Upload
alkrawiecka
View
222
Download
0
Embed Size (px)
Citation preview
8/13/2019 CVS BIMS Revision Session 2014
1/101
8/13/2019 CVS BIMS Revision Session 2014
2/101
Electrical Activity of the Heart
The Cardiac Cycle
Regulation of Cardiac Output
Anti-Arrhythmic Drugs
Heart Failure
8/13/2019 CVS BIMS Revision Session 2014
3/101
The heart is formed out of two
types of muscle cells
o Cardiac Myocytes
o
Cells of the cardiacpacemaker-conduction
system
The cells of the pacemaker-
conduction system generate an
electrical signal
Propagated signal elicits
myocytes contraction
8/13/2019 CVS BIMS Revision Session 2014
4/101
Cardiac myocytes arranged
in an end-end fashion
separated by intercalated
discs
At rest, there is high PK+ &low PNa+, PCa2 +
Resting potential at rest is
stable
Depolarisation threshold of
-65mVs
Depolarisation caused by
influx of Na+and Ca2 +
Unique plateau phase -
inward current of Ca2 +
Results in long refractory
periods
Repolarisation occurs via
efflux of K
+
8/13/2019 CVS BIMS Revision Session 2014
5/101
8/13/2019 CVS BIMS Revision Session 2014
6/101
Initial resting potential of -70 mVs
Electrically unstableautomatically
generates repetitive rhythmic action
potentials
Due to unique recycling changes in
the PK+, PNa2+, PCa2 +
Threshold potential is -50 mVs
Depolarisation is facilitated by influx
of Na2+and Ca2 +
Repolarisation is facilitated by K+
efflux
The SAN has intrinsic rate
of 100 bpm; AVN 40 bpm
AVN adds 100 msec
delay
8/13/2019 CVS BIMS Revision Session 2014
7/101
8/13/2019 CVS BIMS Revision Session 2014
8/101
ParasympatheticVagus (CN X)
o Innervates SAN & AVN predominantly
o Decrease HR by decreasing SAN firing frequency and increasing AVN
delay
Sympathetic
o
SAN, AVN and ventricular muscle
o Increase HR by increasing SAN firing frequency and decreasing AVN
delay
o Increase ventricular contractility
8/13/2019 CVS BIMS Revision Session 2014
9/101
8/13/2019 CVS BIMS Revision Session 2014
10/101
Normal heart beat70 bpm
Cycle duration850 msecs; two thirds in diastole
Relative pressure gradient between chambers and their outlets
determine position of the valves
1st heart sound = AV valve closure
2nd heart sound = Aortic & pulmonary valve closure
EDV = volume in left ventricle at the opening of the aortic valve
ESV = volume at closure of aortic valve
8/13/2019 CVS BIMS Revision Session 2014
11/101
8/13/2019 CVS BIMS Revision Session 2014
12/101
CO is total volume of blood ejected from the left ventricle into the
systemic circulation per unit of time
CO = HR x SV ; CO = ABP/TPR
SV is dependent on 2 opposing factors:o Energy of myocyte contraction
o TPR(After load)
Energy of myocyte contraction is in turn dependent on two
processes:
o Myocyte contractility
o EDV (Pre-load)
8/13/2019 CVS BIMS Revision Session 2014
13/101
Innate strength with which a myocyte contracts from a given initial
stretch
Increased by nervous, hormonal and chemical influences
Is dependent on Ca2+induced Ca2+release from the SR
1. Ca2+binds to Troponin on the Tropomyosin
2. Frees the Myosin binding sites on Actin filament
3. Leads to the formation of cross links
4. ATP hydrolysis facilitates breakage of cross links which pulls the
filament towards the centre of the sarcomere
8/13/2019 CVS BIMS Revision Session 2014
14/101
8/13/2019 CVS BIMS Revision Session 2014
15/101
Through his experiments, Starling found that if other factors such as TPR
and ABP are kept constant, an increased EDV leads to an increased SV
Increased EDV due to increased venous return leads to:
1. Increased EDP
2. Greater distension and stretch of ventricular myocytesmore
filament overlap
3. Ventricles develop greater contractile energy
4. Larger SV
The force of ventricular contraction depends on the length of
the ventricular muscle fibres during diastole (EDV)
8/13/2019 CVS BIMS Revision Session 2014
16/101
8/13/2019 CVS BIMS Revision Session 2014
17/101
HR - >180 bpm
Atrial Contractionat high rates, EDV is more atrial dependent
TPRreduce stroke volume and therefore increase ESV
CVPlargest influence on EDV of the right heart
o Increased blood volume
o Increased activity of skeletal muscle pump
o Increased activity of the respiratory pump
o Increased venous tone
o Posture
8/13/2019 CVS BIMS Revision Session 2014
18/101
Clinical syndrome arising from an inability of the heart to produce
a cardiac output that is sufficient for the metabolic demands of
the body
Caused either by intrinsic diseases of the myocardium (i.e.
cardiomyopathies) or by chronic overloading of the myocardium
(i.e. valvular disease/hypertension)
Symptoms include dyspnoea, PND, orthopnea and peripheral
oedema
Causes a rightward shift in Starling curveSV is reduced at normal
filling pressures
8/13/2019 CVS BIMS Revision Session 2014
19/101
HF leads to the activation of compensatory neuro-hormonal
mechanisms
Whilst this initially compensates for the reduced CO, chronic activation
leads to increases in the pre & after load, thus increasing cardiac work
8/13/2019 CVS BIMS Revision Session 2014
20/101
Aims of treatment are two fold:
o Block the pathways that cause further deterioration
o Improve symptoms
Drugs used:
o Diuretics
o ACE Inhibitors
o AT Receptor Antagonists
o Aldosterone Receptor Antagonists
o Cardiac glycosides
o Vasodilators
o - blockers
8/13/2019 CVS BIMS Revision Session 2014
21/101
8/13/2019 CVS BIMS Revision Session 2014
22/101
Elastic Arteries
Arterioles
Capillaries
Venous Vessels
Pulmonary Circulation
Coronary Circulation
8/13/2019 CVS BIMS Revision Session 2014
23/101
ABP = CO x TPR; MABP = DP
+ 1/3(PP)
Elastic arteries are the
primary site where ABP is
determined
Coverts the intermittent flow
into continuous flow
Can distend under pressure
to accommodate blood
flow during systole and
maintain blood pressure
during diastole by recoiling
This is due to the distinct
biomechanical properties conferred by
the tunica media
8/13/2019 CVS BIMS Revision Session 2014
24/101
During systole, opening of
aortic valve results in the
ejection of the SV into the
aorta
Approximately 20% of the
ejected blood flows straight
through the vessels
80% distends the aorta and
this stretching is stored as
potential energy
During diastole, elastin
recoil returns this energy to
the blood to maintain flow
This creates a travelling
pressure wave
8/13/2019 CVS BIMS Revision Session 2014
25/101
The composition of the elastic arteries is prone to change with age
There is loss of elasticity of the tunica media leading to a decrease
in compliance
This increased rigidity leads to an increase in the SBP
The decreased recoil results in a decrease in DBP
Leads to age dependent increase in PP
8/13/2019 CVS BIMS Revision Session 2014
26/101
Blood is a homogenous fluid
Flow is in a laminar pattern
Each successive laminae from the edge to the centre is of a higher
velocity
Maximum velocity is at the centre of the vessel which is occupied by
RBCs
Laminar blood flow is silent
8/13/2019 CVS BIMS Revision Session 2014
27/101
Blood may also be turbulent
Here the currents swirl in random
moving patterns
Dissipates pressure energy as heat
and sound
Occurs during high blood velocities,
pregnancy, hyperthyroidism and at
sites of atheroma formation
Turbulent flow leads to bruit
8/13/2019 CVS BIMS Revision Session 2014
28/101
SBP
Increased SV
Increased Contractility
High CO states
DBP
Increased TPR
Increases in HR
8/13/2019 CVS BIMS Revision Session 2014
29/101
Main site of resistance in the vascular system and therefore the main
component of the TPR
Through constriction and dilatation, arterioles can increase or
decrease ABP
As such they are the main regulators of ABP
This is due to the higher density of smooth muscle and sympathetic
receptors allowing arterioles to exhibit wider control of changes in the
diameter in reaction to local influences
8/13/2019 CVS BIMS Revision Session 2014
30/101
8/13/2019 CVS BIMS Revision Session 2014
31/101
Endothelium derived substances
o NO, PG2
Myogenic tone
o An increase in BP causes vasoconstriction allowing flow to remain the
same
Metabolic vasodilators
o Dilatation caused by products of metabolism
Nerve fibres
o Sympathetic supply to arterioles evoke constriction. Parasympathetic
supply to arterioles of the brain, heart and genitalia causes dilatation
Hormones
o Circulating noradrenaline causes constriction whilst adrenaline causes
dilatation in the skeletal muscle. ADH and AII cause constriction
8/13/2019 CVS BIMS Revision Session 2014
32/101
Relative constancy of flow
despite changes in ABP
over a certain range
Thought to occur through
myogenic tone
Independent of neuro-
hormonal influences
8/13/2019 CVS BIMS Revision Session 2014
33/101
The delivery of metabolic substrate to tissues occurs across the
capillary wall
It is also the site of fluid exchange between the plasma and the
interstitial compartments
Capillaries do not have any smooth musclethey are of a fixedresistance
Blood velocity is lowest in the capillaries which in conjunction with
the increased TSA make the region ideal for exchange
Exchange can occur through two mechanisms:
o Diffusion
o Filtration
8/13/2019 CVS BIMS Revision Session 2014
34/101
8/13/2019 CVS BIMS Revision Session 2014
35/101
The rate of diffusion is dependent on:
1. The permeability of the capillary
2. The concentration gradients across the capillary walls
3. The surface area available for diffusion
Mathematically= Px (C1-C2)x A
8/13/2019 CVS BIMS Revision Session 2014
36/101
Passive movement of fluids across the capillary wall
The net rate/direction of fluid across any given segment of the
capillary wall depends on the net filtration pressure
Net filtration pressure = hydrostatic pressure gradientthe oncotic
pressure gradient
o CHP = 35 mmHg; decreases to 15 mmHg at venous end
o THP = 0 mmHg
o COP = 25 mmHg
o TOP = 2-3 mmHg
8/13/2019 CVS BIMS Revision Session 2014
37/101
8/13/2019 CVS BIMS Revision Session 2014
38/101
8/13/2019 CVS BIMS Revision Session 2014
39/101
Arteriolar constrictiono Increase arteriolar resistance and reduce downstream flow and
pressure
o This will cause momentary cessation of blood flow thus reducing
capillary surface area available for diffusion and decrease the CHP
o Lead to decreased filtration
Arteriolar dilatation
o Decrease resistance and increase downstream flow and pressure
o This will increase capillary recruitment and CHP
o Lead to increased filtration
o This can lead to oedema if the lymphatic system cant cope
8/13/2019 CVS BIMS Revision Session 2014
40/101
Increased CHPFluid out > Fluid in
Decreased CHP
Fluid out < Fluid in
8/13/2019 CVS BIMS Revision Session 2014
41/101
Changes in capillary or tissue oncotic pressure can also affect the netfiltration process
An increase in COP will lead to greater reabsorption of fluid
This will increase blood volume and can occur due to water loss,
diarrhoea, vomiting and profuse sweating
Conversely a decrease in COP will lead to greater filtration
This will lead to oedema and can be due to decreased synthesis of
plasma proteins or increased loss of plasma proteins
Whilst the TOP is relatively small, it may increase when the vascular
permeability increases during inflammation
This will decrease the oncotic pressure gradient and favour filtration
8/13/2019 CVS BIMS Revision Session 2014
42/101
Increased COPFluid out < Fluid in
Decreased COPFluid out > Fluid in(Increased TOP)
8/13/2019 CVS BIMS Revision Session 2014
43/101
Compared to arteries and
arterioles, veins have:
o Greater compliance
o Larger proportion of theblood volume
o Larger diameter
o Larger cross sectional area
o Lower resistance
o More branched
o Have valves
8/13/2019 CVS BIMS Revision Session 2014
44/101
Compliance is a feature of collagen
found in the walls of the vein
In a low volume supine state, the
collagen is pleated
As volume increases, the collagenunfolds allowing for a more rounded
shape
Veins also have smooth muscle in the
tunica media which can contractupon sympathetic stimulation
This limits the distension of a vein and
therefore makes them less compliant
8/13/2019 CVS BIMS Revision Session 2014
45/101
1. Veins are one of the determinants of filtration of fluid across
capillaries
2. Veins act as a major reservoir of blood which can be mobilised
depending on the bodys need
3. Veins are an important determinant of the EDV of the right heart
8/13/2019 CVS BIMS Revision Session 2014
46/101
The pressure in veins depends on how much volume they contain
and the state of their smooth muscle
Passive influences:
o Blood volume
o Posture
o Skeletal muscle pump
o Respiratory pump
Active influences:
o Sympathetic NA nerve activity
8/13/2019 CVS BIMS Revision Session 2014
47/101
Low pressure
Loss of pressure from
arteries to capillaries is
more gradual
MPABP is approximately
12-14 mmHg
Low resistance
Larger diameter
Shorter in length
High compliance
8/13/2019 CVS BIMS Revision Session 2014
48/101
Passive influences:
o Blood volume
o Posture
Active influences:
o Sympathetic nerve activity
o Hypoxia
o Chemical mediators such as histamine and bradykinin
8/13/2019 CVS BIMS Revision Session 2014
49/101
Provides oxygen at a high rate to
keep pace with cardiac demand
Two main arteries : RCA & LCA
Receives 3-4% of the total CO whichequates to 80-90 mls of oxygen per
min per 100 g of muscle
Large percentage of oxygen
extraction by the myocardium70% -
80%
8/13/2019 CVS BIMS Revision Session 2014
50/101
The branches of the coronary artery (particularly LCA) within the
myocardium are exerted to compression during each ventricular
systole
During systole, LV pressure rises to 120 mmHg, pushing blood through
the aorta and coronary vessels at the same pressure
However as coronary vessels enter the depths of the myocardium,
they get smaller and increase in resistance
The pressure here reduces to 80 mmHg
As such during systole, there is occlusion of the myocardial coronary
vessels due to mechanical compression from the LV
8/13/2019 CVS BIMS Revision Session 2014
51/101
During diastole, ventricular relaxation results in a decrease in LV
pressure to about 8 mmHg
The recoil of the elastic arteries maintains an initial coronary pressure
of 80 mmHg
Again due to the increased resistance, the coronary vessels of theinner myocardium have a minimal pressure of 40 mmHg
However since this is greater than the LV pressure, there is no
occlusion of the vessels
Note: The right ventricular pressures are always lower than the
systolic and diastolic blood pressures and as such there is no
occlusion of blood flow. However overall average flow is the RCA is
lower.
8/13/2019 CVS BIMS Revision Session 2014
52/101
8/13/2019 CVS BIMS Revision Session 2014
53/101
8/13/2019 CVS BIMS Revision Session 2014
54/101
Myocardialhypoxia
SystemicHypoxia
Increasedmyocardialmetabolism
Decreasedcoronary flow
Activates 5
nucleotidase
8/13/2019 CVS BIMS Revision Session 2014
55/101
5 nucleotidase catalyses the formation of adenosine from AMP.
Adenosine accumulates in the interstitial fluid and induces coronary
vasodilatation
This mechanism is occurring continuously even at rest
However if cardiac work increases and an individual doesnt have a
large capacity for further vasodilatation, angina develops
Therefore it can be seen that the local factors of mechanical
compression and chemical factors involving adenosine are the most
important influences on coronary flow
8/13/2019 CVS BIMS Revision Session 2014
56/101
The coronary vessels also receive sympathetic and parasympathetic
nerve supply
Increased sympathetic NA activity causes vasoconstriction
Increased Parasympathetic cholinergic activity causes
vasodilatation
However in both these effects tend to be overcome by the effects
on CW and subsequent adenosine release
8/13/2019 CVS BIMS Revision Session 2014
57/101
Usually caused by coronary artery disease secondary to
atherosclerosis
Treatment:
o Vasodilators
o blockers
o Diuretics
o PCTA or CABG
Variant angina is pain associated with a constant level of cardiac
work. This occurs because of coronary artery spasm possibly due to
selected activation of sympathetic fibres leading to vasoconstriction
8/13/2019 CVS BIMS Revision Session 2014
58/101
8/13/2019 CVS BIMS Revision Session 2014
59/101
Baroreceptor reflex
Atrial Volume reflex
Orthostasis
Cardio-Respiratory Interactions
Exercise reflex
The Alert-Defence Response
8/13/2019 CVS BIMS Revision Session 2014
60/101
The baroreceptor reflex is thepredominant homeostatic regulator of
ABP on a beat to beat basis
The baroreceptors are stretch receptors
that are located in two specific locations:
o The carotid sinus
o The aortic arch
They respond to changes in the ABP via
the stretch it evokes on the arterial wall
Stimulation brings about reflex
mechanisms which return ABP to the
normal value
8/13/2019 CVS BIMS Revision Session 2014
61/101
Baroreceptors arecontinually active and
monitor ABP via the stretch it
causes
Afferent nerve activity
reflects the changes in the
pressure exerted within the
artery
Receptors are not only
sensitive to the amount of
stretch, but also the rate of
change
8/13/2019 CVS BIMS Revision Session 2014
62/101
8/13/2019 CVS BIMS Revision Session 2014
63/101
8/13/2019 CVS BIMS Revision Session 2014
64/101
Afferent fibres via CN IX and X enter the NTSthese are excitatory
neurones
NTS sends inhibitory neurones to the pre-motor sympathetic neurones
in the brain
Also sends neurones to the pre-optic hypothalamus which in turn also
send inhibitory signals to the pre-motor sympathetic neurones
The NTS also sends excitatory neurones to the NA
This increases vagal tone to the heart
A final branch is sent to the supra-optic and paraventricular nuclei
which inhibits ADH release from the posterior pituitary
8/13/2019 CVS BIMS Revision Session 2014
65/101
8/13/2019 CVS BIMS Revision Session 2014
66/101
8/13/2019 CVS BIMS Revision Session 2014
67/101
Volume receptors are located in the right atrium
They are stretch receptors that respond to increased venous
return
Send afferents via CN X to the NTS
Increased stimulation brings about reflex changes which return
atrial volume to normal
Reflex has two components:
o Transient increase in sympathetic supply to the heart
o Large decrease in sympathetic activity to the kidneys and
the pituitary gland
8/13/2019 CVS BIMS Revision Session 2014
68/101
Bainbridge reflex NTS increases sympathetic
stimulation of the heart
Increases the HR
Reduces the time the heart
has to fill and prevents over-
stretching of the atria
Initial protective function
Main reflex
NTS decreases sympathetic
supply to the kidneys leading
to vasodilatation
This reduces activation of the
RAAS
Furthermore NTS inhibits
pituitary secretion of ADH
This reduces fluid retentionOverall:
Decrease venous return
Decrease atrial filling
8/13/2019 CVS BIMS Revision Session 2014
69/101
When supine, ABP is uniformly distributed throughout the body at
approximately 95 mmHg
At the level of the heart it is 100 mmHg
Similarly venous pressure is uniformly distributed through the body at 5
mmHg
At the level of the heart it is 3 mmHg
100 mmHg
3 mmHg
95 mmHg
5 mmHg
95 mmHg
5 mmHg
8/13/2019 CVS BIMS Revision Session 2014
70/101
Upon standing, there is a redistribution of blood towards the lower
extremities
55 mmHg
-35 mmHg
100 mmHg1 mmHg
195 mmHg105 mmHg
8/13/2019 CVS BIMS Revision Session 2014
71/101
8/13/2019 CVS BIMS Revision Session 2014
72/101
8/13/2019 CVS BIMS Revision Session 2014
73/101
Respiratory influences on the heart can take the form of mechanicaland neural influences
The mechanical influence involves the respiratory pump
The neural interaction causes an increase in HR during inspiration
This is physiologically normal and known as RSA
Increased HR
Expiration
Inspiration
Decreased HR
8/13/2019 CVS BIMS Revision Session 2014
74/101
8/13/2019 CVS BIMS Revision Session 2014
75/101
Mechanism 1
Mechanism 2
8/13/2019 CVS BIMS Revision Session 2014
76/101
Peripheral chemoreceptors are responsible for the homeostatic
regulation of primarily Pa02
These receptors are located in the carotid and aortic bodies, in
close proximity to the carotid and aortic baroreceptors
Reflexes from the peripheral chemoreceptors include:
o Primary cardiovascular reflex
o Secondary cardiovascular response
8/13/2019 CVS BIMS Revision Session 2014
77/101
8/13/2019 CVS BIMS Revision Session 2014
78/101
8/13/2019 CVS BIMS Revision Session 2014
79/101
When respiration can increase, systemic hypoxia evokes
tachycardia in addition to vasoconstriction
Increased respiration leads to modulation of the primary
cardiovascular reflex
This occurs via:
o Activation of the pulmonary stretch receptor reflex
o Direct inhibition of the NA from the inspiratory centres of the brain
8/13/2019 CVS BIMS Revision Session 2014
80/101
8/13/2019 CVS BIMS Revision Session 2014
81/101
Reflex elicited by stimulation of the trigeminal afferents in the
face/nose
Trigeminal afferents travel to the NTS which sends inhibitory neurones
to the inspiratory centre
This result in total inhibition of the central inspiratory drive
This leads to expiratory apnoea
There is increased NA activity leading to bradycardia
In addition the increased sympathetic tone to the vessels leads tovasoconstriction
8/13/2019 CVS BIMS Revision Session 2014
82/101
8/13/2019 CVS BIMS Revision Session 2014
83/101
Two types of exercise:o Static
o Dynamic
Both forms of exercise evoke some CV changes:
o HR increases
o CO increases
o Blood flow increases
The cardiovascular response to exercise involves the exercise reflex
superimposed upon the local responses to metabolic activity in the
muscles and the heart
8/13/2019 CVS BIMS Revision Session 2014
84/101
During static exercise, the heart rate increases in proportional to the
amount of exercise done
During dynamic exercise, again the HR increases in proportional to
the amount of exercise done
However the increase is usually greater compared to static exercise
8/13/2019 CVS BIMS Revision Session 2014
85/101
During static exercise, blood pressure increases in proportion to the
level of exercise
This is due to the compressive impairment of muscle perfusion which
increases the activity of the muscle metaboreceptors
This leads to a strong exercise pressor reflex which causes
vasoconstriction
During dynamic exercise, the increase in CO is nearly totally
balanced by a fall in TPR and therefore mABP changes very little
SBP increases due to the increased HR and CO
However DBP does not increase and may even fall
8/13/2019 CVS BIMS Revision Session 2014
86/101
During static exercise, there is an overall increase in blood flow
The greatest increase in blood flow occurs during relaxation
This is because contracting muscle exerts a mechanical occlusive
force on the blood vessels, thus increasing the resistance
During dynamic exercise, here is also a general increase in blood
flow
The increase occurs regardless of contraction/ relaxation
This is because dynamic exercise involves cycles of
contraction/relaxation and there is no great occlusive effect on the
vessels
8/13/2019 CVS BIMS Revision Session 2014
87/101
8/13/2019 CVS BIMS Revision Session 2014
88/101
Reflex is elicited by metaboreceptors located in the muscle
These are free nerve endings in the interstitial space between
muscle fibres
Upon stimulation by metabolites, they send afferents to the
hypothalamic locomotor region
Via efferent pathways, the reflex response involves:
Increase in respiration
Increase in HR
Increase in contractility
8/13/2019 CVS BIMS Revision Session 2014
89/101
The exercise reflex also increases sympathetic NA supply to theskeletal muscles, GIT and kidneys
This mediates vasoconstriction
However working muscles overcome this neural influence via local
metabolic hyperaemia
8/13/2019 CVS BIMS Revision Session 2014
90/101
Negligible role during mild to moderate exercise
They respond predominantly to changes in PaO2and PaCO2
Central chemoreceptors are responsible for responding to changes
in PaCO2
Peripheral chemoreceptors are responsible for regulating PaO2
However the peripheral chemoreceptors may also respond to
arterial pH during severe exercise which induces acidosis
8/13/2019 CVS BIMS Revision Session 2014
91/101
8/13/2019 CVS BIMS Revision Session 2014
92/101
8/13/2019 CVS BIMS Revision Session 2014
93/101
8/13/2019 CVS BIMS Revision Session 2014
94/101
The magnitude of the response is dependent of the strength of the
stimulus
The alerting response is common to mammalian species
The response can show habituation or sensitisation
It can be conditioned
Activation of the alert response suppresses the baroreceptor reflex
8/13/2019 CVS BIMS Revision Session 2014
95/101
Located primarily in the hypothalamus
However there are multiple connections from the hypothalamus to
other important areas:
o To the amygdaloid defence area
o
Up past the fornix to the stria terminaliso Stria terminalis in turn sends connections back to the amygdaloid
defence area
This forms a circuit between the 3 regions which positively reinforces
the pathway meaning that the response can often outlast the
stimulus
8/13/2019 CVS BIMS Revision Session 2014
96/101
Connection toamygdaloiddefence area
Connection to striaterminalis
Connection back toamygdaloiddefence area
8/13/2019 CVS BIMS Revision Session 2014
97/101
The prefrontal cortex provides either positive or negative modulation
via the main integrating areas
From the defence area, connections leave the brain via the ventral
medulla from where synapses to the efferent nerves are formed
8/13/2019 CVS BIMS Revision Session 2014
98/101
In type A personalities, continuous or repeated exposure to stressful
stimuli may lead to strong alerting responses
Repeated activation and subsequent suppression of the baroreceptor
reflex may be associated with the development of essential
hypertension
This is supported by the link between essential hypertension, stress
levels and type A personalities
Furthermore there is also the acute dangers of an uncontrolled rise in
ABP in patients with cerebrovascular disease, coronary artery disease
and aortic aneurisms
8/13/2019 CVS BIMS Revision Session 2014
99/101
GIT and skeletal muscle vasoconstriction
The skin if in thermal balance will undergo vasoconstriction
If there is a large change in ABP, there will be renal
vasoconstriction
This will lead to further constriction via activation of the RAAS
The cerebral and coronary circulation is not affected as they
lack a large sympathetic supply
8/13/2019 CVS BIMS Revision Session 2014
100/101
8/13/2019 CVS BIMS Revision Session 2014
101/101