Control of arterial blood pressure Flashcards
what are korotkoff sounds?
the sounds heard when doing blood pressure
what is record systolic blood pressure and record diastolic blood pressure?
record systolic = 1st appearance of sound
record diastolic = point where sound disapears
what drives blood around systemic circulation?
a pressure gradient between the aorta and RA drives blood
- since RA pressure is close to 0 →driving force for blood flow is MAP (mean arterial blood pressure)
how to calculate pressure gradient?
mean arterial blood pressure - central venous (RA) pressure (CVP)
what is systemic vascular resistance?
sum of resistance of all vasculature in systemic circulation
what are 2 common areas for baroreceptors?
- carotid
- aorta
what happens in normal baroreceptor reflexes in prevention of postural hypotension?
when normal person stands up from sitting:
- venous return of heart decreases - effect of gravity
- MAP very transiently decreases
- this reduces the rate of firing of baroreceptors
- vagal tone to heart decreases and sympathetic tone to heart increases, this increases the HR and SV
- the sympathetic constrictor tone increases, this increases the systemic vascular resistance - arterioles are main SVR site
- sympathetic constrictor tone to veins increases the venous return to heart & SV
= the result is rapid correction of transient fall in MAP (HR increase, SV increase, SVR increase)
what is postural hypotension?
results from failure of baroreceptor responses to gravitational shifts in in blood, when moving from horizontal to vertical position
what are risk factors for postural hypotension?
- age related
- medications
- certain diseases
- reduced intravascular volume
- prolonged bed rest
what is a positive result for postural hypotension?
a positive result is indicated by a drop within 3 minutes of standing from lying position
- in systolic blood pressure of at least 20 mmHg (with or without symptoms)
- a drop in diastolic blood pressure of at least 10 mmHg (with symptoms)
what are symptoms of postural hypotension?
lightheadedness, blurred vision, faintness, dizziness, falls
what do baroreceptors only respond to?
acute changes in blood pressure
- Baroreceptors “re-set” - they will fire again only if there is an acute change in MAP above the new higher steady state level
how can blood volume of MAP be regulated?
regulating the extracellular fluid volume
→plasma volume and hence steady state blood volume and MAP would be regulated if ECFV is regulated
what is extracellular fluid?
plasma volume (PV) + Interstitial fluid volume (IFV) →this is the fluid which bathes the cells and acts as the go between the blood & body cells
what does body do if plasma volume falls?
compensatory mechanisms shift fluid from interstitial compartment to plasma compartment
what are the 2 main factors that affect extracellular fluid volume?
- water excess or deficit
- Na+ excess or deficit
what regulates the extracellular fluid volume (including plasma volume) and how?
Hormones act as effectors to regulate the extracellular fluid volume (including Plasma Volume) by regulating the Water and Salt Balance in our bodies
= Healthy people stay in a stable water and salt balance, where water input = water output
what are the 3 main hormone mechanisms that regulate extracellular fluid volume?
- renin-angiotensin-aldosterone- system = RAAS
- Natriuretic Peptides – NPs
- Antidiuretic Hormone (Arginine Vasopressin) - ADH
what happens in RAAS hormone regulation?
renin = released from kidneys & stimulates formation of angiotensin 1 in the blood from angiotensinogen (produced by liver)
angiotensin 1 is converted to angiotensin 2 by angiotensin converting enzyme - ACE (mainly produced by pulmonary vascular endothelium)
angiotensin 2
1. stimulates release of aldosterone from adrenal cortex
2. causes systemic vasoconstriction → increases SVR
3. also stimulates thirst and ADH release i.e. contributes to increasing plasma volume mainly brought about by aldosterone
aldosterone (steroid hormones) acts on kidneys to increase Na+ and water retention = increases plasma volume
what is purpose of RAAS?
to increase plasma volume (which makes more fluid and increases pressure)
what are the 3 results of angiotensin 2?
- vasoconstriction (increases SVR and blood pressure)
- increases ADH release and increase thirst (increases plasma volume and blood pressure)
what is the rate limiting step for RAAS?
renin secretion
what releases renin? (specifically)
in kidney = Juxtaglomerular apparatus is a region comprising the macula densa, extraglomerular mesangial cells and granular cells release renin
what is renin angiotensin aldosterone system (RAAS) regulated by?
regulated by mechanisms which stimulates renin release from juxtaglomerular apparatus in kidney:
- Renal artery hypotension -caused by systemic hypotension (↓ blood pressure)
- stimulation of renal sympathetic nerves
- Decreased [Na+] in renal tubular fluid – sensed by macula densa (specialised cells of kidney tubules)
describe what happens in natriuretic peptides to regulate extracellular fluid volume?
peptide hormones (synthesised by heart - and brain & other organs) are released in response to cardiac distension (stretching) or neurohormonal stimuli
- they cause excretion of salt & water in kidneys, thereby reducing blood volume & blood pressure
decrease renin release = decrease blood pressure
act as vasodilators = decrease SVR & blood pressure
- NP’s provide a counter-regulatory system for RAAS
what are the 2 types of natriuretic peptides?
- atrial natriuretic peptide (ANP)
- brian type natriuretic peptide (BNP)
what is atrial natriuretic peptide?
ANP - 28 amino acid peptide synthesised and stored by atrial muscle cells (atrial myocytes)
→it’s released in response to atrial distension (hypervolemic states= decreased volume of blood circulating in body)
what is brain type natriuretic peptide?
BNP is a 32 amino acid peptide synthesised by: heart ventricles, brain (where it was originally identified) and other organs
- BNP is first synthesised as prepro-BNP, which is then cleaved to pro-BNP (108 amino acids) and finally BNP (32 amino acids)
- Serum BNP and the N-terminal piece of pro-BNP (NT-pro-BNP, 76 amino acids) can be measured in patients with suspected heart failure
what is ADH?
antidiuretic hormone - also called vesopressin
Peptide hormone derived from a pre-hormone precursor synthesised by the hypothalamus and stored in the posterior pituitary
what is secretion of ADH stimulated by?
- reduced extracellular fluid volume
- increased extracellular fluid osmolality (main stimulus)
ADH release is stimulated by increased plasma osmolality
what does plasma osmolality indicate?
relative solute-water balance
what is plasma osmolality monitored by?
monitored by osmoreceptors mainly in the brain in close proximity to hypothalamus
what does ADH do?
- acts in the kidney tubules to increase the reabsorption of water (conserve water) - i.e. concentrate urine (antidiuresis)
- This would increase extracellular and plasma volume and hence cardiac output and blood pressure
- also acts on blood vessels to cause vasoconstriction - increase SVR and blood pressure: the effect is small in normal people but becomes important in hypovolaemic shock (e.g. haemorrhage)
what are the factors of Fick’s law of diffusion?
Fick’s law of diffusion describes the rate at which a gas or solute diffuses across a fluid membrane
factors:
- surface area
- concentration gradient
- membrane permeability
- membrane thickness
you do top 3 x together then divided by membrane thickness (think like need a thick base)
