Control of arterial blood pressure

Question 1

what are korotkoff sounds?

Answer 1

the sounds heard when doing blood pressure

Question 2

what is record systolic blood pressure and record diastolic blood pressure?

Answer 2

record systolic = 1st appearance of sound
record diastolic = point where sound disapears

Question 3

what drives blood around systemic circulation?

Answer 3

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)

Question 4

how to calculate pressure gradient?

Answer 4

mean arterial blood pressure - central venous (RA) pressure (CVP)

Question 5

what is systemic vascular resistance?

Answer 5

sum of resistance of all vasculature in systemic circulation

Question 6

what are 2 common areas for baroreceptors?

Answer 6

• carotid
• aorta

Question 7

what happens in normal baroreceptor reflexes in prevention of postural hypotension?

Answer 7

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)

Question 8

what is postural hypotension?

Answer 8

results from failure of baroreceptor responses to gravitational shifts in in blood, when moving from horizontal to vertical position

Question 9

what are risk factors for postural hypotension?

Answer 9

• age related
• medications
• certain diseases
• reduced intravascular volume
• prolonged bed rest

Question 10

what is a positive result for postural hypotension?

Answer 10

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)

Question 11

what are symptoms of postural hypotension?

Answer 11

lightheadedness, blurred vision, faintness, dizziness, falls

Question 12

what do baroreceptors only respond to?

Answer 12

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

Question 13

how can blood volume of MAP be regulated?

Answer 13

regulating the extracellular fluid volume
→plasma volume and hence steady state blood volume and MAP would be regulated if ECFV is regulated

Question 14

what is extracellular fluid?

Answer 14

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

Question 15

what does body do if plasma volume falls?

Answer 15

compensatory mechanisms shift fluid from interstitial compartment to plasma compartment

Question 16

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

Answer 16

1. water excess or deficit
2. Na+ excess or deficit

Question 17

what regulates the extracellular fluid volume (including plasma volume) and how?

Answer 17

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

Question 18

what are the 3 main hormone mechanisms that regulate extracellular fluid volume?

Answer 18

1. renin-angiotensin-aldosterone- system = RAAS
2. Natriuretic Peptides – NPs
3. Antidiuretic Hormone (Arginine Vasopressin) - ADH

Question 19

what happens in RAAS hormone regulation?

Answer 19

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

Question 20

what is purpose of RAAS?

Answer 20

to increase plasma volume (which makes more fluid and increases pressure)

Question 21

what are the 3 results of angiotensin 2?

Answer 21

1. vasoconstriction (increases SVR and blood pressure)
2. increases ADH release and increase thirst (increases plasma volume and blood pressure)

Question 22

what is the rate limiting step for RAAS?

Answer 22

renin secretion

Question 23

what releases renin? (specifically)

Answer 23

in kidney = Juxtaglomerular apparatus is a region comprising the macula densa, extraglomerular mesangial cells and granular cells release renin

Question 24

what is renin angiotensin aldosterone system (RAAS) regulated by?

Answer 24

regulated by mechanisms which stimulates renin release from juxtaglomerular apparatus in kidney:

1. Renal artery hypotension -caused by systemic hypotension (↓ blood pressure)
2. stimulation of renal sympathetic nerves
3. Decreased [Na+] in renal tubular fluid – sensed by macula densa (specialised cells of kidney tubules)

Question 25

describe what happens in natriuretic peptides to regulate extracellular fluid volume?

Answer 25

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

Question 26

what are the 2 types of natriuretic peptides?

Answer 26

1. atrial natriuretic peptide (ANP) 2. brian type natriuretic peptide (BNP)

Question 27

what is atrial natriuretic peptide?

Answer 27

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)

Question 28

what is brain type natriuretic peptide?

Answer 28

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

Question 29

what is ADH?

Answer 29

antidiuretic hormone - also called vesopressin Peptide hormone derived from a pre-hormone precursor synthesised by the hypothalamus and stored in the posterior pituitary

Question 30

what is secretion of ADH stimulated by?

Answer 30

1. reduced extracellular fluid volume 2. increased extracellular fluid osmolality (main stimulus) ADH release is stimulated by increased plasma osmolality

Question 31

what does plasma osmolality indicate?

Answer 31

relative solute-water balance

Question 32

what is plasma osmolality monitored by?

Answer 32

monitored by osmoreceptors mainly in the brain in close proximity to hypothalamus

Question 33

what does ADH do?

Answer 33

- 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)

Question 34

what are the factors of Fick's law of diffusion?

Answer 34

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)