BIOC21H3 Lecture Notes - Lecture 7: Tunica Intima, Pulmonary Vein, Coronary Circulation
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Lecture 7-Blood Vessels
Circulatory System
- A closed circuit (mostly) where you have blood flowing by the heart into arteries, passing
through capillaries
Blood Vascular System
1. Pulmonary Circulation-capillaries pump blood to lungs
2. Coronary Circulation-pump blood to heart (lots of capillaries in cardiac myocytes)
3. Systemic Circulation-through system; come back through vena cava
- Blood vessels is the pathway to which blood, oxygen, nutrients, and waste collect
- Helps maintain temperature (muscles generate heat = released into vascular system = blood
travels to surface of skin = to remove as much heat as possible = to cool down core =
thermoregulation)
- Distribution of hormones and immune system
- Structure of blood vessels : artery, vein, capillary depends on what it has to deal with
Arteries
- Deal with higher blood pressure (closer to the heart arteries = has to deal with cardiac output of
blood being pumped out; heart contracts and relaxes so doesn’t deal with high pressure all the
time); release of pulsitle flow
- So need to be able to deal with constant change of pressure; arteries can smooth pressure out
because arteries get thinner (so want lower pressure to prevent rupturing; want a constant
stream rather than on/off flow)
- Not a function of veins
- Walls needs more muscle and elasticity because it needs to be able to expand when pressure is
high and recoil; allows us to smooth out flow (need to have smooth muscle and elasticity)
- One of the ways that smooth muscle can be activated to contract is pressure and pull against it =
contracts back
Veins
- Vessels that return blood to heart (not all is deoxygenated because pulmonary veins are rich in
oxygen)
- Return blood to heart after passing through capillary beds
- Blood is flowing against gravity = need valves that prevents backflow and they themselves will
have a pumping action around them controlled by the muscle (e.g. legs) contraction = expands
sideways and thickens a little bit = compresses veins which creates pressure pushing blood
forward
- Structure of veins (walls) is thinner than arteries because they need to be able to collapse and
compressed to allow blood flow = goes towards heart due to valves
- Blood reservoir because blood flows at slow right about 70% of blood in veins (larger lumen
than artery); thinner wall
General Organization
1. Tunica intima = innermost layer
- Sub endotheilia CT = thin (might not see it); becomes thicker with age
- Internal elastic membrane (wavy layer of material; elastin in blood vessels tend to be contained
in this continuous sheet of elastin = continuous membrane that lines the interior of blood vessel;
has pores in it that will allow diffusion)
- Dark line = border b/w T.intima and T.media (smooth muscle; thickened arteries and think veins)
- External elastic membrane (not as continuous as IEM); connective tissue underneath it which is
relatively dense which will connect blood vessel to other vessels or other organs
- Innermost part of is endothelium (squamous cell = fairly inactive = most part is true)
- One of the main functions in blood vessel is to act as a boundary b/w components in blood
stream and underlying tissue
o Endothelium is non-thrombogenic = resists the formation of blood clots; important
because platelets activated by contact with collagen; the moment you have damage to
endothelium, blood clotting begins = begins process of healing
o Epithelia cells have ability to allow transport and diffusion of oxygen and nutrients to
feed tissue of endothelium
o Pores in IEM to allow diffusion of nutrients to reach muscle cell
o Endothelial activation = happens when there is actual damage; changes function
completely (pro thrombogenic); release factors that increase clotting; produces
adhesive molecules and molecules on surface that allows WBCs to stick to ot; produce
cytokins = signalling molecules that will direct WBCs to damaged area; produce
signalling molecules hat will cause muscle constriction (muscle in T.media will contract)
causes lumen in blood vessels to become smaller so prevent excessive bleeding
- Sub-endothelia CT
o Fibroblasts; but main cell type is smooth muscle (have divided within T.media and then
travel across pores of IEM and into sub-endothelial CT)
o Cholesterol accumulates in T.media in SECT. initially, macrophages will internalize
cholesterol and store it but macrophage will look; eventually smooth muscle fibres will
accumulate foam cells as well; eventually calcium will be deposited as well = streaks
within walls of arteries; tend to make it more stiff and rigid preventing arteries to be as
expansive and elastic as before = hardening of blood vessels = high blood pressure
(lumen size decreases which increase vascular resistance = atherosclerosis)
o Over time we accumulate endothelia tissue (more fibres get build up); Tunica intima
grows in size = lumen size decreases = increases blood pressure (tends to generate more
vascular resistance on surface of endothelium = small damage to it which might cause
some blood clots = attached to sides of blood vessels which will then detach to circulate
and lodge itself in some blood vessel and so blood stops flowing to that part; easily
broken up via enzymes but when we have a larger blood clot that travels to wrong place
= heart attack, stroke; tunica intima because CT comes thicker with age and lumen
becomes smaller = increases with age (more at risk)
- IEM
o Boundary line between T.I. and TM
o Continuous sheet of thick layer elastic fibre
o Pores in it to allow diffusion from Ti to TM
o If you see it in a vessel = most likely looking at artery because only LARGE veins show
this (all arteries have this even smallest ones); IEM allows blood vessel allows it recoil
back to original shape (veins don’t so don’t require as much elastic)
o
2. Tunica media = middle