THE HEART

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THE HEART
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Heart Facts

• The heart pumps blood through an average of
  60,000 miles of blood vessels in the body
• At rest, it pumps about 5 liters to the lungs and
  about 5 liters to the rest of the body every
  minute.
• It beats 100,000 time a day.

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Location

• Heart lies on the diaphragm.
• Located in the mediastinum.
• Tilted to the left 2/3rds of mass to the left
• Between ribs 2-6

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Transverse Section
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Anterior View

• Base is superior
• Apex is inferior
• Lies between lungs

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The Pericardium

• Membrane that surrounds heart-composed of three
  layers one fibrous layer and one serous layer
  that has two parts
• Fibrous layer
• Dense irregular c.t.
• Prevents overstretching of heart, protects,
  anchors heart in mediastinum through central
  tendon
• Serous layer-epithelial membrane
• Parietal layer-fused to fibrous layer
• Visceral layer-fused to heart also called the
  epicardium
• Review discussion of membranes in chapter 4

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Pericardium contd

• Pericardial fluid-slippery secretion produced by
  the serous layer
• Reduces friction between the layers of the
  pericardium
• Pericardial cavity
• The space between the parietal and visceral
  layers of the serous periacardium
• Contains the pericardial fluid

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LAYERS OF THE HEART WALL

• Epicardium -visceral layer of serous pericardium
• Myocardium-the bulk of the heart that is composed
  of cardiac muscle. Fibers swirl diagonally and
  interlock. Striated, involuntary muscle.
• Endocardium-thin layer of endothelium (s.sq.
  epithelium) that is continuous with the
  endothelial (s. sq. lining of large vessels
  attached to the heart. Endothelium overlies a
  thin layer of C.T.
• Review chapter 4 for details of cardiac muscle,
  connective tissues, and epithelial tissues

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Chambers of the heart

• 2 atria
• Receive blood into heart
• 2 ventricles
• Expel blood from heart

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Accessory Features Associated With the Chambers

• Auriclessack like pouches attached to the atria
  to increase their volume
• Sulci-grooves that contain blood vessels that
  service the heart itself and some fat
• Coronary sulcus-encircles most of heart and lies
  between the atria and ventricles
• Anterior interventricular sulcus
• Between ventricles on anterior surface
• Posterior interventricular sulcus
• Between ventricles on posterior surface

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Deoxygenated blood flows into the right atria,
then into the right ventricle which pumps it to
the lungs. Once in the lungs, the blood looses
its carbon dioxide and picks up oxygen. Then the
blood returns to the left atrium of the heart,
passes to the left ventricle and is expelled
into general circulation.
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Right atrium

• Receives blood from
• Superior vena cava
• Deoxygenated blood from upper body
• Inferior vena cava
• Deoxygenated blood from lower body
• Coronary sinus
• Deoxygenated blood from the heart itself

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Features of the Right Atrium

• Pectinate muscles
• Muscular ridges on anterior wall and in auricle
• Interatrial septum
• Separates atria
• Fossa ovalis
• Depression representing remnant of foramen ovale,
  an opening in the fetal heart that closes soon
  after birth
• Tricuspid valve
• Separates the right atrium from the right
  ventricle
• Composed of dense irregular c.t. covered by
  endothelium

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Pectinate muscles not shown, as they are located
on anterior wall which has been removed.
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The Right Ventricle

• Receives blood from the right atrium.
• Forms most of anterior surface of heart.
• Trabeculae carneae
• Papillary muscles
• Chora tendinae
• Fibers involved with electrical conduction in the
  heart
• Interventricular septum divides right and left
  ventricles.

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Valves of the Right Heart

• Tricuspid valve divides the right atrium from the
  right ventricle.
• Its cusps are attached to corda tendenae which
  are attached to cone shaped trabeculae carneae,
  called papillary muscles.
• This attachment prevents prolapse of the valve
  into the atrium when the ventricle contracts.
• Pulmonary semilunar valve opens into the
  pulmonary trunk, an artery, which divides and
  carries deoxygenated blood to the lungs.

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The Left Atrium

• Forms most of the base of the heart.
• Receives oxygenated blood from the lungs through
  4 pulmonary veins.
• Pectinate muscles only in auricle.
• Blood passes through the bicuspid, mitral, valve
  to the left ventricle.

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Left Ventricle

• Forms the apex of the heart.
• Has trabeculae carneae and corda tendenae that
  anchor bicuspid valve to the papillary muscles.
• Oxygenated blood flows through the aortic
  semilunar valve to the ascending aorta.

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The Aorta

• The first branches off the ascending aorta are
  the right and left coronary arteries.
• Then the aorta arches and gives rise to three
  large arteries
• Brachiocephalic artery
• Left common carotid artery
• Left subclavian artery
• Continues inferiorly as the descending aorta.

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The Ligamentum Arteriosum

• During fetal life the lungs, of course, do not
  function.
• There is no need to send blood to them except to
  maintain them as any other organ.
• A shunt between the pulmonary trunk and aorta
  called the ductus arteriosus exists as a short
  cut into systemic circulation, bypassing the
  lungs.
• It closes shortly after birth, leaving the
  ligamentum arteriorsum as a remnant.

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Myocardial Thickness

• The atria are thin walled most flow to the
  ventricles is courtesy of gravity, so not much
  muscle is necessary the atrial contractions
  account for only a part (about 1/3) of the flow
  to the ventricles.
• The ventricles are thicker, as they are the
  chambers that propel blood into circulation.
• The left ventricle is the thickest because it
  must send blood into systemic circulation.

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• Despite the variation in thickness between the
  right and left sides of the heart, the respective
  chambers eject equal amounts of blood.

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The Fibrous Skeleton of the Heart

• Dense connective tissue rings forming structural
  foundation around the heart valves
• Keep valves from overstretching
• Fuse with IV septum
• Point of insertion for cardiac muscle
• Electrical insulation between atria and
  ventricles

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Fibrous Skeleton
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Heart Valve Operation

• The valves insure one way flow of blood.
• AV valves stop the backflow of blood into the
  atria (regurgitation). The papillary muscles
  contract and snap them shut when ventricular
  pressure pushes them toward the atria.
• The semilunar valves prevent backflow from the
  aorta and the pulmonary trunk. Blood is caught
  in the crescent shape which causes contraction of
  the valves.

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Mitral Valve Function
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Semilunar and AV Valves
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Circulation of Blood

• The right side of the heart pumps deoxygenated
  blood to the lungs where it trades carbon
  dioxide, a waste product of aerobic respiration,
  for oxygen.
• The left side of the heart pumps oxygenated blood
  into systemic circulation. This includes the
  heart and lungs, as they, too, are organs.

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Note that red means oxygenated and blue means
deoxygenated
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Pathway of flow
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Coronary Circulation Oxygenated

• Left coronary artery
• Anterior interventricular in anterior IV sulcus
  artery serves both ventricles and left atrium
• Circumflex branch in coronary sulcus-left atrium
  and left ventricle
• Right coronary artery
• Right coronary artery supplies the right atrium
• Posterior interventricular branch in posterior IV
  sulcus-both ventricles
• Marginal branch in coronary sulcus-right
  ventricle
• Many anastomosis

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Coronary Circulation Deoxygenated

• Great cardiac vein-drains anterior of heart
• Both ventricles and left atrium (area supplied by
  left coronary artery)
• Middle cardiac vein drains posterior right and
  left ventricles (area supplied by posterior IV
  branch of right coronary artery)
• Small cardiac vein drains right atrium and right
  ventricle
• Anterior cardiac veins drain right ventricle and
  open directly into right atrium
• Most deoxygenated blood empties into the coronary
  sinus in the right atrium

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Heart Muscle Histology

• SEE CHAPTERS 4 AND 10 FOR COMPARISON TO OTHER
  MUSCLE TYPES
• Branched cells
• Centrally located nucleus (1 or 2)
• Relatively abundant cytoplasm
• Relatively abundant, large mitochondria

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Heart Muscle Histology Contd

• Transverse tubules located at z discs
• Scanty sarcoplasmic reticulum-some calcium comes
  from interstitial fluid
• Cells junctions at intercalated discs which
  contain desmosomes and gap junctions, enabling
  fibers of atria to contract at one time same for
  ventricles

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Autorhythmic Cells

• The heart has inherent electrical and rhythmical
  electrical activity that causes it to beat
  continuously.
• Autorythmic cells are self excitatory.
• They generate action potentials that trigger
  heart beat.
• About 1 of cardiac muscle fibers develop into
  these cells during embryonic life to function as
  pacemakers and conduction systems.

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Autorhythmic cells contd

• These cells insure that the chambers contract in
  a coordinated movement, resulting in an effective
  pump.

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Factors That Modify Autorhythmicity

• ANS
• Hormones
• These factors only modify the basic rhythm set by
  the hearts own cells.

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The Conduction System

• The SA node is the pacemaker and causes atrial
  contraction and an action potential in the AV
  node.
• The AV nodes action potential continues into the
  AV bundle, right and left bundle branches and
  Purkinje fibers
• The Purkinje fibers cause ventricular contraction
  about .2 seconds after the atria contract.

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Rates of Action Potential Propogations

• The SA node sets a rhythm of 90-100 action
  potential (beats) per minute. This node is the
  natural pacemaker, whose beat is modified by
  hormones and ANS.
• The AV node sets the rhythm at 40-50 per minute.
  It takes over if the SA node does not function.
• The AV bundle, the bundle branches and the
  Purkinje fibers generate actions potential at
  20-40 per minute too slow to sustain life. An
  artificial pacemaker is definitely called for if
  the SA and AV nodes are not functioning.

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Physiology of Contraction Atrial Contraction

• The SA node depolarizes spontaneously because of
  Na leakage channels.
• When it reaches threshold, an action potential is
  triggered, which spreads rapidly to the cells of
  the atria via gap junctions located in
  intercalated discs.
• They, in turn, depolarize, reach their own
  thresholds and contract

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Physiology of Contraction Ventricular Contraction

• The action potential of the SA node also reaches
  the AV node, which directs it into the AV bundle.
• The action potential continues through the bundle
  branches, then through the Purkinje fibers and
  finally to the cells of the ventricles.
• The muscle cells of the ventricles then
  depolarize, reach threshold and contract.
• The rapid spread of the action potentials is
  through gap junctions of intercalated discs, as
  before.

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Calcium Ion

• Calcium ion must bind to troponin for contraction
  to occur.
• Only about 1/2 that is needed is stored and
  released from the S.R.
• The muscle cells action potential causes release
  of Ca from the S.R. and also causes voltage
  gated Ca channels to open, allowing Ca to
  diffuse into cell from ECF.
• Ca channels open after Na channels close and
  prolong the time membrane is depolarized this is
  called the plateau.

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The Plateau

• The plateau results in a long refractory period
  and prevents the heart from going into spasm, as
  skeletal muscles often do.

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Repolarization

• K channels open in response to the action
  potential, after the Na and Ca channels close,
  thus restoring electrical balance.
• Na/K pumps and Ca pumps then restore the
  chemical gradients.

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The Physiology of Contraction
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The Electrocardiogram

• A measure of the electical currents generated by
  the action potentials spreading through the
  heart.
• Contraction follows the action potentials.
• Detected on surface of the skin using up to 12
  electrodes.

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The Electocardiogram

• P-Atrial depolarization
• QRS-ventricular depolarization (atrial
  repolarization is embedded)
• T-ventricular repolarization

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The Cardiac Cycle
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Pathologies Waves

• P wave enlarged enlarged atria
• Q wave enlarged acute myocardial infarction
• R wave enlarged enlarged ventricles
• T wave flattened hypoxia
• T wave elevated hyperkalemia

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Pathologies Intervals and Segments

• P-Q interval lengthened increase in time for
  action potential to travel from SA node to points
  beyond. Coronary artery disease (RF can cause
  scarring that can lead to this).
• S-T segment elevated acute myocardial
  infarction
• S-T segment depressed hypoxia
• Q-T segment lengthened myocardial damage,
  cardiac ischemia, conduction abnormalities

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The Cardiac Cycle Events That Occur During One
Beat

• The atria and ventricles alternately contract and
  relax.
• Blood is forced from areas of high pressure
  caused by contraction or gravity into areas of
  low pressure created by relaxation.

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Ventricular filling rapid, diastases, atrial
systole (30) EDV130 ml ESV60 ml SVEDV-ESV70
ml
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Heart Sounds

• S1LUBAV valves closing and associated blood
  turbulence
• S2DUBsemilunar valves closing and associated
  blood turbulence
• S3usually inaudibleturbulence during rapid
  ventricular filling
• S4usually inaudibleturbulence in atrial
  contraction

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Murmurs

• Sounds due to regurgitation through unclosed
  valves
• Range from inconsequential to life threatening

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Cardiac Output

• COSV x HR
• CO70 ml/beat x 75 beats/min5.25L/min
• Cardiac reserve
• MAX CO RESTING CO
• 4-5 times resting value is average as high as
  7-8 in top athletes very little or none with
  severe heart disease.

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FACTORS THAT AFFECT CO
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Factors affecting stroke volume

• ESV
• Preload
• Contractility
• Autonomic
• Hormones
• Drugs
• Positive and negative inotropic agents
• Increase or reduce calcium ion entry,
  respectively
• Afterload

• EDV
• Preload
• Proportional to EDV
• EDV and stroke volume
• More inmore out
• Keeps the volume equal in both ventricles

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The Frank-Starling Law

• This law states that within limits, the more the
  cardiac muscle is stretched, the more it will
  contract.
• Stretching, of course, is due to increased blood
  volume in the chambers.
• This phenomena balances the two sides of the
  heart in the event that an unbalance occurs and
  one side pumps a little more blood than the
  other.
• Say the right side pumps a little extra. Then the
  left side receives an increased volume from
  pulmonary circulation. The next contraction of
  the left side will be more forceful, and balance
  is then restored.

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ANS Regulation of Heart
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the end