regulation of blood pressure Flashcards
what is said to be normal blood pressure
systolic pressure - less than 140mmHg
diastolic pressure - less than 90 mmHg
= mean arterial pressure - 79-105mmHg
what is the mean arteriol pressure (MAP) needed to perfuse coronary arteries, brain and kidneys
at least 60mmHg
why must the MAP be regulated within a narrow range
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
how do we calculate mean arterial pressure
MAP = CO X TPR (total peripheral resistance)
OR
MAP = (SV x HR) x TPR
what is total peripheral resistance
TPR is the sum of
resistance of all
peripheral vasculature
in the systemic
circulation
What is the major resistance vessel
arterioles - account for 50% of TPR
arteries - 20%
veins 10%
capillaries 20%
how is the TPR regulated and controlled
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
how is the TPR controlled by vascular smooth muscle
neurotransmitters noradrenaline act on alpha adrenergic receptors on smooth muscle
what is meant by the term “vasomotor tone”
Vascular smooth muscles are partially constricted at
rest.
how is vasomotor tone caused
tonic discharge of sympathetic nerves resulting in continuous release of noradrenaline
describe how the TPR is modified by the autonomic nervous system
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
what is the baroreceptor reflux important in
moment-to-moment regulation of arterial blood pressure including prevention of postural changes
what are baroreceptors
pressure sensitive receptors found in walls of major arteries
where are baroreceptors found
wall of carotid artery
arch of aorta
what is the role of the carotid baroreceptor and the aortic baroreceptor
monitor pressure of blood flowing towards central nervous system
monitor the pressure of blood flowing in the systemic circulation
what is the function of baroreceptors
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
how do the baroreceptors regulate the mean arterial blood pressure
negative feedback loop that underlies the baroreceptor reflex.
this is used to minimise any disturbance to controlled variable(MAP)
describe the effect of baroreceptors initiated by a decrease in blood pressure
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
what does an increase in sympathetic activity also result in
increase in vasomotor tune leading to vino and vasoconstriction
what is the result of vinoconstriction
increase in venous return to heart therefor (frank starling mechanism) increase in stroke volume
what is the result in vasoconstriction of arterioles
increase in total peripheral resistance
what is the result then of both vaso and vineconstriction
increase in both CO and TPR leads to increase in arteriole blood pressure
describe the effect of baroreceptors initiated by a increase in blood pressure
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
what does an decrease in sympathetic activity also result in
decreases vasomotor tone leading to both vino and vaso dilation
what is the result of vinodilation
decrease in venous return to the heart
what is the result of vasodilation of arterioles
decrease in total peripheral resistance
what is the result then of both vaso and vinodilation
combined decrease in CO and TPR = decrease in arterial blood pressure
baroreceptors only respond to acute changes in blood pressure
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
how can blood volume and MAP be regulated
by controlling the extracellular fluid volume
how do you calculate the total body fluid
intracellular fluid + extracellular fluid
how do you calculate the extracellular fluid
plasma volume + interstitial fluid volume
what happens if plasma volume falls
compensatory mechanisms shift fluid from interstitial compartments to plasma compartments
what are the 2 main factors that affect the extracellular fluid volume
- Water excess or deficit
- Na+ excess or deficit
how are the factors that affect the ECFV regulated
Hormones act as effectors to control extracellular fluid volume (including plasma volume) by regulating the water
and salt (Na+) balance in our bodies
what does the endocrine regulation of the ECFV include
- The renin-angiotensin-aldosterone system (RAAS)
- Antidiuretic hormone (ADH) a.k.a. Arginine
Vasopressin - Atrial natriuretic peptide (ANP)
what is the role of the renin-angiotensin-aldosterone system
regulation of plasma volume and TPR and MAP
What are the 3 components of the renin-angiotensin-aldosterone system and what is their function
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
what is the function of the steroid hormone aldosterone
acts on kidneys to increase sodium and water retention which in turn act to increase plasma volume
where is Antidiuretic hormone (ADH) aka vasopressin derived from and stored
derived from prehormone precursor synthesised by hypothalamus
stored in posterior pituitary gland
what are the secretions of the Antidiuretic Hormone stimulated by
- reduced extracellular fluid volume
- increased extracellular fluid osmolarity (normal is 280 milli-osmoles/L)
how is plasma osmolarity monitored by
osmoreceptors in brain in close proximity to hypothalamus - increased
plasma osmolarity will stimulate the secretion of ADH from the posterior pituitary
where are the atrial natriuretic peptide stored and when are they released
28 amino acid peptides synthesized and stored by atrial muscle cells
released in response to atrial distension
what is the role of ANP
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)
