THE HEART
• Location: Thoracic cavity directly behind
the breastbone(sternum)
• Surrounded by the pericardium
• 4 Chambers: 2 atria and 2 ventricles
• Blood vessles:
– Veins:
• Superior vena cava
• Inferior vena cava
• Pulmonary veins – left and right
• Arteries:
– Aorta
– Pulmonary
• Blood is pumped through the chambers,
aided by four heart valves
• The valves open and close to let the blood
flow in only one direction
• Valves:
– Atrioventricular valves:
• Tricuspid
• Bicuspid (mitral)
– Semilunar valves
• Aortic
• Pulmonary
• Where
• are the four heart valves?
– The tricuspid valve is between the right atrium
and right ventricle
– The pulmonary (semilunar) valve is between
the right ventricle and the pulmonary artery
– The bicuspid (mitral) valve is between the left
atrium and left ventricle.
– The aortic valve is between the left ventricle
and the aorta.
• Valves open when the pressure in the
preceding chamber is higher than that in
the next chamber and they close when
pressure in the preceding chamber falls
below that in the next chamber.
• What causes the familiar “lubb-dupp”
sounds associated with the heart?
• The closing of the heart valves causes
blood to splash against the valves. This
causes the heart sounds.
• Each heart beat is one cardiac cycle.
• There are three parts to each cycle:
– Part 1: two atria contract (systole) at once.
two ventricles are relaxed (diastole).
– Part 2: two ventricles contract at once.
two atria are relaxed
• Part three: all chambers relax
• The heart contracts and relaxes through
this cycle on average about 70 times a
minute
• Each heart beat lasts just under a minute.
• Blood flow during the beat:
• Atrial systole – ventricular filling
• Ventricular systole – blood forced through
semilunar valves into circulation
The Meaning of Blood Pressure
• Pressure = force of blood pushing against
blood vessel wall
• Example: 120/80
• Systolic number = pressure of ventricular
contraction
• Diastolic number = pressure when heart is
relaxed
Intrinsic Control of Heartbeat
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Cardiac conduction system
SA node
AV node
AV bundle
Left and right bundle branches
Purkinge fibers
Allows impulse conduction to spread first to atria
and then after delay to ventricles
• Allows for adequate filling of all chambers
Extrinsic Control of Heartbeat
• Medulla oblongata (in the brain stem)
• Norepinephrine – released by the adrenal
medulla (on top of kidney) during exercise,
can increase heart beat
Electrocardiogram
• P wave: occurs just before the atria
contract
• QRS complex: occurs just before
ventricular contraction
• T wave: ventricular relaxation
Blood Vessels
• Arteries
– Take blood away from the heart
– Thick (three layers) and muscular
– Blood enters arteries under pressure
• Veins
– Channel blood towards the heart
– Thinner walls
• Capillaries
– Walls are only one cell thick
– Precapillary sphincters regulate flow into capillary
beds
Blood Flow back to the Heart
• How does blood get back to the heart with
such little pressure?
– Valves play a big role
– Muscular pumps
• Pathway of the Blood
– Pulmonary circuit (to lungs)
– Systemic circuit (to body tissues)
– Coronary arteries supply heart muscle with
blood
Pulmonary Circulation
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Right atrium – from superior vena cava
Right ventricle
Pulmonary trunk – semilunar valve
Pulmonary arteries
Lungs (pulmonary capillaries)
Pulmonary veins – oxygen rich
Left atrium
Systemic Circulation
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Left atrium
Left ventricle
Aorta
System arteries
Systemic capillaries
Systemic veins
Superior vena cava
Right atrium
• Cardiovascular disease
– #1 killer; 1 in 2 Americans die of it
– High blood pressure ( hypertension)
• Damages organs, especially heart, kidneys
• Contributes to atherosclerosis, stroke risk
– Heart disease – atherosclerosis
• Narrowing of arteries – lipid buildup, thickening of
walls
• Coronary arteries especially susceptible
• Restricted blood flow  angina
• Blocked flow  heart attack
• Treatments: balloon angioplasty, coronary bypass
– Heart muscle dies after 2 hrs without oxygen
– Signs of heart attack: chest pains, nausea,
and dizziness
• Stroke = cutoff of oxygen to brain cells –
cell survival – only 5 minutes
• Taking care of your heart
– Exercise (aerobic, at least 20 minutes)
– Good nutrition (control fats & body weight)
– QUIT SMOKING
Summary of Main Points
• The heart is a double pump that operates
continuously
• Arteries take blood away from the heart
• Veins take blood back to the heart
• Capillaries are the exchange vessels
• Pulmonary and systemic circulations serve the
lungs and body respectively
• Blood consists of plasma, oxygen-carrying red
blood cells, and defensive white blood cells
• Cardiovascular disorders can be genetic or a
result of poor decisions