Download Distribution of blood flow

Distribution of blood flow
–At rest
• the systemic demand for oxygen
from muscles is low (20%)
• Cardiac Output (Q = SV x HR) is
approximately 5 litres per minute
•HR and BP are at resting levels
•Breathing is at resting levels
Arteriovenous Difference
• a - VO2 diff is the difference in O2
concentration between arteriole blood
venous blood.
– At rest
•
•
•
•
Oxygen in arteries is 20ml / 100ml
Oxygen in Veins is 15 / 100ml
a - VO2 difference is 5ml / 100ml
Oxygen use is approx 25%
During Exercise
• During physical activity, working
muscles demand much more oxygen.
• To supply the demand for oxygen, more
oxygen needs to be breathed in.
• More blood needs to circulate the body
to deliver the extra oxygen.
How?
•
•
•
•
•
Muscle demand for O2 increases
Breathing = More incoming O2
HR x Stroke Volume
= Cardiac Output (Q)
To increase blood O2 distribution to
meet demand
• Blood flow (Q) can increase up to 25
litres per minute.
Arteriovenous Difference
– during exercise
• a - VO2 difference as high as 15ml 18ml / 100ml
• O2 use is approx 75%
• The working muscles are responsible
for this extra O2 use.
Distribution of blood flow
– During exercise
• The body redistributes blood flow according
to the demands for oxygen.
• This is affected by the intensity of the
exercise
• Working muscles during maximal exercise
can take up to 80 - 85% of blood flow!!!
• This can be in excess of 20 litres per minute!!!
However
– Note that
• Actual blood flow to certain organs
hardly changes!!!
– Example
• Brain receives about 750ml per minute
at rest (15%)
• Brain receives about 750ml - 1 litre
during exercise (3 - 4%)
• Why do you think this is???
Cardiac Output at rest
(5l)
Cardiac Output during
exercise (25l)
%
Actual
%
Actual
Liver / Intestines
20-25
1-1.25l
3-5
750ml-1.25
Heart
4-5
200-250ml
4-5
1-1.25l
Kidneys
20
1l
2-4
500ml-1l
Bones / Marrow
3-5
150-250ml
0.5-1
125-250ml
Brain
15
750ml
3-4
750ml-1l
Skin
4-5
200-250ml
Muscles
15-20
750ml-1l
80-85
20 litres +
How does the body control
blood flow?
• Vasoconstriction - a decrease (constriction)
in the diameter of blood vessels, that results
in a decreased blood flow to the area that the
blood vessel supplies.
– This occurs in inactive areas of the body or where
demand for oxygen is lower.
How does the body control
blood flow?
• Vasodilation - an increase in the diameter
(dilation) of a blood vessel, that results in
increased blood flow to the area that the
blood vessel supplies.
– This occurs in the areas of the body that
have an increased oxygen demand, like
the working muscles!
Bibliography
• Smyth et al, (2011) ‘Live it Up 2, VCE
Physical Education Units 3 & 4 (3rd Ed),’
John Wiley & Sons, Queensland.
• Malpeli et al, (2010) ‘ Physical Education VCE
Units 3 & 4 (5th Ed),’ Nelson Cengage
Learning, Victoria.
• Powers & Howley, (2009) ‘Exercise
Physiology; Theory and Application to Fitness
and Performance (7th Ed),’ McGraw-Hill, New
York.