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Blood Vessels
Circulation
• All blood is constantly moving
along the circulatory system
• The most vital nutrient which is
used most quickly is oxygen, so
blood is usually divided into
oxygenated and deoxygenated
blood in graphs
– Realistically even “deoxygenated”
blood usually still has about 2550% oxygen load
Road Analogy
• If cells are houses and must receive
service via streets, the largest blood
vessels are freeways
• Note that like a freeway, major
blood vessels such as arteries and
veins do NOT deliver oxygen or
nutrients but rather move blood
quickly to different parts of the
body
• Almost all nutrient and waste
exchange happens in small, leaky
blood vessels called capillaries
Arteries and Veins
• Arteries move blood away
from the heart
• Arteries in the body have high
pressure and are bright red from the
oxygen content
• Veins move blood towards the
heart and have very low
pressure
– Deoxygenated blood is NOT
blue, but it is dark, and the vein
coverings make it appear blue
Blood Vessel Sizes
• Main arteries lead directly away
from the heart before branching
into arterioles
• Arterioles branch further to
become capillaries, then rejoin
to become venules
• Venules combine to form veins
– Many veins have valves to
prevent backflow since there is so
little blood pressure
– Blood is moved through veins by
muscle movement, which is why
stretching feels good
Capillaries
• All tissues (except cartilage,
epidermis and the lens of
the eye) have capillaries
that blood flows into from
the arteries
• Capillaries are very thin and
leaky so nutrients can
diffuse out of the blood into
the surrounding tissues
• Also allows wastes to diffuse
into the blood
Anatomy of Blood Vessels
• Major blood vessels (arteries and
veins) have smooth muscle and
coverings
– Smooth muscle helps squeeze
blood through and constricts
when the blood vessel is damaged
• All blood vessels have a smooth
inner lining called endothelium
which reduces
friction/turbulence
• The inner space of a vessel is
called the lumen
Blood Flow Regulation
• When a blood vessel increases in
diameter it is said to vasodilate
– Increases blood flow to an area
– Provides additional nutrients, helps
be more active and also helps heal
damaged tissue
• When a blood vessel decreases in
diameter it is said to vasoconstrict
– Cuts off blood supply to ensure
more blood goes elsewhere, or to
prevent bleeding
Variable Flow
• Capillaries can also be opened
and closed to change blood
flow to different organs
– Blood flow to skin = “flush” to
help cooling
– Blood flow to muscles =
adrenaline rush
– Blood flow to digestive system =
food coma
• Much of this is accomplished
with smooth muscles around
the start of the capillaries,
called precapillary sphincters
Blood Pressure
• Blood pressure decreases as the
blood travels through arteries,
capillaries, and veins
– The more viscous the blood (from
more RBCs) the faster the pressure
drops
• The blood pressure at the start of
the capillary squeezes plasma into
the tissues (this is called capillary
blood pressure)
– The lower pressure at the other
end of the capillary sucks fluid back
in, which is called blood colloid
osmotic pressure
Blood Volume
• Two hormones work against each
other to balance blood pressure:
– Aldosterone (secreted by adrenal
cortex) causes sodium retention
and therefore water retention
– ANP (atrial natriuretic peptide) is
secreted by the atria of the heart
and promote excretion of salt and
water by the kidneys
– Question: what does ADH do?
• Note that the heart literally asks
the kidneys to pee more when it
gets overworked
Obesity and Blood Pressure
• Clearly junk food is “unhealthy”
but why exactly?
– Extra calories are stored as excess
body fat, increasing blood volume
– Extra cholesterol above what’s
needed can form plaques that can
block blood vessels
– Extra sodium increases blood
volume and water retention
• These factors may, as a pattern,
lead to obesity, which is strongly
correlated with heart disease
Hooray cheerful weekend!
• Next week is the exam week!
• Don’t forget the online quiz!!!!1