Transcript The Vascular System SJW

The Vascular System
Blood consists of blood cells and platelets floating in plasma,
8% of body weight:
Plasma makes up 55% of blood volume
Red blood cells contain iron-rich protein called haemoglobin,
which combines with oxygen and transports it in blood.
White blood cells protect the body by fighting infection and
disease.
Platelets are responsible for clotting the blood.
KEY FUNCTIONS OF BLOOD
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TRANSPORTATION of:
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oxygen
carbon dioxide
waste products of respiration
food fuels, vitamins, minerals
plasma
hormones
Blood vessels
Arteries, arterioles,
venules and veins all
have a similar structure.
Vessels
Arteries
Arterioles
Structure and Function
Vessels
Arteries
Arterioles
Structure and Function
Carry blood away from heart, further from heart they get
smaller (Arterioles)
 Carry blood at high pressure
Aorta is main artery
 Walls made up of elastic fibres that enable them to
stretch
 Generate wave of pressure (pulse)
 They can Vasoconstrict, reducing diameter to reduce
amount of blood flow to inactive organs
 Can also relax the elastic fibres to Vasodilate,
increasing diameter for more O2 to reach muscles
This mechanism of blood redistrubution is called
Vascular Shunt
Arteries have No Valves
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Vessels
Veins
Venules
Structure and Function
Blood from capillaries is transported back towards
the heart via veins and venules
Carry deoxygenated blood back to heart at low
pressure
Less elastic, but involuntary muscle help return
blood
Pocket valves exist in veins which aid return of
blood to heart, ensuring there is no backflow
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Vessels
Capillaries
Structure and Function
Blood from arterioles enter a network of capillaries
that surround the tissues
 Walls are just one cell in thickness so diffusion
distance is short for oxygen and other nutrients
 Narrow diameter, blood flow is slow, maximising
diffusion
Vast number of capillaries, huge surface area
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VENOUS RETURN
Gravity
Respiratory
pump
Venous
Return
Smooth
muscle
in veins
Skeletal
muscle
pump
Pocket
Valves
Venous Return Mechanism
VENOUS RETURN is affected by :
SKELETAL MUSCLE PUMP
 Walls of veins are thin and contraction of
muscles squeeze and pump blood back
to heart
 contraction of skeletal muscle exerts
pressure on veins forcing blood to
flow towards the heart
 backflow is prevented by pocket valves
Venous Return Mechanism
POCKET VALVES
 These exist in veins which snap shut, ensuring no backflow
SMOOTH MUSCLE WITHIN VEINS
 Located in the walls is smooth muscle to squeeze the blood back to the
heart
 Pre-capillary sphincters regulate blood flow into capillaries by narrowing or
opening
RESPIRATORY PUMP
 Increase rate and depth of breathing create pressure in abdomen which
compresses veins and squeeze blood in veins
 blood moves up from compressed high pressure (in abdomen) to low
pressure (in thorax)
 during expiration, pocket valves prevent backflow of blood into abdomen
GRAVITY
 In the upper body, gravity assists the flow
During exercise
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Venous return mechanism is
particularly important at the start of
exercise in order to increase stroke
volume and cardiac output.
Blood Pressure & Blood Flow
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Blood pressure is the force exerted by the
blood against the blood vessel wall.
Ejection of blood by the ventricles contracting
creates a high pressure pulse of blood, which
is systolic pressure.
The lower pressure as the ventricles relax is
known as the diastolic pressure.
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During exercise, changes in blood pressure occur,
but these depend on the type and intensity of the
exercise being performed.
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Systolic pressure increases during aerobic
exercise due to an increase in cardiac output,
whilst diastolic pressure remains constant
Blood Velocity
The velocity of blood flow changes as it passes
from one type of blood vessel to another
(affected by the diameter of the blood vessels).
The velocity is related to the force with which the
blood is pumped and the cross-sectional area
of the vessels the blood is passing through.
The smaller the cross-sectional area, the faster
the blood flows (water hose effect).
Blood viscosity describes the thickness of the
blood. If high then blood does not flow quickly
Vascular Shunt mechanism
-Redistribution of blood during exercise
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The vascular shunt mechanism is regulated by the process of
vasomotor control (located in medulla oblongata)
As we exercise, the destination of blood flow changes dramatically.
Blood flow can be diverted away from non-essential tissues and
organs and directed to working muscles
During exercise muscles gain 85-90% of total blood flow
Destination
Rest
Maximal exercise
Muscle
20%
88%
Brain
15%
3%
Heart
5%
4%
Skin
10%
3%
Liver & Intestines
30%
1%
Kidneys
20%
1%
Redirection is important to:
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Increase blood supply to the working muscles
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Provides muscles with fuels (glucose and fatty acids)
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Removes CO2 & lactic acid
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Maintains body temperature
Copy Fig. 4.16 The redistribution of blood flow during
exercise
Vasomotor control
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Chemical changes in the blood are detected by
Chemoreceptors which inform the vasomotor centre
to stimulate the sympathetic nerves
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Sympathetic nerves will cause vasoconstriction of
arterioles and pre-capillary sphincters supplying
non-essential muscles and organs
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At same time vasodilation will supply more blood to
the active working muscles
Putting it all together
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Draw a flow diagram using Fig. 4.20 of what
happens to the cardiovascular system when
we exercise, page 74
Training effects upon the vascular system
Page 79. Draw a revision diagram outlining
the long term effects of exercise on the
vascular system
CARDIAC HYPERTROPHY
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REGULAR AEROBIC TRAINING
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results in hypertrophy of the cardiac muscle, meaning that the
muscle becomes larger and stronger
this means that the heart pumps a larger volume of blood out
per beat, hence the stroke volume is larger
this is termed bradycardia and has the consequence of
producing a resting HR below 60 bpm
at rest, a bigger stronger heart pumps more blood out per beat
hence resting heart rate decreases, with the net effect of an
unchanged cardiac output
highly trained sportspeople tend to have resting heart rates of
well below 60 bpm
during maximum exercise, an increase in heart rate, coupled
with an increase in stroke volume, results in an increase in
cardiac output
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EFFECTS OF EXERCISE ON THE CARDIOVASCULAR SYSTEM
increase in
blood volume
and blood cells
reduced
resting heart
rate
increased
heart stroke
volume
bigger /
stronger heart
increased
elasticity of
muscle in
arterial walls
EFFECT OF
EXERCISE ON THE
CARDIOVASCULAR
SYSTEM
improved
blood flow to
heart muscle
balance of
triglycerides
and cholesterol
improved
resting blood
pressure
lowered
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Complete questions at the back of the Heart
stapled booklet.
Make sure you have a complete glossary of
terms for the Heart
Revision of Chapters 1-4 work covered so far
– use the revision handout for the level of
understanding