AnatomyII-Test One part 3 Flashcards
Heart Cells
Some cardiac muscle cells are self-excitable (autorhythmic) and initiate the depolarization of the whole heart
All cardiac muscle cells contracts as a unit
Have a long (250 ms) absolute refractory period
Have more mitochondria than skeletal muscles
Non autorhythmic contract similar to skeletal muscles
Intrinsic Conduction System
Initiate the action potentials which cause the muscles of the heart to contract and pump blood
Network of noncontractile (autorhythmic) cells
Autorhythmicity
Heart depolarizes and contracts without nervous system stimulation (Intrinsic)
Autorhythmic Cells (pacemaker cells)
Unstable resting membrane potentials
pacemaker potentials or prepotentials
Continuously depolarize, never rest
Due to opening of slow Na+ channels
Use calcium influx (rather than sodium) for rising phase of the action potential
Heart is stimulated by the
sympathetic cardioacceleratory center
rate and force
Heart is inhibited by the
parasympathetic cardioinhibitory center
rate
Electrocardiogram
Recorded by electrodes placed at specific points on the skin
Electrical activity resulting from the propagation of many action potentials
Composite of all action potentials generated by nodal and contractile cells at given time
PWave
depolarization SA node atria
QRS Complex
ventricular depolarization and atrial repolarization
TWave
ventricular repolarization
Why EKG
Valuable in diagnosing diseases or ailments that damage the conductive abilities of the heart muscle
Damaged cardiac muscle cells no longer conduct electrical impulses
Electrical signals terminate at the damaged tissue
Alters the manner in which the heart contracts
A patient’s electrocardiogram can help determine the presence of damaged cardiac muscle based on the waveform as well as the time interval between electrical events
Heart Sounds
Heart sounds (lub-dup) are associated with closing of heart valves
First sound occurs as AV valves close and signifies beginning of systole (contraction)
Second sound occurs when SL valves close at the beginning of ventricular diastole (relaxation)
Diastole
Systole
relaxation of heart muscle
contraction of heart muscle
Ventricular filling
mid-to-late diastole
Heart blood pressure is low as blood enters atria (passively) and flows into ventricles
AV valves are open, then atrial systole occurs
Ventricular systole (contraction)
Atria relax
Rising ventricular pressure results in closing of AV valves
Isovolumetric contraction phase
Ventricular ejection phase opens semilunar valves
Isovolumetric Relaxtion
early diastole
Ventricles relax
Backflow of blood in aorta and pulmonary trunk closes semilunar valves
Dicrotic Notch
brief rise in aortic pressure caused by backflow of blood rebounding off semilunar valves
Cardiac Output
amount of blood pumped by each ventricle in one minute
CO is the product of
heart rate (HR) and stroke volume (SV)
HR
SV
the amount of blood pumped out by a ventricle with each beat
the number of heart beats per minute
Cardiac Reserve
difference between resting and maximal CO
EDV
ESV
amount of blood remaining in a ventricle after contraction
amount of blood collected in a ventricle during diastole
Factors Affecting Stroke Volume
Preload
Contractility
Afterload
Preload
Contractility
Afterload
amount ventricles are stretched by contained blood
cardiac cell contractile force due to factors other than EDV
back pressure exerted by blood in the large arteries leaving the heart
Preload
or degree of stretch, of cardiac muscle cells before they contract is the critical factor controlling stroke volume
Most important factor stretching cardiac muscle is venous return – amount of blood returning to heart
Slow heartbeat and exercise increase venous return to the heart, increasing SV
Blood loss and extremely rapid heartbeat decrease SV
