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)
