muscle circulation

DR NILESH KATE

MBBS,MDASSOCIATE 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, May 3, 2023

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 REGULATIONMyogenic 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



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



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.



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.



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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