Cardiac Cycle and Conduction System of the Heart.
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Transcript of Cardiac Cycle and Conduction System of the Heart.
Cardiac Cycle and Conduction System of the Heart
The Cardiac Cycle
The mechanical events that take place in one heartbeat.
The Cardiac Cycle
Contraction of a chamber - systole
Relaxation of a chamber - diastole
1 full contraction and relaxation - cardiac cycle
Systole and DiastolePeak pressure of a chamber or vessel
Stroke volumeamount of blood ejected by the heart (LV) in one contraction
• aprox. 70 cc (60-100 cc)
Relaxation of a chamber
Pressure at its lowest
Cardiac Output
Cardiac Outputamount of blood ejected every minute
• aprox. 5-6L
• SV X HR = CO
• The strength of contraction is directly related to venous return
Starling’s Law
The more a muscle is stretched the harder it will contract (up to a certain point)
Similar to a spring
Muscle fibers will stretch and contract harder when there is a increased blood return
Blood Pressure
The pressure exerted by blood against the walls of a given artery.
Factors Affecting Blood Pressure
1. Blood Volume
2. Strength of heart contractions
3. Heart rate
4. Blood viscosity – thickness of blood
Electrophysiology
Before the heart can contract it must be stimulated.
This is accomplished through a specialized network of cells called the conduction system.
There are numerous “pacemaker” cells to stimulate the heart to contract.
Sinoatrial Node (SA)
Located in high RA
Main pacemaker of heart
Sends out regular impulses at 60- 100 times per minute
Regulated by the Autonomic Nervous System (vagus nerve)
Atrioventricular Node (AV)
Located on floor of TA next to septum and behind CS os
Has 2 main jobsDelay the impulse from the SA node long enough so the ventricles can fill with blood
Protect the ventricles from rapid atrial rates
Inherent rate of 40-70 bpm
Bundle of His (HB)
A fibrous ring around the 4 valves
Only muscular connection between the atria and ventricles
AV node and HB collectively are called the AV junction
The AV junction can pace the heart at rate of 40-60 bpm
Bundle Branches
HB branches into rt.... And lt.. Branches
Lt.. Bundle branch (LBB) then divides into anterior and posterior sections
Purkinje Fibers
Terminal portion of the conduction system
Located in ventricular muscle
Can pace the heart at 20-40 bpm
Electrical Properties of Cardiac Muscle
AutomaticityProperty by which a cell can reach threshold potential (depolarize) and send an impulse without help from an external source
ExcitabilityAbility of cell to reach threshold potential in response to an outside stimulus
ConductivityThe propagation of an impulse form cell to cell through intercalated disks
ContractilityAbility of a muscle to shorten (contract) when stimulated
Electrophysiology cont.....
Electrophysiology Cont.....
The end result of contraction of the heart is electrochemical in nature.
The impulse is sent along the conduction system because of changes in cellular polarity.
Cardiac Emergencies
A thrombosis or embolism may plug the arteries causing a myocardial infarction or “heart attack”
Angina pectoris is used to describe the severe chest pain
infarct