Vascular Physiology Qiang XIA (夏强), PhD Department of Physiology Room C518, Block C, Research Building, School of Medicine Tel: 88208252 Email: firstname.lastname@example.org
Lecture Outline • Functional parts of blood vessels • Hemodynamics • Arterial blood pressure • Microcirculation • Venous pressure and venous return • The lymphatic system
Functional parts of blood vessels • Elastic vessels (Windkessel vessels) • （弹性血管） • Resistance vessels (Precapillary resistance vessels)（阻力血管） • Exchange vessels（交换血管） • Capacitance vessels（容量血管） • Distribution vessels（分布血管） • Shunt vessels（短路血管）
Hemodynamics（血流动力学） • Blood flow Q= DP/R = (P1-P2)/R
Q: cardiac output, 5 L/min R: total peripheral resistance PA: aortic pressure Q= PA/R
Resistance of blood flow Poiseuille Law: Q=pDPr4/8hL h: viscosity r: radius of the vessel L: length of the vessel R= 8hL/pr4 Q= DP/R Jean Louis Marie Poiseuille \pwä-'zəi\ (April 22, 1799 - December 26, 1869) was a French physician and physiologist. Poiseuille was born in Paris, France. From 1815 to 1816 he studied at the École Polytechnique in Paris. He was trained in physics and mathematics. In 1828 he earned his D.Sc. degree with a dissertation entitled Recherches sur la force du coeur aortique. He was interested in the flow of human blood in narrow tubes.
Arterial blood pressure（动脉血压） Arteries
Systolic pressure (SP，收缩压): the maximum arterial pressure reached during peak ventricular ejection Diastolic pressure (DP，舒张压): the minimum arterial pressure just before ventricular ejection begins Pulse pressure (PP，脉压): the difference between SP and DP Mean arterial pressure (MAP，平均动脉压): the average pressure in the cardiac cycle (=DP+1/3PP)
To estimate systolic and diastolic pressures, pressure is released from an inflatable cuff on the upper arm while listening as blood flow returns to the lower arm. 查DynaMed
Classification of blood pressure for adults age 18 years and older The classification chart is based on adults, aged 18 and older, who are not taking high blood pressure medicines and who are not acutely ill. If systolic and diastolic measurements fall into different categories, the higher category should be used to classify the person's blood pressure status.
Factors affecting arterial blood pressure • Stroke volume • Heart rate • Peripheral resistance • Elastic vessels • Blood volume Ventricular ejection
Q: cardiac output (CO) R: total peripheral resistance (SVR) PA: aortic pressure (MAP) Q= PA/R MAP = CO SVR
3 2 1 4 5
The blood moved in a single heart contraction stretches out the arteries, so that their recoil continues to push on the blood, keeping it moving during diastole. Movement of blood into and out of the arteries during the cardiac cycle
In response to the pulsatile contraction of the heart: pulses of pressure move throughout the vasculature, decreasing in amplitude with distance
Microcirculation（微循环） Function: Transfer of substances between blood & the tissues
Structure of microcirculation A-V shunt
2 1 3 A-V shunt 4 5 3 pathways • Circuitous channel (Nutritional channel)（营养通路）
2 1 3 A-V shunt 4 5 • Thoroughfare channel（直捷通路）
2 1 3 A-V shunt 4 5 • Arteriovenous shunt (A-V shunt)（动-静脉短路）
Arterioles（微动脉） • Two major roles: • To be responsible for determining the relative blood flow in individual organs at any given MAP • To be a major factor in determining MAP
Arterioles • Small precapillary resistance vessels (10-50 μ) composed of an endothelium surrounded by one or more layers of smooth muscle cells • Richly innervated by sympathetic adrenergic fibers and highly responsive to sympathetic vasoconstriction via both α1 and α2 postjunctional receptors • Represent a major site for regulating systemic vascular resistance • Rhythmical contraction and relaxation of arterioles sometimes occurs (i.e., spontaneous vasomotion) • Primary function within an organ is flow regulation, thereby determining oxygen delivery and the washout of metabolic by-products • Regulate, in part, capillary hydrostatic pressure and therefore influence capillary fluid exchange
Dynamic adjustments in the blood distribution to the organs is accomplished by relaxation and contraction of circular smooth muscle in the arterioles.
Local Control of Blood Flow • The mechanism independent of nerves or hormones by which organs and tissues alter their own arteriolar resistances, thereby self-regulating their blood flows • Active hyperemia（主动充血） • Flow autoregulation（血流自身调节） • Reactive hyperemia（反应性充血） • Local response to injury（对损伤的局部反应）
Local control of organ blood flow Active hyperemia and flow autoregulation differ in their cause but both result in the production of the same local signals that provoke vasodilation.
Reactive hyperemia – When an organ or tissue has had its blood supply completely occluded, a profound transient increase in its blood flow occurs as soon as the occlusion is released
Response to injury – Tissue injury causes a variety of substances to be released locally from cells or generated from plasma precursors. These substances make arteriolar smooth muscle relax and cause vasodilation in an injured area
Extrinsic Control • Sympathetic nerves（交感神经） • Parasympathetic nerves（副交感神经） • Noncholinergic, nonradrenergic autonomic neurons (NO or other noncholinergic vasodilator substances)（NANC） • Hormones (epinephrine, angiotensin II, vasopressin, atrial natriuretic peptide)
Sympathetic stimulation of alpha-adrenergic receptors cause vasoconstriction to decrease blood flow to that location. Sympathetic stimulation of beta-adrenergic receptors lead to vasodilation to cause an increase in blood flow to that location.
ANGII can be produced directly by conversion of angiotensinogen by the tissue plasminogen activator (tPA), cathepsin G and tonin or by hydrolysis of angiotensin I by chymase and cathepsin G. CAGE = chymostatin-sensitive angiotensin II-generating enzyme
Endothelium-derived vasoactive substances • Vasodilator factors • PGI2 – prostacyclin（前列环素） • EDRF (endothelium-derived relaxing factor, nitric oxide) • EDHF (endothelium-dependent hyperpolarizing factor)
The 1998 Nobel Prize in Physiology or Medicine Nitric oxide as a signaling molecule in the cardiovascular system Louis J Ignarro Ferid Murad Robert F Furchgott