Circulation in parallel

	Circulation in series

	Two important hemodynamic principles

	Poiseuille-Hagen Law: Flow = (P1-P2) πr4/8ηL R = (P1-P2)/Flow = 8ηL/Nπr4 Pa-Pv = CO x TPR Cardiac output = Heart rate x Stroke volume Total peripheral resistance = Blood viscosity x Vascular resistance

	Capacity C = V/P. Capacitance or Compliance Cd = ΔV/ΔP Artery has low capacity and vein has high capacity. Arterial capacitance = Stroke volume/Pulse pressure

	Diastolic pressure ~ Mean arterial pressure Systolic pressure = Diastolic pressure + Pulse pressure Pulse pressure = Stroke volume/Arterial capacitance Mean arterial pressure = Cardiac output x Total peripheral resistance Cardiac output = Heart rate x Stroke volume Total peripheral resistance = Blood viscosity x Vascular resistance

	Application of Poiseuille-Hagen Law in human circulation: Determinants of mean arterial pressure

	Control of blood pressure consists of efferent system, afferent system, and the integrating center in medulla

	Pathways how the reflex control maintains the constancy of arterial blood pressure: an example of homeostatsis.

	Etiology of syncope

	Orthostatic hypotension Venous pooling decreases venous return, decreases stroke volume, decreases cardiac output, decreases mean arterial pressure, increases sympathetic activation, increases heart rate/increases cardiac contractility/venoconstrction/arteriolar constrction, increases blood pressure.

	Carotid sinus syncope Stimulation of sinus nerve activates parasympathetic nerves and inhibits sympathetic nerves.

	Vasovagal syncope Vasodilation from activating the sympathetic cholinergic fibers in blood vessels of skeletal muscle Bradycardia from activating the vagal nerve