Download Cardiovascular System

Cardiovascular System
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Blood Flow through the Human Heart
13.3 Heart actions
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Heart contraction (cardiac cycle)
Heart sounds
Cardiac conduction system
ECG
Regulation of the cardiac cycle
Cardiac cycle
Cardiac cycle – the process of moving
blood through the heart by a series of
coordinated atrial and ventricular
contractions.
 Systole – when a heart chamber
contracts
 Diastole – when a heart chamber
relaxes
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Cardiac cycle
Cardiac cycle moves blood by changing
the pressure in the heart chambers.
 It changes the pressure by
contraction/relaxation of a chamber.
 Pressure in a chamber….like squeezing
a water bottle.
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First, some heart anatomy…
Atrium (atria) vs. ventricle
 Atrioventricular valves
 Semilunar valves
 Papillary muscles and chordae
tendineae
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Cardiac cycle
Starts with diastole (relaxation) of both
atria and ventricles.
 Blood flows into atria from veins
because of low pressure in the atria.
 70% of ventricle is filled at this time from
blood from the atria.
 http://www.nhlbi.nih.gov/health/healthtopics/topics/hhw/contraction.html
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Cardiac cycle
Atrial systole
 Next, the atria contract pushing the
remaining 30% of blood gets pushed
into the ventricles.
 When a chamber (atria or ventricle)
contracts, it increases pressure in that
chamber.
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Cardiac cycle
Now, the ventricle is full of blood but not
yet contracting.
 The A-V is closed because of increased
pressure in the ventricle. Blood cannot
flow back into the atrium.
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Cardiac cycle
Ventricle systole & atrial diastole
 Now, the ventricle contracts. This
increases the pressure inside the
ventricle even more and it pushes the
blood out of the ventricle through the
semilunar valves.
 Blood goes into the arteries (aorta or
pulmonary trunk) and to the body.
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In sum..
1. Atria and ventricle diastole – blood
flowing into the chambers.
 2. atrial systole – pushes remaining
blood into ventricles.
 3. atrial diastole
 4. ventricle systole – pushes blood out
into the arteries.
 5. atrial and ventricle diastole
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Cardiac cycle
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After ventricle systole, there is a
moment of diastole for atria and
ventricles at the same time. This allows
blood to flow back in.
Heart sounds
We all know what a heartbeat sounds
like.
 The sounds come from the valves
closing.
 First heart sound comes when the
ventricles contract and close the AV
valves.
 Second heart sounds occurs during
ventricular relaxation and the semilunar
valves close.
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Cardiac muscle fibers
Heart muscle fibers connect in a
branching network
 Cells contract as a unit at the same time
 Functional syncytium – a mass of cells
that function as a unit
 Animation: Conducting System of the
Heart
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Cardiac conduction system
Coordinates the contractions of the
cardiac cycle
 Made of special muscle fibers that
conduct impulses
 The impulses tell the other muscle cells
when to contract
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Cardiac conduction system
Similar to the nervous system
 An impulse starts at the top, travels
down the heart to signal contraction
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Cardiac conduction system
Sinoatrial node (SA node)
 It starts the impulse
 Called the “pacemaker”
 It does not need neural stimulation like
skeletal muscle.
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Cardiac conduction system
Impulse goes from the SA node down
junction fibers through the atrial
syncytium.
 Atrial muscle cells contract.
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Cardiac conduction system
Impulse reaches the Atrioventricular
node (AV node)
 This node is the only impulse connection
to the ventricles.
 AV node delays the impulse slightly.
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Cardiac conduction system
AV node transmits the impulse down the
AV bundle.
 Bundle splits into branches and carries
the impulse through the ventricular
syncytium. They contract.
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Cardiac conduction system
Purkinje fibers – carry impulses to
papillary muscles in the ventricles
 They attach to chordae tendineae
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In sum…
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Cardiac conduction system coordinates
heart contraction
SA node initiates an impulse
Impulse moves down and causes atrial
contraction
AV node delays the impulse and then
transmits it down to the ventricles
Ventricles contract
Animation: Conducting System of the Heart
Electrocardiogram
ECG or EKG
 Recording of the electrical changes that
occur in the myocardium during a
cardiac cycle.
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ECG
The “waves” on an ECG indicate when
cells depolarize and contract.
 Each wave corresponds with a spot in
the cardiac cycle.
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ECG
P wave = atrial depolarization
 QRS wave = ventricle depolarization
 T wave = repolarization of the ventricles
 Where is the wave for atrial
repolarization?
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ECG
Doctors use an ECG to monitor the
heart’s ability to conduct impulses.
 Why is this important?
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Regulation of heart rate
Under normal conditions, the SA node
controls heart rate. How?
 Sympathetic and parasympathetic
nerves can signal the SA node to
increase or decrease heart rate.
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Regulation of heart rate
When would we need to increase heart
rate? What system does this?
 When would we decrease it? Which
system?
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13.4 Blood Vessels
Arteries – carry oxygenated blood from
the heart to the body
 Veins – carry deoxygenated blood back
to the heart
 Capillaries – smallest diameter BV with
semipermeable walls. Substances (O2,
CO2, nutrients, waste) are exchanged
through the capillary wall.
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Blood vessel structure
3 layers:
 Tunica interna – inner layer
 Tunica media – middle layer of smooth
muscle
 Tunica externa – outer layer of elastic
connective tissue
BV structure
Arteries and veins differ slightly
 Arteries have more smooth muscle
 Veins have valves to
Prevent backflow
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Arteries
Vasoconstriction – smooth muscle of the
artery contracts and the BV lumen
becomes smaller
 Vasodilation – smooth muscle relaxes
and lumen gets bigger.
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Why do this?
 atherosclerosis
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Veins
Similar structure to arteries but with less
smooth muscle.
 They are not elastic like an artery.
 They contain valves that prevent
backflow of blood.
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BVs
Arteries branch into continually smaller
vessels called arterioles.
 Veins branch into smaller vessels called
venules.
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BVs
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Capillary – where an arteriole and
venule meet.
Capillary
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Semipermeable – small slits in capillary
walls allow for substance exchange with
body cells.
Capillaries
Tissues that use a lot of oxygen are
have many capillaries (muscles, nerve
tissue).
 Tissues such as cartilage and the
cornea do not have many capillaries
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Exchanges in capillaries
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Gases, nutrients, and metabolic byproducts are exchanged between the
blood in capillaries and the tissue fluid
surrounding body cells.
Exchange
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Uses three mechanisms:
 Diffusion – concentration gradiants
 Filtration
 Osmotis
Diffusion in capillaries
Most substances move down their
concentration gradient. What?
 High oxygen in arterioles flow to tissues
with low oxygen.
 Carbon dioxide also.
 Same with carbon dioxide.
 Page 345 in book.
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Filtration
Hydrostatic pressure (blood pressure) is
used to force molecules through the
capillary walls.
 Filtration occurs near the ateriole end
because BP is higher there.
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Osmotic pressure
Plasma proteins create osmotic
pressure that is directed into the
capillaries.
 Near the venule end, osmotic pressure
dominates and reabsorption occurs in
the capillaries.
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Blood pressure is important because it
pushes gas and nutrients.
Exchange in capillaries
Oxygen, carbon dioxide, water,
nutrients, and wastes can all be
exchanged.
 Animation: Changes in the Partial
Pressures of Oxygen and Carbon
Dioxide
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BVs
Table 13.2 in the book summarizes BVs.
 Interesting fact: veins act as a blood
reservoir. We can lose up to 25% of our
blood volume and be OK.
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In sum…
Arteries & arterioles
 Veins & venules
 Capillaries – sustance exchange
because of pressure.
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13.5 Blood Pressure
Blood pressure – force blood exerts
against the inner walls of BVs (mainly
arteries).
 There is enough pressure to shoot blood
30 ft.
 How do they take blood pressure?
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Blood pressure
Systolic pressure – pressure in the
arteries when the ventricles are
contracting
 Diastolic pressure – pressure in the
arteries when the ventricles are relaxed.
Categories for Blood Pressure Levels in
Adults: Guide to Lowering HBP
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Factors that influence BP
Stroke volume – amount of blood
pumped out by the left ventricle with
each contraction
 Cardiac output – volume pumped by left
ventricle per minute
cardiac output = stroke volume * heart rate
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If they increase then BP goes up
Factors that influence BP
Blood volume – amount of blood in the
vascular system.
 How much is the normal amount?
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Factors..
Peripheral resistance – blood flowing
through vessels causes friction.
 Arteries can constrict/dilate to change
BP.
 How does that work?
 Why do it?
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Factors..
Blood Viscosity – resistance to flow.
 Think honey vs. water
 If blood viscosity goes up so does blood
pressure.
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Control of BP
Starling’s Law of the Heart - relationship
between heart muscle stretching and
contraction strength
 Ensures that the heart doesn’t pump out
more blood than it is receiving from the
veins.
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Control of BP
Baroreceptors – sensory cells in the
walls of the aorta and carotid arteries
that sense changes in blood pressure.
 Tell the medulla oblongata what the BP
is. Medulla makes a decision about what
to do.
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Control of BP
Peripheral resistance – blood vessel
diameter has a large impact on BP.
 If pressure needs to increase, the
medulla oblongata can cause
vasoconstriction via sympathetic nerves.
 If pressure needs to decrease,
sympathetic stimulation slows down and
vasodilation occurs.
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Control of BP
Venous blood flow – blood pressure
decreases as blood moves farther from
the heart.
 The veins use skeletal muscle
contraction, breathing movements, and
vasoconstriction in order to move blood
(not enough push from the heart).
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13.6 Paths of circulation
BVs can be divided into two major
pathways
 Pulmonary circuit – all BVs that carry
blood to and from the lungs
 Systemic circuit – BVs that carry blood
to and from all other parts of the body
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Pulmonary circuit
Blood enters pulmonary trunk from the
right ventricle.
 Pulmonary trunks splits into R & L
pulmonary arteries
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Pulmonary circuit
Pulmonary arteries take blood to the
lungs.
 Arteries branch into small arterioles and
capillaries so gas exchange can occur.
 What is the gas exchange structure in
the lungs called?
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Pulmonary circuit
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Pulmonary veins return oxygenated
blood to the heart. Where in the heart?
Systemic Circuit
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All BVs that take blood to/from
anywhere but the lungs.