Heart Physiology Flashcards
what is the definition of the circulatory system?
oxygen system transporting O2, CO2, nutrients etc.
what are the characteristics of pulmonary circulation?
O2 depleted blood, passes from heart to lungs, returns oxygenated blood to heart
what are the characteristics of systemic circulation?
O2 rich blood, passes from heart to rest of body, returns deoxygenated blood to heart
what blood does the superior vena cava carry?
deoxygenated blood from head, neck and upper limbs
what blood does the inferior vena cava carry?
deoxygenated blood from below level of heart (abdomen, pelvis, lower limbs)
what blood does the coronary sinus contain?
venous blood from the heart
what septal defects can occur in the heart?
atrial, ventricular or atrioventricular (hole in the heart)
interventricular or interatrial
what conditions/diseases can result in end arterial coronary arteries?
coronary artery disease
ischaemia
angina pectoris
infarction
what is a coronary artery bypass graft?
redirecting blood supply if coronary arteries are blocked
what vessels can be used in a coronary artery bypass graft (CABG)?
saphenous vein
internal mammary artery
internal thoracic artery
what are the main functions of the cardiovascular system?
transport - nutrients, O2, waste, heat, hormones
buffers body pH
assists in infection response and urine filtration
what is each heart sound caused by?
first - AV valves closing
second - pulmonary/aortic valves closing
what is the formula for cardiac output?
stroke volume x heart rate
(per min)
what makes the heart contract?
SA node impulses spread across atria then ventricles
L/R sides contract at same time, resulting in a rise and fall of blood pressure in atria then ventricles
how does each node influence HR?
SA - determines HR (pacemaker)
AV - slows HR
how does K+ permeability affect HR?
increased permeability - longer time to threshold, fewer BPM, lower HR
how does Ca+ permeability affect HR?
increased permeability - shorter threshold time, more BPM, higher HR
what does Ca entry do to the cardiac muscle?
depolarisation then contraction
where is the vagal nerve and how does it influence HR?
terminates on nodal tissue (L = AV node, R = SA node)
releases ACl activating M2 receptors reducing HR and increasing K+ permeability
what is the cause of the atria-ventricular delay?
the annulus fibrosis acting as electrical insulator
what can carotid sinus syndrome be caused by?
vagus nerve overactivity
causes syncope/fainting
briefly explain the mechanisms of the cardiac cycle
a systole contraction then a diastole relaxation of the atria then the ventricles
blood flow controlled by valves and the diastole-systole sequence
what are the stages of the cardiac cycle?
atrial systole
atrial diastole
ventricular systole (1st phase)
ventricular systole (2nd phase)
ventricular diastole (early)
ventricular diastole (late)
what occurs during atrial systole?
atrial contraction forces blood into relaxed ventricles
what is the name of the contraction occuring during atrial diastole?
isovolumetric contractions
what occurs during ventricular systole? (1st phase)
ventricular contraction pushes AV valves closed
not enough pressure to open semilunar valves
what occurs during ventricular systole? (2nd phase)
ventricular pressure rises and exceeds arterial pressure, opening semilunar valves and ejecting blood
what occurs during ventricular diastole? (early)
ventricles relax
ventricular pressure drops
blood flows against cusps of semilunar valves forcing them closed
blood flows into relaxed atria
what type of relaxation occurs in ventricular diastole?
isovolumetric relaxation
what occurs during ventricular diastole? (late)
all chambers are relaxed
ventricles fill passively
what changes in the cases of a positive or negative inotropy?
preload of the heart
what is the hearts membrane potential determined by?
ion concentration outside vs inside the cell
explain the changes to the membrane potential when Na, K and Ca currents affect the heart cells
Na and Ca: positive inwards (depolarising)
K: positive outwards (repolarising)
what occurs at phase 0 of the action potential?
upstroke: voltage gated Na channels open allowing Na in and depolarisation
what occurs at phase 1 of the action potential?
notch: voltage dependant inactivation of Na
activation of outwards K causing repolarisation
what occurs at phase 2 of the action potential?
plateau: balance of inwards Ca and outwards K
what occurs at phase 3 of the action potential?
repolarisation: inwards currents are inactivated and outwards K channels repolarise cell
explain the process of an excitation-contraction coupling
after excitation, the increase in Ca due to AP causes myofilaments to contract
(Ca channels in high concentration in t-tubules)
what is the sarcoplasmic reticulum and what is its release mediated by?
an intracellular Ca store
mediated by ryanodine receptor
explain the process of ventricular filling in diastole
driven by venous pressure
walls expand as they fill
atria contract adding 10-20% extra
end diastolic volume is ~120ml
once ventricular pressure exceeds atrial, AV valves shut
name the brain and spinal nerves associated with CVS regulation and whether they are sympathetic or parasympathetic
glossopharyngeal (P)
vagus (P)
vasomotor (S)
cardiac accelerator (S)
what structure does the sympathetic and parasympathetic nervous activity impact in the heart?
SA node
explain the sympathetic response to HR regulation
nerve terminals release noradrenaline as response to stimulation
downstream effects mediated by messenger system involving cAMP production
explain the parasympathetic response to HR regulation
nerve terminals release ACl in response to stimulation
downstream effects mediated by ACl-regulated K channels coupled to muscarinic receptors (ACl binds to these)
why is ACl rapidly decayed in the parasympathetic HR response?
SA and AV nodes contain cholinesterase (hydrolyses ACl)
what is resting HR regulated by?
parasympathetic response (stronger than sympathetic)
what is stroke volume determined by?
contractility
in what ways is stroke volume regulated?
sympathetic - increases stroke volume, magnitude and force rate generated
parasympathetic - decreases stroke volume and weakens contractions
where are baroreceptors found and what do they detect?
found in carotid sinus and aortic arch
detect stretch and pressure changes
what does stretch in arterial baroreceptors do?
increases receptor firing
inhibits sympathetic outflow from pressure origin
explain the result of excitatory and inhibitory post-synaptic potentials
excitatory (EPSP) - depolarises target neuron
inhibitory (IPSP) - hyperpolarises target neuron
what is a convergence neuron?
a neuron influenced by many other neurons
what is a divergence neuron?
many neurons influenced by 1 neuron
what nerves affect HR?
vagus (P) - decreases HR
cardiac accelerator (S) - increases HR and contractility
which parts of the brain control CVS input?
higher brain centres
proprioreceptors
baroreceptors
chemoreceptors
explain the input function of each relevant part of the brain
higher brain centre - cerebral cortex, limbic system and hypothalamus
proprioreceptors - joint movements
baroreceptors - BP
chemoreceptors - blood acidity
what changes are seen in the heart during exercise?
increase:
cardiac output (25l/min)
HR (140bpm)
stroke volume (180ml)
decrease:
filling time (33%)
compare the ECG times of a resting HR and an exercised HR
resting:
AV systole - 0.48s
diastole - 0.32s
exercised:
AV systole - 0.3s
diastole - 0.1s
how is BP controlled during exercise?
when CO increases, skeletal muscle vascular beds dilate reducing PR
what does TPR depend on and what is it controlled by?
depends on arteriole diameter
controlled by local metabolic factors
low O2 and high CO2 levels act on smooth muscle to relax/dilate
why does BP increase during static exercise?
increase in SV with no change in TPR
where do the parasympathetic nerves regulating HR originate from and where do they act?
vagal motor nuclei in brainstem (medulla)
left side acts on AV node
right side acts on SA node
describe the course of the sympathetic nerves affecting HR and where they supply
cardiac sympathetic fibres exit spinal cord at T1-5
long nerve fibres run along great vessels
left side supplies ventricles
right side supplies atria
what is the sympathetic neurotransmitter increasing HR and what does it do?
noradrenaline - binds to a1 adrenoreceptors
increases AV conduction, decreases myocyte AP length, increases SV and increases relaxation rate
what is the parasympathetic neurotransmitter decreasing HR?
ACl - activates M2 muscarinic receptor hyperpolarising SA node and reducing AP’s generated
what is the SA node firing rate affected by?
changes in autonomic nerve activity
circulating hormones (hyper/hypothyroidism)
serum ion concentration (hyper/hypokalaemia)
cellular hypoxia
drugs
explain the bruce protocol
fitness test involving different stages of exercise in 3 minute intervals
speed/gradient are gradually increased to measure cardiac work and identify areas of poorly perfused myocardium
explain how hypoxia from exercise can appear on an ECG
O2 consumption increases with exercise, O2 delivery cant keep up
ST segment on ECG shows electrophysiological changes in O2 delivery
how do nitrates work in reducing cardiac work?
venodilation
reduces venous pressure and preload
what can be the problem of an increased preload? (venous return to RV)
heart has to work harder to pump blood out
can result in heart failure, coronary artery disease and angina
