heart physiology Flashcards
what receptor does noradrenaline bind to (sympathetic stimulation)
beta 1
what effect does noradrenaline have on the heart (to whole heart)
increases cAMP production increase in SAN phase 1 depolarisation increase Ca slow channels increase Na through funny channels increase chronotropic effect
where does acetylcholine bind
parasympathetic stimulation
M2 receptors
what effect does parasympathetic stimulation have (mostly to SAN)
reduces rate of phase 1 depolarisation
hyperpolarises membrane potential
increases extent and duration of opening of K+ channels
negative chronotropic effect
what is the intrinsic rate of the SAN
90 per min
what is the intrinsic rate of the AVN
60 per min
bundle of his intrinsic rate
50 per min
what is the formula for the observed signal on an ECG
E x Cos theta
smallest angle is largest observed signal
what is the length of the PR interval
0.15 - 0.2
what is the length of the QRS complex
0.08-1.2
what is the length of the QT interval
0.25- 0.35
what channels are opened by the action potential
L-type dihydropyridine
what does DHP activation cause
release of CA2+ from sarcoplasmic reticulum via ryanodine release channels
what is the absolute refractory period of cardiac muscle
245 ms
(skeletal is 1-2 ms)
this means summation is not really possible because of inactivation of Na channels
what percentage of ventricular filling is passive
80%
what are the stages of ventricular contraction
isovolumic/isometric
period of rapid ejection (1/3)
period of slow ejection(2/3)
isovolumic period of relaxation
what is the approximate pulmonary pressure
30 / 12
how are imbalances between the left and right heart adjusted
frank starling
what causes vascular resistance to decrease
age and vasoconstriction
how do you calculate MABP
diastolic + 1/3 pulse pressure
how do you calculate pulse pressure
systolic - diastolic
how do you calculate arterial pressure
cardiac output x total peripheral resistance
how do you calculate flow (poiseuille eqn)
change in pressure / resistance
what factors increase resistance
decrease vessel radius (big impact due to power 4)
increased viscosity
increased length of vessel
what is Reynolds number
high Reynolds number = high turbulence
(velocity of flow x radius of vessel ) / viscosity
also abnormal vessel wall increases turbulence
what is a thixotropic fluid
flow affects viscosity
what is la place’s law
tension = distending pressure x radius
t=pr
what is flow autoregulation
response to change in arterial pressure
increased pressure, arterioles constrict to reduce flow and vice versa
what factor causes vasoconstriction
endothelin 1 released from endothelial cells
what hormones act as vasodilators
adrenaline
atrial naturetic peptide
also NO releasing nervers
what local factors cause vasodilation
adenosine
NO
bradykinin
what local factors cause vasoconstriction
endothelin 1
what hormones cause vasoconstriction
adrenaline
angiotensin 2
vasopressin
what is the difference between bulk flow and diffusion
bulk flow is distribution of extracellular fluid
diffusion is net movement of nutrients, O2 and metabolic end products
what generates oncotic pressure
plasma proteins, mainly albumin
what is the approximate pressure of the venous system
3-18 mmHg
60% total blood volume
what controls venous return
sympathetic innervation
muscle pumps
inspiratory movements
blood volume
what nerve are aortic baroreceptors connected to
vagus
what nerve are carotid body chemoreceptors and sinus connected to
herrings nerve and glossopharyngeal (ninth cranial)
what is the primary purpose of the baroreceptors
controls minute to minute variations of arterial pulse
what do cardiopulmonary baroreceptors sense
central blood volume
what is the Bainbridge reflex
sympathetic mediated response to increased blood in the atria
increases HR and contractility
where are BP signals integrated
the MCVC centre or vasomotor centre
what is found in the sensory area
input from baroreceptors
what is found in the lateral portion
efferent sympathetic nerves
what is found in the medial portion
efferent parasympathetic nerves (vagal)
what is the predominant tone in the blood vessels
sympathetic vasoconstriction
veins: decreased capacitance, increased venous return, stroke volume and CO
what happens in the CNS ischaemic response
peripheral vasoconstriction
sympathetic stimulation of the heart
increased systemic arterial pressure
how is blood pressure in organs decreased if blood pressure rises too high
myogenic (vascular depolarisation of smooth muscle)
metabolic theory
local factors washed out
where is ADH released from
posterior pituitary
atrial baroreceptors normally inhibit its release
where is the integration centre for blood osmolality
hypothalamus
where is renin released from
kidney juxtaglomerular cells
what is renin converted to
angiotensin
what does angiotensin do
vasoconstriction and salt and water retention
what does atrial naturetic peptide do
opposes effects of RAAS
counteract volume overload
what is class 1 shock
10-15 % blood loss
what is class 4 shock
40%
what are the immediate responses to hypovolaemia
increased HR and total peripheral resistance
what are the later responses to hypovolaemia
arteriolar constriction fluid reabsorption decreased renal blood flow thirst water retention
describe priming of the cvs before exercise
decrease parasympathetic tone
increase CO and TPR
release ADH
reset baroreceptors
how is arterial blood pressure maintained
reducing blood flow to non essential organs
increase CO
what is the biggest difference between static and dynamic exercise
static- large increase in TPR due to contraction of muscles so large increase in MABP
dynamic - small or no change
what is the fick principle
uptake of a substance is dependant on the arterio venous concentration difference and the blood flow
cardiac output =
rate of O2 consumption / arteriovenous O2 difference
decreased alveolar O2 causes what
decreased local blood flow
blood doesn’t go to poorly ventilated areas
how is coronary blood flow controlled
local metabolism
sympathetic stimulation
what receptor does adrenaline bind to in skeletal muscles
beta 2- causes vasodilation
what does catch 22 stand for
cardiac abnormalities abnormal facies thymic aplasia cleft palate hypothyroidism
aka digeorge syndrome due to partial deletion of chromosome 22
what is allelic heterogeneity
different mutations at the same locus can lead to the same phenotype
locus heterogeneity
mutations at different loci can cause the same phenotype
defects in different genes can cause the same phenotype
what is penetrance
the proportion of individual with a mutation that express the phenotype
Compound heterozygosity
2 recessive alleles for the same gene that are different causing disease
Cascade testing
is the identification of close relatives of an individual with a disorder to determine whether the relatives are also affected or are carriers of the same disorder. .
how does diabetes affect the cvs
metabolic disorders incl hyperglycaemia
increased oxidative stress leading to accelerated vascular damage
hypertension
how does COPD affect the CVS
pulmonary hypertension, cor pulmonale
how does amyloidosis affect the cvs
leads to heart failure - amyloid deposits in the heart
also nephrotic system
how does RA affect the heart
pericarditis cardiomyopathy vasculitis arrhythmia atherosclerosis due to chronic inflammation
how does thyroid dysfunction affect the heart
heart failure
what drugs can affect the heart
anti cancer
immunosuppressive
diabetogenic
anti inflammatory
describe a methodical approach to ecg analysis
identify and standardise rate and rhythm p wave pr interval qrs qt st t cardiac axis other interpretation
what does 1cm equal on an ecg
1 mv
how do you calculate rate on an ecg
300/ large squares
describe a sinus rhythm
normal p waves
normal qrs
p wave followed by qrs
regular rhythm
