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Mammalian Transport System
Ch. 8 Part 4 Heart Function
Structures to Know
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Atria (Atrium) or auricle
• Upper chambers
• Receive blood from veins
Ventricles
• Lower chambers
• Blood flows into from the atria and out through
arteries
Aorta
Pulmonary artery
Venae cavae (vena cava)
Pulmonary veins
Coronary arteries
• Bring oxygenated blood back to the heart
Septum
• Wall of muscle that separates chambers on the right
side of the heart from the chambers on the left side of
the heart
• Blood cannot pass through
Valves and Nodes to know
• Atrioventricular valves (between the atrium and the ventricle)
• Mitral/bicuspid valve (LEFT SIDE OF HEART)
• Tricuspid valve (RIGHT SIDE OF HEART)
• Semilunar valves
• Pulmonary Valve
• Aortic Valve
• Sinoatrial node (SAN)
• Patch of specialized muscle fibers in RIGHT ATRIUM
• Pacemaker
• Atrioventricular node (AVN)
• Patch of conducting muscle fiber located in upper septum
• Purkyne tissue
• Conducting muscle fibers running down septum, along the
right and left ventricles
Valves
• Atrioventricular valves
(between the atrium and
the ventricle)
• Mitral/bicuspid valve
(LEFT SIDE OF
HEART)
• Tricuspid valve
(RIGHT SIDE OF
HEART)
• Semilunar valves
• Pulmonary Valve
• Aortic Valve
Important!!!!
• Heart is myogenic does NOT need outside nerve
impulses to initiate heart beat
• Valves in heart do NOT actively open and close
• Valves open and close due to PRESSURE changes in
chambers
Closing of valves
create thump-thump
of heartbeat
Structure of Heart
• Atrium walls thin, muscular walls
• Low pressure exerted
• Ventricle walls  thick and muscular
• Right ventricle  small force
needed to push blood to lungs
• Left ventricle  large force needed
to push blood all over body
• VERY MUSCULAR
• Greater pressure developed in
left ventricle than left atria
The Cardiac Cycle
• Sequence of events that
make up 1 heart beat
• Heart beats about 70x a
minute
• 3 stages of the cycle
1. Atrial systole
2. Ventricular Systole
3. Ventricular Diastole
Systole  Contraction
Diastole  Relaxation
Atrial Systole
• Heart filled with blood
• Muscle in atrial walls (very
thin) contract
• Not a lot of pressure from
this contraction
• Enough pressure to force
blood in atria through
ATRIOVENTRICULAR
VALVES (AV) into
ventricles
• No back flow of blood into
pulmonary veins or vena
cava b/c of semilunar
valves
Ventricular Systole
• Ventricles contract 0.1 s after atria
contracts
• Thick, muscular ventricle walls
push blood out (exert high
pressure)
• AV valve shut when pressure in
ventricles exceeds pressure in
atria
• Semilunar valves open
• Blood rushes up into aorta &
pulmonary artery
• Lasts for 0.3 seconds
Ventricular Diastole
• After 0.3 seconds, ventricular muscle
relaxes
• Ventricle pressure decreases
• Semilunar valves shut, preventing
backflow of blood
• Blood only fills in cusps of valves
• Blood from veins flow into the 2 atria
• Blood is at low pressure
• Walls of atria expand to accommodate
blood (very little resistance)
• Some blood trickles into ventricles
through AV valve
• Atria contracts and cardiac cycle begins
again
Control of the Heart Beat
• Myogenic muscles
• Naturally contracts and relaxes
• No nerve impulses required
• Sinoatrial Node (SAN)
• Set out rhythm for all other muscle
cells to contract
• SAN contraction rhythm slightly
faster than the rest of the heart
• SAN contracts wave of
excitation (depolarization) sent
across all of the atria & muscles of
atria contract
Things NOT to say when
describing nodes:
• “Signal”
• “Wave” alone
• “Pulse”
• “Message”
• “Nerve impulse”
You SHOULD describe the function of SAN
using:
• “Wave of excitation”
• “depolarization”
• “impulse”
Ventricle contraction
• SAN causes contraction of all atria muscles
• Ventricle muscles delayed due to band of
fibers between the atria and ventricles that
does NOT conduct electric impulses
• Only path for impulses to reach ventricles is
through path of conducting fibers in septum
called ATRIOVENTRICULAR NODE (AVN)
• AVN receive excitation from atria, delays it 0.1s
and then passes it to another bunch of
conducting fibers called the PURKINJE
FIBERS or PURKYNE TISSUE
• Wave of excitation is sent up ventricle walls—
bottom-up
Fibrillation
• When muscular walls of heart flutter
rather than contract and relax as a
whole
• Rapid, irregular, unsynchronized
contraction of muscle cells
• Atrial fibrillation (non fatal) Afib
• Can lead to stroke
• Ventrical fibrillation (fatal) Vfib
• Faint, cardiac arrest
• Caused by:
• Electric shock or damage to large
areas of muscle in walls of heart
• Miss firing of electric impulse from
atria
• Instead of electrical impulse going
from atria to AVN to Purkinje tissue in
the ventricle, all muscle cells in
ventricle get excited in all directions
Electrocardiograms (ECGs)
• Graph plotting voltage vs. time
• Records electrical potentials of heart
over time
• Place electrodes over opposite sides of
heart
• P= wave of excitation over atrial walls
• Q, R, S= wave of excitation over
ventricle walls
• T = recovery of ventricle walls
• Contraction time = time b/t Q and T
• Filling time = time b/t T and Q
• EKG paper is a grid where time is measured along the horizontal axis.
• Each small square is 1 mm in length and represents 0.04 seconds.
• Each larger square is 5 mm in length and represents 0.2 seconds.
• Voltage is measured along the vertical axis.
• 10 mm is equal to 1mV in voltage.
How To Read an ECG
Calculating Heart from ECG
1. Determine rate of strip
• Time of strip is given; measure strip with
ruler and divide length by sec of strip or…
• May be given 20mm * s-1
2. Measure distance of one cardiac cycle
• Beginning of one P to the beginning of the
next P