muscle circulation
TRANSCRIPT
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.
Tuesday, May 2, 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.
Tuesday, May 2, 2023
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
Tuesday, May 2, 2023
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.
Tuesday, May 2, 2023
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.
Tuesday, May 2, 2023
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.
Tuesday, May 2, 2023
Tuesday, May 2, 2023
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.
Tuesday, May 2, 2023
AUTO REGULATION Ability of organ to
adjust its vascular resistance & maintain a relatively constant blood flow over a range of arterial pressure.
Tuesday, May 2, 2023
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.
Tuesday, May 2, 2023
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.
Tuesday, May 2, 2023
NERVOUS CONTROL MECHANISM.
Skeletal muscle blood vessels are supplied by both
Sympathetic vasoconstrictors & sympathetic vasodilators.
Tuesday, May 2, 2023
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
Tuesday, May 2, 2023
SYMPATHETIC VASOCONSTRICTOR CONTROL
During muscular exercise – Exercise Hyperemia is independent of sympathetic discharge & is mainly due to Metabolic factors.
Tuesday, May 2, 2023
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.
Tuesday, May 2, 2023
SYMPATHETIC VASODILATOE FIBRES.
Sympathetic fibers have Acetylcholine as neurotransmitter.
Fibers are activated by Corticohypothalamic-reticulospinal pathway.
Operate during emergency, mental stress, emotions & hypothalamic stimulation.
Tuesday, May 2, 2023
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.
Tuesday, May 2, 2023
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.
Tuesday, May 2, 2023
THANK YOU.
Tuesday, May 2, 2023