regulation and adaptation of the heart Flashcards
what factors determine the membrane potential?
concentration gradients of K, Na,Ca
electrical conductance of the memebrane being regulated by ion channels
what is an electrogenic pump?
contributes to the resting membrane potential
what maintains a negative charge inside the cell?
na/K pump
how does electrical activity pass through the heart?
contractile fibres
how do myocardial cells work?
SAN depolarises across all cells
cells dont contract though till they recieve this activity much like a wave
what is the prepotential?
tendency for K and Na chennels to open allowing influf of positive ions into cells
causes depolariasation
what affects the prepotential?
autonomic nervous system
what is the sloping prepotetial caused by?
slowly declining membrane potential is called the pre-potential, the slope detemines the heart rate
it is caused by the Na pacemaker current
describe the steps of the impulse conduction through the heart
- SA node fires wave of depolarization across atria
- stimulus spreads across atria reaching AV node
- millisecond delay at AV node before atria contraction begins
- impulse travels along septum with th AV bundle and Purkinje fibres into ventricles
- impulse distributed by Purkinje fibres and relayed throughout the ventricular myocardium and ventricular contraction begins
how can the ECG be used as a diagnostic tool
electrical axis heart rate activation sequencce disorders drugs electrolyte imbalance carditis pacearker issues coronary circulation hypertrophy arrhythmias
what is sinus tachycardia
impulses from SA node at rapid rate
what is an atrial flutter
impulses travel in circular route across atria
ventricular response irregular
what is atrial fibrillation
impulses have chaotic, random pathways in the atria
ventricles irregular too
what is ventricular fibrilation
very serious as output decreased
rapid, wide, irrregular venticular complexes
what is stroke volume dependent on?
energy of contractios
atrial pressure
muscles ability
what does cardiac output depend on?
affected by activity
changes affected by heart rate and stroke volume
define inotropy
strength of contraction
define chronotrophy
contraction frequency
define bradycardia
decreased heart rate
define tachycardia
increased heart rate
define dromotrophy
the velocity of signal conduction
define lusitropy
myocardial relaxation
define bathmotropy
myocardial excitability
what does the sympathetic nerve innervation do?
increases heart rate and force of contraction
what does the parasympthtic nerve innervtion do?
slows the heart rate down
what happens during sympathetic regulation?
inotropy up chronotrophy up dromotrophy up bathmotrophy up lusitriophy up faster, harder
what increases sympathetic innervation
exercise
standing up
stress
haemorrhage
what happens to the ejection fraction during sympathetic inervation?
increases
what hapens to stroke volume during sympatetic innervation
increased
what causes increased luisotrophy during symatheic innervation
phosphorylation of actin filaments
what mediates sympathetic innervation?
B-adrenergic receptors
what mediates parasympathetic innervation?
M2 muscarinic acetylcholine receptors
what happens during parasympathetic innervation?
chronotrophy down
inotrophy down
bathotrophy down
dromotrophy down
at rest what keeps heart rate suppressed?
parasmpathetic
what is the anrep effect?
increased arterial pressure causes increased contractility of myocardium
what is the effect of temperature
fever increased heart rate
cooling is used in surgery to slow heart rate
what is the frank-starling mechanism?
the more the ventricle is filled with blood during diastole, the greater the stroke voume
what does increased blood volume cause in the frank-starling mechanism
increased stretch of the myocardium equalling and increase force to pump the bloo out
when does the law become invalid ( frank-starling)
after a certain LVEDP
left ventricular end-diastole pressure
what is the calcium tension curve
sensitivity of calcium depends on the sarcomere length
what does a long sarcomere mean for calcium?
myofilaments mroe sensitive to calcium
more Ca can bind to thin filaments as there is less overlsp
what does a short saarcomere mean for calcium?
more overlap, less sensitive
what is Laplaces law?
tension on the wall of the heart is product of the pressure times the radium of the chamber
the tension is invertly related to the thickness of the wall
equation of laplace’s law
internal presssure P = 2Tension / radius
as the radius increased what happened? Laplace’s law
pressure decreases
what is preload?
stretch of the cardiac muscles when exposed to diastole conditons
what affect preload?
venous presssure, rate of venous blood flow, venous tone and volume of circulating blood
define afterload?
tension produced by the heart in order to eject blood into vessels
what affects afterload?
blood pressure
what affects the venous pressure?
blood volume gravit/posture muscle pump respiratory pump cardiac output
where are baroreceptors found?
arotic arch
what are baroreeptors?
nerve ending in the adventitia of carotid sinus and aortic arch
sense distortions in vessels in blood pressue
what do baroreceptors sense?
degree of pressure through stretch
what is the baroreceptor refex?
depression of the heart rate by activating vagus nerve
vasodilation through decreasing sympathetic activity
loweres blood pressure
contraction strength reduced too
what can be reduced to lower blood presure?
Bp is result of cardiac output and total peripheral resistance so can chnge one of these two
natura causes of long term myocardial adaptation
exercise
pregnancy
what happens when the heart is stressed?
undergoes hypertrophy and changes gene expression
what is hypertrophy
process where the heart changes gene expression in response to new envirnental requirements
how does hypertrophy actually occur?
- expression of genes changes
- isoform shifts in cytoskeletal proteins and ECM
what is physical hypertrophy?
temp increase in heart size due to enlargement of cardiac myocytes as a result of exercise
improves functioning
what is pathological hypertrophy?
stress leading to change. leads to inability of the heart to deliver blood and oxygen
what can pathological hypetrophy lead to?
abnormalities in metabolism
more heart stress
heart failure
what is heart failure defined as?
progressive disrder which damages the heart
weakens the cardiovascular system
what does heart failure cause in the body?
inadequate blood flow to tissues
blood pressure issues
causes of heart failure
myocardial infarction
cornary heart disease
valve diease
hyerptension
what is dilated cardiomyopathy?
los of myocytes being replaced by fibrobasts
heart cannot contract as cell
what happens in cardiac hypertrophy on a cellular level?
wall thickens
no proliferations
cells get bigger
what is the P wave
depolaristion of the atria
what is the QRS complex
depolaristion of the venticles
what is the T wave
repolarisation of the venticles
