11. Blood Pressure Flashcards
Large arteries:
Elastic vessels with high
blood flow, under high pressure
Small arteries/arterioles:
Strong muscular
walls allowing them to regulate their
lumen size and thus resistance. The high
resistance results in a large pressure drop.
Capillaries:
exchange vessels, low flow,
thin walls
Veins:
Smooth muscle allows modulation
of the diameter.
Capacitance vessels:
example
can “store” large changes in blood volume with little
change in pressure
vein
When veins are constricted large quantities of blood are
transferred to the heart thereby increasing _______ _____
Any given change in volume within the arterial tree results in
larger increases in pressure than in ____
cardiac output
veins
Compliance
The stretchability at various points along the P/V curve. i.e. the local change in volume for a given pressure change. Reflects the elasticity of the vessel.
Blood pressure (mmHg)
is the force exerted by the blood against any unit area of vessel
wall
Mean Systemic Arterial pressure=?
What is Systolic
Distolic
= ~100 mmHg
Systolic ~ 120 mmHg
Distolic ~ 90 mmHg
Does tends to increase with age
Mean Pressure formula=
MAP = CO x TPR
Determinants of Pulse Pressure
Systolic pressure - Aortic compliance - Stroke volume (and ejection rate) Diastolic pressure - Aortic compliance - Diastolic run off: Heart rate Total peripheral resistance
Pulse pressure =
Systolic pressure – diastolic pressure
During ____the aorta stretches to
absorb the blood
systole
Flow continues during diastole due to
_______nature (elastic recoil) of
blood vessels
compliant
The more _____ large blood vessels
the smaller the pulse pressure.
compliant
The compliance of the arteries ensures
capillary flow continues throughout the
cardiac cycle. Flow becomes _________by the time it reaches the
_____arterioles
nonpulsatile
small
Compliance (∆V/ ∆P) of the aorta tends to decrease with
age
As a result of a decrease in compliance:
- Systolic pressure increases
- Diastolic pressure may decrease
A less compliant aorta will result in a larger
pulse pressure
Increasing the stroke volume delivered
to the aorta increases
the arterial pulse
pressure
SV determined by:
- preload
- afterload
- chronotropy
- Inotropy
exercise can increase ________ pressure
systolic pressure
Diastolic pressure is determined by the
“diastolic run off”, i.e. the ability of the
blood to flow forward,
Diastolic pressure is dependent on:
• Total peripheral resistance (increased resistance increases diastolic pressure) • Heart rate (increased heart rate increases diastolic pressure)
Different mechanisms dominant in
blood pressure control over
different time scales:
•Short term: neural reflexes •Minutes to hours: hormonal (Ang II) and fluid shifts •Hours to days: blood volume regulation (renal mechanisms)
Blood pressure control comprises
multiple mechanisms and a high amount of ?
redundancy i.e. backups
to cope with changes in
environmental factors
The ______ rapid changes in arterial pressure
ensure that perfusion (delivery of blood to a capillary bed) of vital organs remain adequate during day to day
activity
Buffers
Increase in arterial pressure results in
an increase in what firing?
in baroreceptor firing
afferent activity
• Increase in activity to the \_\_\_\_\_\_\_\_control centres results in an increase in vagal activity and inhibition of \_\_\_\_\_\_\_nerve activity (\_\_\_\_\_pathway)
cardiovascular
sympathetic
efferent
The decrease in cardiac
output and vascular resistance
restores ________
arterial pressure
Receptor endings: located in
the adventitia of the ???
i.e. in large arteries
carotid
bifurcation and aortic arch,
Afferent activity carried in:
Carotid sinus nerve –
glossopharyngeal nerve (IX cranial)
Afferent activity carried in:
Aortic depressor nerve –
vagus (X cranial)
Pressure-activity relationship of the arterial baroreceptors
Response is almost linear over
physiological range, in the presence
of an arterial pulse
Baroreceptor responses to a
step change in pressure
Stretch receptors: increased stretch =
increased firing. Mediated by non-selective
cation channels.
Very sensitive to rapid changes in pressure,
but show adaptation
Afferent baroreceptor endings 1st
synapse in the
NTS (Nucleus tractus
soltarius).
Interneurons project to both :
vagal and
sympathetic pathways:
Vagal activity activated via the
Nucleus Ambiguus (NA), and dorsal motor nucleus.
- Sympathetic activity pathway
involves the _ _ _ _
caudal ventrolateral
medulla (CVLM) INHIBITING the
rostral ventrolateral medulla (RVLM)
Peripheral chemoreceptor reflex come from?
carotid bodies and aortic bodies (i.e.
very close to the baroreceptor endings). Central - medulla.
chemoreceptor reflex Respond to
decrease in arterial oxygen
(peripheral) or pH or increase in arterial CO2
(central) . Needs to be big change in pressure!
chemoreceptor reflex Sensory information carried in
glossopharyngeal
and vagus nerve (i.e. afferent nerves fibres are in
the same bundles as the baroreceptor afferents)
chemoreceptor reflex Primary cardiovascular response to a reduction in
oxygen is
an increase sympathetic tone and
vasoconstriction. Cardiac effects are
complicated
cerebral ischemia
is a condition in which there is insufficient blood flow to the brain to meet metabolic demand
An “emergency” or “last ditch” response.
Unsustainable
CNS ischemic response
Only seen once BP is ?
Responds to high what or low what?
Dramatic increase in what activity?
~ 60 mmHg, and
strongest when BP <20 mmHg.
Responds to high CO2 or low pH as a response to
decreased brain blood flow
sympathetic activity driving
increased peripheral resistance.
Cerebral
Ischemia affects what body systems?
Vasomotor Center
Incr Sympathetic Activity
Incr Arterial Pressure
