MUSCLE CIRCULATION

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

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

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.

 During Exercise.
 Increases to 20
times,50-
80ml/min/100gm –
Exercise Hyperemia.
 Cause – dilatation of
Arteriole & Precapillary
sphincters by local
metabolite

 But blood flow–
Intermittent.
 During contraction-
muscle squeezes vessels
– flow stop – again
during relaxation, flow
increases
 Myoglobin – O2
acceptor.

 Sustained, severe
contraction >10 sec,
cessation of blood flow,
fatigue & ischemic Pain.
 Also after severe phasic
exercise– flow
decreases slowly
Due to O2 Debt.

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.

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.

REGULATION OF FLOW
 AUTO REGULATION
 METABOLIC CONTROL
MECHANISM
 NERVOUS CONTROL
MECHANISM.

AUTO REGULATION
 Ability of organ to
adjust its vascular
resistance &
maintain a relatively
constant blood flow
over a range of arterial
pressure.

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.

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.

NERVOUS CONTROL
MECHANISM.
 Skeletal muscle blood
vessels are supplied by
both
 Sympathetic
vasoconstrictors &
sympathetic
vasodilators.

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

SYMPATHETIC
 During muscular
exercise – Exercise
Hyperemia is
independent of
sympathetic discharge
& is mainly due to
Metabolic factors.

SYMPATHETIC
 During circulatory shock &
other circulatory stress.
 Muscle capillary load is very
large.
 Sympathetic vasoconstriction
reduces muscle blood flow &
divert blood to the vital
organs.

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

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.

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.

THANK YOU.

MUSCLE CIRCULATION

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