Blood Pressure

Question 1

haemodynamics

arteries

Answer 1

under high pressure
recieve blood directly from heart
vol of blood = stressed volume (high pressure)
artery is folded when not stretched by blood

Question 2

haemodynamics

arterioles

Answer 2

smallest branch of arteries
walls have extensive tonicallu active smooth muscle (always contracted)
maintains pressure for effective movement of blood
site of highest resistance to blood flow
resistance changed in response to: sympathetic nerves, circulating catecholamines and other vasoactive substances
extensively innervated by sympathietic adrenergic nerve fibres
alpha 1 adrenergic receptors on arterioles of several vascular beds e.g. skin and splanchnic vasculature
when activated receptors cause contraction/constriction of vascular smooth muscle = dec diameter of arteriole, inc resistance to blood flow
less common beta 2 adrenergic receptors in skeletal muscle arterioles dilate and relax

Question 3

haemodynamics

capillaries

Answer 3

site of exchange, but not all perfused with blood - less than 25% at rest
controlled by dilation/constriction of arterioles (pre capillary sphincters in mesentry and brain)
regulated by sympathetic innveration of vascular smooth muscle and vasoactive metabolites produced in tissue e.g. angiotensin, bradykinin, histamine, nitric oxide

Question 4

haemodynamics

venules and veins

Answer 4

walls contain much less elastic tissue than arteries
large capacitance - much more than arteries, capable of accepting/storing large volumes of blood
contain largest %of blood in CV system (unstessed volume)
smooth muscle in walls innervated by sympathetic fibres - can constrict slightly
inc activity via alpha 1 adrenergic receptors - contraction to reduce capacitance - dec in unstressed volume

Question 5

velocity of blood flow

Answer 5

blood vessels vary in diameter and cross sectional area = large effect on velocity and blood flow
in identical flow - inverse relationship between velocity and cross section area
V = Q/A
Q = flow ml/s
A = cross sectional area cm2
V = velocity cm/s

Question 6

blood flow determined by…

Answer 6

pressure difference between inlet and outlet, resistance of vessel to blood flow

Question 7

total peripheral resistance TPR

Answer 7

resistance of entire systemic vasculature

resistance in single organ can be calculated by substituting e.g. renal flow for flow

Question 8

resistance to blod flow (Poiseuille’s law)

Answer 8

blood vessels and blood offer resistance to flow, factors involved: blood vessel diameter, vessel length, series/parallel arrangement, blood viscosity
resistance to flow = directly proportional to vessel length and blood viscosity (haematocrit)
but indirectly proportional to 4th power of radius
R = 8nl/Pir4

Question 9

vessel arrangment

Answer 9

series resistance (within organ)
total resistance = sum of individual resistance
pressure decrease through each sequential component
largest decrease in pressure in arterioles - largest resistance: change in pressure = resistance x flow
parallel resistance is less than any individual resistance = no loss of pressure

Question 10

pressures in CVS

Answer 10

blood pressure varies throughout
decrease occurs as blood flows - as energy is consumed overcoming frictional resistance
aorta = high cardiac output and low compliance (highest of arteries)
healthy aorta = more compliant than old/damaged

Question 11

pressure in arteries

Answer 11

remains high due to high elastic recoil

Question 12

pressure in arterioles

Answer 12

dramatic fall due to high resistance to flow —> R = 8nl/Pir4

Question 13

pressure in capillaries

Answer 13

frictional resistance to flow and filtration

Question 14

pressure in venules and veins

Answer 14

high capacitance and low pressure

Question 15

arterial pressure - systemic circulation

Answer 15

oscillations in arterial pressure reflect pulsatile activity of the heart

Question 16

pulsatile

Answer 16

as heart ejects pulse from ventricles

Question 17

diastolic pressure

Answer 17

lowest arterial pressure during ventricular relaxation

Question 18

systolic pressure

Answer 18

highest arterial pressure in arteries after blood ejected from ventricle during systole

Question 19

dicrotic notch

Answer 19

incisura

blip when aortic valve closes - brief period of retrograde backflow

Question 20

pulse pressure =

Answer 20

systolic - diastolic

reflects blood volume ejected from left ventricle (stroke volume)

Question 21

mean arterial pressure =

Answer 21

diastolic + 1/3 pulse pressure

average pressure in complete cardiac cycle

Question 22

pressure changes throughout day

Answer 22

higher in day

lower at night

Question 23

rapid regulation of blood pressure

Answer 23

baroreceptors - carotid and aortic sinuses in arteries
nucleus tractus solitarius receives info and directs changes in output of para/sympathetic nervous system via cardiovascular centres
CV centres in brainstem are in reticular formations of the medulla and lower pons

Question 24

parasympathetic control

Answer 24

parasympathetic outflow via vagus nerve on SAN to decrease heart rate and reduce blood pressure

Question 25

sympathetic control

Answer 25

has 4 components to elevate blood pressure
1 - SAN to increase heart rate
2 - cardiac muscle to increase contractility and stroke volume
3 - arterioles to produce vasoconstriction and increase total peripheral resistance
4 - veins to produce vasoconstriction and decrease unstressed volume

Question 26

medium/long term control of arterial pressure

Answer 26

Pa
renin-angiotensin-aldosterone system (RAAS) regulates blood volume (hormonal control)
dec Pa —> dec renal perfusion pressure detected by kidney afferent arteriole mechanoreceptors
prorenin —> renin
angiotensinogen — angiotensin 1 —- angiotensin 2

Question 27

angiotensin II

Answer 27

acts on adrenal cortex to synthesise and secrete aldosterone
inc Na reabsorption, stimulates Na-H exhange in kidney and reab Na and HCO3
acts on hypothalamus to increase thirst and ADHsecretion (inc water reab in collecting ducts)
vasoconstriction of arterioles to increase TPR
Pa = cardiac output x TPR

Question 28

other regulatory mechanisms for blood pressure homeostasis

Answer 28

chemoreceptors for O2 in carotid and aortic sinus bodies - stimulates arteriole vasoconstriction
chemoreceptors of CO2 in brain - stimulates arteriole vasoconstriction
ADH (AVP): V1 receptors in vascular smooth muscle cells and V2 receptors in collecting dcuts of kidney
atrial natriuretic peptide (ANP): powerful vasodilator, inc diuresis, dec ciruclating volume

Question 29

chronic hypertenison

Answer 29

densenitises baroreceptors
info from carotid sinus baroreceptors carried to brainstem (joins CN IX)
aortic arch info via CN X
in chronic hypertension baroreceptors reset = hypertension maintained not corrected

Question 30

hypertension

Answer 30

dont experience nightime ‘blip’
small inc in blood pressure is associated with inc risk of mobility and mortality
if blood pressure is too high - puts strain on other vessels and organs
can lead to:
heart disease - damage on endothelium on coronary arteries
heart attack
strokes

Question 31

treatments of hypertension

Answer 31

angiotensin-onverting enzyme inhibitors
angiotensin II receptor blockers - stop effects
diuretics - release water
beta blockers - block adrenaline effects
Ca channel blockers - reduces power of contractions
alpha agonists - reduce sympathetic outflow