Lecture 8 - Blood Vessels Flashcards
What is referred to as the plumbing of the heart?
Blood vessels
Delivery of Oxygen and Nutrients to the body
What are all blood vessels lined with?
SLIPPERY,SMOOTH surface of ENDOthelium (thin flattened layer of cells)
What is the role of Elastin Fibres?
Allow vessels to stretch
What is the role of Smooth Muscle Fibres?
Smooth Muscle Fibres are wrapped AROUND vessels allowing the DIAMETER to be ADJUSTED
What is the role of Collagen Fibres?
Collagen Fibres are TOUGH, INelastic STRANDS which PREVENT the vessel wall from STRETCHING to the point of RUPTURE
What is the role of Arteries?
Arteries carry blood away from the heart
Arteries have plenty ELASTIC fibres so have High COMPLIANCE - so walls can Easily STRETCH or EXPAND . and the walls are also THICKER as there is more pressure
heart has LARGE ELASTIC arteries, which divide into MEDIUM size MUSCULAR arteries which BRANCH OUT into various regions of the body (gradual (charge or vessel))
What sort of arteries does the Heart consist of?
LARGE ELASTIC arteries, which divide into MEDIUM size MUSCULAR arteries which BRANCH OUT into various regions of the body (gradual (charge or vessel)
What are Elastic Arteries?
also called CONDUCTING arteries
Elastic Arteries are the FIRST VESSELS which LEAVE the heart (first 15 cm)
they are GREATER than >1cm (FINGER size)
What is the Function of Elastic Arteries?
- very LARGE arteries NEAR the heart which have ELASTIC WALLS
- during SYSTOLE (contraction) the heart is trying to Reduce Volume, generating More Pressure. Elastic arteries EXPAND to STORE the BOLUS of blood Leaving the ventricle. The KE from contraction is converted and STORED as ELASTIC ENERGY.(for use in diastole)
- during DIASTOLE (relaxation) elastic arteries PUSH blood OUT into the ARTERIAL TREE by ELASTIC RECOIL of the elastiN SHEETS in the elastic artery wall. Elastic Energy is converted to KINETIC ENERGY. SMOOTHS out the PULSATILE nature/flow of pump/blood Leaving the Ventricles. Will only pump in SHORT SPURTS every second with the elastic arteries expanding and contracting to accommodate that.
(PRESSURE ABSORBER)(rigid pipes would transmit pressure through the arterial tree, and your Capillaries CANNOT HANDLE High Pressure)
What is the Structure of Elastic Arteries?
THIN SHEETS of ELASTIN in the MIDDLE tunic
acts as a PRESSURE RESERVOIR
Elastin has a Higher Proportion of Elastic Fibres (layers of up to 50 SHEETS of elastin fibres)-good at storing elastic energy and recoiling
Walls THIN comparatively
Which is easier to see, arteries or veins?
arteries
veins collapse and fold onto itself without blood
What is the first branch of the aorta called?
Brachiocephalic artery
What are the main qualitative features of arteries?
rubbery
soft
pliant
What is a bolus?
a “lump” of blood
What is the nature of the cardiovascular pump?
pulsatile nature of blood/pump flow
What do Elastic Arteries Always do?
Elastic arteries ALWAYS are pumping blood down the ARTERIAL TREEE, EVEN during Filling
What is a comparison between Muscular arteries and Elastic arteries?
Muscular Arteries are MORE ABUNDANT than elastic arteries
more common
What are Muscular Arteries?
0.1 - 10mm diameter
pen –> pin
Muscular Arteries as Tunica Media has More SMOOTH MUSCLE and Fewer elastin fibres than Elastic arteries
What is the Function of Muscular Arteries?
“coarsely channel”/DISTRIBUTE blood around the body at HIGH PRESSURE (and the LUNGS at MEDIUM pressure)
very good at DIVERTING blood to WHERE it is NEEDED
BULK Transport
the Rate of blood flow is adjusted via BULK TUNING using SMOOTH MUSCLE (2-40 layers) to VARY the RADIUS of the vessel depending on how much pressure is needed via SYMPATHETIC NERVOUS CONTROL.
Vasoconstriction (narrowing of diameter)
vasodilation (increase in diameter)
Flow is proportional to the FOURTH power of the Radius
therefore a SMALL CHANGE in radius has a LARGE EFFECT on the flow rate
How is the flow of blood calculated in Muscular Arteries?
The flow of blood in MUSCULAR arteries is proportional to the FOURTH POWER of the RADIUS
What is the structure of Muscular Arteries?
consists of 3x TUNICs (outer, middle and inner tunics)
Externa –> Media –> Intima/Interna
What does the Externa consist of?
Tunica EXTERNA =Outer Tunic
consists of ELASTIC and COLLAGEN fibres
What does the Media consist of?
Tunica MEDIA = Middle Tunic
THICKEST layer
is often the FUNCTIONAL layer
consists of SMOOTH Muscle, CT and ELASTIC Fibres
the Smooth Muscle allows for VASOCONSTRICTION/DILATION
What does the Intima/Interna consist of?
INTIMA =intimate
Tunica INTERNA=Inner Tunic
consists of inner ELASTIC LAMINA which is a THIN SHEET of ELASTIN FIBRES \+ BASEMENT MEM. for PHYSICAL SUPPORT \+ ENDOthelium
What is the change like as you go down the arterial tree?
There is a GRADUAL change in histology gradual increase in the properties of the next class of arteries
What does “arteries of the body” refer to?
Muscular arteries
as muscular arteries are more common and more abundant in the body
What is Vasoconstriction?
DECREASE in diameter of arteries
What is Vasodilation?
INCREASE in diameter of arteries
What control is smooth muscle under?
Sympathetic and Parasympathetic control
+
under the right conditions
sympathetic and parasympathetic is involuntary control
What is the function of Arterioles?
Controls blood flow into CAPILLARY BEDS
It is the FINAL place of FINE TUNING the blood before it Enters the CAPPILARIES
- Last Responsibility for CONTROL and have the CORRECT PRESSURE
THIN 10-100microns (HAIR) but have a THICK MUSCULAR wall (HALF the size of the LUMEN), relative to the size of any other blood vessel
undergoes the GREATEST PRESSURE DROP and the GREATEST RESISTANCE to flow
the Degree of Constriction of arterioles determines the TOTAL PERIPHERAL resistance (over ALL(hence total) arterioles), which IMPACTS the MEAN ARTERIAL blood pressure to decide WHICH capillary network the blood goes to
What do arteries often flow beside?
Companion Veins
if the Artery Supplies the organ, the Companion Vein will often Drain the Organ
(flows are Usually similar)
What is the difference between Artery and Vein wall thickness?
Reflects the Influence of PRESSURE
What is the size of red blood cells and what do they look like?
Readily Looked for
9 microns
Black dots
Increase in # of red blood cells = Higher Power
What are Arterioles?
Vessels which only have 2-3 layers of smooth muscle
What is the Structure of Arterioles?
1-3 layers of circular SMOOTH muscle which is WRAPPED AROUND a vessel in the middle of the tunic lined by ENDOthelial cells
What are all Red Blood cells lined with?
Endothelial Cells
Which vessel has the thickest walls relative to their size?
Arterioles
wall is 1/2 size of lumen
Where are arterioles situated?
between your elastic and muscular arteries
What is important about the Mean Arteriol Pressure?
It is important to maintain it within a range
120/80
controlled by arterioles to COARSELY DISTRIBUTE the blood to a certain CAPILLARY NETWORK
What determines Mean Arteriol Pressure?
Quantity of blood being pushed into the “cylinder”
and
Total Peripheral Resisitance
What is the size of Capillaries?
very thin
the size of RBC(can fit one through)(edges touch therefore capillary)
4-10microns
What is the function of capillaries?
Blood flow is SLOW(due to be small) in order to allow TIME for EXCHANGE to occur
Capillaries exchange and form (through leakage) with INTERSTITIAL Fluid (interstitial/tissue fluid interacts with cells)
capillaries are LEAKY vessels, meaning they have GAPS and PLASMA ESCAPES(so can form tissue fluid)
Cannot handle high pressures
HYDROSTATIC pressure in capillaries DRIVES fluid OUT
most of the LOST Plasma is IMMEDIATELY RECOVERED due to an OSMOTIC GRADIENT-draw back fluid into capillary but not all
Need to DRAIN EXCESS fluid form tissues (done by the LYMPHATIC SYSTEM)
What is a Capillary?
TINY vessel which is THIN WALLED to allow the EXCHANGE of GASES,NUTRIENTS and WASTES between the BLOOD and the Surrounding TISSUE FLUID (not straight to the cells)
What is EDEMA?
When capillary DRAINAGE is IMPAIRED
results in SWOLLEN TISSUE
filtration > reabsorption
MORE FLUID squeezed OUT of capillaries e.g. Lower limbs when Standing too long
What is the Structure of Capillaries?
The diameter of a capillary is just Wide Enough to admit 1 RBC
Capillary wall is a SINGLE LAYER of ENDOthelium with an EXTERNAL BASEMENT MEMBRANE
Capillaries contain NO SMOOTH Muscle, therefore it CANNOT ADJUST its DIAMETER
Capillaries also contain NO CT
What do capillaries look after?
Interstitial fluid
What does interstitial fluid look after?
cells
interstitial fluid = “cell fluid”
What cant capillaries tolerate?
High Pressures due to being SO THIN (only one layer of endothelial cells)
What is the Function of Venules?
LOW Pressure vessels which DRAIN Capillary Beds
During INFLAMMATION and INFECTION, venules are the sites where WBC (=CT cells) LEAVE Blood Circulation to ATTACK Bacteria in the CT
What is the Structure of Venules?
a venule is SIMILAR to CAPILLARIES (2-500RBC in diameter)therefore Larger than a Capillary
SMALL venule=ENDOthelium and CT
LARGE venule = SINGLE layer of SMOOTH Muscle
Which vessels of the heart are involved in Exchange?
Elastic Arteries
Muscular Arteries
Arteriole
Capillary
Which vessels of the heart are involved in Drainage?
Venule
What does drainage involve?
bringing blood back to the heart
What does Venule mean?
Little Vein
Where are Venules situated?
immediately after capillaries
looks like a large cappilary
How are WBC Transported?
WBC use the CARDIOVASCULAR System to be transported around the body.
move through the circulatory system
when alerted that they are needed they STICK to the WALLS of Venules (able to do this due to the SLOW flow) and then slip through the Endothelial cell wall, through the CT
Final goal is to get out into CT
What features of vessels benefit exchange?
Capillaries have thin flattened single endothelial cell wall, with the cytoplasm stretched out and reduced to a very thin layer and overlaps neighbouring cells
designed to make fluid easy to GET OUT and be exchanged and flow into interstitial fluid outside
What does longitudinal mean?
Along the LENGTH of the structure
What does a RBC look like when it is damaged in capillaries?
Parachute
Mechanical Damage
edges are touching edge of capillary but fluid is coming in PUSHING the red blood cell forward and can DESTROY the red blood cells
only last a few weeks
What happens to damaged RBCs?
spleen and bone marrow recycle
What is the benefit of Capillaries only being 1 RBC in diameter?
the RBCs can RUB up again the capillary wall and SLOW it down, allowing MORE TIME for EXCHANGE
What does a longitudinal slide of a venule in infection look like?
lots of RBC
WBC STICK to the wall
will eventually go through and look for the pathogens causing the infection
What is the function of veins?
Veins are THIN walled, LOW pressure vessels with a BIG LUMEN which DRAIN blood back into the ATRIA at a SLOW rate
Except PORTAL veins which drain blood back into another Capillary Bed
A SMALL Change in Venous Blood PRESSURE causes a LARGE change in Venous Blood VOLUME
Veins act as a RESERVOIR (doesn’t ‘store’ as blood doesn’t ‘stop’)
64% blood volume = systemic VEINS and VENULES
13% blood volume = systemic ARTERIES and ARTERIOLES
What are DVTs?
Deep Vein Thrombosis
Thrombi = little blood clots
blood stops,
This is what happens if you sit in a plane for too long
What is the Structure of Veins?
Walls are THING, SOFT and they STRETCH easily (compliant)
-if veins need blood they VASOCONSTRICT - push blood from periphery
-if veins don’t need blood to the heart they VASODILATE
Adjust Diameter to change volume of blood
Similar structure to Muscular Artery, but with a Much THINNER wall for their size (much less Muscle and CT)
LARGER veins (e.g. in legs) have a Large LUMEN and VALVES which Prevent blood flow
DEEP veins also have Skeletal Muscle
As leg muscles alongside the vein Alternatively contract and relax during walking, the system acts as a Venous Pump, which returns blood right to the atrium
What is Vasoconstriction?
what happens when veins NEED blood
the vein walls (Muscle Pumps) contract/shorten and thicken/Bulge (soft compliant)
which Compresses the blood and pushes the blood towards the heart(atria)
“Aided Superiorly” displacing any of the blood above it
What is Vasodilation?
what happens when veins DONT need blood
Occurs in the veins which are CLOSER to the heart(atria)
the veins RELAX, allowing the blood to naturally flow
Aids Venous Return
What are veins affected by?
Gravity
so are us bipedal organisms
Hard to push blood from a metre and a half under Low Pressure
Leg Veins have an Adaptation
they have BICUSPID VALVES
Bicuspid valves are found b/w something HARD and a MUSCLE (can be 2x muscles)
Muscle Pumps aid venous return
What happens if you don’t walk enough?
You do not aid venous return to your heart
Stare your brain of oxygen = faint
need to use your Muscle Pumps
Why do people get Varicose Veins?
Typically Elderly get Varicose veins on their Legs
Common in Lower Limb’s Superficial veins and in Oesophagus
Veins have STRETCHED so much that the valves no longer meet, and therefore Wont Function properly, and blood POOLS
Leaky venous valves(weakened) allow backflow of blood, which causes pooling of blood,creates pressure that distends the vein, allows fluid to leak into surrounding tissue (inflamed and tender), blood doesn’t reach brain (faintness), veins become Dilated and Twisted.
Cause: Congenital, Mechanical Stretch due to Prolonged Standing/Ageing
some young people get it
Itchy and Painful
Can be Cut out/Laser Treatments/Chemicals
What is the function of Coronary Arteries?
Supply the heart (Myocardium) with Oxygenated blood, as the heart needs its own supply
Coronary arteries attach at the coronary Atria and exits the ascending aorta just above the aortic valve leaflets
on the Outside and send Branches into the myocardium
Forms a Crown around the top of the heart
Match Stick Thickness Common Muscular Arteries
Coronary arteries are critically important because of the tissues they supply (muscle is a very active organ, always contracting)
Get the Best Blood(O2 rich) and Best (Highest) Pressure
First branch of the aorta are the RH and LH Coronary arteries
Deoxygenated blood is drained from the myocardium by Cardiac Veins or Coronary Arteries, which return the blood to the Right atrium (no clinical importance)
1/3 of population have problems
Where does the Left Coronary Artery supply blood?
Left side of the Heart
Front side of the heart
Where does the Right Coronary Artery supply blood?
Right side of the Heart
Posterior side of the heart
Is the Brachiocephalic branch the first branch off the aorta?
No
technically it is the coronary arteries
Why are coronary artery branches needed?
Because the walls of the myocardium are too thick for oxygen to diffuse from the cappilaries
How is deoxygenate blood drained from the myocardium?
Cardiac Veins
back to the Right side of the heart
What is Atherosclerosis?
Wall of the Elastic artery become LESS COMPLIANT (stiff) so there is Less Energy stored in the stiffer arteries during Systole
Leads to CLOGGING,NARROWING and HARDENING of arteries
Occurs in Large Branches on the SURFACE of the heart
Fatty Plaque inside walls of vessels
-Narrows the Lumen of vessels, therefore Less Space for blood to flow
Blockage upstream affects many downstream branches
the Heart must Pump Harder to Maintain same blood flow
If a coronary artery is narrowed by 20% of normal cross section by ATHEROMA a significant obstruction to blood flow occurs
Myocardial Infarction/heart attach is when there is Not enough O2 delivered to heart, leading to Death of the Heart Wall
During exercise the myocardium supplied by a diseased artery runs low on O2 (ISCHEMIA) causing chest pain (ANGINA)(SNS to T1-T5 (arm,nipple,chest))
Sever ANGINA=death/Infarction of local area of myocardium
Sometime ANASTOMOSES (artery-artery junctions) between Small Penetrating branches of main coronary arteries WIDEN slowly so the Ischaemic area can be supplied with oxygenated blood from a Distant Artery.
More prevalent the older you get
What is Ischemia?
“Without oxygen”
Inadequate blood supply to an organ or part of the body, especially the heart muscle
run out of O2 supply
What is Angina?
severe chest pain and down arm (deferred pain)
Where is the sympathetic nerve supply?
T1-T5
Why does the heart wall look so?
Juicy and Red
because it is Rich in blood supply(lots of capillaries)
Aerobic Organ
What is the danger of having a thrombus?
can Not know you have a thrombus (blood clot)
Grow
Break free and enter circulatory system
comes across an area of coronary artery which is narrowed can Block the artery
can result in an instantaneous effect of low O2 supply to having No O2 supply at all
What does a survived myocardial infarction tissue look like?
white and scarred
developed collagen fibres and scarred over
What can cause you to have sequential myocardial infarctions?
No change in Diet or Lifestyle
