Cardiovascular System: Blood Flow & Pressure Flashcards
what tissue(s) are present in artery walls; purpose?
- elastic and fibrous
- provides stiffness and flexibility
- act as pressure reservoirs allowing for smooth blood flow
- elastin can act like springs (elastic force stored and passive recoil)
how can arteries act like pressure reservoirs
- arteries have low compliance
- large ↑ in pressure won’t lead to large degree of expansion of vessel wall
- ensures smooth flow of blood even when heart is in diastole
how can veins act like volume/blood reservoirs
- veins have high compliance
- large ↑ in pressure leads to large ↑ in vessel wall expansion
define compliance
measure of how pressure of a vessel will change with a change in volume
how are systolic and diastolic blood pressure different
systolic = maximum; diastolic = minimum
what causes systolic blood pressure
ejection of blood into aorta
what causes diastolic blood pressure
elastic recoil
what does diastolic blood pressure refer to
slow decline in pressure to minimum right before the next systole
define MAP
- mean arterial pressure
- average pressure in arteries that occurs during one cardiac cycle
how do we measure blood pressure
- arterial pressure estimated using brachial artery
- systolic (SP)/diastolic (DP)
what does korokoff sound refer to
“vibrations” made from pressure in artery when checking blood pressure
how can we determine pulse pressure (PP)
systolic (SP) - diastolic (DP)
what is the importance of pulse pressure
high pulse pressure (especially amongst older individuals) can indicate hardening of the arteries (thickened and rigid from plaque) leading to a decrease in stretch
how can we find MAP
[SP + (2*DP)] / 3
MAP is weighted mean (single cardiac cycle is at maximum for short amt of time whereas minimum is at twice the amt of time)
describe arterioles
- smaller than arteries
- aka resistance vessels
- connectors of arteries to capillaries or metarterioles
- have rings of smooth muscle that regulate radius and resistance
how are arterioles and resistance related
- arterioles are best site where resistance to flow can be regulated
- > 60% of total peripheral resistance attributed to arterioles
- largest pressure drop in vasculature occurs along here since they have greatest resistance to blood flow
define TPR
- total peripheral resistance
- combined resistances of all blood vessels with the circuit in the systemic system
how is resistance in arterioles regulated by
contraction/relaxation of circular smooth muscle
what are the main functions of arterioles
- control blood flow to individual capillary beds
- regulate MAP
how can arteriole radius change
- dependent on contraction state of smooth muscle in arteriole wall
- arteriolar tone
- vasoconstriction
- vasodilation
how does vasodilation affect arteriole radius
↑ radius due to ↓ contraction
how does vasoconstriction affect arteriole radius
↓ radius due to ↑ contraction
define arteriolar tone
when contraction level (radius) is independent of extrinsic influences
describe hyperemia
higher than normal blood flow rate
list the ways that intrinsic control of arteriole smooth muscle happens
- changes in metabolic activity
- changes in blood flow
- stretch of smooth muscles in arterioles
- local chemical messengers
describe how changes in metabolic activity affect arteriole smooth muscle
- vasodilation generally happens with ↑ metabolic activity
- vasoconstriction generally happens with ↓ metabolic activity
- smooth muscle sensitive to ECF conditions and respond to CO2, K+, H+ concentrations
- EX active hyperemia
how does active hyperemia happen
changes from O2 and CO2 in response to metabolic activity change
how does reactive hyperemia happen
changes from O2 and CO2 in response to blood flow change
arterial blood pressure refers to pressure in
aorta
draw out the flow of smooth muscle stretch in arterioles
Increase in perfusion pressure → arteriolar smooth
muscles contract → vasoconstriction → increased
resistance → decreased flow
describe myogenic response of smooth muscle in arterioles
- reflex response of afferent arterioles to changes in blood pressure
- some tissues have stretch-sensitive fibres that stretch when BP in arterioles ↑
which local chemical messengers are important for intrinsic control of arteriole smooth muscle and why
- nitric oxide and prostacyclin (vasodilation)
- endothelin-I (vasoconstriction)
what are some extrinsic factors of arteriole smooth muscle control
- sympathetic nerves
- epinephrine
- vasopressin (ADH)
- angiotensin II
how do sympathetic nerves affect arteriole radius, and how does that affect MAP
vasoconstriction; ↑ MAP
how does epinephrine affect arteriole radius, and how does that affect MAP
- depends on the receptor
- α adrenergic: vasoconstriction
- β2 adrenergic: vasodilation
- ↑ MAP bc α is dominant
how does vasopressin affect arteriole radius, and how does that affect MAP
vasoconstriction; ↑ MAP
how does angiotensin II affect arteriole radius, and how does that affect MAP
vasoconstriction; ↑ MAP
how does blood flow regulate in microcirculation
through arterioles, metarterioles, precapillary sphincters
define microcirculation
- simplest way to regulate exchange of material across capillary walls
- arterioles to precap sphincter to metarterioles/capillaries to venules
describe precapillary sphincter
rings of smooth muscle before capillary bed
what are the transport mechanisms of capillary wall material exchange
- simple diffusion
- mediated transport
- transcytosis
describe metarterioles
- intermediate structure between arterioles and capillaries
- rings of smooth muscle
- acts like shunts from arterioles to venules
why are precapillary sphincters important
- they regulate flow thru capillary bed
- contraction leads to capillary contraction leading to ↓ in flow thru capillary bed
when there is high or low resistance to flow in metarterioles, where does blood flow occur
inc in capillary beds; dec in capillary beds
pulsing manner between metarterioles and capillary beds based on conditions
what are the transport mechanisms of capillary wall material exchange
- simple diffusion thru membrane cells and pores
- mediated transport
- transcytosis
describe bulk flow across capillary walls
- capillary walls are water- and small solute permeable
- fluids are able to move from blood to interstitial fluid (vice versa)
what is filtration
blood to interstitial fluid material transport
what is absorption
interstitial fluid to blood material transport
define edema
shift of fluid from plasma to interstitial fluid (ie swelling)
define starling forces; what are some examples
- forces that drive movement of fluid in/out of cell
- capillary hydrostatic pressure (P CAP)
- interstitial fluid hydrostatic pressure (P IF)
- capillary osmotic pressure (π CAP)
- interstitial fluid osmotic pressure (π IF)
draw out material exchange b/w plasma and interstitial fluid
…
define capillary hydrostatic pressure (P CAP) and its direction of force
hydrostatic pressure exerted by presence of fluid inside the capillary; filtration
define interstitial fluid hydrostatic pressure (P IF) and its direction of force
hydrostatic pressure exerted by presence of fluid outside the capillary; absorption
define capillary osmotic pressure (π CAP) and its direction of force
osmotic force due to presence of proteins in plasma; absorption
define capillary osmotic pressure (π IF) and its direction of force
osmotic force due to presence of proteins in interstitial fluid; filtration
define net filtration pressure (NFP) and its direction of force
- difference bw forces for filtration and absorption (eqn = filtration pressure - absorption pressure);
Answer is + then filtration occurs at arteriole end, - then absorption occurs at venule ends
why is P cap displayed as a range in values
- pressure varies across capillary beds
- initial value represents venous ends
- end value represents arteriole ends
list factors that influence venous pressure and return
- skeletal muscle pump
- respiratory pump (inspiration/exhalation)
- blood volume
- venomotor tone
how do skeletal muscle pumps affect venous pressure and return
- skeletal muscles contract (squeezing of veins, blood flows to heart) and relax (blood flows to veins)
- there are one-way valves in peripheral veins, whereas none in central veins
describe inspiration
- diaphragm moves down which ↓ pressure in thoracic cavity and ↑ pressure in abdominal cavity
- gradient is made to favour blood movement in TC
- blood moves from abdominal veins to central veins in TC which causes blood to flow towards the heart
describe exhalation
reversal of pressure and creates pressure gradient that would favour bkwd movement of blood (but doesn’t happen)
why does bkwd movement of blood from exhalation not happen
due to the one-way valves
what is the relationship b/w blood volume and venous pressure
directly proportional (inc leads to inc, dec leads to dec)
what is venomotor tone
smooth muscle tension in veins
what are the effects of increased venomotor control
- constriction of veins ↑ venous pressure which makes blood move towards heart
- ↑ wall tension reduces compliance which ↑ venous pressure and ↑ stroke volume
define stroke volume
volume of blood ejected from each ventricle during a single heartbeat
describe the flow of oxygenated blood in the heart
- arteries carry oxygenated blood to arterioles then capillary beds
- gas exchange occurs
- blood flows to venules then veins then vena cava then back to heart to be oxygenated again
what is the significance of large arteries
have little resistance to flow
how is it that the diameter and thickness of the veins is so low
the pressure of blood flowing thru it is much lower, which allows it to withstand the flow
what is the importance of valves in veins
prevent back flow since it’s going upward
draw out the generic vasculature of blood flow to and away from heart
…
what is diastole
small period of time when the heart is not pumping
what is the importance of elastin fibres in vessel walls
- act like a spring
- during systole, pressure of left ventricle is greater than pressure in arteries
- this causes blood to flow into arteries which leads to a stretch to compensate for increased volume
- in diastole, valves close and allow walls to passively recoil inwards to help push blood along (result of stored elastic force)
define elasticity
resistance to change
