Overview: Cardiovascular System and the Heart

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Overview Cardiovascular System and the Heart

• Circulatory System heart, BVs, and blood
• Cardiovascular System passageways for blood
  heart, arteries veins, etc.
• Two Hearts
• Pulmonary Circuit (right side) - takes blood to
  lungs for gas exchange
• Systemic circuit (left side)- takes oxygen rich
  blood to the organs and oxygen poor blood back to
  the heart

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• Right side of heart gets O2 poor blood
• Pulmonary artery takes it away from heart to
  lungs
• Pulmonary veins bring it back O2 rich
• Left side of heart serves systemic system
• Aorta takes O2 rich blood out to organs
• Superior vena cava brings it back from head,
  neck, upper limbs
• Inferior vena cava brings it back from organs
  below diaphragm.

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Pericardium

• Double walled sac enclosing heart
• In the pericardial cavity is pericardial fluid
  that allows the heart to beat without friction
• Pericarditis is the pain caused by friction when
  the membranes are dry

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Heart wall

• Epicardium
• outer layer
• fatty
• Myocardium
• thickest layer
• cardiac muscle that pulls against a fibrous
  skeleton of fibers
• focuses the movement of electricity
• Endocardium
• Smooth inner lining

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Chambers

• Right and left
• atria receive returning blood
• have an easier workload
• Right and left ventricles eject blood

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Heart Valves

• Ensure one way flow
• Made of flaps called cusps
• Open close as a result of pressure changes
• When ventricles relax, valves are open
• Full ventricles contract pressure pushes valves
  shut

AV valves between atria ventricles Right AV
tricuspid valve Left AV bicuspid valve (aka,
mitral valve) Semilunar valves bet.
ventricles the great arteries
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Coronary Circulation

• Getting blood to your heart
• 3 billion beats over an 80 year life span
• Heart needs 5 of bodys O2
• delivered by coronary arteries
• Myocardial Infarction fat deposits blocking
  arteries leading to necrosis of tissue
• Anastomoses our bodys defense
• Two arteries covering the same area
• If the damage is extensive, the
• heart beat becomes inefficient
• - coronary bypass may be necesssary

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Cardiac Muscle and The Cardiac Conduction System

• Cardiocytes short, thick branched cells
• -mononucleated, striated
• -myogenic will beat rythmically
• w/o CNS stimulation
• -inherent contractile activity controlled
• by the ANS
• Intercalated discs join cells end to end
• Gap junctions allow ions to flow between cells,
  keep electrical current flowing from one cell to
  the next
• The action potential travels thru all cells
  connected together forming a functional syncytium

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Cardiac conduction system

• Our brain can modify the heartbeat, but not
  create it. Disembodied hearts can beat for hours.
• Sinoatrial (SA) node the pacemaker
• -initiates heart beat and determines heart rate
• -damage to SA node results in slower heart rate
  implant an artificial pacemaker
• Atrioventricular node sends signals to the
  ventricles

Purkinje fibers arise from bundle branches near
the apex and then spread throughout the
myocardium.
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Control of Heart Rate

• Without nervous system control, the heart would
  beat about 100 times per minute
• Both sympathetic and parasympathetic nerves
  innervate the SA node
• When you are relaxed, your parasympathetic
  nervous system (via the vagus nerve) sets a
  resting heart beat rate at about 70 beats/min
• When exercising or anxious, the sympathetic
  nervous system ? heart beat via hormones like
  adrenaline this ? flow of O2 blood to muscles
• Average maximum heart rate is 220 minus your age

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Electrical Contractile Activity
Contraction systole Relaxation diastole These
can apply to parts (e.g., atrial systole), or
just to the ventricles Sinus rhythm normal beat
triggered by SA node Can have ectopic focus
(alternate source of beat, instead of SA node)
called nodal rhythm Arrhythmia abnormal rhythm
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Physiology of the SA node

• The nerves of the SA node are always slowly
  moving toward an action potential
• As soon as the heart beats its already starting
  toward another beat
• Avg. 75 beats per minute
• Cardiac muscle has a sustained contraction, and a
  longer refractory period
• This prevents tetanus continual contraction

Membrane potential starts around -60mV. Pacemaker
potential is a gradual drift upward (slow inflow
of Na w/o outflow of K). Fast calcium channels
inflow of Ca.
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Electrocardiogram (ECG/EKG)

• Composite reading of many action potentials
• P wave atria contract
• QRS complex AV node fires, ventricles start to
  contract
• T wave ventricles repolarizing
• U wave not always seen repolarization of
  papillary muscles or Perkinje fibers

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Electrocardiogram
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Cardiac cycle
Lub-dub sounds are made when the heart valves
that separate the chambers of the heart open and
close in sequence.
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Now, you can

• Identify the chambers and valves of the heart
• Trace the flow of blood through the heart
  chambers
• Contrast cardiac vs. skeletal muscle
• Describe the physiological properties of cardiac
  muscle
• Describe the hearts electrical conduction system
• Describe the physiological mechanism of control
  of rate of heart beat

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