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Physiology And Pharmacology Of Systems > Regulation of blood pressure > Flashcards

Regulation of blood pressure Flashcards

1
Q

Definition of systolic

A

BP in aorta and large arteries that increases rapidly during L ventricular contraction

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2
Q

Definition of diastolic

A

BP when cardiac ejection stops due to the aortic valve closure
Minimum pressure reached before next systole

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3
Q

Definition of total peripheral resistance

A

Made up of resistance arteries and arterioles in the system

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4
Q

Definition of mean arterial blood pressure

A

Pressure in aorta

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5
Q

Definition of central venous pressure

A

Pressure in vena cava, normally near 0

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6
Q

Definition of afterload

A

Heart pumps against blood already in the blood vessels

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7
Q

Definition of capacitance

A

Ability to accommodate a greater blood volume

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8
Q

Definition of mechanoreceptors

A

Stretch sensitive, found in baroreceptors

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9
Q

Definition of pressure natriuresis

A

Mechanism within the kidneys by which increased renal perfusion due to increased BP leads to increased Na excretion

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10
Q

What does BP consist of
Where is it measured
How does BP vary in the body

A

Refers to the pressure in large arteries and oscillates with cardiac cycle

Systolic and diastolic, normally 120/80, mean = 93mmHg

Measured in the brachial artery at the height of the heart
BP is lower in the head and higher in the lower limbs

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11
Q

How does pressure change in there arteries

A

Blood ejected => P and F rapidly propagated
P wave increases down arterial tree due to greater stiffness
Enters arterioles and capillaries, P falls due to increased elasticity

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12
Q

How does pressure change in low resistance vascular beds

A

Low resistance vascular beds = kidney, brain, heart

P wave smoothed out less, high pulsatility can damage structures

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13
Q

How does flow in the aorta change

A

Pulsatile but smoothed out as blood => arterioles and capillaries
Elastic vessels take up energy from pressure and pulsatility

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14
Q

What happens to arterial BP and flow in systole

A

75% of SV transiently stored in aorta and large arteries as vessels are compliant

25% SV pushed into smaller arteries

Pressure energy stored in elastic walls

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15
Q

What happens to arterial BP and flow in diastole

A

Still distended but rebound

Arterial recoil pushes blood into smaller arteries

Stored energy keeps flow in diastole

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16
Q

How does the speed of the pressure waves compare to the rate of blood flow

A

Pressure wave propagates faster than blood flow

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17
Q

What is mean arterial blood pressure

A

95mmHg

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18
Q

What is the central venous pressure

A

0-5mmHg, v little resistance

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19
Q

Which arteries have the most R resistance and why?

How does this affect P

A

Resistance arteries, arterioles due to friction

P falls steeply

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20
Q

What is the relationship between Pressure difference, MABP and CVP

A

P difference = MABP - CVP

21
Q

What is the relationship between ABP, F and R

A

ABP = F x R

22
Q

What is the relationship between ABP, CO, TPR

A

ABP = CO x TPR

23
Q

What are the short term factors that affect BP

A

Sleep
Posture
Exercise
Stress

24
Q

How does pressure change over a day

A

Oscillates in small range

Average does not change much

25
Q

Why is the baroreceptor reflex important

A

In carotid sinus and aortic arch
Maintains BP in upper body, preserving flow to brain
Allows body to change F to some organs without affecting F to others
-Due to parallel circulation
Can alter BP set point, allow body to cope with stress/exercise

26
Q

What does arterial tone affect

A

Total peripheral resistance

27
Q

What does the total peripheral resistance affect

A

Afterload

28
Q

What can affect CVP preload/Starling forces

A

Venous capacitance

BV

29
Q

What can affect stroke volume

A

Afterload can decrease SV
Cardiac contractility
CVP preload/Starling forces

30
Q

What can affect venous capacitance

A

Venous tone

31
Q

What can affect BV

A

Na excretion/retention

32
Q

What does the ANS affect as a result of the baroreceptor reflex

A

Arterial and venous tone
Cardiac contractility
HR and SV

All of these stabilize MABP

Can also modulate RAAS

33
Q

What determines MABP in the long term

What does it act on

A

RAAS system
Receives input from BP

Acts on Na+ excretion/retention
Arterial and venous tone

34
Q

What are the effects of increased Na retention

A

Increased Na
Increased H2O
Increased BP
Increased MABP

And vice versa

35
Q

Describe how afferents of the baroreceptor loop reach the brain

A

Aortic nerve from aortic arch => 4th cranial nerve/vagus

Carotid sinus nerve from external carotid => 9th cranial nerve/glossopharyngeal nerve

Both reach nucleus solitairius tractus and are compared to the set point

36
Q

What happens in the efferents of the baroreceptor loop when the BP is too low

A

Increased sympathetic drive => b1 => HR and force increase

Increased sympathetic drive => a1 => increased veno and arterial constriction, CVP, TPR

Decreased parasympathetic drive => M2 => HR increase

All of these contribute to an increased CO

37
Q

How do the baroreceptors function

A

Mechanoreceptors sensitive to stretch
Thin carotid sinus wall => small P changes detected
Increased P => increased firing => NST which mediates response

38
Q

When are the baroreceptors most sensitive

A

When mean BP = 80-150mmHg but sensitivity increased by large pulse pressure

39
Q

What happens in the baroreceptor reflex when there is a new sustained pressure

A

Can adapt to new sustained pressure but not for long terms

40
Q

When is adrenaline secreted and what adrenergic receptors does it stimulate?

A

Adrenal secretions during

  • Exercise
  • Hypotension
  • Hypoglycaemia

a1, VC most vascular beds
b1, +ve chronotrope, inotrope
b2, VD in skeletal muscle

41
Q

When is noradrenaline secreted and what adrenergic receptors does it stimulate?

A

Sympathetic secretion
-Mediates SNS efferents
More often used, more important

a1, VC most vascular beds
b1, +ve chronotrope, inotrope
b2, has a low affinity

42
Q

Describe mechanisms for the long term regulation of MABP

A

Due to maintenance of constant ECF via [Na] in ECF/plasma

43
Q

What happens if the amount of Na consumed is too low

A 
Less Na consumed 
Decreased plasma [Na]
Decreased Posm
Decreased ADH secreted
Decreased water consumption/Increased water excretion

Decreased BV and preload
Decreased BP
Decreased diuresis and natriuresis

Overall, mean BV and BP lowered and then stabilised

44
Q

How is the RAAS system activated when BV, plasma [Na] and BP are too low

A

Decreased CVP => decreased atrial stretch => decreased ANP released

Decreased atrial stretch => decreased activation of cardiopulmonary receptors => increased SNS outflow to kidney => Renin released from juxtaglomerular cells

45
Q

How does the RAAS system function in the kidney

A

Renin release => Angiotensinogen converted to Ang1

Ang1 =ACE=> Ang2

Ang => Increased VC, ADH, renal Na reabsoprtion, aldosterone secretions

46
Q

How does increased VC, ADH, renal Na reabsorption and aldosterone secretion increase BV, BP and plasma [Na]?

A

Increased VC => increased R so P increases to maintain flow

Increased ADH secretion => more water retained => increases BV and BP

Increased renal Na reabsorption and aldosterone => increased plasma [Na] => increased water reabsorbed => increased BV and BP

47
Q

How does ANP affect the RAAS system

A

If less ANP released => increase in renal Na reabsorption

48
Q

Describe the process of renal regulation of Na excretion by pressure natriuresis

A

Increased renal perfusion due to increased BP => increased Na excretion

Only small changes in MABP needed to cause large response

Increased renal perfusion P
Increased in BF in vasa recta
Increased in intrarenal release of NO => VD
Greater outward P from VR, favours secretion => Decrease in renal Na reabsorption

49
Q

Describe other mechanisms to maintain BP in the long term other than RAAS

A

SNS activation => increased BP when kidneys denervated, can contribute to long term control

Changes in BP don’t always affect Na excretion
Na excretion can occur without BP changes

Baroreceptor reflex does not turn off completely after a short time

Physiology And Pharmacology Of Systems (22 decks)

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