Mechanism of the regulation of blood flow Mechanisms

Mechanism of the regulation of blood flow

Mechanisms for regulation of blood flow Neural or Hormonal/Extrinsic regulation Local /Intrinsic regulation MYOGENIC regulation METABOLIC Regulation

Local regulation of blood flow Autoregulation Active Hyperemia Reactive Hyperemia

Myogenic mechanism • If the pressure within a vessel is suddenly increased, the vessel responds by constricting. (Or) • When the VSM is stretched it contracts. • Mainly based on stretch activated cation channel.

Arterial pressure� Arterioles are stretched VSM in the vessel wall contracts Causing constriction of VSM (Resistance�)

Autoregulation • It is defined as the intrinsic ability of an organ to maintain a constant blood flow despite changes in perfusion pressure.

Metabolic mechanism • O 2 delivery to a tissue can be matched to the O 2 consumption by altering the RESISTANCE of the arterioles, which in turn alters blood flow.

Metabolic activity � Production of different vasodilator metabolites � Vasodilation of arterioles Which decreases resistance Increases flow To meet increased demand for O 2 Eg: CO 2, H+, K+, Lactate, adenosine

Active hyperemia • Concept that states that the blood flow to an organ is proportional to it’s metabolic activity • Blood flow increases because the increased oxygen consumption of during muscle contraction stimulates the production of vasoactive substances that dilate the resistance vessels in the skeletal muscle.

You exercise a LOT Metabolic activity in the skeletal muscles � Production of vasodilator metabolites increases Metabolites cause local VASODILATION of the skeletal m arterioles Thus local blood flow � Increasing O 2 delivery to to meet increased demand

Reactive hyperemia • Increase in blood flow in response or reacting to a prior period of decreased blood flow or • Reactive hyperemia is the transient increase in organ blood flow that occurs following a brief period of ischemia (e. g. , arterial occlusion) • The longer the period of occlusion, the greater the metabolic stimulus for vasodilation leading to increases in peak reactive hyperemia and duration of hyperemia.

Organs without AUTOREGULATION Eg: SKIN • MYOGENIC MECHANISM- suppressed by NO • METABOLIC MECHANISM- very low, due to low metabolism.

Neuronal regulation • Action of the sympathetic ns on vascular smooth muscles • And action of vasoactive substances eg histamine, bradykinin and prostaglandins • Mainly in the skin and GIT

alpha receptors (cause vasoconstriction) Some SNS terminal are cholinergic (Cause vasodilation) Sympathetic system Adnergic Beta receptors(Cause vasodilation)

Adrenaline ANP Hormonal regulation Serotonin and Bradykinin Prostagladins Angiotensin

Coronary circulation • Mainly controlled by local metabolites (Factors – hypoxia and adenosine) • Sympathetic innervation small role

Cerebral circulation • Almost entirely controlled by local metabolites. • Exhibits all three examples of local reg • Most imp vasodilator is CO 2 • PCO 2 � H+ � p. H� Causes vasodilation in cerebral arterioles. Blood flow �

Pulmonary circulation • O 2 is the most important • The effect is OPPOSITE • Hypoxia causes local VASOCONSTRICTION. (Blood is shunted away from the poorly ventilated areas as it would be ‘wasted’ and instead flown toward well ventilated areas where gas exchange can take place)

Renal circulation • It is maintained by autoregulation • It is independent of sympathetic innervation • FUN FACT!! It is retained even when the kidney is denervated(transplanted kidney)

Skeletal muscle circulation • At rest Sympathetic activity Vasoconstriction(alpha) Resistance � Blood flow � • During exercise Local metabolites Metabolites(Lactate, adenosine, K+) All three examples of local reg

Skin circulation • Dense sympathetic innervation • Body temp� sympathetic centers for cutaneous blood flow are INHIBITED • Vasoactive substances- HISTAMINE

References and sources • http: //www. cvphysiology. com/Blood%20 Flow/BF 003 • http: //www. wikilectures. eu/w/Regulation_Mechanisms_of_Blood_Fl ow_in_Organs • Constanzo • Guyton’s