control of heart function Flashcards
what are the main anatomical features of the heart
Muscle cells (cardio-myocytes)
Specialised electrical cells
Vessels
describe the muscle cells function
can contract and relax in response to electrical stimuli. Essential for pumping blood around the body
function of specialised electrical cells:
cells that create spontaneous currents and those that transmit currents exist within the heart. Essential for regulating contraction of the cardio-myocytes
Vessels
he major blood vessels are responsible for transporting blood in and out of the heart, whilst the coronary blood vessels are responsible for supplying blood to the heart
what are the most prominent cells in controlling heart function
specialised electrical cells
what are the nodes in the heart
sa node
av node
what is the sa node function
Pacemaker of the heart: 60-100 bpm
where is it
Junction of crista terminalis; upper wall of right atrium & opening of superior vena cava
function of av node
Has pacemaker activity: slow calcium mediated action potential
where
Triangle of Koch at base of right atrium
what are the tracts in the heart
Bundles of His & bundle branches
Purkinje fibres
what are the bundles of his
Specialised myocytes. AV node: His bundle branches at intraventricular septum apex
what are purkinje fibres
Specialised conducting fibres
function of bundle of his
serves to transmit the electrical impulse from the AV node to the Purkinje fibres of the ventricles.
function of purkinje
purkinje fibers allow the heart’s conduction system to create synchronized contractions of its ventricles, and are essential for maintaining a consistent heart rhythm
how many phases in nodal ap
3
what are they
0 3 4
what is phase 0
upstroke (depolarisation
what is it caused by
ca2+ influx
what is phase 3
repolarisation
what is it caused by
k+ efflux
what is phase 4
pre potential
what is the nodal cell resting potential
Nodal cells do not have a resting membrane potential - only a pre-potential due to Na+ influx through a ‘funny’ channel
continous deploirasation and repolarisation
what causes phase 4
sodium influx through funny channel (GOOGLE GRAPH TO SEE SHAPE)
what does the duration of Cardiac muscle action potential control
contraction of the heart
what is longer cardiac muscle ap or nodal ap
cardial ap is ~200x longer
what are charactiristics of an effective pump
long slow contraction
how many phases
5
what are they
0 1 2 3 4
what is the Absolute refractory period (ARP)
= time during which no AP can be initiated regardless of stimulus intensity
what si Relative refractory period (RRP)
period after ARP where an AP can be elicited but only with larger stimulus strength
what is phase 0
upstroke/depolarisation
phase 1
early repolarization
phase 2
plateau (still depolarised but starting to decrease)
phase 3
repolarisation
phase 4
resting membrane potential
Google to see graph shape
what causes phase 0
sodium influx (remember they are ions)
what causes phase 1
potassium efflux
causes phase 2
calcium influx
phase 3 and 4
potassium efflux
what 3 major organs control heart function
The brain/central nervous system
The kidneys
The blood vessels
function of the brain/cns
can effect immediate changes through nerve activity or slower changes through hormonal activity
The kidneys function in controlling the heart
the heart and kidneys share a bi-directional regulatory relationship usually through indirect mechanisms
how do blood vessels control heart function
by regulating the amount of blood that goes to and from the heart the blood vessels are able to influence cardiac activity.
what are subbranches of the autonomic nervous system
para
and symp
function of para
rest and digest
effect of para on the heart
decrease heart rate (HR) – decreases the slope of phase 4
function of sympathetic nervous system
‘fight or flight’
effect of symp on the heart
increase HR (chronotropy) – increases the slope of phase 4 increase force of contraction (inotropy) – increases Ca2+ dynamics
what nerve to heart
vagus
how does para decraese heart rate
effects pre potential in nodal cell
what does phase 4 determine
how quickly it can contract again
where do para nerves originate from
cranial part of spinal cord
sacral part of spinal cord
what nerves do they have
pre and post ganglionic fibres
what neurotransmitter do they release
Ach
what do para nerves achieve
controlling heart rate
where do symp originate from
thoracic and lumbar
what type of nerve
pre and post
what strcuture do symp nerves tend to synapse on
synpathetic chain (paraveterbral ganglia)
what neurotrasnmitter do they release at pre
Ach
and post
Can be nora a
so what does symp control
circulation
where is the vasomotor centre located
located bilaterally in reticular substance of medulla & lower third of pons
what 3 areas are they composed of
pressor area
depressor area
Cardio-regulatory inhibitory area
what is the pressor area aka
vasoconstrictor area
depressor aka
vasodilator
what is the vmc controlled by
Many higher centers of the brain such as the hypothalamus can exert powerful excitatory or inhibitory effects on the VMC.
what 2 portions of the vmc control the heart
lateral and medial
how does the lateral portion of the vmc control the heart
Lateral portions of VMC controls heart activity by influencing heart rate and contractility
dont really need to know
medial
Medial portion of VMC transmits signals via vagus nerve to heart that tend to decrease heart rate.
dont really need to know
distally
Transmits impulses distally through spinal cord to almost all blood vessels
how does para innervate
ACh binds to m2 muscarinic receptor on cm of sa node bind to (inhibotory ]) g protien, inhibits of adenyl cyclase
and symp
releases nora acts on beta 1 receptor
stimulate adenyl cyclase
increase level of protien kinsae
what will para do to heart
decrease heart rate
symp
increase
what would happen if you cut para
heart rate increase q
cut symp
heart rate decrease
symp nerve innervating kidney
less glomerular filtration
less na+ excretion
increase blood volume (aldosterone)
what is the blood volume detected by
Detected by venous volume receptors
what else does symp innervation do
more renin secreation
more angiotensin 2
causing vasoconstriction
high blood pressure
what is blood pressure detected by
detected by arterial baroreceptors
how do kidney affect heart
affect blood volume and vlood pressure
how does kidney increase blood volume
less na+ excretion
hoe does the kidney affect blood pressure
increase secretion of ang II
increasing blood pressure
angiotensin 2 also secretes what
aldosterone
what do. the symp nerve fibre innervate
afferent and efferent atrerioles of glomerulus
what affect on afferent arterioles
symp inneravtion causes vasoconstriction by activation of a1- adrenoceptor
what is the nuerotransmitter
noradrelaline
what does that cause
decrease glomerular filtration rate
less na filtered
function of juxtaglomerlular cells
the site of synthesis, storage & release of renin
which recpetor causes renin secretion
b1 adrenoceptor
increases aldesterone
increases blood volume
define inotropic
increases contractility
chronotropic
increases heart rate
What effect will activation of renal arteriole alpha-1 receptor eventually have on the heart?
Increased chronotropy & inotropy
what happens when there is a decrease in heart filling
less baroreceptor firing
more symp nerve activity
increases heart rate
what happens in distention
higher barorecpetor firing
less sns activity
what is decrease in fillling caused by
less blood coming back to the heart
distention.
more blood coming back to the heart
what controls how much blood comes back to the heart
kidney and blood vessels
what are large pulmonary vessels sensitive to
Volume sensors (also atria & right ventricle): send signals though glossopharyngeal & vagus nerves
what are Arterial circuit
Aortic arch, carotid sinus & afferent arterioles of kidneys
sensitive to
Pressure sensors: send signals though glossopharyngeal & vagus nerves
when there is a decrease in pressure
less barorecptor firing
higher sns
increase in pressure
high barorecpetor firing
less sns
what is venous volume affected by
Venous volume distribution affected by peripheral venous tone, gravity, skeletal muscle pump & breathing
what determibes the amount of blood flowing back to the heart
Central venous pressure (mean pressure in the right atrium) determines amount of blood flowing back to heart.
what determines stroke volume
Amount of blood flowing back to the heart determines stroke volume
what does constriction in veins cause
In veins, constriction reduces compliance and increases venous return
what does arteriole constrcition cause
Blood flow to downstream organs
Mean arterial blood pressure
The pattern of blood flow to organs
what affects atrial pressure
venous return
what affects vebous return
venous pressure
what affects venous pressure
↑Blood volume
↑SNS activation of veins
↑Skeletal muscle pump
↑Respiratory movements
