physiology Flashcards
what triggers contraction of cardiac muscle cells
action potentials
what are the 2 types of cardiac muscle cells
- contractile cells
- autorhythmic cells
are the cardiac cells stable
no they express spontaneous pacemaker activity
what does it mean by pacemaker activity
their membrane potential slowly depolarises until threshold is reached
what is it called when cell membrane is drifting to threshold
pacemaker potential
what ion movements cause pacemaker potential
- increased inward Na+ current
- decreased K+ current
- increased Ca+ current
what is it called when cell becomes less negative
depolarisation
what is it called when cell becomes more negative
hyperpolarisation
what is inward Na+ called
funny current
what calcium channels open during pacemaker potential
T tubules
what does T stand for
transient
what happens once threshold is reached
- L type calcium channels open
2. K+ channels open (efflux)
where is SA node located
in right atrial wall near the opening of the SVC
where is AV node located
base of right atrium near septum
what does bundle of His split into
right and left branches
what heart cells have the fastest rate of action potential initiation
SA node cells
how is the action potential spread
via gap junctions
what is the SA node known as
pacemaker of the heart
what is the next fastest cells
AV node
what drives the heart if the atrial cells fail
Purkinje fibres
what is it called when atria and ventricles are contracting at different rates
complete heart block
what is ectopic focus
when one of the slower cells goes faster initiating a premature action potential
what does complete ventricular filling require
that atrial contraction precede ventricular contraction
what state are the AV valves in during cardiac relaxation
open
how does the remaining 20% of blood fill the ventricles
during atrial contraction
do the cardiac chambers contract simultaneously or individually
simultaneously
what is fibrillation
when the cardiac muscle fibres contract uncoordinately
what does ventricular fibrillation cause
death
what is the interatrial pathway
from SA node in right atrium to left atrium
what is the internodal pathway
SA node to AV node
what is special about the AV node
only point of contact between atria and ventricles
does the AV node have fast or slow conduction potential
slow
why is the slow AV node conduction beneficial
ensures time for complete ventricular filling
what does the membrane potential reverse to in phase 0
-90mv to +20mv
what causes the upstroke in cardiac action potential
Na+ influx
what causes phase 1
K+ efflux (partial)
what is unique about a cardiac action potential
plateau phase
what causes plateau phase
Ca+ influx through L-channels
what causes falling phase in action potential
- inactivation of Ca+ channels
- activation of K+ channels
what does calcium entry trigger
the opening of nearby ryanodine calcium release channels in adjacent lateral sacs in sarcoplasmic reticulum
= calcium induced calcium release
where is calcium stored
in sarcoplasmic reticulum
what is the role of calcium in cytosol
bind with the troponin-tropomyosin complex and pull it aside so that cross bridge can bind
what does an increase in calcium concentration cause
prolonged plateau phase
how does verapamil work
blocks the L-type calcium channels, reducing the force of contraction
what does a refractory period ensure
that a second action potential cannot be triggered
what are the Na+ channels like during the refractory period
inactivated
where does ECG lead I go
from right arm to left arm
where does ECG lead II go
right arm to left leg
where does ECG lead III go
left arm to left leg
what are the waves of an ECG
- p
- QRS
- T
what does p wave represent
atrial depolarisation
what does QRS complex represent
ventricular depolarisation
what does T wave represent
ventricular repolarisation
what does PR segment represent
AV nodal delay
what does ST segment represent
systole
- ventricles contracting and emptying
what does TP segment represent
diastole
- ventricles relax and filling
why is the p wave much smaller than the QRS
because atria have much smaller muscle mass than the ventricles so generate less electrical activity
what is tachycardia
rate over 100bpm
what is bradycardia
rate less than 60bpm
characteristics of atrial flutter
- rapid regular
- rate of 200-380bpm
- atrial rate is high and ventricular is normal
characteristics of atrial fibrillation
- rapid, irregular
- no p waves
ventricular fibrillation
- rhythmic abnormalities
- impulses travel in all directions around the ventricles
- death is imminent
what is heart block
- atria beat regularly but ventricles occasionally fail
- there is varying degrees
what happens during systole
contraction and emptying
what happens during diastole
relaxation and filling
how does contraction occur
spread of excitation across the heart
what reflects diastole on ECG
TP interval
when does the SA node reach threshold
late in ventricular diastole
what on the ECG corresponds to spread through atria
p wave
what is the pressure of the atria in atrial depolarisation
atrial pressure exceeds ventricular pressure
what is the end diastolic volume
maximum amount of blood that the ventricle will contain
what does QRS complex represent
ventricular excitation
when does AV valve close
when ventricular pressure exceeds atrial pressure
when does aortic valve open
as ventricular pressure continues to exceed atrial pressure
ventricle is closed so no blood can leave or enter
when does ventricular ejection occur
when ventricular pressure exceeds atrial pressure
how much blood leaves the ventricle during ventricular ejection
50%
what does T wave represent
ventricular repolarisation
when does aortic pressure close
when ventricular pressure falls below aortic pressure
what does closure of aortic valve cause
dicrotic notch
when do AV valves open
ventricular pressure falls below atrial pressure
when does atrial pressure rise
as incoming blood pools in the atrium
what is the first heart sound
lub
what is the second heart sound
dub
what causes the first heart sound
closure of AV valves
what causes the second heart sound
closure of semilunar valves
does valves opening cause a sound
no
how does blood flow normally
laminar
does laminar flow produce a sound
no
what kind of blood flow produces a sound
turbulent
what is a stenotic valve
stiff, narrowed valve that does not open completely
when does turbulence occur
blood flows back through the insufficient valve and collides with blood moving in opposite direction
what is the backflow of blood known as
regurgitation
what is valvular stenosis and insufficiency caused by
rheumatic fever
when does a systolic murmur occur
between first and second heart sound
when does diastolic murmur occur
between second and first heart sound
what is a stenotic sound
whistling
what is cardiac output
volume of blood pumped by each ventricle per minute
what determines cardiac output
stroke volume and heart rate
what is stroke volume
volume of blood pumped per beat
what is average cardiac output
5L
what is cardiac output during exercise
30L
why is the SA node the pacemaker
because it has the fastest spontaneous rate of depolarisation
what happens when SA node reaches a threshold
action potential is generated
what is average heart rate
70 beats per minute
how does parasympathetic get to heart
vagus nerve
what does parasympathetic supply
SA, AV node
what does sympathetic supply
SA, AV, myocardium
what does the vagus nerve release
acetylcholine
what does acetylcholine bind to
muscarinic receptor
what is muscarinic receptor coupled to
Gi that reduces adenyl cyclase
what does sympathetic activate
B1
what does B1 cause
Gs –> adenyl cyclase
what does cAMP lead to
phosphorylation
what effect does parasympathetic nerve have
decrease heart rate
what does parasympathetic do to cAMP
reduce it
how does ACh slow heart rate
increase K+ permeability
what effect does parasympathetic have on AV nodal delay
increases it, prolonging transmission
does parasympathetic stimulation affect contraction
no
what does sympathetic stimulation do to the heart
increase the heart rate
how can rate of depolarisation increase
as a result of the greater inward movement of sodium and calcium
what does sympathetic stimulation do to the AV node
reduces AV nodal delay
does sympathetic stimulation affect force of contraction
yes
what dominates under resting conditions
parasympathetic discharge
how does parasympathetic dominate
acetylcholine suppresses sympathetic activity by inhibiting the release of norepinephrine from sympathetic endings
what secretes epinephrine
adrenal medulla
how does epinephrine affect heart rate
increases it
what is stroke volume
the volume of blood pumped out by each ventricle per beat
what controls stroke volume
- intrinsic
- extrinsic
what is intrinsic control of stroke volume
venous return
what is extrinsic control of stroke volume
sympathetic discharge
what determines EDV
venous return
what is the main determinant of cardiac muscle fibre length
the degree of diastolic filling
what does the frank starling law connect
EDV and stroke volume
what is frank starling law
increased venous return results in increased stroke volume
what is filling known as
pre-load
what does increased contractility result from
increased calcium influx triggered by epinephrine
how does sympathetic stimulation affect Frank Starling law
shifts it to the left
what is the ejection fraction
ratio of stroke volume to end diastolic volume
does sympathetic stimulation affect venous return
yes increases it
what does sympathetic stimulation do to veins
constricts the veins
this squeezes more blood forward from the veins to the heart increasing EDV
calculating cardiac output
= HR x SV
what is afterload
arterial blood pressure
= the workload imposed on the heart after the contraction has begun
what is heart failure
the inability of the cardiac output to keep pace with the body’s demand for supplies
what happens to Frank Starling law in heart failure
shifts downwards and to the right
what has more consequences right sided or left sided heart failure
left sided
what does backward failure of the left side lead to
pulmonary oedema
how does left sided heart failure affect kidneys
they retain more salt and water in the body
what is diastolic failure
ventricles do not fill normally
do cardiac muscle cells contain mitochondria
yes an abundance
does the heart get O2 via diffusion
no muscle walls are too thick
how does the heart muscle receive blood
via the coronary circulation
where do coronary arteries branch from
aorta
where do coronary veins empty
into the right atrium
when does heart receive most of its blood
during diastole
what does adenosine cause
vasodilation of coronary vessels
what is atherosclerosis characterised by
plaques forming beneath the vessel lining within arterial walls
what does atherosclerosis start with
injury to the blood vessel wall
what accumulates beneath the endothelium
LDL
what happens to LDL
becomes oxidised
what ingests OXLDL
macrophages
what do macrophages full of OXLDL look like under a microscope
foamy
what to the macrophages with OXLDL form
fatty streak
what does OXLDL inhibit
the release of NO
what are fibroblasts
scar-forming cells
what precipitates in the plaque in the later stages
calcium
what does atherosclerosis in the brain cause
stroke
when do the symptoms of angina occur
during increased O2 demands
what does nitroglycerin bring about
coronary vasodilatation as it is converted to NO
what happens when a platelet contacts collagen
they stick to the site and help promote the formation of a blood clot
when does heart attack occur
when a coronary vessel is completely plugged
what is collateral circulation
when small terminal branches from adjacent blood vessels nourish the same area
what are the sources of cholesterol
- dietary intake (egg, red meats, butter)
- manufacture of cholesterol by cells (liver)
is lipid soluble in water
no
how are lipids transported
bound to lipoprotein
examples of lipoproteins
HDL
LDL
VLDL
is LDL good or bad
bad
is HDL good or bad
good
what does HDL do
remove cholesterol from cells and transports it to the liver for elimination from the body
