More of the Circulatory
System
Things to Consider


The heart of a blue
whale is the size of
a Volkswagon Bug!
Most kids could use
its arteries as
waterslides!
Blood Supply to the Heart
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Coronary arteries – first two branches of
aorta supply blood to myocardium
Coronary veins – run parallel to c.a., drain
blood that has passed through myocardial
capillaries (and thus deoxygenated)
Coronary sinus – enlarged vein combining
other coronary veins that empties into right
atrium
Cardiac Cycle
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Two actions made of combinations of
chamber contraction and relaxation
The first action requires atrial systole
(contraction) and ventricle diastole
(relaxation)

Blood is forced out through cuspid valves
into ventricles as atria empty
Cardiac Cycle cont.
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The second action has atrial diastole
and ventricle systole

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Blood is forced out through pulmonary
and aortic valves, while atria fill w/ blood
Cardiac cycle – series of events
described above creating a complete
heartbeat
Heart Sounds

Lubb-dupp
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Lubb portion during ventricular
contraction when A-V valves close
Dupp portion during ventricular relaxation
when pulmonary and aortic valves close
Cardiac Conduction System

Sinoatrial node (S-A node) –
conducts impulse for atrial contraction;
rhythmic activity

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As atria contract, impulse passes along
fibers to atrioventricular node (A-V
node)
A-V node delays impulse (allowing time
for atria to fully contract and empty)
before conducting it to A-V bundle
Cardiac Conduction cont.

A-V bundle conducts impulse to
Purkinje fibers which cause
ventricles to contract forcing blood
away from heart
Arteries and Arterioles

Arteries carry blood AWAY from the
heart
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Subdivide into thinner tubes  branched
arterioles
Tunica interna – inner most layer that
prevents blood from clotting by providing
smooth surface (5)
Arteries cont.
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Tunica media – middle layer making up
bulk of wall, made of smooth muscle
fibers and a thick layer of elastic CT (2)
Tunica externa – thin layer of CT that
attaches artery to surrounding tissues (4)
Arteries cont.
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Vasoconstriction – smooth muscles
contract to reduce diameter of vessel
thus increasing BP
Vasodilation – smooth muscles relax
to dilate vessel thus reducing BP
Capillaries

Capillaries – smallest in diameter
blood vessel, connecting smallest
arterioles to smallest venules

Gases, nutrients, and metabolic by
products are exchanged through diffusion,
filtration, and osmosis
Veins and Venules

Veins carry blood back towards the
heart
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Venules are smaller vessels that combine
to form veins
Layers similar to that of arteries except
for middle layer that is poorly developed
Why?
Veins cont.
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Blood is under much lower pressure
Some veins (especially in limbs) contain
flap-like valves to prevent backflow
Blood Pressure

Force blood exerts against the inner walls of
blood vessels

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Arterial pressure rises and falls
corresponding to cardiac cycle

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Human heart creates enough pressure to squirt
blood 30 feet!
Systolic pressure – max pressure when
ventricles contract
Diastolic pressure – lowest pressure when
ventricles relax
Pulse – caused by stretch and recoil of
arterial wall
Factors Affecting BP
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Stroke volume – volume of blood
discharged from left ventricle w/ each
contraction
Cardiac output – blood output per
minute (mL/min)  multiply stroke
volume (mL) by heart rate (b/min)
BP varies w/ cardiac output, thus
increases in heart rate or stroke volume
results in an increase in output 
increase in BP
Factors cont.
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Blood volume – sum of formed
elements and plasma volumes in the
vascular system
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BP directly proportional to blood volume
 increase in volume = increase in BP
Peripheral resistance – friction
between blood and walls of blood
vessels
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Constriction of arteries leads to increase
in per. resistance and an increase in BP
Factors cont.
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Viscosity – ease at which a fluid’s
molecules flow past one another

Greater viscosity  greater resistance to
flowing  increase in BP
Paths of Circulation
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Pulmonary Circuit – vessels that carry
blood from the heart to the lungs and
back to the heart
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Deoxygenated blood taken to lungs and
returns to heart oxygenated
Systemic Circuit – vessels that carry
blood from the heart to all other parts of
the body and back again

Freshly oxygenated blood travels to tissues
and returns to heart deoxygenated
Arterial System
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Aorta – largest diameter artery in
body
Table 13.30 and Fig. 13.28 show
principal branches of aorta
Fig. 13.32 shows major vessels of
arterial system
(We can take notes on where each
supply blood to if you want)
Venous System

Veins generally run parallel to arteries
and thus often have the same name

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Ex. Renal artery (to the kidney)…renal
vein (away from the kidney)
Fig. 13.35 and 13.36 show major
vessels of venous system