Vascular disease are responsible for some of the most common and lethal conditions afflicting mankind. Although most clinically significant disorders involve arterial lesions, venous pathologies also can wreak havoc. Vascular disease develops through two principal mechanism：

·Narrowing or complete obstruction of vessel lumina,occurring?either?progressively(e.g.?by?atherosclerosis) or acutely(e.g.?by thrombosis?or?embolism)

·Weakening?of?vessel?walls, causing dilation and?rupture.

血管疾病是危害人類健康最常見原因，也是常見的死亡原因。大多數(shù)具有臨床意義的血管疾病為動脈病變，但是靜脈病變同樣可以肆虐人體。血管疾病通過這兩種主要的機(jī)制發(fā)作：

·血管腔的狹窄或完全阻塞，通常為進(jìn)行性（血管硬化）或急性（血栓形成或栓塞）發(fā)作。

·血管壁變得薄弱，導(dǎo)致擴(kuò)張和破裂。

STRUCTURE?AND?FUNCTION OF?BLOOD?VESSELS

Blood?vessels are fundamentally all tubes?composed of smooth muscle cells (SMCS)?and extracellular?matrix(ECM),?with?an?inner luminal face?covered by?a continous lining?of endothelial cells（ECs).?However, the?relative amounts of?SMCs and?ECM?, and?the properties of the?ECs, vary?throughout?the?vasculature depending on?unique functional?needs.?To accommodate pulsatile flow?and higher?blood pressures,?arterial walls are?thicker than veins and?invested with several reinforcing layers of?SMCs.?As arteries narrow to?arterioles?,the?ratio of wall?thickness to?lumen?diameter increases?to allow more?precise?regulation of intervascular pressure.?Veins?, on the?other hand ,are?thin-walled vessels with?high?capacitance.?To facilitate?maximal?diffusion, capillaries?are?essentially single-cell linings of?ECs?lying on a basement?membrane.

血管的基本結(jié)構(gòu)是平滑肌細(xì)胞、細(xì)胞外基質(zhì)以及內(nèi)層內(nèi)皮細(xì)胞組成，為一管道系統(tǒng)。然而，平滑肌細(xì)胞與細(xì)胞外基質(zhì)的相對數(shù)量，以及內(nèi)皮細(xì)胞的性質(zhì)會根據(jù)其在循環(huán)系統(tǒng)中的不同功能而改變。為適應(yīng)脈沖式血流及較高的血壓，動脈壁比靜脈更厚，平滑肌細(xì)胞增厚為主。對小動脈而言，血管壁厚度與管腔直徑的比值會進(jìn)一步改變以適應(yīng)更加精確的血壓調(diào)節(jié)。另一方面，靜脈是一種有著很大容量的薄壁血管。為了促進(jìn)最佳的組織灌注量，毛細(xì)血管則是由單層內(nèi)皮細(xì)胞覆蓋于基膜形成的血管。

Since?various vessels have unique?structural features, it is?not surprising that?certain?lesions characteristically?involve only specific?regions of the vasculature.?For?example,?atherosclerosis occurs mainly in large?, muscular arteries, while hypertension?affects small?arterioles, and?specific forms of?vasculitis selectively?involve?vessels of only?a certain?caliber.

因為不同的血管有著不同的結(jié)構(gòu)特征，因此特定的病變會有代表性地影響特定的血管系統(tǒng)部分。例如，動脈粥樣硬化主要發(fā)生在大的肌性血管，而高血壓影響小動脈，特定類型的血管炎會選擇性地發(fā)生在一定直徑的血管。

Vessel walls are?organized into?three?concentric?layers:?intima, media,?and adventitia.?These?layers are?present in?all?vessels but?are most?apparent in larger?vessels and particularly?arteries.?The?intima?consist of?an?EC monolayer on a?basement membrane?with?minimal?underlying ECM; it is?separated from?the media?by a dense?elastic membrane?called?the?internal?elastic lamina.?The?media?is composed predominantly?of?SMCs and?ECM,?surrounded by loose?connective tissue, nerve fibers, and?smaller vessels of?the?adventitia.?An?external elastic laminal is present in?some arteries and?defines the?transition between media and?adventitia.?Diffusion?of oxygen?and?nutrients from?the lumen is adequate to?sustain thin-walled?vessels and the?innermost?SMCs of?all?vessels.?In?large?and medium-sized?vessels, however, small arterioles?within the adventitia?(called?vasa?vasorum?literally, "vessels of the?vessels")?perfuse the?outer half to?two-thirds of?the media.

血管壁可分為同軸的三層：內(nèi)膜，中間層，外膜。這些血管層會出現(xiàn)在所有的血管當(dāng)中，但在大血管以及特定的動脈最為典型。內(nèi)膜由單層的內(nèi)皮細(xì)胞覆蓋在一層基膜以及少量的細(xì)胞外基質(zhì)組成；內(nèi)膜與中間層之間被一層致密的彈性層分開，被稱為內(nèi)彈性層。中間層主要由平滑肌細(xì)胞與細(xì)胞外基質(zhì)組成，同時被包含疏松結(jié)締組織，神經(jīng)纖維，細(xì)小的營養(yǎng)血管的外膜所包繞。某些動脈中會出現(xiàn)一層外彈性層，成為中膜與外膜的過渡。直接從管腔中擴(kuò)散的氧氣與營養(yǎng)物質(zhì)可以滿足薄壁血管與所有血管最內(nèi)層的平滑肌細(xì)胞的需求。然而在大動脈和中動脈中，外膜中的小血管（稱為血管滋養(yǎng)管，即血管的血管）會為中膜外層三分之二的平滑肌細(xì)胞提供養(yǎng)分。