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Principles > Feedback control with the Cardiovascular System > Flashcards

Feedback control with the Cardiovascular System Flashcards

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1
Q

What is the definition of blood pressure?

A

Blood pressure is the outwards (hydrostatic) pressure exerted by the blood on blood vessel walls.

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2
Q

In practice what type of blood pressure is normally measured.

A

The Systemic arterial blood pressure is normally measured and is expressed as the systolic and diastolic blood pressures.

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3
Q

What is the definition of systemic systolic arterial blood pressure?

A

it is the pressure exerted by the blood on the walls of the aorta and systemic arteries when the heart contracts.

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4
Q

What is the systolic pressure normally under resting conditions?

A

It is normally <140mm Hg under resting conditions.

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5
Q

What is the definition of systemic diastolic arterial blood pressure?

A

It is the pressure exerted by the blood on the walls of the aorta and systemic arteries when the heart relaxes.

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6
Q

What is the diastolic pressure normally under resting conditions?

A

It is normally <90mm Hg.

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7
Q

Is the ideal normal arterial blood pressure the same for every individual?

A

The ideal normal arterial blood pressure varies from one individua; to another.

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8
Q

What is the definition of hypertension?

A

A clinic blood pressure of 140/90 mmHg or higher and a day time average of 135/85 mmHg or higher.

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9
Q

What are the ranges for Low blood pressure, ideal blood pressure, pre-high blood pressure and high blood pressure?

A

Low blood pressure is 90/60 or less
Ideal blood pressure is >90/60 to 120/80
Pre high blood pressure is from >120/80 to 140/90
High blood pressure is >140/90

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10
Q

What is the definition of pulse pressure?

A

It is the difference between systolic and diastolic blood pressures.
e.g. if the systolic blood pressure is 120mmHg and the diastolic blood pressure is 80mmHg. Pulse pressure = 40mmHg

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11
Q

What is the normal range for pulse pressure?

A

between 30 and 50 mmHg

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12
Q

How is the Mean Arterial Blood Pressure (MAP) regulated in the short term?

A

its short term regulation is by negative feedback mechanisms.

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13
Q

What is the definition of Mean Arterial blood pressure (MAP)?

A

It is the average arterial blood pressure during a single cardiac cycle, which involves contraction and relaxation of the heart.

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14
Q

Why is the average arterial blood pressure (MAP) not obtained by averaging the systolic and diastolic pressures?

A

Because suring a normal cardiac cycle, the relaxation (diastolic) portion of the cardiac cycle is about twice as long as the contraction (systolic) portion of the cardiac cycle.

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15
Q

How is the Mean Arterial Blood Pressure estimated?

A

MAP= ((2xDiastolic) + Systolic) divided by 3
So if the systolic pressure is 120mmHg and the diastolic pressure is 80mmHg, then: MAP=((2x80)+120)divided by 3 = (160+120)/3=280/3=93.3mmHg
MAP can also be estimated by adding DBP + (1/3 x pulse pressure)
MAP=DBP + 1/3 difference between SBP and DBP
So, if the resting blood pressure is 120/80 mmHg:
MAP=80+1/3(120-80)=80+1/3(40)=93.3mmHg

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16
Q

What is the normal range of the mean arterial Blood Pressure?

A

70-105mmHg

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17
Q

What is the minimum MAP needed to perfuse the brain, heart and kidneys?

A

A MAP of atleast 60mmHg is needed.

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18
Q

Why must the mean arterial blood pressure (MAP) be regulated within a narrow range?

A

To ensure that the pressure is high enough to perfuse the internal organs including the brain, heart and kidneys
and to ensure that the pressure is not too high to damage the blood vessels or place an extra stain on the heart.

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19
Q

How does negative feedback in the form of baroreceptors act as a regulatory method in the short-term regulation of mean arterial blood pressure?

A

The Baroreceptor reflex acts as a negative feedback mechanism in the short-term regulation of mean arterial blood pressure (MAP)

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20
Q

Where are the baroreceptors located in the body?

A 
They are located strategically within the body.
Brainstem
Glossopharyngeal nerve IX
Hering's nerve
Vagus
Carotid sinus
Aorta
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21
Q

How do signals from the baroreceptors reach the medulla?

A

The carotid baroreceptor’s signals reach the medulla via the IXth CN
The Aortic baroreceptor’s signals reach the medulla vi the Xth CN

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22
Q

How does the blood pressure affect he physical state of the baroreceptors?

A

The Baroreceptors are mechanoreceptors which are sensitive to stretch.
The higher the blood pressure the more they will stretch, the lower the blood pressure the less they will stretch.

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23
Q

How does blood pressure affect the firing rate in baroreceptor’s afferent neurons?

A

When the MAP increases, the firing rate in baroreceptor’s afferent neurons increases.
When the MAP decreases, the firing rate in barorceptor’s afferent neurons decreases.

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24
Q

What is the 4-step process whereby baroreceptros send afferent impulses to the cardiovascular control centre in the medulla of the brainstem?

A
  1. The cardiovascular control centre receives CVS afferent information. Nucleus tractus solitaries (NTS) is the site of 1st synapse for all CVS afferents in the medulla.
  2. NTS relays information to other regions in the brain e.g. medulla, hypothalamus, cerebellum.
  3. Generates vagal (parasympathetic) outflow to heart - relay to nucleus ambiguous in the medulla.
  4. Regulates spinal sympathetic neurons
25
Q

What are 3 important relationships to know?

A

MAP=Cardiac Output (CO) x Systemic vascular Resistance (SVR)
CO=Stroke volume (SV) x Heart rate (HR)
(MAP)=(SV) x (HR) x systemic vascular resistance

26
Q

What is the definition of cardiac output (CO)?

A

Cardiac output is the volume of blood pumped by each ventricle of the heart per minute

27
Q

What is the definition of stroke volume (SV)?

A

Stroke volume is the volume of blood pumped by each ventricle of the heart per heart beat

28
Q

Why can the heart be thought of as two separate pumps?

A

The left side of the heart pumps blood around the body and the right side of the heart pumps blood around the lungs.

29
Q

What is the definition of systemic vascular resistance?

A

The sum of resistance of all vasculature in the systemic circulation.

30
Q

What can be regulated, to regulate the MAP?

A

Heart rate
Stroke Volume
Systemic Vascular Resistance
(Increasing these variables increases the blood pressure. Decreasing these variables, decreases the blood pressure).

31
Q

How is the heart controlled?

A

The heart is an electrically controlled muscular pump which sucks and pumps blood.

32
Q

Where are the electrical signal that control the heart generated?

A

They are generated within the heart itself.

33
Q

Is the heart capable of beating rhythmically in the absence of external stimuli?

A

Yes and this is called autorhythmicity

34
Q

How is the heart rate modified?

A

By the Automatic (“involuntary”) Nervous system (ANS)

35
Q

In what way does sympathetic division stimulation affect the heart rate?

A

It increases the heart rate (tachycardia)

36
Q

What is the role of nonadrenaline (norepinephrine)?

A

It acts on Beta1 receptors

37
Q

In what way does parasympathetic division affect the heart rate?

A

It stimulates the vagus nerve (10th cranial nerve) slowing down the heart rate (bradycardia)

38
Q

What is the role of acetylcholine?

A

it acts on muscarinic receptors.

39
Q

The stroke volume is modified (regulated) by what?

A

The automatic nervous system

40
Q

How does increasing the contractile strength of the heart affect stroke volume?

A

It increases the stroke volume.

41
Q

What method do sympathetic nerves use to affect stoke volume and what affect do they have?

A

Sympathetic nerves innervate the ventricular myocardium, and stimulation increases the force of contraction and increases stroke volume.

42
Q

What nerve has little direct effect on ventricular contraction?

A

The vagus (parasympathetic) nerve.

43
Q

What is intrinsic control?

A

This is where control comes from within the organ itself.

44
Q

How does the intrinsic (i.e. within the heart itself) control the stroke volume?

A

Intrinsic control is carried out through the Frank-Starling Mechanism or the Starling’s Law of the heart.

45
Q

What type of vessel is the major site of systemic vascular resistance?

A

Arterioles

46
Q

How is systemic vascular resistance regulated?

A

Through vascular smooth muscles

47
Q

How do the vascular smooth muscles affect SVR and MAP?

A

Contraction of vascular smooth muscles causes vasoconstriction and increases SVR and MAP (i.e. pressure upstream)
Relaxation of vascular smooth muscles causes vasodilation and decreases SVR and MAP.

48
Q

The vascular smooth muscles are supplied by what nerve fibres and what neurotransmitter is acting on what receptors?

A

The vascular smooth muscles are supplied by sympathetic nerve fibres. The neurotransmitter is nonadrenaline acting on alpha receptors.

49
Q

What is the term used for the fact that vascular smooth muscles are partially constricted at rest?

A

Vasomotor tone

50
Q

Systemic vascular resistance is controlled by what?

A

Vascular smooth muscles.

51
Q

What causes vasomotor tone?

A

It is caused by the tonic discharge of sympathetic nerves resulting in continuous release of nonadrenaline.

52
Q

What does increased sympathetic discharge lead to?

A

It will increase the vasomotor tone resulting in vasoconstriction (increase SVR and MAP-pressure upstream)

53
Q

What will decreased sympathetic discharge lead to?

A

It will decrease the vasomotor tone resulting in vasodilation (decrease SVR and MAP).

54
Q

There is no significant parasympathetic innervation of arterial smooth muscles. There are 2 exceptions what are these?

A

The penis and the clitoris.

55
Q

Systemic vascular resistance is modified by what?

A

The automatic nervous system.

56
Q

If high arterial blood pressure is sustained how does that affect the Baroreceptor’s firing?

A

The Baroreceptor’s firing decreases.

57
Q

Baroreceptors “re-set”. What causes them to fire again?

A

They will fire again only if there is an acute change in MAP above the new higher steady state level.

58
Q

What can the baroreceptors not supply information about?

A

prevailing steady state arterial blood pressure.

59
Q

Control of MAP in the longer-term is largely control of what?

A

blood volume via hormones

Principles (57 decks)

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