Cardiac Output 1 Flashcards
cardiac output
the volume of blood ejected from a ventricle per minute (L/m)
what is the cardiac output a product of and is therefore controlled by?
stroke volume and heart rate
typical stroke volume
~70ml
typical heart rate
~70
typical cardiac output
~5L/m
what regulates the cardiac output
autonomic nervous system - sympathetic
parasympathetic
barosympathetic
what intrinsically regulates the cardiomyocytes
frank starling law of the heart
name 4 things ANS controls
blood pressure temperature digestion reproductive function (all regarding homeostasis)
what segments of the spinal chord does the Sympathetic Nervous System contain
thoraco-lumbar
Segments T1-L2
what segments of the spinal chord does the Parasympathetic Nervous System contain
cranio-sacral
cranial nerves III, VII, IX, X sacral segments 2,3,4
SNS primarily acts via…
catecholamines
how does the SNS change cardiac output
increase heart rate
stroke volume
increase blood pressure
what hormones are released from SNS and where
noradrenaline - from nerve endings
adrenaline - from adrenal gland
sweating/pilorecetion but ACh
SNS action is mediated by …
the α- and β-adrenoceptors
the most important adrenoreceptor for the heart is
β1 -adrenoceptor
what particular adrenoreceptors play a role in heart
a1
B2
where are the adrenoreceptors B1, B2, a1 in the heart
SA node
AV node
atria and ventricle
what type of receptor is B-adrenoreceptor and what is it linked to.
This leads to the increase of what
G protein couple receptors adenylate cyclase
increase of cAMP which in turn activates protein kinase A (PKA)
Depolarising current in SA node comes from what channel
Na+/K+
HCN channels
HCN
hyperpolarisation-activated, cyclic nucleotide-gated
– current through this is increased by the binding of cAMP
Adrenergic Action of the Heart
• The β-adrenoceptor is a G-protein couple receptor linked to adenylate cyclase
– increases cAMP which in turn activates protein kinase A (PKA)
• The main depolarising current in the SA node comes from the Na+/K+ HCN
– current through this is increased by the binding of cAMP
• In the myocytes (atria and ventricles) cAMP/PKA increases the entry of Ca2+ into cells
– this increases the force of contraction
Cardiac contraction
Ca2+ binds to troponin on actin
allows myosin to interact
Ca2+ comes from outside of cardiomyocytes
categories of acetylcholine
muscarinic and nicotinic cholinergic receptors
PNS acts via
acetylcholine
where are nicotonic cholinergic receptors found
– nicotinic are ion channels found in nerves and skeletal muscle
muscarinic cholinergic receptors are found
G - protein coupled receptors
how is PNS innervated to the heart
via the vagus nerve
– cranial nerve X (CNX)
maine cholinergic receptor in the heart
M2
What does the vagus cranial nerve innervate
SA node
AV node
parts of the atria
function of M2 receptor
r inhibits adenylate cyclase
– and so the amount of cAMP
how does the M2 receptor inhibiting adenylate cyclase affect the SA node
, this decreases the Na+ influx and so the rate of depolarisation
– it decreases the rate of SA node firing and so heart rate has small effect on force atrial contraction but none on ventricle
tachycardia is a sign of
sympathetic activation
caused by exercise, anxiety
how do Beta blockers change cardiac output
drop heart rate from 70 to 60bpm
what is the intrinsic rate of SA node but what gives the heart its normal 70bpm
The intrinsic rate of the SA node is about 100 bpm, it is vagal
stimulation that gives the “normal” 70 bpm
cardiac output is intrinsically tied to …
blood pressure
more blood in system -> higher pressure
how to calculate mean arterial pressure
cardiac output x total peripheral resistance
control of blood pressure is managed by
regulating cardiac output via the autonomic nervous system
what type of loop is baroreceptor reflex
negative feedback loop
sensory afferents -> central processing- > effector efferents
what do sensory fibres detect and where are they located
detect stretch
located in aortic arch
carotid sinus
firing is proportional to stretch
where do the signals from the sensory fibres in the aortic arch and carotid sinus go to?
brain stem
– the nucleus tractus solitarius (NTS) of the medulla oblongata
what does the medulla regulate
SNS/PNS outflow of the heart
drop in pressure - increase SNS and cardiac output
rise in pressure - increase PNS and decrease cardiac output
exercise is related to what Nervous System
increase SNS activity
cardiac out put changes in exercise
increase heartrate
increase cardiac output
how does the systolic pressure change
drastic increase
how does the mean arterial pressure change
slight increase
how does the diastolic pressure change
slight decrease
how does the cardiac output change
drastic increase
how does the peripheral resistance change
drastic decrease
why can’t heart rate increase above 200 bpm
length of action potential
high rates = decreased perfusion as it occurs in diastole
why can’t heart rate increase above 200 bpm
length of action potential
high rates = decreased perfusion as it occurs in diastole
