Vasa Vasorum in Saphenous Vein for CABG: A Review of Morphological Characteristics

ABSTRACT This short article discusses selected scanning electron microscope and transmission electron microscope features of vasa vasorum including pericytes and basement membrane of the human saphenous vein (SV) harvested with either conventional (CON) or no-touch (NT) technique for coronary artery bypass grafting. Scanning electron microscope data shows the general damage to vasa vasorum of CON-SV, while the transmission electron microscope data presents ultrastructural features of the vasa in more detail. Hence there are some features suggesting pericyte involvement in the contraction of vasa blood vessels, particularly in CON-SV. Other features associated with the vasa vasorum of both CON-SV and NT-SV preparations include thickened and/or multiplied layers of the basement membrane. In some cases, multiple layers of basement membrane embrace both pericyte and vasa microvessel making an impression of a "unit" made by basement membrane-pericyte-endothelium/microvessel. It can be speculated that this structural arrangement has an effect on the contractile and/or relaxing properties of the vessels involved. Endothelial colocalization of immunoreactive inducible nitric oxide synthase and endothelin-1 can be observed (with laser confocal microscope) in some of the vasa microvessels. It can be speculated that this phenomenon, particularly of the expression of inducible nitric oxide synthase, might be related to structurally changed vasa vessels, e.g., with expanded basement membrane. Fine physiological relationships between vasa vasorum endothelium, basement membrane, pericyte, and perivascular nerves have yet to be uncovered in the detail needed for better understanding of the cells'specific effects in SV preparations for coronary artery bypass grafting.

A brief comment on vasa vasorum of human saphenous vein: relevance for coronary artery bypass surgery

Abstract The importance of the vasa vasorum and blood supply to the wall of human saphenous vein (hSV) used for coronary artery bypass grafting (CABG) is briefly discussed. This is in the context of the possible physical link of the vasa vasorum connecting with the lumen of hSV and the anti-ischaemic impact of this microvessel network in the hSV used for CABG.

Saphenous vein vasa vasorum as a potential target for perivascular fat-derived factors

Abstract Perivascular adipose tissue (PVAT) is a source of factors affecting vasomotor tone with the potential to play a role in the performance of saphenous vein (SV) bypass grafts. As these factors have been described as having constrictor or relaxant effects, they may be considered either beneficial or detrimental. The close proximity of PVAT to the adventitia provides an environment whereby adipose tissue-derived factors may affect the vasa vasorum, a microvascular network providing the vessel wall with oxygen and nutrients. Since medial ischaemia promotes aspects of graft occlusion the involvement of the PVAT/vasa vasorum axis in vein graft patency should be considered.

Effect of Simiao Yongan Tang on Permeability of Vasa Vasorum of Atherosclerotic Plaque / 中国实验方剂学杂志

Objective:To observe the effect of Simiao Yongan Tang on the pathologic morphology of atherosclerosis (AS) vulnerable plaque and the permeability of vasa vasorum (VV), and to explore its intervention mechanism with VV as the target. Method:Healthy male ApoE-/- mice were randomly divided into model group, Simiao Yongan Tang group(11.7 mg·kg-1·d-1)and simvastatin group(2.6 mg·kg-1·d-1). High-fat diet supplemented with 1.1% L-methionine was given to induce the animal model, while C57BL/6 mice were used as the control group. The model was evaluated after 8 weeks of feeding. After successful modeling, continued drug intervention was given for 8 weeks, and the pathological changes of the mouse aorta were observed by oil red O staining. The expression levels of matrix metalloproteinase-9 (MMP-9) and tissue inhibitor of metalloproteinase-1 (TIMP-1) proteins in the outer membrane of aortic root plaques were observed by immunohistochemical staining. Result:The results of oil red O staining showed that as compared with the control group, the plaque area of the aortic wall was significantly increased in the model group (PPPPPPConclusion:Simiao Yongan Tang can reduce the area of mouse aortic plaque, reduce the VV permeability of the outer plaque by regulating the expression of MMP-9 and TIMP-1, and stabilize the vulnerable plaque.

Histological changes secondary to use of anti-angiogenic therapy after interruption of vasa vasorum flow in the descending aorta: results in a porcine model / Alterações histológicas secundárias à interrupção dos vasa vasorum na aorta descendente com o uso de terapia antiangiogênica: resultados em modelo suíno

Background Anti-angiogenic regulators may have therapeutic implications for onset and progression of atherosclerosis. Objectives To demonstrate histological changes secondary to the use of bevacizumab in the aorta of pigs after interruption of flow in the vasa vasorum. Methods Twelve pigs were divided into two groups. The intercostal arteries of the descending aorta were dissected and ligated and wrapped with a polyvinyl chloride membrane. The treatment group received an intravenous dose of bevacizumab. After 15 days, the animals were euthanized and the aorta removed. Histological slides were prepared for control and treatment groups and for non-manipulated areas and analyzed for degree of angiogenesis, injury, inflammation, and intimal thickening. Data were expressed as mean (SD) of scores and groups were compared using the Mann-Whitney test. The Poisson distribution was used to calculate 95% confidence intervals for mean scores, in order to determine effect statistics. Results Bevacizumab had adverse effects on all treated pigs. The analysis using a Scale of Magnitudes for Effect Statistics showed a trend toward a decrease in angiogenesis [0.58 (1.79/-0.63)] and injury [0.55 (1.76/-0.66)] and an increase in inflammation [0.67 (1.89/-0.55)] with threshold moderate effects. There was no difference in intimal thickening [0 (1.19/-1.19)]. Conclusions The medication exhibited a trend toward reduced angiogenesis and injury, but no reduction in the inflammatory process or intimal thickening of the aortic wall. These findings are in disagreement with studies that correlate neovascularization with increased migration of inflammatory cells. Bevacizumab exhibited toxicity in the porcine model

Agentes antiangiogênicos podem ter implicações terapêuticas na progressão e manifestação da aterosclerose. Objetivos Demonstrar a alteração histológica secundária ao uso de bevacizumabe na aorta descendente de suínos submetida à interrupção dos vasa vasorum. Métodos Em doze suínos, divididos em dois grupos, foi realizada dissecção da aorta torácica, além de ligadura das artérias intercostais e proteção com polivinil. O grupo tratamento recebeu dose endovenosa de bevacizumabe. Após 15 dias, os animais foram sacrificados para retirada da artéria e preparo das lâminas histológicas dos grupos tratamento, controle e áreas não manipuladas para análise quanto aos graus de angiogênese, injúria, inflamação e espessamento intimal. A análise estatística foi conduzida através da média e do desvio padrão dos escores. As comparações entre os grupos foram realizadas pelo teste de Mann-Whitney. A distribuição de Poisson calculou os intervalos de confiança de 95% para as médias, a fim de determinar o efeito estatístico. Resultados O bevacizumabe causou efeitos adversos em todos os suínos tratados. As variáveis analisadas através da Escala de Magnitude para Efeito Estatístico demonstraram tendência de redução da angiogênese [0,58 (1,79/-0,63)] e da injúria [0,55 (1,76/-0,66)] e aumento da inflamação [0,67 (1,89/-0,55)] no limite do moderado. Não ocorreu diferença no espessamento intimal [0 (1,19/-1,19)]. Conclusões A medicação utilizada mostrou tendência de redução da angiogênese e da injúria, mas não reduziu o processo inflamatório ou o espessamento intimal da parede arterial. Esses achados contrariam estudos que correlacionam a neovascularização com o aumento da migração de células inflamatórias. O bevacizumabe mostrou toxicidade no modelo suíno

Correlation of Adventitial Vasa Vasorum with Intracranial Atherosclerosis: A Postmortem Study / 대한뇌졸중학회지

BACKGROUND AND PURPOSE: Vasa vasorum (VV) have been believed to be rare or non-existent in small-caliber intracranial arteries. In a series of human cerebral artery specimens, we identified and examined the distribution of VV in association with co-existing intracranial atherosclerosis. METHODS: We obtained cerebral artery specimens from 32 consecutive autopsies of subjects aged 45 years or above. We scrutinized middle cerebral artery (MCA), vertebral artery (VA), and basilar artery (BA) for the presence of adventitial VV. We described the distribution of VV, and the characteristics of co-existing atherosclerotic lesions. RESULTS: Among 157 intracranial arteries, adventitial VV were present in 74 of the 157 specimens (47%), involving MCA (n=13, 18%), BA (n=14, 19%), and VA (n=47, 64%). Although qualitatively these 74 adventitial VV distributed similarly in arteries with or without atherosclerotic lesions (disease-free arteries n=4/8; arteries of pre-atherosclerosis n=17/42; and arteries of progressive atherosclerosis n=53/107), the presence of adventitial VV in intracranial VA was associated with a heavier plaque load (1.72±1.66 mm2 vs. 0.40±0.32 mm2, P < 0.001), severer luminal stenosis (25%±21% vs. 12%±9%, P=0.002), higher rate of concentric lesions (79% vs. 36%, P=0.002), and denser intraplaque calcification (44% vs. 0%, P=0.003). Histologically, intracranial VA with VV had a larger diameter (3.40±0.79 mm vs. 2.34±0.58 mm, P < 0.001), thicker arterial wall (0.31±0.13 mm vs. 0.23±0.06 mm, P=0.002), and a larger intima-media (0.19±0.09 mm vs. 0.13± 0.04 mm, P=0.003) than VA without VV. CONCLUSIONS: Our study demonstrated the distribution of adventitial VV within brain vasculature and association between vertebral VV and progressive atherosclerotic lesions with a heavier plaque load and denser intraplaque calcification.

Role of dynamic contrast enhanced MRI in assessing early curative effect of rosuvastatin on carotid atherosclerotic plaques / 中华老年心脑血管病杂志

Objective To study the role of dynamic contrast enhanced MRI (DCE-MRI) in assessing early curative effect of rosuvastatin on carotid atherosclerotic plaques.Methods Twenty-five patients with lipid-rich necrotic core carotid atherosclerotic plaques received intensive rosuvastatin treatment (5-20 mg/d) for 2 years,and carotid artery DCE-MRI at baseline before treatment and at months 3,12 and 24 after rosuvastatin treatment.Their adventitial transfer constant (K) and fractional plasma volume (Vp) were measured and compared during the rosuvastatin treatment.Results The Vp was significantly smaller at months 3,12 and 24 after rosuvastatin treatment than at baseline before rosuvastatin treatment (0.09±0.05,0.07±0.04 and 0.06±0.05 vs 0.12± 0.06,P＜0.05) with a reduction of 25.0％ after 3 months of rosuvastatin treatment and a gradual reduction after 24 months of rosuvastatin treatment (P＜0.05).The adventitial K was mildly reduced after 24 months of rosuvastatin treatment (P＞0.05).Conclusion DCE-MRI can assess the early curative effect of rosuvastatin on carotid atherosclerotic plaques.

Experimental Study of Si-Miao Yong-An Decoction Regulating Vasa Vasorum Remodeling in ApoE-/-Mice with Atherosclerosis Vulnerable Plague / 世界科学技术-中医药现代化

This study was aimed to observe the effect of Si-Miao Yong-An (SMYA) decoction intervention in atherosclerosis (AS) vulnerable plaque,and to further explore the action mechanism from the entry point of vasa vasorum (VV) neovascularization.Male ApoE-/-mice were randomly divided into the model group,simvastatin group and SMYA group.High-fat diet added 1.1％ L-methionine was fed for 8 weeks to establish the AS vulnerable plaque model.The C57BL/6 mice were used as control.After 8 weeks' continuous medication,mice were sacrificed.HE staining were used to observe the pathological changes of mice aorta;immunohistochemical staining was used to observe the VV density in AS plaque and aortic adventitia;macrophage infiltration in plaque was also detected;the blood-lipid changes of TC,TG,LDL-C and HDL-C were detected;western blot was used to detect essential proteins of HIF-1α-Apelin/APJ signal pathway.The results showed that SMYA decoction decreased the plaque area and the ratio of plaque area and lumen area,increased the minimum thickness of fibrous cap,which significantly improved the pathological feature of aortic plaque in mice.The function of increasing the minimum thickness of fibrous cap was obviously superior to simvastatin.SMYA decoction effectively suppressed the VV neovascularization and decreased the macrophage content.SMYA decoction effectively decreased the serum level of TC,TG and LDL-C;however,it had no effect on HDL-C.SMYA decoction decreased the protein expression of HIF-1α.Its function was obviously superior to simvastatin.SMYA decoction can down-regulate the protein expressions of Apelin,APJ,Phospho-MEK1/2 (Ser217/221),Phospho-p44/42 MAPK (Erk1/2) (Thr202/Tyr204) and Phospho-p70 S6 Kinase (Thr421/Ser424).It was concluded that SMYA decoction regulated the HIF-1α-Apelin/APJ signal pathway,suppressed VV neovascularization and stabilized AS vulnerable plaque.

Treatment Progress of Traditional Chinese Medicine And Western Medicine on Regulating Vasa Vasorum for Atherosclerosis Vulnerable Plaque Stabilization / 世界科学技术-中医药现代化

The major clinical risk of atherosclerosis (AS) lesion is instability and vulnerability of plaque.Intraplaque vasa vasorum (VV) has structure defects with the characteristics of immature,irregular,fragile,and prone to extravasation and intraplaque hemorrhage due to the compromised structural integrity.It stimulates inflammatory reaction and provides channel for hemocyte and blood soluble composition entering into the plaque.Intraplaque VV can promote AS plaque formation and is closely related to the intraplaque hemorrhage,plaque rupture and occurrence of clinical cardiovascular events.In-depth study of VV function and key signaling pathways related to AS pathological process are promising to fundamentally prevent vulnerable plaque development,unstable plaque rupture and its complications.This article summarized the effect and mechanism of VV in pathological process of AS and related treatment,in order to provide theoretical basis for stabilization of AS vulnerable plaque.

Influence of Guishaotongluo on angiogenesis of adventitial vasa vasorum and oxidative stress in early stage of atherosclerosis / 中国药理学通报

Aim To observe the effect of Guishao-tongluo ( GSTL ) on the angiogenesis of vasa vasorum and oxidative stress in the early stage of atherosclero-sis. Methods The rabbits ( n =84 ) were randomly divided into 7 groups (n=12):control group,high-fat group, adventitial injury group, GSTL high(GH)and medium ( GM ) dose group, atorvastain group ( ATO ) , and Tongxinluo group ( TXL ) . The normal group was fed with common foodstuffs, and high-fat foodstuffs for the high-fat group to establish an early model of hyper-lipidemia, and all the other groups were fed with high-fat diet combined with carotid artery cannula to build early atherosclerosis carotid artery injury rabbit mod-els. The GSTL high and medium dose was given Guishaotongluo ultrafine powder 4. 16,2. 08 g·kg-1 · d-1 respectively. The atorvastain group and Tongxinluo group were given suspension of atorvastain solution 2. 5 mg·kg-1 ·d-1 , Tongxinluo supermicro powder 0. 6 g ·kg-1 ·d-1 . All groups were treated with gastric per-fusion for 4 weeks. Biochemical method was applied to detect blood lipid change. HE staining was used to ob-serve the pathological morphology of intima-media. Aactivity of serum superoxide dismutase( SOD) ,malon-dialdehyde ( MDA ) content and the total antioxidant capacity ( T-AOC ) in artery serum were detected. NADPH subunits p22phox mRNA, gp91phox mRNA in carotid arteries were located and semi-quantitated by fluorescence in situ hybridization. The expression of VEGF, VEGFR-2 in the carotid artery adventitia was detected by Western blot. Results Compared with normal group,the contents of TC,TG and LDL-C were significantly increased, and VEGF, VEGFR-2 protein levels were remarkly increased in high-fat and adventi-tial injury group. The carotid artery injuries,the degree of angiogenesis of vasa vasorum and NADPH subunits p22phox, gp91phox mRNA in adventitia tissue of the GH,GM, ATO and TXL group were milder in varying degrees compared with those of the vasa injury group. Also the activity of SOD,T-AOC increased,while MDA content,VEGF,VEGFR-2 protein levels were remarkly decreased ( P < 0. 5 or P < 0. 01 ) . Conclusions GSTL can inbibit adventitial neovascularization in the early stage of atherosclerosis, and its mechanism might be related to the increase of total antioxidant capacity of the vascular system and adventitia tissue.

La adventicia arterial: actor olvidado del sistema cardiovascular

Actualmente se acepta que la adventicia tiene: un importante rol fisiológico al determinar el nivel de nutrición, oxigenación, reparación arterial, regulación de la vasomotricidad, control de la poscarga ventricular, control de la función arterial, etcétera, a la vez que tiene una importante participación en procesos patológicos (por ejemplo, aterosclerosis, hipertensión arterial, génesis de aneurismas de aorta abdominal). Sin embargo, dado lo reciente de la mayoría de los estudios que han redefinido el rol de la adventicia, aún persiste mucho desconocimiento en la comunidad biomédica acerca de la fisiología de la capa adventicia arterial. El presente trabajo tiene como objetivo revisar el rol que actualmente se reconoce para la capa adventicia de la pared arterial.

Interventional effects of Tongxinluo combined with Atorvastatin and Aspirin(ATS) on the angiogenesis of vasa vasorum in the early stage of atherosclerosis / 中国药理学通报

Aim To observe the effect of a treatment proposal named “Golden Triangle” ( Atorvastatin, Tongxinluo,and Aspirin) on the vasa vasorum angio-genesis of early atherosclerosis lesions in rabbits carotid artery. Method Seventy-two healthy New Zealand rabbits with half males and half females were divided into 6 groups randomly ( n =12 ):control group, model group, Tongxinluo group ( TXL ) , atorvastatin group ( ATO ) , aspirin group ( ASP ) , golden triangle group ( ATS) . The control group was fed with common feed-stuff, and all the other groups′ right carotid arteries were equipped with the silicone tube,and were then fed with fatty feedstuff. The Tongxinluo group, the Atorvas-tatin group and the Aspirin group were given suspen-sion of Tongxinluo supermicro powder(0. 3 g·kg-1 · d-1 ) , Atorvastatin ( 2. 5 mg · kg-1 · d-1 ) and Aspirin (12 mg·kg-1·d-1),the golden triangle group were given suspension of Tongxinluo supermicropowder (0. 3g·kg-1 ·d-1),atorvastatin(2. 5 mg·kg-1 · d-1 ) and Aspirin ( 12 mg · kg-1 · d-1 ) . All the groups were fed with medicine for 4 weeks. Tissue slice of carotid artery was stained with HE and observed un-der light microscope. The change of blood liquid was detected by biochemical assay. Immunohistochemical staining was used to detect the protein expression of CD34 around the carotid artery adventitia. Color micro-sphere method was used to detect the blood flow vol-ume change of the cartoid artery microvascular. VEFG, VEGFR-2 gene and protein expression in the cartoid artery were detected by Real-time PCR and Western Blot. Result Compared with the control group,the content of VEGF, VEGFR-2 gene and pro-tein expression and the microvascular blood flow vol-ume of cartoid artery microvascular in the model were significantly increased ( P 0. 05 ) . The content of CD34 was de-creased in TongxinLuo group,atorvastatin group,aspirin group and ATS group. Conclusion The ATS project can reduce the expression of VEGF,VEGFR-2, inhibit the vasa vasorum angiogenesis and decrease proinflam-matory substances in the tunica media and intima of vascular wall. It plays an important role in intervening in the process of AS.

Efeitos da remoção da túnica adventícia da aorta descendente em suínos / Effects of removal of the adventitia of the descending aorta and structural alterations in the tunica media in pigs

OBJETIVO: Investigar os efeitos da remoção da adventícia da aorta em suínos. MÉTODOS: O experimento foi realizado com oito suínos. Removeu-se a camada adventícia da aorta descendente. Após a eutanásia com duas, quatro, seis e oito semanas, o segmento aórtico era removido. Após, eram feitos cortes histológicos com a coloração de hematoxilina e eosina (HE) e pelo método de Weigert - Van Gieson. RESULTADOS: Após duas semanas identificou-se um leve desarranjo do terço externo da túnica média. Nos animais sacrificados após quatro semanas observou-se um desarranjo estrutural dos terços externos da túnica média. Após seis semanas observou-se necrose da parede aórtica. Finalmente, após oito semanas além da fibrose da parede aórtica identificou-se a destruição da lâmina elástica interna. CONCLUSÃO: A remoção da adventícia da aorta em suínos levou à alterações degenerativas da média, determinando perda da estrutura da parede aórtica que é variável em sua localização, intensidade e forma, dependendo do tempo a partir do qual se estabeleceu a lesão isquêmica.

OBJECTIVE: To investigate the effects of removal of the adventitia on the tunica media in a pig model. METHODS: The experiment was performed in eight pigs. The adventitia of the descending aorta was removed. Following euthanasia, at two, four, six and eight weeks, the aortic segment was removed. Next, slices of the aorta were stained with hematoxylin and eosin (HE) and Weigert - Van Gieson. RESULTS: After two weeks there was a slight cellular breakdown in the outer third of the media. After four weeks structural breakdown of elastic fibers was observed in the outer two thirds of the same layer. In six weeks, several areas of necrosis and almost complete disruption of elastic fibers were identified. Finally, after eight weeks, there was fibrosis of the entire wall with disruption of the internal elastic lamina. CONCLUSION: The removal of the adventitia leads to degeneration of the media, determining loss of the normal structure of the aortic wall that is variable in its location, intensity and shape, depending on the length and duration of the ischemic insult.

Ruptura dos vasa vasorum e hematoma intramural da aorta: um paradigma em mudança / Rupture of vasa vasorum and intramural hematoma of the aorta: a changing paradigm

A ruptura dos vasa vasorum tem sido reconhecida como uma das causas do hematoma intramural da aorta há 90 anos. Esta breve revisão apresenta sistematicamente a fisiologia desses vasos e o seu papel na fisiopatologia das alterações parietais da aorta que ocorrem na hipertensão arterial, na arteriosclerose e na síndrome aórtica aguda. A hipótese defendida aqui é a de que a ruptura dos vasa vasorum ocorre como um fenômeno secundário e não como um dos fatores causais na fisiopatologia do hematoma intramural.

Rupture of vasa varorum has been recognized as one cause of intramural hematoma of the aorta for 90 years. This brief revision presents systematically, the physiology of these vessels and its role in the physiopathology of the alterations in the aortic wall secondary to hypertension, arteriosclerosis and in Acute Aortic Syndrome. The hypothesis is that rupture of vasa vasorum is a secondary phenomenon and not one causal factor in the physiopathology of intramural hematoma.

La adventicia: estado actual del conocimiento / The Adventitia: Current State of Knowledge

La adventicia se ha definido como la capa de tejido conectivo más externa de un vaso y no formaría una unidad con la estructura vascular. El término "adventicia" proviene del latín adventicius, que significa "venido de afuera, extraño". Estos conceptos tal vez constituyan la causa de la subestimación del papel fisiológico de esta túnica. Al presente es bien conocido que la adventicia contiene vasa vasorum y nervi vasorum con funciones nutricionales y de control, respectivamente. A ello se suma la presencia de factores bioquímicos que serían responsables de cambios en la conducta elástica y viscosa de la pared arterial a través de una regulación de la función muscular lisa. En este trabajo se realiza una síntesis del papel estructural y fisiológico de la adventicia; se analizan además datos clínicos y experimentales que se comparan con resultados originales publicados por el autor.

The adventitia has been defined as the outermost connective tissue covering of a vessel, and does not form an integral part of the vascular structure. The term "adventitia" comes from the Latin word adventicius, meaning "coming from abroad, foreign". These concepts may explain why the physiological role of this tunic has been underestimated. It is well known that the adventitia has vasa vasorum and nervi vasorum with nutritional and control functions, respectively. In addition, biochemical factors may probably account for changes seen in elastic and viscous behaviour of the arterial wall due to changes in smooth muscle function. This study reports a summary of the structural and physiological role of the adventitia: clinical and experimental data are also analyzed and compared with the original outcomes published by the author.

Capillary Plexus and Vasa of the Rat Lung as Revealed by Scanning Electron Microscope of Corrosion Casts

The pulmonary microvasculatures of rats were studied by injection replicas prepared from Mercox. This medium enabled us to easily obtain consistent, stable, and complete injected replicas of the pulmonary vasculature. In order to investigate the three dimensional structures of the tributaries of the bronchial artery, such as the capillary plexus and vasa vasorum, we performed a scanning electron microscopic(SEM) study of the vascular casts, using Mercox CL-2B as a media. The alveolar capillaries revealed hexagonal or pentagonal rings of vascular networks. In some areas, the vascular rings composed a square network, The bronchial tree was supplied by the bronchial arteries which form a coarse capillary extending as far as the terminal bronchioles. Occasionally the capillary plexus was connected with adjacent capillary networks in and around the alveolar walls. The walls of the pulmonary artery revealed only a single layer of the vasa vasorum, but those of the pulmonary vein were surrounded by more complicated and well developed vasa vasorum than the pulmonary arterial side. The mean diameters of the venous vasa vasorum are greater than the arterial vasa vasorum.