Ch. 13/14 Day 2 Flashcards
If pressure in the heart goes high enough, the valve can prolapse. How is this prevented?
Papillary muscles contract w/ increasing pressure, exerts force on chordae tendineae to prevent valves from going too far.
Chordae tendineae are connected to the?
Papillary Muscle
Anatomy of the heart
See diagram on Ch. 13 notes (p. 28-29)
Atrioventricular (AV) Valves
Between atria and ventricles
Tricuspid valve on right side
Bicuspid valve, or mitral valve, on left side
Semilunar Valves
Between ventricles and arteries
Pulmonary valve
Aortic valve
What ensures the one-way flow of blood in the heart?
Valves
Ventricular Contraction
AV valves closed
Semilunar valves open
Ventricular Relaxation
AV valves open
Semilunar valves closed
Heart
Pump generating driving pressure for blood flow through the circulation.
Pumping is periodic, i.e. cardiac activity characterized by repeated cycles of active pumping (systole) followed by resting (diastole).
Heart generates pressure when it contracts (systole), pumping blood into arteries [ventricular contraction].
Arteries maintain pressure by acting as an elastic pressure reservoir between cardiac contractions (i.e. during diastole) [ventricular relaxation].
Pressure Changes during the cardiac cycle
- Ventricles begin contraction, pressure rises, and AV valves close (lub); isovolumetric contraction
2) Pressure builds, semilunar valves open, and blood is ejected into arteries
3) Pressure in ventricles falls; semilunar valves close (dub); isovolumetric relaxation
4) Pressure in ventricles falls below that of atria, and AV valve opens. Ventricles fill
5) Atria contract, sending last of blood to ventricles
Dicrotic Notch
Slight inflection in aortic pressure during isovolumetric relaxation
EDV-ESV
1) EDV - ESV = SV
2) Ventricle does not eject all its volume - can be altered
EDV: end diastolic volume
ESV: end systolic volume
SV: stroke volume
Stroke Volume (SV)
Overall work being done by heart; increases as EDV and ESV get farther apart over time
Cardiac Muscle: Contractile Cells
Striated fibers organized into sarcomeres
Cardiac Muscle: Autorhythmic (pacemaker) Cells
Signal for contraction
Smaller and fewer contractile fibers
No organized sarcomeres
–so no real function to contract; instead send electrical signals
Cardiac Muscle: Myocardial Muscle Cells
Branched, have single nucleus, and are attached to each other by specialized junctions known as intercalated discs
Electrical Conduction in Myocardial Cells
Autorhythmic cells spontaneously fire action potentials. Depolarizations of autorhythmic cells spread rapidly to adjacent contractile cells through gap junctions.
70 bpm
Electrical Activity of the Heart
Automatically
Sinoatrial node (SA node) - “pacemaker”; located in R. Atrium
AV node and Purkinje fibers - secondary pacemakers; slower rate than the “sinus rhythm”
Conduction System of the Heart
Action potentials spread via intercalated discs
SA node –> AV node (atrial contraction)
AV node (base of R. Atrium) and Bundle of His conduct stimulation to ventricles.
In Interventricular Septum, Bundle of His –> R. and L. Bundle Branches
Bundle Branches –> Purkinje fibers –> ventricular contraction
Electrical Conduction: Sinoatrial (SA) Node
Sets the pace of the heartbeat at 70 bpm
AV node (50 bpm) and Purkinje fibers (25-40 bpm) can act as pacemakers under some conditions
Electrical Conduction: Atrioventricular (AV) Node
Routes the direction of electrical signals so heart contracts from apex to base (i.e. from bottom –> top)
AV node delay due to slower conduction through nodal cells
If SA node not working properly, AV node takes over (treatment can fix this, such as pacemaker)
How does cardiac muscle contraction differ from skeletal muscle contraction?
B/c some Ca2+ coming from cytoplasmic space
Why does Tetany NOT occur in cardiac muscle?
Cardiac muscle fiber refractory period lasts almost as long as the entire muscle twitch
VS
Skeletal muscle fiber refractory period compared w/ duration of contraction
Pacemaker and Action Potentials
Slow, spontaneous depolarization; aka “diastolic depolarization” - between heartbeats, inward I(Na+) triggered by hyperpolarization
At -40mV, voltage-gated Ca2+ channels open, triggering action potential and contraction
Repolarization occurs w/ opening of voltage-gated K+ channels
Electrocardiogram (ECG)
Represents the summed electrical activity of the heart recorded from the surface of the body
Picks up movement of ions in body tissues in response to this activity
- -does not record action potentials, but results from waves of depolarization
- -does not record contraction or relaxation, but electrical events leading to contraction and relaxation
ECG Waves
P wave: atrial depolarization
P-Q interval: atrial systole
QRS wave: ventricular depolarization
S-T segment: plateau phase, ventricular systole
T wave: ventricular repolarization
ECG: Pressures and Heart Sounds
“Lub” occurs after QRS wave as the AV valves close
“Dub” occurs at the beginning of the T wave as the SL valves close
