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bioregulatory systems 🦠 > control of heart function > Flashcards

control of heart function Flashcards

1
Q

what cells can contract and relax in response to electrical stimuli

A 
muscle cells (cardiac myocytes)
essential for pumping blood around the body
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2
Q

what do specialised electrical cells do

A

they are cells that create spontaneous currents and those that transmit currents exist within the heart - essential for regulation contraction of cardiac myocytes

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3
Q

what are the vessels responsible for

A

the major blood vessels are responsible for transporting the blood in and out of the heart
while the coronary blood vessels are responsible for supplying blood to the heart

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4
Q

what cells are the most prominent in controlling heart function

A

electrical cells

although cardiac myocytes and vessels of the heart are able to modulate function

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5
Q

what are the 2 nodes of the heart

A

SAN

AVN

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6
Q

what is the SAN and where is it found

A

pacemaker of the heart - 60-100 bpm

at the junction of crista terminalis - upper wall of right atrium and opening of superior vena cava

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7
Q

what is the AVN and where is it found

A

has pacemaker activity : slow calcium mediated action potential
traingle of Koch at the base of right atrium

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8
Q

what is the bundle of His and bundle branches

A

internodal tracts - specialised myocytes
connect the SAN to AVN
bundle of His that goes from the atria down through interventricular septum

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9
Q

what are purkinje fibres

A

specialised conducting fibres along ventricles of the heart

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10
Q

how many phases does nodal action potential have

A

3 phases (0, 3 and 4)
in the order 4 0 3
(pre potential, upstroke and then repolarisation)

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11
Q

what is upstroke and what is it due to

A

depolarisation due to Ca2+ influx

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12
Q

what is repolarisation due to (in terms of ions)

A

K+ efflux

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13
Q

do nodal cells have a resting membrane potential

A

no

only a pre potential due to Na+ influx through a “funny” channel

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14
Q

why do different parts of the heart have different action potential shapes

A

caused by different ion currents flowing and different ion channel expression in cell membrane

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15
Q

which AP is longer - cardiac or nerve

A

cardiac AP

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16
Q

what does the duration of AP control the duration of

A

contraction of the heart

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17
Q

what kind of contraction is required to produce an effective pump

A

long slow contraction

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18
Q

how many phases does AP have

A

5 phases labelled 0-4

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19
Q

describe phase 0

A

upstroke

start off with resting membrane potential around -80/90 mV then upstroke takes it up to 20/30 mV

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20
Q

describe phase 1

A

early repolarisation

brings the membrane potential back down to a slightly more negative value

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21
Q

describe phase 2

A

plateau

maintains the cell at a level of depolarisation

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22
Q

describe phase 3

A

repolarisation

repolarisation at around 270 ms

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23
Q

describe phase 4

A

resting membrane potential

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24
Q

what is the absolute refractory period (ARP)

A

time during which no AP can be initiated regardless of stimulus intensity
(phases 0, 1 and 2)

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25
what is the relative refractory period (RRP)
period after ARP where an AP can be elicited but only with larger stimulus strength (phases 3 and 4)
26
what are 3 major organ systems that have the ability to modulate the activity of the heart
the brain/CNS the kidneys the blood vessels
27
how can the brain/CNS modulate heart activity
can effect immediate changes through nerve activity or slower changes through hormonal activity the CNS also impacts other systems > subsequently affecting the heart
28
how can the kidneys modulate heart activity
the heart and kidneys share a bidirectional regulatory relationship usually through indirect mechanisms
29
how can the blood vessels modulate heart activity
by regulating the amount of blood that goes to and from the heart, the blood vessels are able to influence cardiac activity
30
how is the autonomic nervous system involved in CNS control of the heart
cairo-regulatory centre and vasomotor centres in medulla
31
how is the parasympathetic nervous system involved in CNS control of the heart
rest and digest PS nerves leave from medulla and goes via vagus nerve to heart PS nerve is activated > causes a decrease in HR decreases slope of phase 4 reducing HR by affecting SAN affects pre-potential of AP within nodal cell
32
how is the sympathetic nervous system involved in CNS control of the heart
fight or flight increase in HR (positive chronotrophy) - increases the slope of phase 4 (sympathetic nerves decreases time taken to get back to depolarisation phase) increase force of contraction (inotropy) - increases Ca2+ dynamics
33
what does an increase in volume and pressure activate
baroreceptors | reduce SNS activity and HR
34
design of the ANS
split into PNS and SNS
35
describe the parasympathetic nervous system
parasympathetic nerves arising from cranial part of spinal cord and sacral part of spinal cord rest and digest preganglionic fibres (long) use ACh as NT PNS post ganglionic NT = ACh PNS is important for controlling the HR
36
describe the sympathetic nervous system
arises from thoracic vertebrae and lumbar vertebrae fight or flight preganglionic fibres (short) use ACh as their NT SNS post ganglionic NT = NA (noradrenaline) SNS is important for controlling the circulation
37
where is the vasomotor complex located
located bilaterally in reticular substance of medulla and lower third of pons
38
what is the vasomotor cortex composed of
vasoconstrictor (pressor) area vasodilator (depressor) area cardioregulatory inhibitory area
39
where are impulses transmitted through
distally through spinal cord to almost all blood vessels
40
what can exert powerful excitatory or inhibitory effects on the vasomotor complex/centre
many higher centres of the brain such as the hypothalamus
41
what do lateral portions of Vasomotor complex/centre control
heart activity by influencing heart rate and contractility
42
what do medial portions of the vasomotor complex/centre transmit
signals via the vagus nerve to the heart that tend to decrease heart rate
43
what does the PS release to inhibit the SAN
releases ACh acts on M2 muscarinic receptors on cell membrane of SAN cell and by a G protein known as Gi protein > inhibition of adenylyl cyclase > prevents conversion of ATP to protein kinases
44
what does the sympathetic system release to activate/stimulate the SAN
releases noradrenaline > acts on beta 1 receptors > stimulates adenylyl cyclase and cause increase in level of protein kinase A
45
what is shown if you cut sympathetic nerves
the heart rate goes down suggesting that there was already some level of S activity occurring all the time
46
describe how sympathetic nerves in the renal system regulate blood volume and can therefore affect BP
sympathetic nerves innervate the kidneys | they reduce glomerular filtration (less filtered) > decreases Na+ excretion > increasing blood volume (aldosterone)
47
what is blood volume detected by
venous volume receptors
48
sympathetic nerves can also increase activity | how do the kidneys regulate blood volume and pressure with increased renin secretion?
increased renin secretion > releases angiotensin 2 (causes release of aldosterone - impacts blood volume/increased production of aldosterone leads to vasoconstriction and increases blood pressure)
49
what cells is blood pressure detected by
arterial baroreceptors | decreases SNS activity and decreases HR
50
what nerve fibres innervate afferent and efferent arterioles of the glomerulus and nephron tubule cells
sympathetic nerve fibres
51
where is the primary site of sympathetic activity
afferent arterioles
52
STEPS for what happens at afferent arterioles upon release of NA
release of NA 1) activation of alpha 1 adrenoreceptor 2) reduced chronotropy and increased intropy for heart 3) activation of receptors causes vasoconstriction (reduces GFR and increases blood volume) 4) reduction in GFR = reduction in Na+ filtered 5) sympathetic nerves act on juxtaglomerular cells (site of synthesis, storage and release of renin) 6) stimulation of beta 1 adrenoreceptor leads to renin secretion 7) renin increases blood volume by sympathetic nerves at the kidney
53
what do volume sensors do
also atria and right ventricle | send signals through glossopharyngeal and vagus nerves
54
what does a decrease in filling (less blood returning to the heart) lead to
reduction in baroreceptor firing > increased SNS activity | increased HR
55
what does distension (heart is full - more blood returning to the heart) lead to
increased baroreceptor firing | decreased SNS activity
56
what regulates how much blood coming back to the heart
kidneys and blood vessels
57
what is involved in the arterial circuit
aortic arch carotid sinus afferent arterioles of the kidneys
58
what do pressure receptors do
send signals through glossopharyngeal and vagus nerves
59
what does a decrease in pressure lead to
reduction in baroreceptor firing | increases SNS activity
60
what does an increase in pressure lead to
increased baroreceptor firing | decreased SNS activity
61
what is the relationship between baroreceptor firing and SNS activity
they are reciprocals
62
how many circulations are there and what are their names
2 circulations pulmonary and systemic right heart > lungs > left heart > body
63
what is venous volume and what is venous volume distribution affected by
venous volume = amount of volume in veins | affected by peripheral venous tone, gravity, skeletal muscle pump and breathing
64
what is central venous pressure and what does it determine
mean pressure in right atrium determines the amount of blood flowing back to the heart determines filling pressure and distension of the heart
65
what determines stroke volume
the amount of blood flowing back to the heart (Starling's Law of the heart)
66
in veins, what does constriction do
constriction reduces compliance and increases venous return - greater pressure (bigger effect than decreased volume due to constriction)
67
in arterioles (less blood but higher pressure) constriction determines? (3)
blood flow to downstream organs mean arterial blood pressure the pattern of blood flow to organs
68
what are local mechanisms for regulating blood flow (characteristics not actual things)
intrinsic to smooth muscle (or closely associated) | important for reflex local blood flow regulation within an organ
69
what are some endothelium derived vasodilators
Nitric oxide | prostacyclin
70
what are some endothelium derived vasoconstrictors
thromboxane A2 | endothelins
71
what does NO do
potent vasodilator | diffuses into vascular smooth muscle cells
72
what does prostacyclin do
vasodilator | has antiplatelet and anticoagulant effects
73
what does thromboxane A2 do
aka TXA2 | vasoconstrictor that is also heavily synthesised in platelets
74
what do endothelins do
ET | vasoconstrictors generated from nucleus of endothelial cells
75
what are characteristics of systemic mechanisms
extrinsic to smooth muscle | these include the autonomic nervous system and circulating hormones
76
what are some non endothelium derived vasodilators
kinins | atrial natriuretic peptide (ANP)
77
what are some non endothelium derived vasoconstrictors
vasopressin noradrenaline/adrenaline angiotensin 2
78
what do kinins do
vasodilator | binds to receptors on endothelial cells and stimulates NO synthesis
79
what does atrial natriuretic peptide (ANP)
vasodilator | secreted from the atria in response to stretch to reduce BP
80
what does vasopressin do (ADH)
vasoconstriction secreted from the pituitary gland binds to V1 receptors on smooth muscles to cause vasoconstriction
81
what does noradrenaline/adrenaline do
vasoconstriction | secreted from the adrenal glands (and SNS) causing vasoconstriction
82
what does angiotensin 2 do
potent vasoconstrictor from the renin-angiotensin-aldosterone axis also stimulates ADH secretion

bioregulatory systems 🦠 (54 decks)

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