THE UNIVERSITY OF ARIZONA

Biology 182 Spring 1998 Section #9,#13
Lab 8 Notes A.K. Huxley

I. External Heart Anatomy

 1) Located in center of the thoracic cavity called the mediastinum
 2) Apex points to the left side of the thorax, related to two lobes of the left lung.
 3) Base located at the top of the mediastinum, allows great vessels to enter and exit from the heart.
 4) Anterior interventricular sulcus separates the two ventricles anteriorally.
 5) Posterior interventricular sulcus separates the two ventricles posteriorally.
 6) Coronary sulcus separates the atria from the ventricles.
 7) Right, left auricles are ear-like flaps found on the atria.  These structures are derived from separate embryonic tissues.
 8) Location, structure of great vessels

  a) Superior, inferior vena cava into right atrium
  b) Pulmonary Trunk from right ventricle
  c) Pulmonary Veins into left atrium
  d) Aortic arch from left vetricle

 1) Atria are located on top, separated into right and left components
 2) Connected to ventricles by valves, right side has tricuspid, left side has bicuspid or mitral
 3) Ventricles are located on bottom, separated by right and left components
 4) The atria are separated from each other by an interatrial septum

  a) septum has foramen ovale before birth
  b) septum has fossa ovale after birth

 5) The valves are located in the wall of the atrioventricular septum
 6) The ventricles are separated by the interventricular septum

One of the best ways to tell the right side from the left in a coronal section of the heart is to look for left ventricular hypertrophy. Because the left ventricle has to work so much harder to pump blood to the body against gravity, the myocardium hypertrophies.  This is easily seen, since the wall is about double the thickness of the right.  Once the left ventricle has been identified, the rest of the internal structures are easily labelled.  There are conditions, however, that lead to right ventricular hypertrophy, such as high altitude conditions during growth and development and a few diseases associated with the respiratory system.

III. Valves

 1) Tricuspid Valve - Atrioventricular Valve

a) The tricuspid valve is located between the right atrium and the right ventricle.
b) the valve has three flaps (i.e. tri) which are attached by tendinous cords, like parachute strings, to the three (ant, post, med) papillary muscles from the trabeculae carnaiae of the right atrium
c) the function of the valve is to prevent back flow of blood from the right ventricle to the right atrium when the ventricle is nearly filled with blood and ready to contract

 2) Pulmonary Semilunar Valve

  a) The pulmonary semilunar valve is located in the pulmonary trunk, which comes from the right ventricle
  b) the valve have three crescent shaped flaps that originate from the aortic semilunar valve during embryonic development
  c) the function of the valve is to prevent back flow of blood from the pulmonary trunk into the right ventricle

 3) Bicuspid Valve (Mitral Valve) - Atrioventricular Valve

a) the bicuspid valve is located between the left atrium and the left ventricle
b) the valve has two flaps (i.e. bi) which are attached by tendinous cords to the (ant, post) papillary muscles from the trabeculae carnaiae of the left ventricle
c) the function of the valve is to prevent back flow of blood from the left ventricle into the left atrium during ventricular filling and contraction

 4) Aortic Semilunar Valve

  a) the aortic semilunar valve is located in the ascending aorta, which comes from the left ventricle
  b) the valve has three crescent shaped flaps that originate from the pulmonary truck during embryonic development
  c) The function of the valve is to prevent back flow into the left ventricle during ventricular contraction
  d) in the wall of the semilunar valves are holes that form the right and left coronary arteries
 

Adult Circulation

SVC/IVC/Coronary Sinus --> Right Atrium --> Tricuspid Valve --> Right Ventricle --> Pulmonary Trunk --> Pulmonary Semilunar Valves --> Pulmonary Arteries (carry deoxygenated blood) --> Lungs --> Pulmonary Veins (carry oxygenated blood) --> Left Atrium --> Bicuspid Valve --> Left Ventricle --> Ascending Aorta --> Aortic Semilunar Valves --> Aortic Arch --> Body

Fetal Circulation

SVC/INC/Coronary Sinus --> Right Atrium  -- > ( Foramen Ovale -->  Left Atrium) --> Tricuspid Valve --> Right Ventricle --> Pulmonary Trunk --> Pulmonary Semilunar Valves --> Before Pulmonary Arteries -->( Ductus Arteriosus --> Aortic Arch) --> Pulmonary Arteries (very little blood to lungs) --> Lungs --> Pulmonary Veins (very little blood to left atrium) --> Left Atrium --> Bicuspid Valve --> Left Ventricle --> Ascending Aorta --> Aortic Semilunar Valves --> Aortic Arch --> Body

V. Conduction System and the Pacemaker

 1) Cardiac Muscle Histology is important to understanding of muscle contraction

  a) the tissue branches to form two general units of contractile fibers

1) atrial bundle
2) ventricular bundle
3) atrial branch is insulated from the ventricular branch by layers of fat and connective tissue under the coronary sulcus between the atria and ventricles

b) the units are connected together by branching fibers that are held into place by intercalated disks (thickenings in the sarcolemma)
c) the intercalated disks have a unique structure

   1) desmosomes act as rivets to hold the cells together
   2) gap junctions, connected by connexon proteins, allow the intracellular fluid to pass from one cell to another

d) histological structures will allow for action potentials to spread quickly from one cell to another

2) Conduction system refers to specialized cells that produce an action potential for muscle contraction, and the coordinated spread of the action potential throughout the heart

  a) autorhythmic cells located in the sinoatrial node of the right atrium

   1) cells set the rhythm of the heart
   2) beat of heart is inherent - do not need outside innervation
   3) minimum number of beats 60-100 per minutes
   4) beginning of conduction system

  b) SA Node fires and spreads over both atria

   1) this portion of the conduction system narrows thereby slowing propagation of AP to the Bundle of His

  c) AV node fires and carries message down the atrioventricular bundle (Bundle of His)
  d) The atrioventricular bundle quickly divides into the right and left bundle branches in the interventricular septum
  e) Purkinge fibers are smaller branches off of the right and left bundle branches that will carry AP to mass of myocardium
  f) Flow chart : Sinoatrial Node, Atrioventricular Node, Atrioventricular Bundle (Bundle of His), Right and Left Bundle Branches, Purkinge Fibers

VI. Electrocardiogram (ECG/EKG)

 1. Functions

  a) measurement of electrical energy (action potential) art as measured from various area on the body (Lead II,RA-->LL)
  b) results can indicate enlargement of the heart
  c) results can indicate damage to the heart

 2. Structure
 3. Wave

  a) P-wave represents atrial depolarization

   1) SA Node --> AV Node
   2) Pathologies

a) large P-waves would indicate atrial enlargement (hypertrophy) through mitral stenosis would lead to left atrial hypertrophy

  b) QRS Complex represents ventricular depolarization

   1) AV Node --> Bundle of His --> RL Bundle Branches --> Purkinge Fibers
   2) QRS Complex covers/blocks effects of atrial repolarization
   3) Pathologies

    a) Increased, lengthened PQ due to coronary artery disease, scar tissue from rheumatic fever
    b) Increased Q due to myocardial infarction
    c) Increased R due to increased ventricular size

  c) T Wave corresponds to ventricular repolarization

  1) AV node will begin to fire shortly after this event
   2) Pathologies

    a) Increased ST due to myocardial infarction
    b) Decreased ST due to hypoxia
 

 1. Events associated with a single heart beat
 2. Divided into three main phases:

  a) Relaxation period -

   1) period after the T-wave
   2) all four chambers of the heart are relaxed
   3) AV valves are closed

  b) Ventricular filling -

   1) P-wave begins
   2) AV valves open and blood rushes into the ventricles
   3) atrial contraction occurs (30 ml) after most of the blood (100 ml) moves into the ventricles by gravity
   4) loss of sinoatrial node would lead to loss of atrial contraction; most blood moved without contraction

  c) Ventricular systole

   1) QRS Complex begins
   2) blood moves in, circles upward and closes AV valves
   3) closure of valves create lubb sound
   4) ventricles contract and push blood up either the aortic or pulmonary trunk
   5) about 60 ml remains behind in the ventricles
   6) blood back flows onto semilunar valves creating dubb sound

VIII. Relationship between Heart Beat and Blood Pressure

 A. Cardiac Output

  1. Defined as the amout of blood out of the left ventricle for one minute
  2. Cardiac Reserve is cardiac output at rest versus cardiac output during exercise

 B. Regulation of Stroke Volume; volume of blood pushed out of the ventricles

  1) three factors affect stroke volume

   a) Preload - more the myometrium is streched, the stronger the force of contraction
   b) Contractability - strength of contraction at any given filling (preload)
   c) Afterload - pressure necessary to overcome the closed semilunar valves