Arterial and venous systems Flashcards
Aorta/Arteries
: consist of endothelium , elastic tissue , smooth muscle, and fibrous tissue. Work to transport blood away from heart at high pressures.
Arteries are pressure reservoirs .13% of blood volume
Arterioles
consist of endothelium and smooth muscle. Much smaller than arteries and have a lot more smooth muscle proportional to thickness . As a result, arterioles maintain blood pressure (and flow) and a large source of resistance . 7% of blood volume
Capillaries
consist of endothelium and allow for easy exchange of nutrients in tissues . Lower pressure allows for this. 7% of blood volume
Pulmonary capillaries
Site of O2 and CO2 exchange with alveoli
Systemic capillaries
Site of exchange between plasma and tissues or lungs
Water
Solutes
Gases
Venules
: Consist of endothelium and fibrous tissue .
Have the lowest pressure. 64% Of Blood volume
Veins
consist of endothelium , elastic tissue , smooth muscle, and fibrous tissue (less than arteries). Veins have a larger diameter and have very low pressure. Able to constrict and dilate. Serve as a blood reservoir.
64% Of Blood volume
Describe how blood flow velocity is related to cross sectional area and how these differ in different vessel types.
Velocity is inversely related to cross sectional area ; A increase in velocity = Decrease cross sectional area .Arteries have the lowest CSA
while capillaries have the highest. Capillaries slow velocity allow for diffusion into tissues.
What are the circulation principles ?
① Local blood flow is controlled by specific tissue needs.
↳ ex. digestion , exercise
② CO is controlled by the sum of all local tissue flows
③ BP is independent of flow
↳ pressure from vessel walls
Velocity of Blood Flow
Velocity is speed of flow
Velocity = Blood Flow/Cross sectional Area
Flow
Quantity of blood that passes a given point in a given amount of time Generally described in ml/min
Overall flow is 5L/min (cardiac output)
Physics of Flow
Flow through a vessel is determined by
pressure difference between ends of vessel
ΔP or P1 - P2
Resistance of vessel
Flow (Q) – ΔP/R
Laminar flow
is silent
Turbulent flow
causes murmurs
High velocities
Sharp turns
Uneven vessel surfaces
Narrowing of vessels
Murmurs are useful for diagnosis
Blood Pressure
Force exerted by blood against vessel walls
Units: mm Hg or mm H2O (for very low pressures)
Resistance
Opposition to flow
Can be calculated
R = ΔP/F
Define and state the relationships between blood flow , blood pressure, and vascular resistance.
Blood flow is determined by pressure gradient and the resistance of the vessel
Resistance is the opposition to flow
Blood pressure is the force exerted on blood by vessel walls
Q = πΔPr4
8ηl
Autoregulation of Flow
Increase in pressure leads to increase in resistance
Decreases in pressure lead to decreased resistance
Explain why blood flow to the tissues is fairly constant
Autoregulation of blood flow causes resistance to increase and decrease as flow increases and decreases
Vascular Distensibility
Fractional increase in volume for each mmHg rise in pressure
Vascular distensibility =
increase in volume/Increase in pressure X original volume
Vascular Compliance/Capacitance
Total quantity of blood that can be stored in a given portion of the circulation for each mmHg.
Compliance = Distensibility X Volume
Or
Increase in volume
Increase in pressure
Volume Pressure Relationships
Any given change in volume within the arterial tree results in larger increases in pressure than in veins
When veins are constricted, large quantities of blood are transferred to the heart, thereby increasing cardiac output
Define vascular distensibility and compliance & state how volume-pressure curves for arteries & veins differ.
Vascular distensibility is the amount of volume the vessel has at certain pressures Vascular distensibility =
increase in volume/Increase in pressure X original volume
Compliance is the total amount of blood that can be stored in a vessel for each mmHg
Compliance = Distensibility X Volume
Arteries are less distensible and have less compliance than veins , so arterial pressure increase with volume change
Systolic
height of pressure pulse
Diastolic
lowest point of pressure pulse
Pulse Pressure
Systolic Pressure – Diastolic Pressure
Define systolic , diastolic , and PP.
systolic : highest pressure pulse (120)
Diastolic: lowest pressure pulse (80)
pulse Pressure :Sys - Di 140)
Blood Pressure Measurement
BP is measured by auscultation
Blood supply to artery is cut off by inflating the cuff to above-systolic pressure
Pressure is released in cuff while listening for Korotkoff sounds (sound of blood being forced through constricted artery)
First sound is when pressure in cuff is equal to systolic pressure
Last sound is when pressure in cuff is equal to diastolic pressure
Explain how blood pressure is measured
BP is measured by occluding an artery with a cuff and listening for the 1st and last Korotkoff sounds as pressure is released.
Mean Arterial Pressure (MAP)
MAP = Diastolic Pressure + 1/3(Pulse Pressure)
Dependent on cardiac output and total peripheral resistance
MAP = CO X TPR
Indicate the relationship between pulse pressure, stroke volume, and arterial compliance, and how changes in one affect the others.
Pulse Pressure
Depends on stroke volume and compliance
Increased stroke volume increase pulse pressure
Increased compliance decrease pulse pressure
Pulse pressure decreases in smaller arteries due to high resistance
Abnormal pulse pressure contours can be used for diagnosis
Describe vein structure and function.
veins have endothelium and fibrous tissue along with smooth muscle and elastin. Their walls are thin with less muscle,
but contain values that ensure one way flow because decrease in Pressure. They are blood reservoirs . (65%)
Discuss venous pressures.
venous pressure is = 0 When returning blood to the heart, AKA RAP.
Veins as a Blood Reservoir
~65% of blood is in veins
Blood can be transferred to arterial system when needed (to maintain BP)
Other reservoirs in body:
Liver, spleen, large abdominal veins, venous plexus
Central Venous Pressure
Pressure in the right atrium (RAP)
Normally 0 mmHg
Regulated by
Ability of heart to pump blood out
Tendency of blood to flow into right atrium
Define venous return and list factors that control it.
Amount of blood returning to the heart through veins
① sympathetic innervation
② respiratory pump
③ skeletal muscle pump
Increase in venous return leads to increased RAP
Increased blood volume
Increased large vessel tone/peripheral venous pressures
Dilation of arterioles (decreases resistance & allows rapid flow to veins)
Decreased cardiac function
Decrease in RAP
Rapid heart rate
hemorrhage
Venous Resistance
Veins have very little resistance (when distended)
When compressed, they do have resistance
(Peripheral Venous Pressure)
Elevated RAP can lead to
backing up of blood in the veins
elevated peripheral venous pressure
(Peripheral Venous Pressure) Increased abdominal pressures cause
pressure in veins of legs to increase even more
(Peripheral Venous Pressure) Gravitational/ hydrostatic pressure
causes pressure in feet (of standing person) to be high
Opposed by venous valves & pumps
Faulty valves lead to varicose veins
Similar in arteries
