CARDIOVASCULAR
SYSTEM
Circulation
Blood
Vessels and Structure
Starling’s Law
Venous Return and it’s Mechanisms
Blood Pooling
LEARNING OBJECTIVES
1.
Can I identify the differences between
blood vessels?
2.
Am I able to explain the different
mechanisms of Venous Return?
CIRCULATION
• SYSTEMIC CIRCULATION
• Oxygenated blood from the left ventricle to the
body tissues and deoxygenated blood back to the
right atrium
• PULMONARY CIRCULATION
• Deoxygenated blood from the right ventricle to the
lungs and oxygenated blood back to the left atrium
BLOOD VESSELS AND
STRUCTURE


Arteries are the largest blood vessels, as they
get further away from the heart they reduce in
size to become arterioles and finally into
capillaries (one cell thick to allow gaseous
exchange)
Capillaries then flow into larger venules and
then into even larger veins before entering the
right atrium from either the superior vena
cava (from the upper body) or inferior vena
cava from the lower body
BLOOD VESSELS AND
STRUCTURE

BLOOD VESSELS
ARTERIES transport oxygenated blood away from
the heart and towards tissue/muscles
•

VEINS transport deoxygenated blood back to the
heart
•

This is true with the exception of the Pulmonary Artery
(carries deoxygenated blood)
This is true with the exception of the Pulmonary Vein
(carries oxygenated blood)
CAPILLARIES bring blood directly into contact with
the tissues where O2 and CO2 are exchanged
BLOOD VESSELS AND
STRUCTURE



All blood vessels have 3 layers (apart from singlewalled capillaries)
Arteries and arterioles have a large middle layer of
smooth muscle (involuntary muscle within blood
vessel walls) to allow them to vasodilate (widening
of arteries) and vasoconstrict (narrowing of
arteries) to regulate blood flow
Arterioles have a ring of smooth muscle surrounding
the entrance to the capillary networks to control
blood flow. These are pre-capillary sphincters,
they vasodilate and vasoconstrict to regulate blood
flow
BLOOD VESSELS AND
STRUCTURE


Larger veins have pocket valves to prevent
backflow of blood and direct blood back to
the heart
Venules and veins have a thinner muscular
layer allowing them to venodilate (widening
of veins) and venoconstrict (narrowing of
veins) and a thicker outer layer to help
support the blood that sits within each pocket
valve
STARLING’S LAW



•
STARLING’S LAW
This states that stroke volume is dependent upon venous
return. If VR increases, SV increases. If VR decreases
then SV decreases. If SV increases or decreases, so does
Q. Therefore, VR will determine SV and Q
At rest VR is sufficient to maintain SV and Q to
supply the demand for O2. During exercise the
pressure of blood in the veins is too low to maintain
VR and then SV and Q decrease
Therefore the body needs additional mechanisms to
help blood return to the heart against gravity to
increase VR and so SV
VENOUS RETURN AND IT’S
MECHANISMS





Pocket Valves
•
Prevent backflow of blood and direct it back
to the heart
Muscle Pump
•
Veins are situated between skeletal muscle which help push blood
back to the heart when they contract and relax
Respiratory Pump
•
Pressure changes in the thorax and abdomen during exercise. The
increase in pressure in the abdomen, squeezes large veins in that
area and forcing blood back to the heart
Smooth Muscle
•
Contraction and relaxation of smooth muscle in the middle layer of
veins helps push blood back to the heart
Gravity
•
Blood from the upper body is aided by gravity as it descends to the
heart
BLOOD POOLING




VR requires a force to push the blood back to the heart. If
there is insufficient force then the blood will sit in the
pocket valves in the veins. This is Blood Pooling
At rest gravity, pocket valves and smooth muscle are
enough to maintain VR at rest, but not during or
immediately after exercise
Therefore, the skeletal and respiratory pumps are needed
to maintain VR during exercise and immediately after
exercise
In order for this to happen, an active cool down must take
place to maintain these two pumps and help maintain VR
and redistribute Q to prevent blood pooling
VENOUS RETURN’S IMPACT ON THE
QUALITY OF PERFORMANCE
 Venous Return (VR) is important to
performance as it determines SV and Q
 If SV/Q decreases, oxygen transport to the
working muscles decreases, which reduces
the ability to contract/work aerobically
 The impact on performance is that exercise
intensity has to be reduced or muscles will
have to work anaerobically, which will result
in muscle fatigue.
 A good VR in anaerobic activities will speed
up recovery and therefore allow performers
to work anaerobically for longer.
HOMEWORK

Complete exam questions from handout