Transcript Heart - Catherine Huff`s Site

The Heart
The heart or cardiac muscle is a
hollow cone shaped muscular
organ that is divided into four
chambers. The heart straddles the
midline within the thoracic cavity
just dorsal to the sternum
The base of the heart is located
craniodorsally and the apex points
ventrally and to the left. The
apex is free within the
pericardium. The heart is a pump
that circulates blood throughout
the body to nourish and remove
waste
The Structure of the Heart
The heart is covered by a saclike
membrane which has 3 layers
*pericardium
tough external layer
*parietal
the lining of the pericardium
*visceral
covers the surface of the heart
The space between the inner layers is the
pericardial space which contain
pericardial fluid
The heart is composed of three layers
The outer layer (epicardium)
The middle layer (myocardium, the
muscle itself)
The inner most layer (endocardium, lines
the chambers and covers the valves)
The Chambers of the Heart
The heart is divided into a right
and left side. The hollow of the
heart is divided into four
chambers. The cranial chambers
are called the atrium and the
ventral chamber is called the
ventricle
A wall (interatrial septum) divides
the atria into right and left sides. A
wall (the interventricular septum)
divides the ventricles into right
and left sides. There is no
communication between the two
sides.
The atrium have thin walls and
are receiving chambers. The
ventricles do the pumping and
have thick walls
The right side of the heart receives blood from the body and
sends it to the lungs to be oxygenated.
The left side of the heart receives
oxygenated blood from the lungs
and sends it to all tissues.
Because the left ventricle pumps
the blood to all of the body the
walls are much thicker.
Valves
Between the atria and ventricles
are valves that ensures that blood
flows in only one direction.
The right atrium and ventricle
are separated by the tricuspid
valve and the left atrium and
ventricle is separated by the
mitral or bicuspid valve.
The semilunar valves prevent
backflow from the arteries into
the ventricles and are located at
the base of the pulmonary and
aortic arteries.
Conduction System
The heart begins pumping in
utero. This action consists of:
sinoatrial node (SA node): called
the pacemaker. This impulse
contracts the atrium and forces
blood into the ventricles
The atrioventricular node (AV
node)
This consists of cells that conduct
the electrical impulses down to:
The atrioventricular bundle
(bundle of his)
This continues down as the
Purkinje fibers which stimulate
ventricular contraction
Purkinje fibers
Nerve Function:
The autonomic nervous system
has two divisions with opposite
actions within the heart.
The parasympathetic division:
Mainly supplies the SA and AV
nodes. This slows the heart rate,
reduces impulse conduction and
constricts the coronary arteries
The sympathetic division:
Through cardiac nerves and also
acts on the SA and AV nodes to
increase heart rate and impulse
conduction and dilate the
coronary arteries
Cardiac Cycle:
The cycle includes the contraction
(sysole) and relaxation (diastole) of the
atria and ventricles. The heart chambers
do not contract all at once. The two atria
contract in unison and as they relax the
two ventricles contract, as the ventricles
relax the atria contract.
When the atria contract they
force blood through the bicuspid
and tricuspid valves into the
ventricles, the semilunar valves
close to prevent blood from
entering the arteries
When the atria relax blood enters
the atrial chambers from the
pulmonary veins (left) and the
vena cava (right) and the
ventricles contract. When the
ventricles contract the bicuspid
and tricuspid valves close to
prevent backflow of blood into
the atria
Blood vessels:
arteries
capillaries
veins
Arteries:
Arteries carry oxygenated blood
to all structures of the body.
Ateries are elastic tubes with
thick walls composed of three
layers:
*tunica intima (inner)
*tunica media (middle)
tunica adventitia (outer)
Arterioles, capillaries and venules
Ateries become smaller and
smaller becoming arterioles. The
arterioles feed the blood into the
capillaries. The capillaries
distribute blood to all tissue and
return to the venules which pass
the blood into the veins which
return blood to the heart
Veins:
These are tubes similar to
arteries but have thinner and less
elastic walls. These transport
blood back to the heart. The
smallest veins (venules) collect
the blood from the capillaries
and connect to larger veins and
finally join the vena cava that
returns the blood to the heart