Blake_Physio_10_Arterial Venous and Lymphatics Flashcards
Vascular Distensibility =
= increase in Volume/increase in Pressure*Original volume
Comparison of distensibility between arteries and veins: (3)
- Veins are about 8x more distensible
- Pulmonary vein distensibilities are about the same as for systemic veins
- Pulmonary artery distensibilities are about 6x that of systemic arteries
Vascular compliance (aka:______) =
Definition
Capacitance = Increase in voulume/increase in pressure
the total quantity of blood that can be stored in a given portion of the circulatory system
Capacitance describes WHAT about blood vessels?
In what way?
- distensibility
- Tells us the total quantity of blood (mL) that can be stored in a given portion of the circulation for each rise in pressure (mmHg)
How is capacitance related to elastance?
Capcitance is INVERSELY proportional to elastance.
What is the relationship of Compliance (capacitance) to Volume?
=> how can compliance be described using Volume, Distensibility and original volume?
Compliance = distensibility*volume
VD=Vinc/(Pinc*Vorig)
=>
VD*Vorig=Vinc/Pinc
[VD = vascular distensibility]
Vascular compliance and Elastance
Capacitance is __________ proportional to volume and __________ proportional to pressure
directly
inversely
Vascular Compliance and Elastance
Capacitance describes how volume changes in response to_______________
a change in pressure
Vascular Compliance and Elastance
Capacitance of veins vs arteries
Capacitance is much greater for veins
Vascular Compliance and Elastance
How does age affect vascular compliance?
Capactitance decreases with age
The greater the amount of elasic tissue in a blood vessel: (2)
- the higher the elastance
- the lower the compliance
Compliance is a measure of the ease with which a hollow viscus may be ______; i.e., the volume change resulting from the application of a unit ______ ________ between the inside and outside of the viscus; the ______ of elastance
distended
pressure differential
reciprocal
Vascular Elastance is a measure of the tendency of a hollow viscus to ______ towards its ______ _____ upon removal of a _______ or ______ force
recoil
original dimensions
distending or collapsing
A systematic vein is about 8x as distensible as its corresponding artery and has a volume of about 3x as great. How wold its compliance compare to that of its corresponding artery?
24x as compliant
Explain the following observation:
When the arterial system contains 700ml of blood, the mean arterial pressure is 100mmHg. But when the arterial system contains 400ml of blood, the mean arterial pressure is 0mmHg.
The decreased volume of blood is not enough to apply a distending force agains the wall of the vessel.
Explain the follosing observation:
The venous system contains a volume of blood ranging from 2000-3500ml. Removing several hundred mL from the normal venous volume only changes venous pressure 3 to 5mmHg.
The high elasticity of the venous system compensates for the loss of volume and maintains pressure.
Define: Pulse Pressure
~stroke volume/arterial compliance
also equal to the difference between systolic and diastolic pressures
Factors Affecting pulse pressure (2)
- Stroke volume output of the heart
- most important determinant of Pulse pressure
- diastolic pressure remains unchanged during the ventricular systole; pulse pressure increases to the same extent as systolic pressure
- Compliance of the arterial tree
- decreases in compliance, i.e. aging, result in an increase in pulse pressure
Pulse Pressure:
COnditions causing abnormal contours of the pressure pulse wave:
- Aortic Valve Stenosis
- Atherosclerosis
- Patent ductus ateriosus
- Aortic regurgitation
Aortic Valve Stenosis
- diameter of the aortic valve opening is reduced significanly, and the aortic pressure pulse is decreased significanly
- Blood flow through aortic valve is diminished
Patent ductus arteriosus
- half or more of the cardiac output flows back into the pulmonary artery and lung blood vessels
- diastolic pressure falls very low before next heartbeat
Aortic regurgitation
- the aortic valve is absent or will not close completely
- Aortic pressure may fall all the way to 0mmHg between heartbeats
define “damping” of the pressure pulses
the progressive reduction of the pulsations in the periphery
How does a blood pressure cuff work?
- Pressure cuff cuts off flow to brachial artery
- no sound is heard when there is no blood flow
- Pressure cuff is gradually reduced
- Sound is heard when tubulent blood flow begins to enter semirestricted artery
- Pressure cuff is gradually reduced
- No sound is heard when laminar flow is resumed
Why is mean arterial pressure closer to the diastolic pressure?
Because 60% of the cardiac cycle is spent in the diastole
Mean arterial pressure calculation
Mean Arterial Pressure=Diastolic pressure +1/3 pulse pressure
Resistance and Cardiac Output
Pressure in the right atrium=
Factors that regulate right atrial pressure: (2)
- = central venous pressure
- Factors that regulate right atrial pressure:
- Ability of the heart to pump blood out of the right atrium/ventrical
- Tendency of blood to flow into the right atrium
Factors that increase venous return (and increase right atrial pressure) (3)
- Increased blood volume
- Increased peripheral venous pressue due to large vessel tone
- Dilation of the arterioles
Large veins offer some resistance (2)
- In a person lying down the pressure in peripheral veins is +4 to +6mmHg greater than the right atrial pressure
- When intra-abdominal pressure increases, the venous pressure in the legs must increase above the abdominal pressure before blood can flow from the legs to the heart through the abdominal veins
Compression points that collapse veins entering the thorax (5)
- Atmospheric pressure colapse in neck
- Rib collapse
- Axillary collapse
- Intrathoracic pressure =-4mmHg
- Abdominal pressure collapse
Effecto f gravitational pressure on venous pressures in standing position
- Sagital sinus ~ -10mm
- Cervical 0mm
- Axial +6mm
- Brachial +8
- Celiac +22mm
- Wrist +35
- Femur +40
- Feet +90mm
How does changing blood volume alter blood pressure
In each case, delayed compliance compensates for additional volume
Arterioles: (3)
- Small arterioles control blood flow to each tissue
- Local conditions in tissues control diameters of arterioles
- Arterioles are highly muscular
- continuous musclular coat is lost in metarterioles
Capillaries
- Smooth muscle fiber encercles capillary at point where it originates from a metarteriole (precapillary sphincter)
- Capillary wall
- unicellular layer of endothelial cells
- thin basement membrane
- Total wall thickness ~0.5µm
- Internal capillary diameter ~4-9µm
Capillaris: Special features
- Slit pores
- Intercellular clefts; 6-7nm
- allow rapid diffusion
- Plasmalemmal vesicles
- formed from caveolins
- play a role in endocytosis and transcytosis
- Some capillaries have pores
- ie: liver, GI tract, kidneys
What is the most important factor regulating vasomotion?
Concentration of Oxygen in the tissues
Diffusion is the most important means for the exchange of substances between the blood and the interstitial fluid: (3)
- Lipid-soluble substances can diffuse readily through the capillary cell memranes (O2, CO2)
- Non-lipid-soluble substances diffuse through the intercellular pores/clefts
- Rate of water diffusion through the capillary membrane is 80x faster than the flow of plasma within the capillary
Rate of diffusion across capillaries is directly proportional to ________
the concentration differences of the diffusing substance
Passage of substances through the interstitium is mostly via diffusion rather than flow: (2)
- This is because of the large numbers of proteoglycan filaments found in the intersitium
- Rivulets that allow fluid to flow through the intersitium do sometimes form
Starling Forces
Starling Forces determine direction of diffusion into or out of a capillary
Forces that determine Starling forces
Capilary pressure (out)
Interstitial fluid pressure (out)
Capillary plasma colloid osmotic pressure (in)
Interstitial fluid colloid osmotic pressure (out)
Sum of the Starling forces =
Net Filtration Pressure
Net Filtration pressure formula:
NFP= Pc - Pif - Πp + Πif
Capillary filtration coefficient
- Kf
- Takes into consideration the number and size of pores
- Filtration = Kf x NFP
When fluid enters the lymphatics, the lymph vessel walls ____________
This causes_____________
contract momentarily and pump fluid into the blood circulation.
a slight negative pressure in the interstitial spaces
Filtration at Arterial End of Capillary:
- Forces moving Fluid outward: (3)
- Total Outward Force = _____
- Forces Moving Fluid inward (1)
- Total Inward Force = _____
- Net Outward Force = ______
- Forces moving Fluid outward:
- Capillary pressure 30mmHg
- Negative interstitial free fluid pressure (3mmHg)
- Interstitial fluid colloid osmotic pressure (8mmHg)
- Total Outward Force = 41mmHg
- Forces Moving Fluid inward
- Plasma colloid osmotic pressure (28mmHg)
- Total Inward Force = 28mmHg
- Net Outward Force = 13mmHg
Filtration at Venous End of Capillary
- Forces moving fluid inward (1)
- Total Inward Force = _____
- Forces moving fluid outward (3)
- Total Outward force = _______
- Net Inward force = _______
- also called ______
- Forces moving fluid inward
- Plasma colloid osmotic pressure (28mmHg)
- Total Inward Force = 28mmHg
- Forces moving fluid outward
- Capillary pressure (10mmHg)
- Negative interstitial free fluid pressure (3mmHg)
- Interstitial fluid colloid osmotic pressure (8mmHg)
- Total Outward force = 21mmHg
- Net Inward force = 7mmHg
- also called Net Reabsorbtion Force
Lymphatic Return
Special features of lymph vessels
- Lymph Vessels posses 1-way valves
- The edges of the vessels themselves act as 1-way valves
- skeletal muscle pumps effect lymph flow
Lymph flow reaches a maximum when_______
Interstitial pressure rises slightly above atmospheric pressure
Factors that increas lymph flow (and also interstitial fluid pressure): (4)
- Elevated capillary hydrostatic pressure
- Decreased plasma colloid osmotic pressure
- Increased interstitial fluid colloid osmotic pressure
- Increase permeability of capillaries
Rate of lymph flow =
interstitial fluid pressure * activity of lymphatic pump
Why do lymph nodes swell during an infection?
Because lymphnodes contain masses of lymphocytes and macrophages which engulf foreign particles.
