Transcript Cardiovascular system

Cardiovascular system
General pattern of blood flow
Heart
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Atria- upper chambers
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Receive blood returning to the heart
Ventricles- lower chambers
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Receive blood from the atria and contract to force blood out
of the heart into the arteries
Right ventricle is thinner than the left
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Right pumps short distance to the lungs, little resistance
Left must force blood to all other parts of the body, high resistance
Septum- solid, wall like separation between the atrium
and the ventricle on the right with those on the left
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Blood never mixes with blood from the other side
valves
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Atrioventricular valve-right tricuspid and left
bicuspid ensure one-way blood flow
Tricuspid valve- blood flows from right atrium to
right ventricle, prevents back flow
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Right ventricle contracts, pressure increases, valve closes
Pulmonary valve- allows blood to leave the right
ventricle,prevents back flow
Bicuspid valve- blood passes from left atrium to left
ventricle, prevents back flow
Aortic valve-opens when ventricle contracts allows
blood to leave
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When closed prevents blood from backing up in ventricle
Path of blood
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Blood low in O2 enters right atrium through vena
cavae and coronary sinus
Right atria wall contracts, blood enters right ventricle
Right ventricle wall contracts and blood moves into
pulmonary trunk and its branches
From pulmonary arteries blood enters capillaries
associated with lungs
Oxygenated blood returns to heart through
pulmonary veins through left atrium
Left atrial wall contracts and blood moves into left
ventricle, left ventricle contracts blood moves to
Heart blood supply
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Coronary arteries supply blood to the heart’s
tissue
Cardiac veins drain blood that has passed
through the myocardial capillaries
Join coronary sinus on the heart’s posterior
surface which empties into the right atrium
Cardiac cycle
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When atria relax blood flows into them
Increases pressure
Most of the blood goes directly to ventricles
Atrial systole– atrial contraction
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Forces the rest of the blood into ventricles
Atrial diastole– atrial relaxation
Cardiac conduction system
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Sinoatrial node (S-A node)Can reach threshold on their own
 Spread to surrounding myocardium and stimulates fibers
 Rhythmic
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Referred to as pacemaker
Left and right contact almost simultaneously
Atrioventricular node (A-V node)
Provides normal conduction
 Fibers have small diameters that slows the impulse
 Allows more time for atria to empty and ventricle fill with
blood
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Muscles are whorls which cause twisting motion when contract
Cardiac conduction system
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During ventricular contraction A-V valves remain
closed, atrial pressure increases
Ventricles relax- vemtricular diastole
A-V valves open
Blood flows to ventricles
Pressure decreases while filling
Atria contracts increasing pressure in ventricle
When pressure exceeds atrial pressure A-V closes
Pressure increases until valves of pulmonary trunk
open and blood flows to arteries
Electrocardiogram (ECG)
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Recording of the electrical changes in the
myocardium during a cardiac cycle
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1st change– P wave
Depolarization of atrial fibers will lead to contraction
 Fibers reach ventricular fibers and depolarize rapidly
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QRS complex– Q wave, R wave, and S wave
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Corresponds to depolarization of ventricular fibers just
prior to contraction of ventricular walls
T wave
Electrical change as ventricular muscle fibers repolarize
 Atrial repolarization is at the same as ventricular fibers
depolarize
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Arteries and arterioles
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Artery
Innermost layer helps prevent blood clotting by
providing a smooth surface and secreting
biochemicals that inhibit platelet aggregation
 May also regulate local flow by secreting substances
that dilate or constrict blood vessels
 Arteries progressively divide into thinner tubes and
eventually give rise to arterioles
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Walls thin as they near the capillaries
Capillaries
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The smallest diameter of blood vessels
Connect the arterioles and venules
 Extensions of the inner linings of arterioles
 Area where exchange of materials occurs
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Exchange in capillaries
Gas, nutrients, and metabolic by products
 The substances exchanged move through capillary
walls through diffusion, filtration, and osmosis
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Filtration forces molecules through a membrane with
hydrostatic pressure
Capillary exchange cont.
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Blood pressure moves blood through arteries
and arterioles
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Pressure decreases as the distance from the heart
increases
Greater in the arteries than arterioles, arterioles greater
than capillaries, etc.
 Filtration effect primarily at arteriolar end
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Veins and Venules
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Venules are microscopic vessels that continue
from the capillaries and merge to form veins
Veins contain flaplike valves
Valves close if blood begins to back yup in a vein
 Aid in returning blood to the heart because they
open if blood flow is toward the heart and close if it
is in the opposite direction
 Also function as blood reservoirs
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If a hemorrhage causes a drop in arterial blood pressure,
veins are stimulated to constrict and help maintain blood
pressure by returning more blood to the heart
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Ensures a nearly normal blood flow even when as much as 25%
is lost
Blood pressure
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Blood pressure is the force blood exerts against
the inner walls of the blood vessels
Arterial pressure rises and falls in a pattern
corresponding to the cardiac cycle
The maximum pressure during ventricular
contraction is called the systolic pressure
The lowest pressure that remains in the arteries
until the next venticular contraction is diastolic
pressure
The alternating expanding and recoiling of the
artery wall is felt as the pulse
Blood pressure factors
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Heart action
Determines how much blood enters the arterial system
 Stroke volume-the amount of blood that is discharged
from the left ventricle with each contraction
 Cardiac output- volume discharged/minute
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Blood volume
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Equals the sum of formed elements and plasma volumes in
vascular system
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Stroke volume x heart rate
Varies with age and sex and directly with body size
Normally directly proportional to blood volume
Can fall if fluid balance is upset
Factors cont.
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Peripheral resistance
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Produced from friction between blood and vessel walls
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Slows blood flow
Contraction of smooth muscles in arteriolar walls
increases pressure
Dilation lessens resistance and drops the pressure in
response
Blood viscosity
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The greater the viscosity, the greater the resistance
Blood cells and plasma proteins increase blood viscosity
 Blood pressure increases as viscosity increases and drops as
viscosity decreases
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Control of blood pressure
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Two important mechanisms for maintaining
normal arterial pressure are:
Regulation of cardiac output
 Regulation of peripheral resistance
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Cardiac output
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Volume of blood discharged from the left ventricle
and heart rate
Starling’s law of the heart--Greater the length of
myocardial fibers the greater the contractional force
Baroreceptors sense changes in pressure
Increases nerve impulse travels to brain, heart rate
decreases
 Triggers cardioinhibitor reflex—cardiac output falls and
blood pressure moves to normal level
 Cardioaccelerator reflex triggered by decreasing arterial
pressure
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Causes heart to beat faster, increases heart rate, and pressure
Peripheral resistance
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Changes in the arteriole diameters regulate
peripheral resistance
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Small diameters offer greater resistance to blood
flow
Vasomotor center controls impulses sent to
arteriole walls
Certain chemicals also influence peripheral
resistance by affecting precapillary sphincters
and smooth muscle in arteriole walls
Venous blood flow
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Blood pressure decreases as blood moves through
the arterial system and into the capillary networks
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Depends on skeletal muscle contraction, breathing
movements, and vasoconstriction of veins
Contracting skeletal muscles- thicken and press
on nearby vessels squeezing blood inside
Respiratory movements- causes pressure changes
in thoracic cavity
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Inspiration- pressure decreases in thoracic cavity and
rises in abdominal cavity which squeezes blood out of
veins
Venous blood cont.
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Vasoconstriction returns venous blood to the
heart
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Venous pressure is low, sympathetic reflexes
stimulate smooth muscle in veins to contract
veins provide blood reservoir that can adapt its
capacity to changes in blood volume
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If blood is lost and blood pressure falls,
venoconstriction can force blood out of reservoir
Paths of circulation
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Two major pathways
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Pulmonary circuit
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Consist of vessels that carry blood from the heart to the
lungs and back to the heart
Systemic circuit
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Carries blood from the heart to all parts of the body and
back again