Cardiovascular Physiology Flashcards
heartbeat
a single contraction of the heart
the entire heart contracts in series
order of contraction within the heart
first atria, then ventricles
2 types of cardiac muscle cells
conducting system
contractile cells
conducting system
controls and coordinates the heartbeat
contractile cells
produce contractions that propel blood
what begins the cardiac cycle
an action potential at the SA node
what happens after the production of an action potential at the SA node
transmitted through conducting system
produces action potentials in cardiac muscle cells(contractile cells)
electrocardiogram
electrical events in the cardiac cycle can be recorded on an electrocardiogram
the conducting system
a system of specialized cardiac muscle cells
- initiates and distributes electrical impulses that stimulate contraction
- automaticity: cardiac muscle tissue contracts automatically
contractile cells
- purkinje fibers distribute the stimulus to the contractile cells, which make up most of the muscle cells in the heart
- resting potential: of a ventricular cell: -90 mV
- of an atrial cell about -80 mV
conduction system ion channels
potassium, sodium, calcium
myocardium ion channels
potassium, sodium, calcium
blood vessels ion channels
calcium, potassium, chlorine
action potential in cardiac muscle
- rapid depolarization
- plateau
- repolarization
rapid depolarization
caused by sodium entry and ends with closure of voltage-gated fast sodium channes
the plateau
caused by calcium entry and ends with closure of the slow calcium channels
repolarization
caused by potassium loss and ends with closure of slow potassium channels
absolute refractory period
long
cardiac muscle cells cannot respond
relative refractory period
short and response depends on degree of stimulus
purpose of the long refractory period in cardiac cells
prevent summation and tetany
contraction of a cardiac muscle cell is caused by
an increase in calcium ion concentration around myofibrils
the role of calcium ions in cardiac contractions
calcium ions enter plasma membrane during the plateau phase
this triggers release of calcium ion reserves from sarcoplasmic reticulum
as slow calcium channels close
intracellular calcium is absorbed by the SR
or pumped out of the cell
cardiac muscle tissue is very sensitive to extracellular Ca concentrations
structures of the conducting system
sinoatrial node
atrioventricular node
conducting cells: throughout myocardium
conducting cells in the atrium
present in internodal pathways
conducting cells in the ventricles
present in the AV bundle and bundle branches
Prepotential
pacemaker potential
resting potential of conducting cells
-gradually depolarizes toward threshold
SA node depolarizes first, establishing the heart rate
the sinoatrial node
- in posterior wall of right atrium
- caontains pacemaker cells
- connected to AV node by internodal pathways
- begins atrial activation
AV bundle
- in the septum
- carries the impulse to the left and the right bundle branches
- which conduct to purkinje fibers
- and to the moderator band
- which conducts to papillary muscles
purkinje fibers
distribute the impulse through the ventricles
atrial contraction is completed
ventricular contraction begins
abnormal pacemaker function
bradycardia
thachycardia
ectopic pacemaker
ectopic pacemaker
abnormal cells
generate high rate of action potentials
bypass conducting system
disrupt ventricular contractions
P wave
atria depolarize
QRS complex
ventricles depolarize
T wave
ventricles repolarize
P-R interval
from the start of atrial depolarization to the start of a QRS complex
Q-T interval
from ventricular depolarization
to ventricular repolarization
the cardiac cycle
is the period between the start of one heartbeat and the beginning of the next
includes both contraction and relaxation
2 phases of the cardiac cycle
systole: contraction
diastole: relaxation
* each is within any one chamber
atrial systole
atrial contraction begins
right and left AV valves are open
atria eject blood into ventricles
atrial systole ends
AV valves close
ventricles contain maximum blood volume
known as end-diastolic volume
ventricular systole
ventricles contract and build pressure: AV valves close and cause isovolumetric contraction
ventricular ejection
ventricular pressure exceeds vessel pressure opening the semilunar valves and allowing blood to leave the ventricle
amount of blood ejected is called the stroke volume
ventricular pressure falls
semilunar valves close
ventricles contains end-systolic volume: about 40% of end diastolic volume
ventricular diastole
ventricular pressure is higher than atrial pressure
all heart valves are closed
ventricles relax: isovolumetric relaxation
atrial pressure is higher than ventricular pressure
AV valves open
passive atrial filling????
passive ventricular filling
blood pressure in any chamber
rises during systole
falls during diastole
blood flows from high to low pressure
controlled by the timing of the contractions
directed by one-way valves
when heart rate increases
all phases of the cardiac cycle shorten, particularly diastole
S1: heart sound
loud sounds
produced by AV valves
S2: heart sound
loud sounds
produced by semilunar valves
S3 and S4 sounds
soft sounds
blood flow into ventricles and atrial contraction
heart murmur
sounds produced by regurgitation through valves
cardiodynamics
the movement and force generated by cardiac contractions
stroke volume
EDV-ESV = -SV
ejection fraction
the percentage of EDV represented by SV
cardiac output
the volume pumped by left ventricle in 1 minute
CO = HR * SV
factors affecting cardiac output
- changes in heart rate or stroke volume
- heart rate is adjusted by the autonomic nervous system or hormones
- stroke volume can be adjusted by changing the EDV or ESV
autonomic innervation
- cardiac plexuses innervate heart
- vagus nerves carry parasympathetic preganglionic fibers to small ganglia in cardiac plexus
- cardiac centers of the medulla oblongata
cardiac centers of medulla oblongata
- cardioaccelatory center: controls sympathetic neurons: increases heart rate
- cardioinhibitory center: controls parasympathetic neurons: slows hart rate
cholinergic receptors
activated by parasympathetic
M2 muscarinic receptors are mainly in the SA node
M2 activation: reduces heart rate: negative chronotropic
adrenergic receptors
activated by sympathetic
B1 adrenergic receptors int he myocardium, SA node
B1 activation: increases contractility(positive inotropic)
: increased heart rate(positive chronotropic)
angiotensin
AT1 Myocardium: positive inotropy
membrane potential of the pacemaker cells
lower than other cardiac cells
rate of spontaneous depolarization depends on:
resting membrane potential
rate of depolarization
sympathetic and parasympathetic stimulation
greatest at the SA node
Acetylcholine
parasympathetic
slows heart
norepinephrine
sympathetic
speeds the heart
atrial reflex
adjusts rate rate in response to venous return
stretch receptors in the right atrium
-trigger an increase in heart rate
-through increased sympathetic activity
the frank-starling principle
as EDV increases, stroke volume increases
afterload
caused by any factor that resists arterial blood flow
afterload increases
stroke volume decreases
preload
degree of ventricular stretching during ventricular diastole
