Blood Vessels L9 Flashcards
Draw out the wigger’s diagram
Function of elastic artery
Very large arteries
near the heart which have
elastic walls. 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. Thus they smooth the pulsatile flow of blood leaving
the ventricles.
Structure of elastic artery
Many thin sheets of
elastin in the middle tunic
Vasoconstriction
When smooth muscle cells contract
Vasodilation
When smooth muscle cells relax, and diameter of the vessel increases
Which one first - elastic or muscular?
Elastic
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.
Flow is proportional to the fourth power of radius.
A small change in radius has a large effect on flow rate.
Structure of the muscular artery
Many layers of circular smooth muscle wrapped around the vessel in the middle tunic
Which has a thicker wall - artery or vein?
Artery - greater pressure
Function of the arteriole
Control blood flow into capillary beds. They have
a thicker muscular wall relative to their size than any other blood vessel. 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:
total peripheral resistance
which in turn affects
mean arterial blood pressure
Structure of arteriole
Between one and three layers of circular smooth muscle wrapped around the vessel in the middle tunic.
Function of the capillary
Tiny vessels which are thin-walled to allow
exchange of gases, nutrients and wastes between
blood and the surrounding tissue fluid. Blood flow is
slow to allow time for exchange to occur. Capillaries
are leaky vessels; plasma escapes (but not blood
cells). Most of the lost plasma is immediately
recovered due to an osmotic gradient.
Oedema
When you have too much pressure at the beginning of your capillaries you are forced to have too much fluid out and your tissue fluids get saturated. Stopped by osmosis.
Structure of the capillary
The diameter is just wide enough to admit
one red blood cell. The capillary wall is a single
layer of endothelium (with an external basement
membrane). No smooth muscle is present within the
wall, (therefore no ability to adjust diameter), and no
connective tissue.
Function of the venule
Low-pressure vessels which drain capillary beds.
During infection and inflammation, venules are the site where
white blood cells leave the blood circulation to attack bacteria
in the tissue alongside. The drawing shows a neutrophil which,
having first adhered to the endothelium, is now squeezing its
way between two endothelial cells to exit the vessel.
Structure of the vein
Similar to a muscular artery but much thinner-walled for their size, (much less muscle
and connective tissue). Larger veins (especially in the legs) have valves which prevent backflow.
As leg muscles alongside the vein alternately contract and relax during walking, the system acts
as a venous pump which returns blood to the right atrium.
What are coronary arteries?
Arteries that arise from the aorta just downstream from the aortic valve
and supply the muscle of the heart (myocardium). They are ordinary
small muscular arteries but critically important because of the tissue
they supply. They are named from their resemblance to a coronarius.
