Cardio 2 Flashcards
99% of myocardium
contractile cells
contractile cells depolarized by
signal fom AR cells
phases of action potential
4 0 1 2 3
Phase 4 –
Resting Vm
Phase 0 –
Depolarization spike
Fast voltage gated Na+ channel
(activation/inactivation gates) open
Phase 1 –
Partial Repolarization
Fast voltage gated Na+ channel close
Phase 2 -
plateau
Transient K+ channels close
L-Type Ca++ channels open
Phase 3 –
Repolarization
L-Type Ca++ channels close
Slow K+ channels open
In skeletal muscle, Contractile response to a single AP is
all or
none – Ca++ released saturates troponin and contraction
strength is maximal.
In Cardiac muscle, contractile response to a single AP is
graded
In “resting” state, AP-induced sarcoplasmic release of Ca++ in cardiac cells does not saturate — sites.
troponin
Strength of contraction depends on
[Ca++]i
[Ca++]i is adjusted to increase — of contraction.
strength
Substances that alter the force of contraction of cardiocytes by
changing [Ca++]cytosol are termed
inotropic agents
Inotropic
agents change
contractility of the heart (how forcefully the
cells contract). Ex. Sympathetic NS/Epinephrine
The cardiac cycle includes all the events involved with
blood flow through the heart during one heart beat
Blood flows down
ΔP
Valves open and close passively due to
ΔP
Events of the cardiac cycle
- Between Beats – Passive Filling
- Atrial systole – Active filling
- Atrial Diastole/Early Ventricular Systole - Isovolumetric
Contraction - Late Ventricular Systole – Ejection phase
- Early Ventricular Diastole – Isovolumetric Relaxation
- Late Ventricular Diastole
Between Beats (4)
Pressure A < Pressure Veins
Pressure A > Pressure V
Pressure V < Pressure Arteries
- Between Beats: referred to as
Period of
Passive Filling
80% of Blood for contraction loaded into
ventricles at this time.
- Atrial Systole (4)
Pressure A incease
Pressure A > Pressure Veins
Pressure A > Pressure V
Pressure V < Pressure Arteries
- Atrial Systole: referred to as
Period of
Active Filling
20% of Blood for contraction loaded into
ventricles at this time.
- Atrial Diastole/Early Ventricular Systole (5)
Pressure A decrease Pressure V incease Pressure A < Pressure Veins Pressure A < Pressure V Pressure V < Pressure Arteries
- Atrial Diastole/Early ventricular Systole: referred to as
Period of
Isovolumetric Contraction
Pressure in V increases
- Late Ventricular Systole (4)
Pressure A < Pressure Veins
Pressure A < Pressure V
Pressure V > Pressure Arteries
- Late VEntricular Systole: referred to as
Ejection Phase
Equal volume of blood ejected into both
circulations
- Early Ventricular Diastole (4)
Pressure V decrease
Pressure A < Pressure Veins
Pressure A < Pressure V
Pressure V < Pressure Arteries
- Early Ventricular Diastole: referred to as
Period of
Isovolumetric Relaxation
Pressure in V decreases
- Late Ventricular Diastole (5)
Pressure A < Pressure Veins
Pressure A > Pressure V
Pressure V < Pressure Arteries
During 6. Late Ventricular Diastole, what begins?
Period of Passive Filling Begins
Pressure/Volume Loop
Δ in Left Ventricular Volume and Pressure
- End Diastolic Volume (EDV)
≈ 135 ml
- End Systolic Volume (ESV)
≈ 65 ml
- Stroke Volume (SV)
=volume of blood ejected/beat
=EDV-ESV
≈70ml/beat
- Ejection Fraction
Fraction of EDV ejected/beat
=SV/EDV
≈52%
Heart Sounds (lub dub) Due to
Valve closures
Heart Murmurs
Abnormal heart sounds
stenosis
failure of valves to open completely
insufficiency or prolapse
failure of valves to close properly
