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physiology > regulation of blood pressure > Flashcards

regulation of blood pressure Flashcards

1
Q

what is said to be normal blood pressure

A

systolic pressure - less than 140mmHg

diastolic pressure - less than 90 mmHg

= mean arterial pressure - 79-105mmHg

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2
Q

what is the mean arteriol pressure (MAP) needed to perfuse coronary arteries, brain and kidneys

A

at least 60mmHg

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3
Q

why must the MAP be regulated within a narrow range

A

to ensure;
 Pressure is high enough to perfuse internal organs AND
 Pressure is not too high to damage the blood vessels or place an
extra strain on the heart (afterload

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4
Q

how do we calculate mean arterial pressure

A

MAP = CO X TPR (total peripheral resistance)
OR
MAP = (SV x HR) x TPR

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5
Q

what is total peripheral resistance

A

TPR is the sum of
resistance of all
peripheral vasculature
in the systemic
circulation

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6
Q

What is the major resistance vessel

A

arterioles - account for 50% of TPR
arteries - 20%
veins 10%
capillaries 20%

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7
Q

how is the TPR regulated and controlled

A

vascular smooth muscles contracting and relaxing

  • Contraction of vascular smooth muscles causes
    vasoconstriction and increases TPR and MAP (i.e. pressure upstream)
  • Relaxation of vascular smooth muscles causes
    vasodilatation and decreases TPR and MAP
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8
Q

how is the TPR controlled by vascular smooth muscle

A

neurotransmitters noradrenaline act on alpha adrenergic receptors on smooth muscle

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9
Q

what is meant by the term “vasomotor tone”

A

Vascular smooth muscles are partially constricted at
rest.

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10
Q

how is vasomotor tone caused

A

tonic discharge of sympathetic nerves resulting in continuous release of noradrenaline

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11
Q

describe how the TPR is modified by the autonomic nervous system

A

Increased sympathetic discharge will increase the
vasomotor tone resulting in vasoconstriction
(increase TPR and MAP)

  • Decreased sympathetic discharge will decrease the
    vasomotor tone resulting in vasodilatation (decrease
    TPR and MAP)
  • There is no significant parasympathetic innervation
    of arterial smooth muscles - exceptions are penis
    and clitoris
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12
Q
A
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13
Q

what is the baroreceptor reflux important in

A

moment-to-moment regulation of arterial blood pressure including prevention of postural changes

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14
Q

what are baroreceptors

A

pressure sensitive receptors found in walls of major arteries

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15
Q

where are baroreceptors found

A

wall of carotid artery
arch of aorta

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16
Q

what is the role of the carotid baroreceptor and the aortic baroreceptor

A

monitor pressure of blood flowing towards central nervous system

monitor the pressure of blood flowing in the systemic circulation

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17
Q

what is the function of baroreceptors

A

both are mechano receptors that respond to stretch e.g. a momentary increase in pressure within an arteries = increase in pressure being applied to vessel wall = increase in stretch being applied to vessel wall = increased activation of barrel receptors, which in turn will signal the change in stimulus via CNX, CNIX. towards medulla

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18
Q

how do the baroreceptors regulate the mean arterial blood pressure

A

negative feedback loop that underlies the baroreceptor reflex.

this is used to minimise any disturbance to controlled variable(MAP)

19
Q

describe the effect of baroreceptors initiated by a decrease in blood pressure

A

baroreceptors sense decrease and decrease signalling activity being sent to cardiovascular integrating centre in medulla, = integrating centre initiated increase in sympathetic activity and decrease in parasympathetic activity = the increase leads to increase in heart rate and contractility of cardiac muscle = increase in stroke volume = increases heart rate and stroke volume results in increase in cardiac output

20
Q

what does an increase in sympathetic activity also result in

A

increase in vasomotor tune leading to vino and vasoconstriction

21
Q

what is the result of vinoconstriction

A

increase in venous return to heart therefor (frank starling mechanism) increase in stroke volume

22
Q

what is the result in vasoconstriction of arterioles

A

increase in total peripheral resistance

23
Q

what is the result then of both vaso and vineconstriction

A

increase in both CO and TPR leads to increase in arteriole blood pressure

24
Q

describe the effect of baroreceptors initiated by a increase in blood pressure

A

increase is sensed by baroreceptors = increase in signalling activity sent to cardiovascular integrating centre in medulla = integrating centre initiates a decrease in sympathetic activity and increase in parasympathetic activity. increase in para leads to decrease in heart rate.
increase in sympathetic activity leads to reduction in HR and reproduction of contractility of cardiac muscle = decrease in SV. therefor reduction in both HR and SV - reduced cardiac output

25
Q

what does an decrease in sympathetic activity also result in

A

decreases vasomotor tone leading to both vino and vaso dilation

26
Q

what is the result of vinodilation

A

decrease in venous return to the heart

27
Q

what is the result of vasodilation of arterioles

A

decrease in total peripheral resistance

28
Q

what is the result then of both vaso and vinodilation

A

combined decrease in CO and TPR = decrease in arterial blood pressure

29
Q

baroreceptors only respond to acute changes in blood pressure

A

e.g - if high blood pressure is sustained for a period of time, baroreceptors reset and only fire again if ther is a change in mean arterial pressure therefor control MAP long term is mediated by control of blood volume

30
Q

how can blood volume and MAP be regulated

A

by controlling the extracellular fluid volume

31
Q

how do you calculate the total body fluid

A

intracellular fluid + extracellular fluid

32
Q

how do you calculate the extracellular fluid

A

plasma volume + interstitial fluid volume

33
Q

what happens if plasma volume falls

A

compensatory mechanisms shift fluid from interstitial compartments to plasma compartments

34
Q

what are the 2 main factors that affect the extracellular fluid volume

A
  1. Water excess or deficit
  2. Na+ excess or deficit
35
Q

how are the factors that affect the ECFV regulated

A

Hormones act as effectors to control extracellular fluid volume (including plasma volume) by regulating the water
and salt (Na+) balance in our bodies

36
Q

what does the endocrine regulation of the ECFV include

A
  1. The renin-angiotensin-aldosterone system (RAAS)
  2. Antidiuretic hormone (ADH) a.k.a. Arginine
    Vasopressin
  3. Atrial natriuretic peptide (ANP)
37
Q

what is the role of the renin-angiotensin-aldosterone system

A

regulation of plasma volume and TPR and MAP

38
Q

What are the 3 components of the renin-angiotensin-aldosterone system and what is their function

A

renin- released from kidneys and stimulates formation of angiotensin I in blood from angiotensinogen produced in liver

angiotensin I - converted to angiotensin II by angiotensin converting enzyme ACE produced by pulmonary vascular endothelium

Angiotensin II - stimulates release of aldosterone from adrenal cortex and causes systemic vasoconstriction - increases TPR
also stimulates thirst and ADH release

39
Q

what is the function of the steroid hormone aldosterone

A

acts on kidneys to increase sodium and water retention which in turn act to increase plasma volume

40
Q

where is Antidiuretic hormone (ADH) aka vasopressin derived from and stored

A

derived from prehormone precursor synthesised by hypothalamus

stored in posterior pituitary gland

41
Q

what are the secretions of the Antidiuretic Hormone stimulated by

A
  1. reduced extracellular fluid volume
  2. increased extracellular fluid osmolarity (normal is 280 milli-osmoles/L)
42
Q

how is plasma osmolarity monitored by

A

osmoreceptors in brain in close proximity to hypothalamus - increased
plasma osmolarity will stimulate the secretion of ADH from the posterior pituitary

43
Q

where are the atrial natriuretic peptide stored and when are they released

A

28 amino acid peptides synthesized and stored by atrial muscle cells

released in response to atrial distension

44
Q

what is the role of ANP

A

causes excretion of salt and water in kidneys thereby reducing blood volume and blood pressure

acts as a vasodilator- decreases blood pressure

decreases renin secretion

acts as a counter regulatory mechanism for Renin Angiotensin Aldosterone System (RAAS)

physiology (9 decks)

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