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Right atrium of heart?

  Systemic veins empty into R Atrium via:

  1. The superior vena cava (SVC)

  2. The inferior vena cava (IVC)

  •   The Eustachian valve protects the lVC

  3. Coronary veins empty into R Atrium via: The coronary sinus

  •   The Thesibian valve protects the coronary   sinus


Characteristics of right ventricle?

  Propels blood to the pulmonary vessels via the pulmonary orifice: infundibulum

  Communicates with R atrium via the tricuspid orifice: chordae tendineae

  Has several muscle bundles:  trabeculae carneae-one of which carries the right branch of the AV bundle


Characteristics of left atirum

  Larger than R atrium

  Superior and posterior to the other chambers

  Receives pulmonary veins

  -Reservoir for oxygenated blood

  -Provides the “atrial kick” in LVEDV-important in certain conditions

  Communicates with the left vetricle via the AV orifice-mitral valve



Characteristics of left ventricle

  Receives oxygenated blood from the LA

  Pumps blood to the body via the Aorta

  Ventricular septum: R and L ventricles

  Upper 1/3 of the septum is smooth

  Lower 2/3 is muscular and covered with trabeculae carneae

  2 large papillary muscles-chordae tendineae-cusps of the mitral valve


What are the AV valves

  •   Tricuspid
    •   Within the R AV orifice
    •   3 leaflets-anterior, posterior, septal
    •   Valve area:  7cm2, symptoms occur at area   <1.5cm2
  •   Mitral valve
    •   Within the L AV orifice
    •   2 leaflets-anteromedial, posterolateral
    •   Valve area:  4-6cm2, symptoms occur at 2-3 cm     


What are the semilunar valves?

  •   Aortic valve:
    •   Out flow tract of the aorta and the LV
    •   Has 3cusps
    •   Sinus of Valsalva
    •   Valve Area: 1-3cm2 area <1/2 or 1/3 symptomatic
  •   Pulmonic valve:
    •   Outflow tract of the pulmonary artery and RV
    •   Has 3 cusps
    •   Valve area: 4cm2 area <1/2 or 1/3 symptomatic


What provides coronary circulation?

  •   Epicardial
  •   Subendocardial
  •   2 Epicardial Coronaries originate from the sinuses of Valsalva
    •   Left Coronary Artery (LCA)
    •   Right Coronary Artery (RCA)


Branches of LCA?

  •   Short left main-ant. inf. & left.
  •   Bifurcates into the:
    •   LAD
      • `diagonal branch
      •  septal perforating branch-feeds the anterior of LV, and the interventricular groove (leads V3-V5)
    •   Circumflex-obtuse margin-feeds the posterior LV and part of RV (lead I)


Branches of RCA?

  Branches into:

  1.  Sinus node artery- feeds SA node and RA Branch-feeds the RA

  2.  Av node artery-feeds AV node (in 90% of   population)

  3.  Anterior RV Branches-feed the RV

  4.  PDA-feeds the posterior 1/3 of the   interventicular septum

  Leads II, III and aVf


How is coronary dominance determined?

  Which artery crosses the crux (junction between the atria and ventricles) to feed the posterior descending coronary branch

  In 50% it is the RC

  In 20% it is the LC

  In 30% a balanced pattern exists


What percent of CO goes to coaronaries?

What determines flow in coronaries?

  •   5% of CO or 250ml/min perfusion
  •   Flow is determined by:
    •   Duration of diastole
    •   CPP=Diastolic pressure-LVEDP
  •   LCA: flow occurs mostly during diastole
  •   RCA: flow occurs in both systole and diastole
  •   Myocardial O2 consumption is high with cardiac venous sat. lowest in the body (30%)


What is coronary autoregulation?

  •   CPP usually autoregulated at 50-120 mmHg
  •   Pressure dependent changes
  •   Myocardial oxygen demand alters autoregulation:  O2 tension acting thru mediators, ie adenosine
  •   Greatest dilation occurs in smallest vessels LCA>RCA in autoregulation


What composes the cardiac conduction system?

  Consists of:

  SA node

  Internodal tracts

  AV node

  AV bundle (bundle of His)

  Purkinje system


What composes the SA node?

  •   Mass of specialized cells
  •   Junction of SVC and RA
  •   2 Cell types
    •   I.  P cells (pacemaker cells)
    •   II. Transitional or intermediate cells- conduct impulses within and away from the node


What composes the internodal tract?

  •   Within the atria
  •   Conduction pathways b/w the SA & AV
  •   Also contain P cells and transitional cells
  •   3 Major tracts:
    •   1.  Anterior (Buchmann’s bundle)-septum
    •   2.  Middle (Wenckebach’s tract)-SVC
    •   3.  Posterior (Thorel’s tract)-septum


What composes the AV node?

  •   Supplied by nerve endings including vagal ganglionic cells.
  •   Causes a delay in the transmission of the action potential:
    •   Size of cells:  smaller
    •   Resting memb. potential:  more negative
      •  (-60  vs -50 for SA node).
    •   Gap junctions:  very few
    •   Resistance to action potential: incr. 
  •   Rate of about 50bpm


What composes the AV Bundle?

  Extends from the AV Node

  Enters the posterior part of the ventricle and Purkinje system.

  Preferential channel for conduction from the atria to the ventricles


What is the purkinje system?

  •   2 systems:  Left and Right
  •   1.  Left:
    •   Spreads under the endocardium
    •   Forms several fascicles-branch over   the left ventricle
  •   2.  Right:
    •   Travels under the endocardium
    •   Base of the anterior papillary muscle


What determines the resting membrane potential of the heart?

  The cell at rest:

  The resting cell is relatively permeable to potassium and much less to either sodium or calcium

  Thus the resting membrane potential of the heart is most dependent on potassium


What are the phases of action potential for ventirular myocte?

  Five phases:

  Phase 0-depolarization Fast Na+ channels

  Phase I- repolarization Na+ influx ends

  Phase II-plateau Slow Ca+ channels open allowing an influx of Ca+

  Phase III-terminal repolarization Slow Ca+ channels are inactivated and efflux of K+ occurs

  Phase IV-diastolic phase Na+ - K+ pump


What is the absolute and refractory phase in ventricular myocte?

  Refractory Pds

  Long lasting action potentials prevent premature excitation

  Absolute:  No response occurs during phase 0- middle of phase III

  Relative:  Middle of phase III to phase IV when a second stimulus will cause a weaker action potential than the first  


What composes the sympathetic nervous system for heart?

  •   Sympathetic:
  • Arise from:
    •   Stellate ganglion and caudal cervical fibers
  • Turn into:
    •   The right dorsal medial and lateral cardiac nerves
    •   They unite to form one large nerve that follows the course of the L main CA
    •   They then branch along the ant. descending and circumflex arteries.
  •   Cholinergic fibers-ventricle
  •  Sympathetic Cnt’d:
    •   Release of ACh-post synaptic nicotinic receptors
  •   Stimulation of:
    •   Norepinephrine activates the β1-adrenergic receptors


WHat provides parasympathetic innervation to heart?


  • Arise in medulla in dorsal vagal nucleus and the nucleus ambiguus

  • Enter via recurrent laryngeal nerve and thoracic vagal nerves

  • Form plexuses that give rise to the R and L coronary cardiac nerves and the L lateral cardiac nerve

  Ganglia occur w/in the heart close to structures innervated by postganglionic neurons

  Post ganglionic transmission occurs by stimulation of nicotinic receptors at junctions and activate the muscarinic receptors in the heart



What are the vagal receptors and sympathetic fibers for cardiac receptors?

  • Vagal receptors
    • Atrial musculature
    • SA and AV nodes
    • Ventricular myocardium
    • Most prevalent in SA node, then AV, RA, LA and ventricles
  • Sympathetic fibers
    • All through the heart
    • RA contains mostly (75%) B1
    • Ventricles contain mostly (85%) B1


What happens during diastole?

  •   Isovolumetric relaxation
  •   Blood returns from the periphery
  •   Aortic valve closes
  •   Ventricular pressure still exceeds atrial pressure for about 0.02-0.04 secs, as the ventricular pressure continues to drop and equalizes and then gets lower than atrial pressure
  •   Ventricular filling
  •   AV Valve begins to open
  •   Then opens completely
  •   Ventricular volume rises rapidly, and then slower as pressure rises slightly until the ventricle is filled and the AV valve closes


What occurs during systole?


  •   Isovolumetric contraction
  •   The AV valve is closed (atrial diastole)
  •   Ventricular pressure continues to rise
  •   The semilunar valve opens
  •   Ventricular systole occurs
  • Ventricular action
  •   Atrial pressure decreases, due to blood now entering the pulmonary artery & aorta
  •   Rapid ejection occurs


What does a pressure volume loop of the heart show?

From pressure-volume loop picture-

  1. closing of mitral valve
  2. aortic valve opening
  3. aortic valve closure
  4. mitral valve opening

a. diastolic filling

b isovolumetric contraction

c. ventricular ejection 

d. isovolumetric relaxation


Volume for 1-4= SV 




What determines cardiac output?

CO= Volume of blood pumped by the heart each minute

  Determined by:

  1.  Preload

  2.  Afterload

  3.  Heart rate 

  4.  Contractility

  5.  Ventricular compliance


What is a frank-starling curve?

  • relationship between SV and LVEDP
    • afterload increases or CO decreases---> frank startling curve downward
    • afterload decreases or increase in CO--> frank starling curve upward


What influences coronary supply and demand?

  •  Supply
    • Can be raised only by increasing coronary blood flow
      • Diastolic time
      • HR
      • CPP
      • Coronary vasc. tone
      • Intramural obstruction
      • Arterial O2 content/extraction
  •   Demand
    • Wall tension
      • Preload
      • Afterload
    • Contractility
    • HR
      • More important to address-easier