Cardiac 3: Blood vessels Flashcards
What is the function of elastic arteries?
very large arteries near the heart which have elastic wall. During systole they expand to store the bolus of blood leaving the ventricle, then during diastole they push blood out into the arterial tree by elastic recoil. They smooth the pulsatile flow of blood leaving the ventricles.
What is the structure of elastic arteries?
many thin sheets of elastin in the middle tunic.
give an example of elastic artery
aorta and pulmonary trunk
what is the function of muscular artery?
distribute blood around the body at high pressure( and lungs at medium pressure)
Rate of blood flow is adjusted by using smooth muscle to vary the radius of the vessel.
A small change in radius has a large effect on flow rate
Channel blood flow
what is the structure of muscular arteries?
many layers of circular smooth muscle wrapped around the vessel in the middle tunic
What are the 3 layers of blood vessel wall?
Outer tunic( Externa) Middle tunic with smooth muscle( media) Inner tunic( Intima/ Interna)
What is the function of arterioles?
control blood flow into capillary beds. These are the vessels in the circulation where the greatest pressure drop occurs and where there is the greatest resistance to flow.
The degree of constriction of arterioles throughout the body determines the total peripheral resistance which in turn affects mean arterial blood pressure.
Structure of arterioles
1-3 layers of circular smooth muscle wrapped around the vessel in the middle tunic.
Arterioles have a thicker muscular wall relative to their size than any other blood vessel
what is the function of capillary?
tiny vessels which are thin-walled to allow exchange of gases, nutrients and wastes between blood and the surrouding tissue fluid. Blood flow is slow to allow time for exchange to occur. Capilaries are leaky vessels: blood plasma escapes. Most of the plasma is immediately recovered due to an osmotic gradient.
Structure of capillaries
diameter just wide enough to admit one RBC. The capillary wall is a single layer of endothelium. ( with an external basement membrane). No smooth muscle(no ability to adjust diameter), no CT
Function of venules
low pressure blood vessels which drain capillary beds. During infection and inflammation, venules are the site where WBC leave the blood circulation to attack bacteria in the tissue alongside.
Structure of venules
small venules have the usual endothelium + a little CT. Larger ones have a single layer of smooth muscle.
Function and structure of veins
thin-walled, low-pressure vessels which drain blood back to the atria( except portal vein whic drain blood to another capillary bed). Their walls are thin and soft, they stretch easily (compliant). A small change in venous blood pressure causes a large change in venous volume. -> veins act as a resevoir which stores blood( 64% of blood volume occurs in systemic veins & venules compared to 13% in systemic arteries & arterioles.)
Structure: similar to a muscualr artery but much thinner-walled for their size( much less muscle and CT). Larger veins (especially in legs) have valves which prevnt backflow. As leg muscles alongside the vein alternately contract and relax during walking, the system works as a venous pump which returns blood to the right atrium.
Function and structure of Coronary arteries
They arise from the aorta just downstream from the aortic valve and supply the myocardium with blood.
Small muscualr arteries
If a coronary artery is narrowed to about 20% of its normal cross-section, signifcant obstruction to blood flow occurs. Sometimes artery-to-artery junctions(anastomoses) between small penetrating branches of the main coronary artery widen slowly so that an ischaemic area of muscle can be supplied by a distant artery.
The deoxygenated blood is draines by cardiac veins to return to the right atrium.
