Blood Pressure Flashcards
what is blood pressure
the outwards (hydrostatic) pressure exerted by the blood on blood vessel walls
name the blood pressure; ‘the pressure exerted by the blood on the walls of the aorta and systemic arteries when the heart contracts’
systemic SYSTOLIC arterial blood pressure
name the blood pressure; the pressure exerted by the blood on the walls of the aorta and systemic arteries when the heart relaxes
Systemic DIASTOLIC Arterial Blood Pressure
what value should Systemic Diastolic Arterial Blood Pressure not reach or exceed
90 mm Hg
what value should Systemic Systolic Arterial Blood Pressure not reach or exceed
140 mm Hg
define hypertension
clinical blood pressure of 140/90 mm Hg or higher and day time average of 135/85 mm Hg or higher
what is pulse pressure
Is the difference between systolic and diastolic blood pressures
what is the normal range of values for pulse pressure
between 30 and 50 mmHg
describe the blood flow in normal arteries
laminar- central, not audible
when does an artery become completely occluded
when external pressure is applied that exceeds the systolic blood pressure- no blood flows through so no sound
what happens when the external pressure is kept between systolic and diastolic
blood flow becomes turbulent and is now audible through a stethoscope
what is the first korotkoff sound
peak systolic pressure
what are the second and third korotkoff sounds
intermittent sounds as blood pressure due to turbulent spurts of flow cyclically exceed cuff pressure
what is the fourth korotkoff sound
last sound, minimum diastolic pressure (muffled/muted)
what is the fifth korotkoff sound
no sound as return to laminar flow
at which korotkoff sound is diastolic pressure recorded
5th as more reproducible, 4th can be interpreted differently
at which korotkoff sound is systolic pressure recorded
1st
why is blood pressure essential
the pressure gradient between the aorta and the right atrium drives the blood around the systemic circulation
what is the main driving force for blood flow and why
MAP (mean arterial pressure) as RA pressure is close to 0
how is pressure gradient calculated
PG= MAP - central venous (right atrial) pressure (CVP)
what does CVP stand for
central venous pressure
what is mean arterial blood pressure (MAP)
the average arterial blood pressure during a single cardiac cycle
explain why the formula for MAP = ((2x diastolic) + systolic) / 3
As the relaxation (Diastolic) portion of the cardiac cycle is about twice as long as the contraction (Systolic) portion of the cardiac cycle
what are the units for MAP
mm Hg
what is the second formula for calculating MAP
DBP + 1/3 pulse pressure
what is a normal range for MAP
70-105 mm Hg
why is a minimum MAP of 60 mm Hg needed
to perfuse the coronary arteries, brain and kidneys
how are blood vessels affected by high blood pressure
damages vessel walls
what is the relationship between MAP, CO and SVR (systemic vascular resistance)
MAP= CO x SVR
as CO= SV x HR
MAP= SV x HR x SVR
what is systemic vascular resistance
the sum of resistance of all vasculature in the systemic circulation
what is total peripheral resistance
systemic vascular resistance
what are the major resistance vessels
the arterioles
what effect does parasympathetic stimulation have on MAP
decreases it (as decreases HR and CO)
what effect does sympathetic stimulation have on MAP
increases it as increases HR, SV and also increases vasoconstriction in the arterioles and veins
how does vasoconstriction in the veins increase MAP
as increases venous return, SV and CO
how does vasoconstriction in the arterioles increase MAP
increases SVR (TPR)
what is the role of the baroreceptor reflex
short term regulation of mean arterial blood pressure
what sense changes in MAP
baroreceptors
what is the control centre of the Baroreceptor Reflex
the medulla
what are the effectors of the Baroreceptor Reflex
heart (HR and SV), blood vessles (SVR)
what does negative feedback act to do
minimise any disturbance to controlled variable
where are the baroreceptors
in aortic arch and carotid sinus
how do signals from the carotid baroreceptors reach the medulla
via the 9th cranial nerve (IXth CN)
how do signals from the aortic baroreceptors reach the medulla
via the 10th cranial nerve (Xth CN)
is the vagus nerve para or symp
para
what happens to cardiac vagal efferent activity when BP increases
increases
what are efferent neurons
efferent neurons are motor neurons that carry neural impulses away from the central nervous system and towards muscles to cause movement
what are afferent neurons
Afferent neurons are sensory neurons that carry nerve impulses from sensory stimuli towards the central nervous system and brain
what causes postural hypotension
when a person stands up from a lying position and the venous return to the heart decreases due to the effect of gravity
what happens to MAP during postural hypotension
very transiently decreases
what does the transient decrease in MAP do to baroreceptors
decreases their firing
how does the baroreceptors reflex prevent postural hypotension
reduce vagal tone to heart and increase sympathetic tone to the heart.
what is the role of sympathetic constrictor tone in preventing postural hypotension
increases due to decrease in MAP and which increases SVR which increases venous return to the heart and stroke volume
during the correction of postural hypotension what does the increase if SVR also cause
increased DBP
what is the term used to describe venous constriction
venoconstriction
what type of changes in blood pressure to baroreceptors respond to
acute changes
what happens to baroreceptors firing when high blood pressure is sustained
decreases
describe how baroreceptors ‘re-set’
will fire again only if there is an acute change in MAP above the new higher steady state level
how is MAP controlled mainly in the long term
via control of blood volume by hormones
how can blood volume and MAP be controlled
by controlling the extracellular fluid
what does total body fluid consist of
Intracellular fluid (2/3rd) + Extracellular Fluid (ECF) - normally 1/3rd of the total
what makes up extracellular fluid volume (ECFV)
plasma volume (PV) + interstitial fluid (IFV)
what is interstitial fluid volume
fluid which bathes the cell and acts as the go- between the blood and body cells
what happens if plasma volume falls
compensatory mechanisms shifts fluid from the interstitial compartment to the plasma compartment
how much body weight is fluid normally
60%- 20% extra cellular (interstitial fluid) 40% intracellular (intracellular fluid)
what two main factors affect extracellular fluid volume
water excess or deficit, Na+ excess or deficit
why does Na affect extracellular fluid volume
as water follows Na+, more sodium = more water
what is hormones role in regulating the extracellular fluid volume
act as effectors to regulate this by regulating the water and salt balance in our bodies
what three hormones regulate long term extracellular fluid volume
The Renin-Angiotensin- Aldosterone System - RAAS
Natriuretic Peptides – NPs
Antidiuretic Hormone (Arginine Vasopressin) - ADH
what hormone is associated with the most therapeutic interventions
renin-angiotensin-aldosterone system RAAS
what is the role of RAAS
regulates plasma volume and SVR and therefore also MAP
what are the three components of RAAS
(1) Renin
(2) Angiotensin
(3) Aldosterone
what releases renin
kidneys
what does renin stimulate
formation of angiotensin 1 from angiotensinogen
what releases angiotensinogen
the liver
what converts angiotensin 1 to angiotensin 2
Angiotensin converting enzyme - ACE
what produces ACE
pulmonary vascular endothelium
what are the 4 things angiotensin 2 stimulates
1- release of aldosterone from the adrenal cortex
2-systemic vasoconstriction
3-thrist
4-ADH relsease
what is aldosterone and what does it do
a steroid hormone that acts on the kidneys to increase sodium and water retention (increases PV and BP)
what is the rate limiting step for RAAS
renin secretion
what is RAAS regulated by
mechanisms which stimulate Renin release from the juxtaglomerular apparatus in the kidney
what are the mechanisms which stimulates Renin release from the juxtaglomerular apparatus in the kidney
1- renal artery hyPOtension
2- stimulation of renal sympathetic nerves
3- decreased Na+ in renal tubular fluid
what causes renal artery hypotension
systematic hypotension
what are natriuretic peptides (NPs)
peptide hormones
what synthesises NPs
the heart (+other organs)
what stimulates the release of NPs
cardiac distension or neurochemical stimuli
what do NPs cause (3)
1- excretion of salt and water in the kidneys ( decreased BV and BP)
2- decrease renin release (decrease BP)
3- vasodilators (decrease SVR and BP)
what system do NPs provide
a counter-regulatory system for RAASystem
what are the two types of natriuretic peptides released by the heart
atrial natriuretic peptide (ANP) and brain-type natriuretic peptide (BNP)
describe ANP, its components, location and course of action
28 amino acid peptide synthesised and stored by artial muscle cells (atrial myocytes) until released in response to atrial distension (hypervolemic states)
describe ANP, its components and where it is produces
32 amino acid peptide synthesised by heart ventricles, brain and other organs
describe the production of BNP
firstly prepro-BNP (longer chain), which is cleaved to pro-BNP (108 amino acids) and then BNP (32 aa)
what is the N terminal piece of pro-BNP called
NT-pro-BNP (76 aa)
what can be measured in patients with suspected heart failure
serum BNP and NT-pro-BNP (measured in the blood)
what is vasopressin
ADH
what is ADH and how is it made
Peptide hormone derived from a prehormone precursor synthesised by the hypothalamus
where is ADH stored
in the posterior pituitary
what is secretion of ADH stimulated by
(1) reduced extracellular fluid volume(will store water) or (2) increased extracellular fluid osmolality
what is the main stimulus of ADH secretion
increased extracellular fluid osmolality
what is osmolality
indicates relative solute-water balance (concentration of solution)
what is plasma osmolality measured by
osmoreceptors close to the hypothalamus in the brain
where and how does ADH act
ADH acts in the kidney tubules to increase the reabsorption of water i.e. concentrate urine
what would the absorption of water cause
would increase extracellular and plasma volume and hence cardiac output and blood pressure
how does ADH act on blood vessels
causes vasoconstriction - increase SVR and blood pressure
when does the vasoconstriction effects of ADH become important
hypovolaemic shock (e.g. haemorrhage)
