2. OBJECTIVES
Skeletal muscle circulation.
Skeletal muscle blood flow –
characteristic features.
Regulation of flow
Auto regulation
Metabolic control mechanism
Nervous control mechanism.
Thursday, March 31, 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.
Thursday, March 31, 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
Thursday, March 31, 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.
Thursday, March 31, 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.
Thursday, March 31, 2016
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.
Thursday, March 31, 2016
8. Thursday, March 31, 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.
Thursday, March 31, 2016
10. AUTO REGULATION
Ability of organ to
adjust its vascular
resistance &
maintain a relatively
constant blood flow
over a range of arterial
pressure.
Thursday, March 31, 2016
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.
Thursday, March 31, 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.
Thursday, March 31, 2016
13. NERVOUS CONTROL
MECHANISM.
Skeletal muscle blood
vessels are supplied by
both
Sympathetic
vasoconstrictors &
sympathetic
vasodilators.
Thursday, March 31, 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
Thursday, March 31, 2016
15. SYMPATHETIC
VASOCONSTRICTOR CONTROL
During muscular
exercise – Exercise
Hyperemia is
independent of
sympathetic discharge
& is mainly due to
Metabolic factors.
Thursday, March 31, 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.
Thursday, March 31, 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.
Thursday, March 31, 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.
Thursday, March 31, 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.
Thursday, March 31, 2016