Lecture 4 - Regulation of Vascular Function 1 Flashcards
Layers of the heart?
tunica adventitia (C.T), tunica media (smooth muscle + external elastic lamina) and tunica intima (endothelium and internal elastic lamina)
Extrusion of fluid?
when capillary hydrostatic pressure (Pc) exceeds tissue pressure (Pt) then fluid extrudes from the vessel, reduced precapillary R increases post-capillary R leading to extrusion
Absorption of fluid?
when Pt exceeds Pc, also increased precapillary R decreases post-capillary R
Autoregulation definition?
intrinsic tendency of an organ to maintain constant blood flow despite changes in perfusion pressure; cutaneous little effect, cerebral high
Autoregulation mechanism?
constriction of vessels keeps flow constant despite changes in perfusion pressure, artery reflects a correction when pressure rises or falls
Reactive hyperaemia?
after vessel is occluded, blood flow rises above pre-occlusion level for a period approx. proportionl to duration of occlusion
Myogenic hypothesis?
increased perfusion pressure increases transmural pressure distending vessel wall, activates stretch-sensitive membrane ion channels and depolarises VSM cells causing contraction
Metabolic hypothesis?
A rise in perivascular metabolites from an exercising muscle (H+ from lactic acid, K, Adenosine) causes the vessel to dilate allowing greater blood flow; potent effect on pre capillary but not post-capillary vessels
Endothelial control?
increased perfusion pressure increases stress on endothelium, NO released acts on VSM to increase intracellular cGMP, relaxing VSM through reduced intracellular Ca, hyperpolarisation, and reduced interaction between myosin and actin
Integrated model of local control?
responsiveness to pressure and metabolites gradual up to small arterioles, responsiveness to flow drops at large arterioles, ATP released by RBC at low pO2 triggers a wave of vasodilation upstream via endothelium
