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Cardiovascular System > 6. Control of the cardiovascular system 2 > Flashcards

6. Control of the cardiovascular system 2 Flashcards

1
Q

Design of the CVS

A

2 Circulations: Pulmonary and Systemic

Right heart- Lungs- Left heart- Body

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2
Q

What is venous volume distribution affected by?

A

Peripheral venous tone (how constricted the veins are)
Gravity
Skeletal muscle pump
Breathing

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3
Q

What is central venous pressure and what does it determine?

A

Mean pressure in the right atrium

Determines the amount of blood flowing back to the heart.

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4
Q

What does constriction of veins do?

A

Reduces compliance

Increases venous return

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5
Q

What does constriction of arteries determine?

A

Blood flow to downstream organs
Mean arterial blood pressure
The pattern of blood flow to organs

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6
Q

Local regulation of blood flow

A

Local mechanisms are intrinsic to the smooth muscle (or closely associated)
Important for reflex local blood flow regulation within an organ/ to an organ.

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7
Q

Systemic regulation of blood flow

A

Systemic mechanisms are extrinsic to the smooth muscle:
Circulating hormones e.g. those released by adrenal gland
Autonomic nervous system

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8
Q

What would lack of local mechanisms regulating blood flow result in?

A

If we drop perfusion pressure, there would be a decrease in flow (as it is primarily determined by pressure difference)

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9
Q

Autoregulation

A

Intrinsic capacity of the vessels to compensate for changes in perfusion pressure by changing vascular resistance
When perfusion pressure drops, resistance in vessels drops to allow flow to get back up to nearly normal (compensatory mechanism)

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10
Q

What are the 2 theories of why auto regulation occurs?

A

Myogenic theory: states that smooth muscle fibres respond to tension in the vessel wall (e.g. as pressure rises, fibres contract; stretch sensitive channels involved)
Metabolic theory: as blood flow decreases, metabolites accumulate downstream and vessels dilate; subsequent increased flow ‘washes’ metabolites away

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11
Q

Name 4 local (endothelium derived) hormones that affect blood flow and state how

A

Nitric oxide: Vasodilator
Prostacyclin: Vasodilator
Thromboxane A2: Vasoconstrictor
Endothelins: Vasoconstrictor (minor vasodilator effect)

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12
Q

Name 5 circulating (non-endothelium derived) hormones that affect blood flow and state how

A

Kinins: Vasodilator
Atrial natriuretic peptide (ANP): Vasodilator
Vasopressin (ADH): Vasoconstricor
Noradrenaline/Adrenaline: Vasoconstrictior
Angiotensin II: Vasoconstrictor

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13
Q

What do pre-ganglionic fibres use as their neurotransmitter?

A

ACh

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14
Q

Describe the Parasympathetic nervous system (PNS)

A

‘rest and digest’
PNS nerves tend to arise from Cranial and Sacral parts of spinal cord
PNS is important for controlling heart rate
Long pre-ganglionic fibres
Ganglia near target organ
Short post-ganglionic neurone

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15
Q

What neurotransmitter is used by the PNS?

A

ACh

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16
Q

Describe the Sympathetic nervous system (SNS)

A

‘fight or flight’
SNS nerves arise from thoracic and lumbar vertebrae
SNS is important for controlling the circulation and vessel radii
Short pre-ganglionic fibres
Long post-ganglionic neurone

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17
Q

What neurotransmitter is used by the SNS?

A

Noradrenaline

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18
Q

Sympathetic innervation to blood vessels

A

SNS fibers innervate the heart and ALL VESSELS except capillaries, precapillary sphincters and some metarterioles

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19
Q

SNS innervation is variable, different vascular beds have different degrees of innervation and different expression levels of receptors

A

Heavily innervated: kidneys, gut, spleen and skin

Poorly innervated: skeletal muscle and brain

20
Q

What does noradrenaline bind to on blood vessels and what does this cause?

A

Binds to alpha-1 adrenoceptors to cause smooth muscle contraction and vasoconstriction

21
Q

Where is the vasomotor centre?

A

VMC is located bilaterally in the reticular substance of the medulla and the lower 1/3 of the pons

22
Q

What is the vasomotor centre composed of?

A 
A vasoconstrictor (pressor) area
A vasodilator (depressor) area 
A cardioregulatory inhibitory area
23
Q

Where does the vasomotor centre transmit impulses?

A

Transmits impulses distally through the spinal cord to almost all blood vessels

24
Q

What can exert excitatory/ inhibitory effects of the vasomotor centre?

A

Many higher centres of the brain e.g. hypothalamus

25
Q

What do the lateral portions of the vasomotor centre control?

A

Heart activity by influencing heart rate and contractility

26
Q

What does the medial portion of the vasomotor centre do?

A

Transmits signals via vagus nerve to heart that tend to decrease heart rate.

27
Q

Nervous control of vessel diameter

A

Blood vessels receive SNS post-ganglionic innervation (noradrenaline (NA))
Always some level of tonic activity (producing a baseline constriction) which can be:
Increased: causing vasoconstriction
Decreased: causing vasodilation
Generally, no PNS innervation to blood vessels

28
Q

How can heart rate be increased?

A

Increased SN activity
Increase in circulating adrenaline or noradrenaline
Decreased PN activity

29
Q

How does the SNS influence force of contraction?

A

NA binds to Beta-1 receptor on heart cells
Increases cAMP
Increases PKA activity
Phosphorlyates Ca2+ handling proteins
Increases influx of Ca2+
Increases amount pumped up to stores and increases amount delivered to myofilaments
Increases force of contraction

30
Q

How can stroke volume be controlled extrinsically?

A

Increase SNS activity to heart: increases force of contraction
Increase plasma adrenaline: binds to Beta-1 receptor on heart: increases force of contraction

31
Q

How can stroke volume be controlled intrinsically?

A

Starling’s law:
Increase venous return: increase end diastolic volume
Increase stretch and increase force of contraction

32
Q

What 3 mechanisms increase cardiac output in a Fight or flight response?

A

Increase in plasma adrenaline: (stroke volume and heart rate)
Increased SNS efferents to heart: (stroke volume and heart rate)
Increased respiratory movements: (stroke volume)

33
Q

Describe the feedback mechanism involved in regulating blood pressure

A

Cardiovascular control centre sends signals to SNS and to evoke release of angiotensin II/ adrenaline/ ADH systemically
Causes vasodilation/ vasoconstriction to produce a new BP
New BP detected by Baroreceptors
Baroreceptors send signals back to cardiovascular control centre

34
Q

Where are baroreceptors found? What do they do?

A

Aortic arch
Carotid bodies
Send pulses back to vasomotor centre

35
Q

Baroreceptors in the carotid bodies send afferent PNS pulses along which nerve?

A

Glossopharyngeal nerve

36
Q

Baroreceptors in the aortic arch send afferent PNS pulses along which nerve?

A

Vagus nerve

Vagus nerve also has efference to SAN

37
Q

How do baroreceptors respond to stretch?

A

More stretch: Fire more

Less stretch: Fire less

38
Q

What type of receptors are baroreceptors?

A

Mechanoreceptors

39
Q

What pressures do the carotid sinus baroreceptors respond to? How?

A

Changes in arterial pressure
Pressures between 60 and 180 mmHg
Fire more when pressure builds up as there is greater stretch in the vessels

40
Q

At which pressures are the baroreceptor reflex most sensitive?

A

90-100 mmHg

41
Q

Describe reciprocal innervation

A

Increased pressure detected by baroreceptors, increase afferent input:
Increases PNS activity to heart (decreases HR)
Simultaneously, it inhibits SNS activity
Inhibitory interneurons can inhibit tonic activity, decreasing activity of SNS, decreasing innervation to heart, arterioles and veins

=Decrease HR at SAN

42
Q

What does decreased sympathetic stimulation of blood vessels cause?

A

Vasodilation

43
Q

How does the PNS respond to increased BP?

A

Increases traffic from baroreceptors fed to vasomotor centre
Nerve traffic in vagus nerve closely mirrors traffic coming from baroreceptors
Increases nerve activity in vagus nerve and PNS
Stimulates SAN to slow HR

44
Q

How does the SNS respond to increased BP?

A

Tonic activity decreased
In sympathetic cardiac nerves, due to recipricol innervation, it does the opposite e.g.
High baroreceptor nerve activity = Low sympathetic cardiac nerve activity, Slows HR
In sympathetic vasoconstrictor nerves there is also little nerve activity = Vasodilation

45
Q

How can venous return be increased?

A

Increasing blood volume returning to right atrium
Increasing SNS activation of veins: Constricts veins and pushes more blood back to heart, decreasing capacitance of veins and venules
Increasing skeletal pump activity and respiratory movements

46
Q

What are the compensatory mechanisms of cardiovascular system when large blood loss occurs e.g. Haemorrhage?

A

Haemorrhage causes decrease in blood volume, which decreases venous pressure and venous return
This decreases EDV and as there is less stretch, SV decreases and CO decreases = Fall in BP
Baroreceptors detect fall in BP
Increases SNS discharge to veins: constricts capacitance vessels to push blood back to heart

47
Q

What reflexes are in place to maintain arterial pressure?

A

Decrease PNS discharge to heart and increase in SNS discharge to heart: Increases contractility: Increases SV: CO
Increase SNS discharge to veins, increases venous tone, increases venous pressure, increases venous return, increases EDV: Increases contraction
Increase SNS discharge to arterioles, increases arteriolar vasoconstriction, increases total peripheral resistance

Cardiovascular System (16 decks)

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