This document discusses skeletal muscle circulation and blood flow regulation. It notes that at rest, skeletal muscle blood flow is relatively low at 2-4 ml/min/100gm but increases up to 20 times during exercise due to arteriole and precapillary sphincter dilation from local metabolites. Blood flow is intermittent during muscle contraction and cessation. Regulation of skeletal muscle blood flow involves auto-regulation via myogenic tone in precapillary vessels, metabolic control from factors like oxygen levels and sympathetic nervous control with both vasoconstrictor and vasodilator fibers.

1. DR NILESH KATE
MBBS,MD
ASSOCIATE PROF
DEPT. OF PHYSIOLOGY
SKELETAL
MUSCLE
CIRCULATION

2. OBJECTIVES
Skeletal muscle circulation.
 Skeletal muscle blood flow –
characteristic features.
 Regulation of flow
 Auto regulation
 Metabolic control mechanism
 Nervous control mechanism.
Wednesday, April 6, 2016

3. SKELETAL MUSCLE BLOOD FLOW –
CHARACTERISTIC FEATURES.
 At rest.
 Blood flow – 2-
4ml/min/100gm.
 Total wt of skeletal
muscle about 30kg so
blood flow – 750-
800ml/min
 Only 20-25% capillary
have flowing blood.
Wednesday, April 6, 2016

4. SKELETAL MUSCLE BLOOD FLOW –
CHARACTERISTIC FEATURES.
 During Exercise.
 Increases to 20
times,50-
80ml/min/100gm –
Exercise Hyperemia.
 Cause – dilatation of
Arteriole & Precapillary
sphincters by local
metabolite
Wednesday, April 6, 2016

5. SKELETAL MUSCLE BLOOD FLOW –
CHARACTERISTIC FEATURES.
 But blood flow–
Intermittent.
 During contraction-
muscle squeezes vessels
– flow stop – again
during relaxation, flow
increases
 Myoglobin – O2
acceptor.
Wednesday, April 6, 2016

6. SKELETAL MUSCLE BLOOD FLOW –
CHARACTERISTIC FEATURES.
 Sustained, severe
contraction >10 sec,
cessation of blood flow,
fatigue & ischemic Pain.
 Also after severe phasic
exercise– flow
decreases slowly
Due to O2 Debt.
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7. REACTIVE HYPERAEMIA.
 Phenomenon by vessel
control blood flow to the
organ after ischemia due to
occlusion.
 Cause – local Hypoxia causes
vasodilatation of arterioles &
precapillary sphincters
 So blood flow exceed the
control level when occlusion
is removed.
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8. Wednesday, April 6, 2016
WHITE VS RED MUSCLE BLOOD
FLOW.
FEATURES WHITE MUSCLE RED MUSCLE
TOTAL MASS 3/4TH
1/4TH
CONTRACTIONS RAPID PHASIC
CONTRACTIONS
STEADY PROLONGED
CONTRACTIONS
ACTION SMALL ACTIONS MAINTENANCE OF
POSTURE
RESTING BLOOD FLOW 2-4ML/MIN/100GM MAY
INCREASE TO 50-80ML
30ML/MIN/100GM
O2 Debt PRONE TO O DEBT NOT PRONE DUE TO
GREATER SURFACE
AREA OF CAPILLARY
BED & RESTING BLOOD
FLOW.

9. REGULATION OF FLOW
 AUTO REGULATION
 METABOLIC CONTROL
MECHANISM
 NERVOUS CONTROL
MECHANISM.
Wednesday, April 6, 2016

10. AUTO REGULATION
 Ability of organ to
adjust its vascular
resistance &
maintain a relatively
constant blood flow
over a range of arterial
pressure.
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11. AUTO REGULATION
Myogenic theory
 Mechanism – Precapillary
Resistance vessels have
high basal Myogenic tone.
 Rise in pressure inside –
stretch induced contraction
of sphincter
 Protect capillaries from
undue rise.
 Mainly in leg muscles &
prevent Pedal oedema.
Wednesday, April 6, 2016

12. METABOLIC CONTROL
MECHANISM
 Muscle contraction
 Increase in metabolic
rate in tissue
 Reduces O2 conc. & rise
in adenosine, K+ ions,
H+ ions, lactic acid CO2
& tissue temperature –
dilatation of arteriole &
precapillary sphincter.
Wednesday, April 6, 2016

13. NERVOUS CONTROL
MECHANISM.
 Skeletal muscle blood
vessels are supplied by
both
 Sympathetic
vasoconstrictors &
sympathetic
vasodilators.
Wednesday, April 6, 2016

14. SYMPATHETIC
VASOCONSTRICTOR CONTROL
 During resting condition –
NA sympathetic nerve
discharge
 At rest – 1 impulses/sec
 Standing 2-3 impulses/sec
 Out of total vascular tone;
mainly by Myogenic tone &
very small part contributed
by Sympathetic
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15. SYMPATHETIC
VASOCONSTRICTOR CONTROL
 During muscular
exercise – Exercise
Hyperemia is
independent of
sympathetic discharge
& is mainly due to
Metabolic factors.
Wednesday, April 6, 2016

16. SYMPATHETIC
VASOCONSTRICTOR CONTROL
 During circulatory shock &
other circulatory stress.
 Muscle capillary load is very
large.
 Sympathetic vasoconstriction
reduces muscle blood flow &
divert blood to the vital
organs.
Wednesday, April 6, 2016

17. SYMPATHETIC VASODILATOE
FIBRES.
 Sympathetic fibers have
Acetylcholine as
neurotransmitter.
 Fibers are activated by
Corticohypothalamic-
reticulospinal pathway.
 Operate during emergency,
mental stress, emotions &
hypothalamic stimulation.
Wednesday, April 6, 2016

18. SYMPATHETIC VASODILATOE
FIBRES.
 Safety valve mechanism
– Prevent sudden rise in
blood pressure at the
beginning of exercise.
 Before exercise even
Thought of exercise –
Increases sympathetic
activity
 Reduce TPR & BP to
safety levels.
Wednesday, April 6, 2016

19. SYMPATHETIC VASODILATOE
FIBRES.
 Stimulation of sympathetic
vasodilator fibers dilates
only arteriole & not
precapillary sphincters so
muscle blood flow not
increases.
 After exercise
precapillary sphincters
dilates by local metabolite
& muscle blood flow
increases.
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20. THANK YOU.
Wednesday, April 6, 2016