Heart Flashcards
Structure heart wall
Epicardium
Myocardium
Endocardium
Epicardium
lubricative outer covering
membrane including blood, lymph capillaries and nerve fibres
Myocardium
cardiac muscle tissue seperated by connective tissue
provide muscular contractions that eject blood from heart chambers
Endocardium
Endothelial tissue
thick layer of elastic/collagenous fibres
protective inner lining of chambers and valves
Contraction of the heart depends on
electrical stimulation of the myocardium
Sinoatrial node
pacemaker
initiates depolarization
Atrioventricular node
passes depolarization to ventricles
brief delay to allow ventricular filling
Bundle branches
connect atria to left and right ventricle
Purkinje fibres
spread wave of depolarization throughout ventricles
Conduction system
Action potentials originate in the sinoatrial (SA) node (the pacemaker) and travel across the wall of the atrium (arrows) from the SA node to the atrioventricular (AV) node
Action potentials pass through the AV node and alongthe atrioventricular (AV) bundle, which extends fromthe AV node, through the fibrous skeleton, into theinterventricular septum.
The AV bundle divides into right and left bundlebranches, and action potentials descend to the apexof each ventricle along the bundle branches.
Action potentials are carried by the Purkinje fibersfrom the bundle branches to the ventricular walls
P wave
atrial depolarization
QRS complex
ventricular depolarization and atrial repolarization
T wave
ventricular repolarization
What is an intrinsic pacemaker rate?
~100 bpm
Relationship between pressure change and ECG
intraventricular pressure rises as ventricles contract (AV valve closes)
falls as ventricles relax (semilunar valve closes)
Atherosclerosis
fatty plaque that narrows coronary arteries
reduces blood flow to myocardium
Regular exercise beneifts on heart
cardioprotective
reduces incidence of heart attacks
improves survival from heart attack
reduce amount of myocardial damage from heart attack
improve antioxidant capacity
improve function of ATP-sensitive potassium channel
PNS
via vagus nerve
slows HR by inhibit SA and AV node
SNS
via cardiac accelerator nerves
increases HR by stimulating SA and AV nodes
Cardiac muscle
highly oxidative
dense network of capillaries
At rest oxygen extraction
high
65-75%
During exercise oxygen extraction
increase +90%
but increased oxygen delivery relies on mainly increase in coronary blood flow
Oxygen consumption by the heart
required for contraction
maintain basal metabolism (10-20% total)
Chronotropic
heart rate increases
