumps the blood from the right
ventricle through the pulmonary artery
towards the lungs.
Stage 6
The heart then pumps the
blood from the left ventricle
out of the heart to the rest
of the body through the
aorta.
Cardiac Circulation
• In reality, blood enters and exits both sides of
the heart at the same time.
blood from the
body
blood from
the lungs
The heart beat begins when the
heart muscles relax and blood
flows into the atria.
• The atria then contract and
the valves open to allow
blood
into the ventricles.
• The valves close to stop blood
flowing backwards.
• The ventricles contract forcing
the blood to leave the heart.
• At the same time, the atria are
relaxing and once again filling
with blood.
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