I.
It includes the heart and blood vessels.
II. Heart structure and location
A. Hollow, cone shaped muscle
B. It lies slightly to the left side of the body and its base
touches the diaphragm.
C. The layered PERICARDIUM
covers the
heart.
1. The outer portion, FIBROUS
PERICARDIUM, is a tough
protective sac. It attaches to
the center of the diaphragm.
2. The inner portion is a double layered membrane.
a. The inner layer, VISCERAL PERICARDIUM,
covers the heart.
b. At the base of the heart the visceral pericardium
turns back on itself to become the PARIETAL
PERICARDIUM.
1. Between the visceral and parietal layers is a
space, the PERICARDIAL CAVITY, that is filled
with lubricating serous fluid.
D. The wall of the heart is made of three layers.
1. The outer EPICARDIUM is a protective membrane.
It has blood and lymph capillaries and nerve fibers.
2. The middle MYOCARDIUM is thick and made mostly
of cardiac muscle. It functions to pump blood.
3. The inner ENDOCARDIUM
lines all heart chambers and
structures (like valves, etc.)
E. Four heart chambers and
valves
1. ATRIA (singular - atrium)
two upper chambers that
receive blood returning
to the heart.
a. Atria separated by INTERATRIAL SEPTUM.
2. VENTRICLES : two lower chambers that force
blood into arteries leaving the heart.
a. Ventricles separated by INTERVENTRICULAR
septum.
3. An ATRIOVENTRICULAR orifice is a space that
allows the atrium and ventricle to communicate.
a. The right atrioventricular valve is called the
TRICUSPID valve. It has three cusps that ensure
that blood only moves from the atrium to the
ventricle.
b. The left atrioventricular valve is
called the MITRIAL valve (or the
BICUSPID).
c. The PULMONARY valves are found
at the base of the pulmonary
arteries (take blood to lungs).
They prevent blood from flowing
back into the ventricles.
4. An AORTIC valve prevents blood from moving back
into the ventricles from the aorta.
a. The aortic and pulmonary valves are also called
semilunar valves.
III. Blood Vessels
A. Arteries are strong, elastic vessels that are designed to
carry blood away from the heart under high pressure.
They branch into the smaller arterioles.
1. Three layered structure
a. The inner layer is smooth surface so platelets
and blood can flow through without being
damaged. It also secretes chemicals that
prevent clotting.
b. The middle layer is elastic to accommodate
changes in blood volume and strength to
withstand the force of blood pressure.
c. The outer layer is thin and attaches the artery
to the surrounding tissues.
2. Artery walls are adapted for
VASOCONSTRICTION and VASODILATION to
control blood flow.
B. Capillaries are the smallest blood
vessels with thin semi-permeable
walls(for gas exchange). They connect
to small arterioles and veinules.
1. The openings in capillaries are slits of overlapping
tissue.
2. Capillary networks are denser in areas with high
metabolism, like muscle and nerve tissues.
3. Precapillary sphincters contract to cut off blood flow.
They relax to restore flow when O2 and
nutrients are low.
C. Veinules emerge from capillaries and
form veins that carry blood back to
the heart.
1. Vein structure is similar to that
of the arteries, except that the
inner layers of vein walls are not
as developed.
2. Veins have valves that keep blood flowing
in one direction, back to the heart.
IV. Path of blood flow
A. The PULMONARY CIRCUIT
consists of vessels that carry
blood from the heart to the
lungs, and back again. It
functions to exchange CO2
and O2.
Right Ventricle
O2 poor blood
Pulmonary trunk divides into right
and left pulmonary artery
In lung, artery leads to smaller arterioles, then capillaries.
O2 gets picked up, then capillaries branch to larger
veinules, then the pulmonary vein.
O2 rich blood
Pulmonary Veins
Left Atrium
V. Blood enters the SYSTEMIC
CIRCUIT at the left ventricle. It
leaves the heart through the aorta and
travels to body tissues, then back to
the heart to enter the pulmonary
circuit. It’s function is to drop off
oxygenated blood at the tissues and
pick up CO2.
Left Ventricle
Aorta
Arteries
Tissues
Veins
Superior / Inferior Vena Cava
VI. A cardiac cycle is a complete heartbeat
A.
Steps
1. Both Atria contract (atrial
SYSTOLE) while both ventricles
relax (ventricular DIASTOLE).
2. Both ventricles contract (ventricular
systole) while both atria relax
(atrial diastole).
3. The atria and ventricles both relax.
B. The cardiac cycle depends on changes in pressure.
1. Early ventricular diastole: Pressure is lower than in
the atria, causing the AV valves to open and
ventricles to fill with about 70% of the blood.
2. Ventricular pressure increases.
3. The atria contracts and forces the remaining 30%
of blood into the ventricles.
4. The ventricles contract, pressure rises and the AV
valves close.
5. Pressure in the atria is now low, causing blood to flow
into them from the veins.
6. Ventricular systole progresses and pressure is
higher than it is in the aorta and pulmonary trunk.
7. Aortic and pulmonary valves open and eject blood into
arteries.
8. Blood leaves the ventricles and pressure drops lower
than it is in the aorta and pulmonary trunk.
9. Semilunar valves close.
10. When ventricular pressure is lower than atrial
pressure, AV valves open and ventricles fill with blood.
11. For a moment,
both the atria and
ventricles are
relaxed.
12. Ventricular systole
begins again.
VII.Heart sounds : Lubb-dupp
A.
Lubb occurs during ventriclular systole when the AV
valves close.
B.
Dupp occurs during ventricular diastole when the
pulmonary and aortic valves are closing.
VIII. Cardiac conduction
A.
Electrical pulses in the
heart are controlled by
bundles of cells called
nodes.
B.
The SINOATRIAL NODE
(SA node) makes an
electrical signal that
causes the atria to
contract. The SA node is
also known as the
pacemaker.
C. The signal travels to the ATRIOVENTRICULAR NODE
(AV node) and causes the ventricles to contract.