Physiology Flashcards
What is autorhymicity
electrical signals generated by the heart, capable of beating in the absence of external stimuli
where does heart excitation occur
SAN
if the heart is controlled by SAN it is said to be in ____
sinus rhythm
what is pacemaker potential
slow depolarisation occurring due to decrease in potassium efflux and constant sodium influx and transient calcium influx from T type calcium channels
what type of calcium channel causes rapid depolarisation of pacemaker cells?
L-type channels
what causes repolarisation of pacemaker cells
inactivation of L-type calcium channels and activating potassium channels
how do impulses from SAN reach AVN
gap junctions
where do electrical impulses travel from AVN
bundle of his, dividing into purkinje fibres
where is the AVN located
base of right atrium
why are impulses delayed in AVN
to allow atrial systole to precede ventricular systole
what is phase 0 of cardiac muscle
depolarisation by fast Na influx from -90 to +20mV
What is phase 1 cardiac muscle
closure of Na channels and transient potassium efflux
what is phase 2 cardiac muscle
calcium influx (L-type). plateau phase for few hundred milliseconds
what is phase 3 cardiac muscle
repolarisation by calcium channel closure and potassium efflux
what is phase 4 cardiac muscle
resting potential
true/false - vagal done is dominant in resting conditions
true
ACh acts on M_ receptors
2
where may atropine be used and what does it do
extreme bradycardia
competitive antagonist of ACh
ACh has a ____ chronotropic effect
negative
sympathetic nerves supply
SAN, AVN, myocardium
noradrenaline acts on
Beta 1 adrenoceptors
noradrenaline causes a ____ chronotropic effect
positive
Lead I ECG has electrodes on?
Left and right arm and earth on right leg
Lead II ECG has electrodes on?
right arm and left leg with ground on right leg
Lead III ECG has electrodes on?
left arm and left leg with ground on right leg
true/false- cardiac muscle has nervous innervation
false - they are electrically coupled by gap junctions
cardiac muscle contains ____ which contains the contractile proteins ____ and ____
myofibril
actin and myosin
how does calcium aid muscle contraction
causes a conformational change in troponin and tropomyosin to expose actin binding site to myosin binding site
What do T tubules of the sarcoplasmic reticulum carry?
action potentials
when calcium enters a cardiac myocyte it binds to channels on the SR. what does it cause
calcium induced calcium release
what si the refractory period
period following an action potential where it isn’t possible to have another
why is the refractory period good for the heart
prevents generation of tetanic contraction
what is stroke volume
volume of blood ejected by the ventricle per minute
SV=?
EDV-ESV
what does starlings law state
the more the ventricle is filled with blood in diastole, the greater the volume ejected during systole
why does cardiac muscle stretch cause better contraction
calcium binds to troponin better so more myosin heads bind to actin for stronger contraction
does starlings law support ventricular matching of stroke volume
yes it does
what is afterload
resistance into where the heart is pumping
afterload prevents a full SV ejection. how else can the heart pump more blood out?
increases EDV so force of contraction is increased
noradrenaline causes a ____ inotropic effect
positive
noradrenaline causes increased cardiac contractility. what does this do to the frank starling curve?
left shift and slightly upwards
true/false - the parasympathetic system has innervatioon all over the heart
false - only over the atria
what is cardiac output
volume of blood pumped by each ventricle per minute
CO=SV x HR
what is cardiac cycle
events occurring from one heartbeat to next
how long does diastole usually last
around 0.5s at 75 bpm
how long does systole usually last
around 0.3s at 75 bpm
during passive filling do the atria or ventricles have a higher pressure?
atria
what is the aortic pressure at passive filling roughly
80mmHg
atrial contraction is seen by what wave on ECG
P wave
what happens in isovolumetric ventricular contraction
ventricular pressure exceeds atrial pressure to close AV valve to produce S1
sharp pressure rise before opening of aortic valve
when does the aortic/pulmonary valve open
when ventricular pressure exceeds arterial pressure
what produces the dicrotic notch
vibration from closure of the aortic valve
isovolumetric ventricular relaxation is…
fall in ventricular pressure following systole
when below atrial pressure AV valves open
S1 is caused by
closure of AV valves
S2 is caused by closure of?
Aortic and pulmonary valves
4 points of auscultaton
right of sternum 2nd intercostal
left of sternum 2nd intercosal
sternal edge 4th intercostal
5th intercostal mid clavicular line
why does aortic pressure not drop to zero during diastole
presence of elastic recoil
the pressure of JVP fluctuates with?
pressure change in the right atrium
what is blood pressure
hydrostatic pressure exerted by blood on blood vessel walls
how can hypertension be defined
clinical blood pressure of >140/90 mmHg or daytime average of >135/85
what is pulse pressure and what is the usual value
difference between systolic and diastolic BP, usually 30-50 mmHg
what is the equation for the driving pressure gradient of systemic circulation
Pressure gradient = MAP - CVP
What is MAP and how is it calculated?
Average arterial blood pressure in a single cardiac cycle
((2 x DBP) + SBP)/3
what is the normal range of MAP
70-105 mmHg
what MAP is required to perfuse brain, coronary arteries and kidneys
at least 60mmHg
what is SVR and what has the most resistance
systemic vascular resistance, sum of all resistance in vasculature. arterioles have the most resistance
BP postural changes are managed by what reflex
baroreceptor reflex
aortic baroreceptors signal via____
vagus nerve
carotid baroreceptors signal via _____
glossopharyngeal nerve
postural hypotension is caused by?
failure of baroreceptor responses to gravitational shifts
a positive result of postural hypotension is…
drop of systolic bp +/- symptoms by 20 mmHg in 3 mins OR
drop of diastolic bp +symptoms by 10 mmHg
can baroreceptors lower chronically high BP
no, they reset to a higher BP
in the long term control of BP, what happens when plasma volume falls
fluid is shifted from interstitial fluid to plasma compartment
what two factors affect ECFV
water excess/deficit
sodium excess or deficit
what does renin do
produced in kidneys and converts angiotensinogen to angiotensin I
what does angiotensin do?
ACE converts angiotensin I to angiotensin II
Systemic vasoconstriction
thirst and ADH release
Aldosterone release
what does aldosterone do?
increases sodium and water retention in kidneys
what stimulates renin production
renal artery hypotension
stimulation of renal sympathetic nerves
decreased sodium in renal tubular fluid
NPs are released in response to?
cardiac distention
what do NPs do?
cause kidney excretion of salt and water
decrease renin release
vasodilators to reduce SVR
two types of NP
ANP
BNP
where is ANP stored/released
response to atrial distention
atrial myocytes
what is the conversion for BNP
prepro-BNP to pro-BNP to BNP
where might serum BNP and pro-BNP be of use?
suspected heart failure
when is ADH released
reduced ECVF or increased ECF osmolality
what does ADH do
water reabsorption to concentrate urine
small vasoconstriction- important in hypovolaemic shock
what vessels acciunt for the majority of SVR
arterioles
resistance to blood flow is directly proportional to _____ and ______ and inversely proportional to _____ by power 4
blood viscosity
blood vessel length
blood vessel radius
what is vasomotor tone?
tonic discharge of noradrenaline by sympathetic nerves on vascular smooth muscle
true/false - there is no parasympathetic innervation in vascular smooth muscle
false - there is in the penis and clitoris
adrenaline binding to alpha receptors causes…
vasoconstriction, in skin, gut and kidney
adrenaline binding to beta 2 receptors causes
vasodilation, in skeletal and cardiac muscles
angiotensin II acting on arterioles causes
vasoconstriction
ADH acting on arterioles causes
vasoconstriction
what local metabolites cause vasodilation and metabolic hyperaemia
increased local PCO2 increased H concentration (lower pH) Increased extracellular potassium increased osmolality of ECF Adenosine release
what chemical agents cause vasodilation
histamine
nitric oxide
bradykinin
Nitric acid lasts how long and is secreted in response to?
a few seconds
calcum release from endothelial stress
chemical agents causing vasoconstriction?
serotonin
thromboxane A2
leukotrienes
endothelin
endothelial produced vasodilators are pro/anti thrombotic, pro/anti inflammatory and pro/anti oxidant
anti thrombotic, anti inflammatory and antioxidant
endothelial produced vasoconstrictors are pro/anti thrombotic, pro/anti inflammatory and pro/anti oxidant
pro thrombotic, pro inflammatory and pro oxidant
cold causes vaso___
constriction
what is sheer stress on arterioles
arteriole dilation that causes further dilation to upstream arteries
what is the myogenic response
regulation of blood flow to brain to maintain blood pressure at constant levels
true/false- capillaries contain most of the bodys blood supply
false- veins do
venomotor tone increases
venous return, SV and MAP
skeletal muscle pump aids
venous return
how does the respiratory pump aid venous contraction
decrease in intrathoracic pressure and increase in intr-abdominal pressure on inspiration. causes increased pressure gradient for venous return
4 ways venous return is increased
blood volume
skeletal muscle contraction
respiratory pump
venomotor tone
metabolic hyperaemia can overcome vasomotor tone in exercise to cause ____
vasodilation
an increase in CO increases ____ BP and decreses _____ BP, causing an increase in _____
systolic
diastolic
pulse pressure
heart rate increase by sympathetic nerves does what to SAN and AVN
increases SAN firing rate
decreases AVN delay
chronic cardiovascular responses to exercise
decreased levels noradrenaline and sympathetic tone
cardiac remodelling
Renin level decrease
less endothelial vasoconstrictors and more vasodilators
lowered arterial stiffening
what is shock
inadequate tissue perfusion and oxygenation resulting in anaerobic metabolism and accumulation
what is hypovolaemic shock
loss of blood volume decreasing venous return, EDV, SV, CO, BP and perfusion
what is cardiogenic shock
hypotension caused by decreased cardiac contractility
decreased contractility lowers SV, CO, BP
what is obstructive shock and explain the mechanism within pneumothorax
shock due to obstruction
PTX increases intrathoracic pressure and decreases venous return
EDV decreases, SV, CO and BP
what is neurogenic shock
loss of sympathetic tone causing massive vaso/velodilation and decreased heart rate
Venous return, SVR and HR lost, CO decreased and BP
what is vasoactive shock
vasoactive mediator release causing massive veno/vasodilation
increased capillary permeability and loss of volume and vasodilation decrese venous return, EDV, SVR, SV, CO, BP
how do you treat shock
high flow O2 volume replacement (except cardiogenic, give inotropes) chest drain tension PTX adrenaline for anaphylaxis vasopressors for septic shock
what is hypovolaemic shock caused by?
haemorrhage
vomiting, diarrhoea, excess sweating
compensatory mechanisms maintain BP up to __% blood loss
30%
haemorrhagic shock presents as
small volume pulse and rapid
cool peripheries
decreased MAP
confusion, lethargy, coma if cerebral blood flow lost
what is TLOC
real or apparent loss of consciousness with loss of awareness and amnesia
loss of motor control, loss of responsiveness for short duration
causes of TLOC
TLOC mimic
head trauma
syncope
epileptic seizure
what is syncope
TLOC due to cerebral hypoperfusion with short duration and spontaneous complete recovery
what is reflex syncope
neural reflexes cause cardioinhibition and vasodepression to cause systemic hypotension
cardioinhibition is by ___ stimulation
vagal
vasodepression is caused by
depression of sympathetic activity to blood vessels
what is vasovagal syncope caused by and what is the commonality
very common
caused by emotional distress or orthostatic distress
symptoms of vasovagal syncope, treatment and main main worry
nausea, dizziness, pallor, sweating
leg crossing or horizontal gravity to enhance venous return
injury when falling
what is situational syncope and how is it treated
syncope in response to a trigger
treat cause if possible and consider cardiac pacing
what is carotid sinus syncope, who is it common in and treatment
syncope triggered by mechanical manipulation of neck, shaving or tight collar
elderly males
cardiac permanent pacing
what is orthostatic syncope and risk factors
failure of baroreceptor response to gravitational shifts in blood
age, prolonged bed rest, medicarions, disease, reduced intravascular volume
symptoms and diagnosis of orthostatic hypotension
lightheadedness, blurred vision, dizziness
in 3 mins:
drop in systolic of 20mmHg +/- symptoms
drop in diastolic of 10mmHg with symptoms
first steps for patient with TLOC
history
12 lead ECG
full physical exam
orthostatic BP measurement
what is cardiac syncope
cardiac event causing sudden CO drop, arrythmia, MI, structural disease, PE, aortic dissection
features that suggest cardiac syncope
structural abnormality of coronary heart disease FHx sudden death young age sudden palpitations before syncope ECG arrythmia syncope when supine or excretion
3 special features of coronary circulation
high basal blood flow
high capillary density
high oxygen extraction
3 ways to intrinsically cause vasodilation of coronary arteries?
decreased pCO2
metabolic hyperaemia
adenosine release
in which phase of pressure does coronary flow occur
diastole
when may coronary flow be reduced?
tachycardia, diastole would be shortened so blood flow limited
when adrenaline binds to B2 receptors does it cause vasodilation or vasoconstriction?
vasodilation
explain how sympathetic activity on the heart causes a vasodilator effect on coronary arteries
coronary arteries directly constricted but increased SV and HR causes metabolic hyperaemia, forcing them open
what supplies the brain with blood
internal carotids and vertebral arteries
what is the circle of willis and why is it good
basilar and carotids anastomose to form a circle of arterial blood supply
prevents total loss of cerebral perfusion if supply from one carotid artery is lost
the brain autoregulates blood pressure between ___-___ mmHg
60-160 mmHg
what pressure does blood have to fall under before confusion, brain damage and fainting usually occur
50 mmHg
hyperventilation causes fainting because….
lack of CO2 causes vasoconstriction
what is regional hyperaemia
blood flow adaptation to active parts of the brain
true/false - baroreceptors control blood pressure in the brain
false
normal ICP range is
8-13 mmHg
cerebral perfusion pressure =?`
CPP = MAP- ICP
what does an increase in ICP do to blood flow
it decreases it
what causes increased ICP
trauma, brain tumour
what is the blood brain barrier and what is it impermeable to
capillaries with tight intracellular junctions to prevent entry of hydrophilic ions to protect the brain from fluctuation of ion levels
what does the systemic bronchial circulation supply
bronchial tree
pulmonary resistance is high/low?
low
range of pulmonary blood pressure
systolic 20-25
diastolic 6-12
true/false - hypoxia causes vasoconstriction in pulmonary arterioles
true - it is to divert blood from areas of poor ventilation
what is stronger in skeletal muscle? metabolic hyperaemia or sympathetic tone
metabolic hyperaemia
varicose veins causes?
pooling of blood in veins in leg due to incompetent valves
is there a decrease in blood volume due to varicose veins?
no, there is a chronic compensatory increase
