HeartPart I Circulatory

1
Heart-Part I Circulatory

• Ch. 14

2
Gross Anatomy

• Heart located in thoracic cavity in the
  mediastinum
• About 2/3 of the heart lies to the left of the
  midsagittal plane
• The superior portion is the base
• The inferior portion is the apex
• The apex tilts to the left
• The adult heart is about the size of a fist

3
Pericardium

• The heart is enclosed in a double walled sac
  called the pericardium
• The parietal pericardium or pericardial sac is a
  tough fibrous layer and a thin, smooth serous
  layer
• The visceral pericardium covers the heart surface
• Between is a pericardial cavity filled with
  pericardial fluid

4
Heart Wall

• Has 3 layers
• Epicardium-is the visceral pericardium containing
  deposits of fat that protect the coronary vessels
• Myocardium-the muscle of the heart and the
  thickest portion
• Endocardium-the inner most layer that lines the
  chambers and valves and is continuous with the
  endothelium of the vessels

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Layers
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Chambers of the heart

• Four chambers
• 2 superior chambers are the right and left atria
  that receive blood returning to the heart
• Each has a small ear like extension called an
  auricle that helps increase the volume slightly
• 2 inferior chambers are the right and left
  ventricles that pump blood into the arteries

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Additional features

• Sulci-mark the boundaries of the four chambers
• Atrioventricular (coronary) sulcus separates the
  atria from the ventricles
• Anterior and posterior interventricular sulci
  extend vertically and mark the boundary between
  the left and right ventricles
• Interatrial septum separates the atria internally

8
Features continued

• Pectinate muscles- internal ridges of myocardium
  found in the right atrium and both auricles
• Fossa ovalis -oval depression in interatrial
  septum which is remnant of foramen ovale in fetal
  heart
• Interventricular septum separates left and right
  ventricles
• Trabeculae carneae- internal ridges found in the
  ventricles
• Left ventricle wall is thicker than right side
• Ligamentum arteriosum -connects arch of aorta and
  pulmonary trunk

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Section through heart
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Another view of heart
11
Valves

• Atrioventricular valves (AV) regulate the
  openings between atria and ventricles
• Right AV valve is the tricuspid with 3 cusps
• Left AV valve is the bicuspid (mitral) valve with
  2 cusps
• Chordae tendineae (heart strings) connect the AV
  valve cusps to papillary muscles of the floor of
  the ventricle

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Valves continued

• Semilunar valves- regulate the flow of blood from
  the ventricles into the great arteries
• Pulmonary semilunar valve- controls opening from
  right ventricle into pulmonary trunk
• Aortic semilunar valve- controls opening from
  left ventricle into aorta

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Valves
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Action of valves

• When ventricles are relaxed, both AV valve cusps
  hang down freely, both AV valves open and blood
  flows from atria into ventricles
• When blood enters and ventricle begins to
  contract, internal pressure increases, pushes
  cusps together and seals the opening
• The papillary muscles contract as the ventricle
  contracts, tugging on the chordae tendineae,
  which prevents prolapse into the atria

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Blood flow through the Heart-Coronary circulation

• The heart uses 5 of circulating blood to meet
  its metabolic needs
• Arterial supply aorta leaves left ventricle and
  gives off right and left coronary arteries that
  begins at the opening deep in the cup formed by
  the cusp of the aortic valves
• Left coronary artery divides into anterior
  interventricular artery (left anterior descending
  LAD)-supplies anterior walls of both ventricles
  and the interventricular septum
• circumflex artery- supplies left atrium and
  posterior wall of left ventricle

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External anterior view
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Blood flow in the heart continued

• Right coronary artery supplies the right atrium
  and gives off two branches
• Marginal artery supplies lateral aspect of right
  atrium and ventricle
• Posterior interventricular artery travels down
  the sulcus and supplies posterior walls of both
  ventricles
• MI (myocardial infarction)-sudden death of a
  patch of tissue deprived of blood supply
• Anastomoses -defense against MI

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Flow of blood through heart (pulmonary
circulation)

• Blood from superior and inferior vena cava empty
  into right atrium
• Blood flows from tricuspid into right ventricle,
  then into pulmonary SL valve into pulmonary trunk
• Pulmonary trunk divides into pulmonary arteries
  which lead into lungs
• From lungs blood (now oxygenated) enter pulmonary
  veins, then left atrium, through bicuspid valve
  into left ventricle, then out through the aortic
  SL valve into aorta

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Venous drainage

• 80 returns to right atrium by following this
  route
• Great cardiac vein collects blood from anterior
  aspect of heart and travels alongside the
  anterior interventricular artery
• It carries blood from apex toward
  atrioventricular sulcus

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Venous drainage continued

• Middle cardiac vein- found in posterior sulcus
  collects blood from posterior aspect of heart and
  carries it from the apex upward
• Coronary sinus collects blood from these and
  smaller cardiac veins and passes across posterior
  aspect of heart in the coronary sulcus and
  empties into the right atrium

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External posterior view
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Cardiac conduction system

• Sinoatrial node- also called the pace maker (SA
  node)-initiates each beat and determines heart
  rate
• AV node- atrioventricular node acts as electrical
  gateway to ventricles
• AV bundle- or bundle of His is a pathway by which
  signals leave the AV node
• Right and left bundle branches -divisions of AV
  bundle that enter interventricular septum and
  head toward apex
• Purkinje fibers -turn upward from apex and spread
  throughout ventricles

23
http//www.medicinenet.com/atrial_fibrillation/art
icle.htm
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Cardiac Rhythm

• Contraction-systole
• Diastole -relaxation
• Normal heartbeat is called sinus rhythm
• Usually 70-80 beats per minute (SA node is
  controlled by vagus nerve to keep this rate)
• Abnormal cardiac rhythm is arrhythmia
• May be caused by heart block-damage to any part
  of the conduction system

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Electrocardiogram

• Also called EKG or ECG
• Electrodes placed at wrist, ankles, and 6 spots
  on chest provide a comprehensive image of the
  hearts activity
• P wave is produced when signal from SA node
  spread thorough atria and depolarize them
• Atrial systole begins about 100 msec after the P
  wave begins during the P-Q segment.
• This segment is about 160 msec long and is the
  time necessary for impulse to travel from SA to
  AV node

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Waves continued

• QRS complex consists of downward Q deflection,
  tall sharp peak (R), and final downward
  deflection (S).
• This is the firing of the AV node and the onset
  of ventricular depolarization
• Ventricular systole begins shortly after QRS
  complex in the ST segment
• Atrial repolarization is masked by the
  ventricular depolarization
• T wave has a rounder peak and is more spread out
  than QRS and represents ventricular repolarization

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http//www.stjosephsatlanta.org/greystone/t_and_p/
heart/TP131.html

• Normal P-QRS-T wave

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Web links

• http//www.nationalgeographic.com/human-heart/
• http//www.gwc.maricopa.edu/class/bio202/cyberhear
  t/hartint_.htm
• http//nobelprize.org/educational_games/medicine/e
  cg/

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Cardiac Cycle

• One complete contraction and relaxation of all
  four heart chambers
• Consists of atrial systole, atrial diastole,
  ventricular systole, ventricular diastole and a
  quiescent period
• Atrial systole-SA node fires and atria depolarize
  (P wave)
• Isovolumetric contraction-atrial repolarization
  and ventricular depolarization (do not eject
  blood yet)

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Continued

• Ventricular ejection-once ventricular pressure is
  greater than atrial pressure, the semilunar
  valves open and blood spurts out quickly at first
  then slows down
• Pressure peaks at 120 mm Hg in left ventricle and
  25 mm Hg in the right ventricle
• Ventricles dont empty completely, each has an
  end-diastolic volume of about 130 mL
• The amount ejected (70 mL) is the stroke volume,
  leaving about 60 mL known as the end-systolic
  volume

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Continued

• Isovolumetric relaxation-early ventricular
  diastole when T wave appears, semilunar valves
  are closed and AV valves havent opened yet
• Ventricular filling-diastolic expansion of
  ventricles causes pressure to drop below that of
  the atria so AV valves open and blood flows into
  ventricles
• Quiescent period is usually 0.4 seconds long

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Cardiac Output

• The amount of blood ejected from ventricles in 1
  minute is CO
• If HR (heart rate) and SV (stroke volume) are
  multiplied it equals CO.
• 75 beats/min x 70 mL/beat 5,250 mL/min
• This means that the bodys total volume of blood
  (4-6 L) passes through the heart every minute

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Heart Rate

• Pulse-number of beats per minutes in a
  superficial artery like the radial artery
• Newborn120 bpm or more
• Adult 60-100 considered the range
• Tachycardia-above 100
• Bradycardia-below 60

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Miscellaneous

• Starlings Law of the Heart-The ventricles tend to
  eject as much blood as they receive
• The more they are stretched, the more forcefully
  they contract (like exercise)
• Heart Sounds-lubb-AV valves closing
• Heart sounds-dubb-Semi-Lunar valves closing