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MD3001 > Control of Blood Pressure > Flashcards

Control of Blood Pressure Flashcards

1
Q

Learning outcomes

A
  • To identify the components of the feed-back system involved in the reflex control of mean arterial blood pressure (including the receptors, integrating centre, target effectors and associated afferent and efferent pathways), where they are located and how they contribute to regulation of MABP.
  • To predict how the cardiovascular system will reflexively respond to physiological changes to maintain mean arterial blood pressure.
  • To explain how tissue demands for blood flow are balanced against the requirement to maintain a mean arterial blood pressure.
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2
Q

Name 2 reasons why integration and control of the heart and blood vessels is necessary

A
  • Integration and control of the heart and blood vessels is necessary to maintain tissue perfusion across the entire body:

1) Needed to keep a relatively constant arterial blood pressure (MABP)
2) Needed to control distribution of total cardiac output

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3
Q

why do we need to control distribution of total cardiac output?

A
  • 5L/minute is not enough to perfuse the whole body
  • Needs to respond to tissue demands
  • Satisfied by local control mechanisms e.g baroreceptors and chemoreceptors (sensory cells associated with reflexes)
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4
Q

what can happen if we have too low or too high MABP?

A
  • Too low, blood flow to organs would fail
  • Too high, damage to vessels and organs would take place
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5
Q

How rapid is sympathetic controller of arterial pressure?

A
  • Nervous control of arterial pressure is rapid
  • Can increase arterial pressure to 2x normal within 5-10 seconds
  • Can decrease arterial pressure to 50% normal within 10-40s
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6
Q

What are the 6 fundamental components of a reflex control system?

A
  • 6 fundamental components of a reflex control system:
    1) Internal variable to be maintained
    2) Receptors sensitive to change in the variable
    3) Afferent pathways from the receptors
    4) An integrating centre for the afferent inputs
    5) Efferent pathways from the integrating
    6) Target effectors that alter their activities
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7
Q

What is mean arterial blood pressure (MABP)?

A
  • Mean arterial blood pressure (MABP) is an average blood pressure in an individual during a single cardiac cycle
  • MABP between 70-100mmHg is considered normal
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8
Q

What is the formula for MABP?

A
  • MABP = Cardiac output x Total Peripheral resistance
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9
Q

What are baroreceptors?

What do they allow? How do they achieve this?

A
  • Baroreceptors are a type of stretch mechanoreceptors that allow for the relay of information about blood pressure within the autonomic nervous system.
  • Information from baroreceptors is passed in rapid sequence to alter the total peripheral resistance and cardiac output, maintaining blood pressure within a preset, normalized range.
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10
Q

what type of feedback loop does baroreceptors use to control MABP?
what is this process Called?

A
  • Baroreceptors uses a negative feedback loop to control MABP
  • This process is known as the baroreceptor reflex, and is a neuronal reflex
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11
Q

Where are the main baroreceptor locations in the arteries?

What afferent fibres are they innervated by?

A
  • Main arterial baroreceptor locations:

1) Walls of aorta
* Subject to high ranges of pressures
* Afferent fibres follow the vagus nerve (10th cranial nerve)

2) Carotid artery
* Subject to lower pressures
* Afferent fibres follow glossopharyngeal nerve (9th cranial nerve)

*

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12
Q

What type of receptors are baroreceptors?

How does blood pressure affect the firing rate of baroreceptors?

How does this lead to blood pressure normalising?

A

Baroreceptors are stretch receptor, which sense the stretch in vessel walls
* When blood pressure increase causes vessel wall stretch increase, the firing rate of baroreceptors increase, the ANS can then decrease blood pressure through increasing parasympathetic activity and/or decreasing sympathetic activity
* When blood pressure decrease causes vessel wall stretch decrease, the firing rate of baroreceptors decrease, the ANS can then increase blood pressure through increasing sympathetic activity and/or decreasing parasympathetic activity
* These changes in ANS firing will alter cardiac output/total peripheral resistance, leading to an increase or decrease in MABP

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13
Q

What is the setpoint of baroreceptors?

When can it change?

What is the primary purpose of the baroreceptor reflex?

A
  • The set point of baroreceptors is the normal resting value of blood pressure that baroreceptors are sensitive around, and is the midpoint of firing rate
  • The set point is different for different systems, and can be changed e.g during hypertension or during exercise
  • The primary purpose of the baroreceptor reflex control is to reduce the minute-to-minute variations of arterial pulse
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14
Q

Primary purpose of Baroreceptors

A
  • The primary purpose of the baroreceptor reflex control is to reduce the minute-to-minute variations of arterial pulse
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15
Q

Arterial baroreceptor flow chart

A
  • Arterial baroreceptor flow chart
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16
Q

Where are cardiopulmonary baroreceptors located?

What do these receptors sense?

How does blood volume in pulmonary circulating affect baroreceptor firing?

How does this affect ANS activity?

What do most vessels not have?

A
  • Cardiopulmonary baroreceptors are located in the atria, ventricles and pulmonary vessels
  • These low-pressure baroreceptors are involved in regulating blood volume
  • If a decrease in blood volume is sensed, the rate of cardiopulmonary baroreceptor firing decreases
  • This change in firing increase sympathetic nerve activity to the heart and blood vessels and decreases parasympathetic activity to the heart (as most vessels don’t have parasympathetic innervation)
17
Q

What is the Bainbridge reflex?

What effect does the Bainbridge reflex have on HR and contractility?

What does this reflex prevent?

What happens if the aortic/baroreceptors detect an increase in blood pressure?

What is the link between the Frank Starling mechanism and the Bainbridge reflex?

A
  • The Bainbridge reflex is the sympathetic-mediated reflex in response to increased blood (increased stretch) in the atria
  • The Bainbridge reflex increase HR (positive chronotropic effect) and increase contractility (positive inotropic effect), both of which increase blood pressure
  • The Bainbridge effect prevents blood from backlogging in the veins
  • If the aortic/carotid baroreceptors sense high pressure, the Bainbridge effect can override this
  • The Frank Starling mechanism also increases contractility, and can be triggered simultaneously with the bainbridge reflex, leading to an even greater increase in contractility
18
Q

Where is integrated control of BP?

What does this centre integrate?

What is found in the sensory area of this centre?

What is found in the lateral portion?

What is found in the medial portion?

A
  • Integrated control of BP is in the medullary cardiovascular vasomotor control centre (MCVCC)
  • This centre can integrate the baroreceptor and Bainbridge reflex signals
  • In the sensory area of this centre, there is the input from baroreceptors
  • In the lateral portion, there are efferent sympathetic nerves
  • In the medial portion, there are efferent parasympathetic (vagal) nerves
19
Q

What are the target effectors in the reflex control of MABP?

How do these changes affect MABP?

A
  • The target effectors in the reflex control of MABP are the heart and blood vessels

 

20
Q

how does the ANS effect blood vessels in the reflex control of MAPB?

A
  • Most vessels don’t have parasympathetic supply
  • Sympathetic vasoconstrictor tone exerts a vasomotor tone on vessels, meaning they are kept partially restricted
  • This continuous low-level tone in vessels affects total peripheral resistance (vascular resistance)
  • Sympathetic control also aids in venous return
  • These changes in total peripheral resistance and cardiac output lead to an increase in MABP
21
Q

what do we do if we want to reduce vascular tone?

A
  • If we want to reduce vascular resistance, we can take away the sympathetic tone, which allows for relaxation of the smooth muscle
22
Q

if we sympathetically constrict veins, how does this lead to an increase in cardiac output?

A
  • Sympathetic constrict veins
  • which decreases capacitance
  • which increases vascular resistance
  • which increases vascular pressure
  • which increases venous return
  • which increases stroke volume
  • which increases cardiac output
23
Q

Control of blood pressure flow chart

A

Control of blood pressure flow chart

24
Q

What is the CNS ischemic response?

What triggers this response?

What 3 changes does this response lead to?

A
  • The CNS ischemic response is an emergency control pressure system (last ditch stand)
  • This response is triggered when the blood flow to the medullary CVCC is greatly reduced
  • This response leads to:
    1) Increased Peripheral vasoconstriction (almost completely occludes some peripheral vessels)
    2) Increased sympathetic stimulation of the heart
    3) Great increase in systemic arterial pressure – as high as 250mmHg for 10 mins (normal value is 120mmhg Systolic and 90mmHg diastolic), which is the biggest increase in pressure possible
25
Q

Do organs auto-regulate blood flow?

How do organs auto-regulate blood flow?

A
  • Organs auto-regulate blood flow independent of innervation/hormonal control, despite the central decision about where we constrict vasculature to modify total peripheral resistance
  • Organs auto-regulate blood flow through Active and reactive hyperaemia
26
Q

What 2 intrinsic ways can we maintain safe blood flow when blood pressure increases?

A
  • 2 intrinsic ways we can maintain safe blood flow when blood pressure increases:

1) Myogenic theory (acute flow auto-regulation)
* Stretch induces vascular depolarisation of smooth muscle due to increase in arterial pressure
* This limits the blood flow that can move through the vessel, preventing damage to the vessels
* This is a myogenic response, where stretch activated Ca2+ channels trigger the process of contraction

2) Metabolic theory (acute flow autoregulation)
* An increase in arterial pressure increases O2 and washes out local factors e.g Breakdown of ATP to ADP and AMP, which can be converted to adenosine in the blood
* High degree of oxygen delivery to smooth muscle is likely to trigger constriction mediated effects in the vasculature, leading to an occlusion of the blood supply downstream, as there is enough oxygen present
* This constriction can reduce flow and protect the vessel walls from being damaged

27
Q

Cardiac output summary

A

Cardiac output summary

28
Q

Total peripheral resistance (vascular resistance) summary

A

Total peripheral resistance (vascular resistance) summary

29
Q

how does the ANS effect the heart in the reflex control of the MABP?

A
  • The sympathetics and parasympathetics both control heart rate and normally function simultaneously
  • At rest, the parasympathetics is the predominant tone
  • When active, sympathetics are the predominant tone, as they can significantly increase contractility, heart rate and stroke volume through changes in calcium handling
  • These changes alter cardiac output, which leads to a change in MABP

MD3001 (56 decks)

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