The Heart The heart or cardiac muscle is a hollow cone shaped muscular organ that is divided into...
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The HeartThe 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
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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
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The Structure of the HeartThe 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
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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)
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The Chambers of the HeartThe 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
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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.
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The atrium have thin walls and are receiving chambers. The
ventricles do the pumping and have thick walls
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The right side of the heart receives blood from the body and sends it to the lungs to be oxygenated.
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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.
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ValvesBetween 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.
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The semilunar valves prevent backflow from the arteries into the ventricles and are located at the base of the pulmonary and
aortic arteries.
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Conduction SystemThe 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
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The atrioventricular node (AV node)
This consists of cells that conduct the electrical impulses down to:
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The atrioventricular bundle (bundle of his)
This continues down as the Purkinje fibers which stimulate
ventricular contraction
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Purkinje fibers
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Nerve Function:The autonomic nervous system has two divisions with opposite
actions within the heart.
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The parasympathetic division:Mainly supplies the SA and AV nodes. This slows the heart rate, reduces impulse conduction and constricts the coronary arteries
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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
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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.
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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
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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
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Blood vessels:arteries
capillaries veins
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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)
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Arterioles, capillaries and venulesAteries 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
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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
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