clinical science team school of nursing and midwifery
TRANSCRIPT
Blood VesselsClinical Science Team
School of Nursing and Midwifery
Blood vesselsLearning outcomes:1. Compare the structure of an artery and a vein2. Explain how the structure of an artery and a
vein relates to its function 3. Describe the structure of a capillary and
explain the physiological significance of this structure
Systemic Circulation
Arteries.Arterioles.Capillaries.Venules.Veins.
Role is to direct the flow of blood from the heart to the capillaries, and back to the heart.
The ARTERY
thick muscle and elastic fibres
Arteries carry blood away from the heart.
the elastic fibres allow the artery to stretch
under pressure
the thick muscle can contract to push the
blood along.
The VEINVeins carry blood towards from the heart.
thin muscle and elastic fibres
veins have valves which act to stop the blood from going in the wrong direction.
body muscles surround the veins so that when they contract to move the body, they also squeeze the veins and push the blood along the vessel.
Differences in artery and vein
The CAPILLARYCapillaries link Arteries with Veins
the wall of a capillaryis only one cell thick
they exchange materials between the blood and other body cells.
The exchange of materials between the blood and the body can only occur through capillaries.
artery vein
capillaries
body cell
The CAPILLARYA collection of capillaries is known as a capillary bed.
Differences between arteries and veins
Blood VesselsWalls composed of 3 “tunics:”
Tunica externa: Outer layer comprised of connective tissue.
Tunica media: Middle layer composed of smooth muscle.
Tunica interna: Innermost simple squamous endothelium. Basement membrane. Layer of elastin.
Why do we have different types of blood vessel?
• Large arteries e.g. aorta are elastic arteries• Smaller arteries and arterioles are
resistance arteries• Capillaries can be continuous,
fenestrated or discontinuous, exchange takes place in these vessels• Veins are the capacity vessels, approx
64% of blood is here
Large veins are considered capacitance hold most
blood within circulatory system (blood reservoirs).
Arterioles are considered resistance vessels because Contain highest % smooth muscle Greatest pressure drop Greatest resistance to flow
Capillaries and are considered exchange vessels because exchange of nutrients gases and other substances take place
Distribution of blood in the vascular system
Blood Vessels & Cardiovascular system
Monitoring Circulatory EfficiencyEfficiency of the circulation is
assessed by: pulse and blood pressure measurements
Vital signs – pulse and blood pressure, respiratory rate and body temperature
Pulse – pressure wave caused by expansion and recoil of elastic arteriesRadial pulse (on radial
artery), routinely usedVaries with health,
body position, activity
Factors Aiding Venous Return
Venous blood pressure alone is too low to promote adequate blood return and is aided by the:
Respiratory “pump” – pressure changes created during breathing
suck blood toward the heart by
squeezing local veins
Muscular “pump” – contraction of skeletal muscles moves blood toward heart
Valves prevent backflow during venous return
Blood flow through the vessels
Blood flow through vessels is directlyproportional to thedifference in pressurebetween the endsof the tube
Blood flow through the vesselsIs inversely proportional to the resistance in the
vessels.
Resistance- determined by blood viscosity, vessel length & vessel radius.
Blood viscosity & vessel length rarely change, radius can be changed by vasoconstriction (reducing radius) or vasodilation (increasing radius)
Blood flow through vesselsNormally laminar, with the blood components
arranged in layersThe plasma forms the outer layer & slides
smoothly along the endotheliumBlood cells form the ‘axial’ layer in the centre of
the blood streamThis allows the blood to flow smoothly, layers
slide over each other, axial part moves fastest.
Blood flow through vessels When we take a blood pressure the sounds we
here are caused by turbulent flow of bloodTurbulent flow -caused by change in vessel
diameter, increase in velocity, & low blood viscosity
Fluid Exchange85% of fluid that leaves blood is returned at
venous endWhat about the other 15%?
SummaryBlood vessels carry blood to and from the
heartArteries carry blood away from the heart,
veins carry blood back to the heartLarge arteries are ‘elastic’Arterioles provide most of the resistance
to blood flowExchange of nutrients and gases takes
place in the capillariesVein are thin walled and distensible and
have valves to prevent backflow of bloodBlood circulates through the blood vessels
as a result of pressure changes.