Search

The intervertebral disc is part of an anatomic unit that consists of an inner gelatinous nucleus pulposus (NP), an outer annulus fibrosus (AF), and the cartilaginous end plates with their associated capillary beds both cranially and caudally. The central NP is a site of collagen secretion and contains numerous proteoglycans (PG), which facilitate water retention, creating hydrostatic pressure to resist axial compression of the spine. The NP is primarily composed of type II collagen. In contrast, the AF functions to maintain the NP within the center of the disc with low amount of PG and is composed of primarily of type I collagen [1, 2].

Vascular Biology Small-diameter arteries link main arteries to capillary beds that feed tissues and organs. Persistent constriction of these arteries may generate high blood pressure (hypertension). Khavandi et al. (see also Hill and Braun) found that arterial constriction initiated the production

Birds have evolved a high-performance cardiovascular system to meet the rigorous demands of running, flying, swimming, or diving in a variety of environments, some of them extreme. Sustained high levels of activity in these environments place severe demands on the cardiovascular system to provide adequate delivery of oxygen to working vascular beds and to provide efficient removal of metabolic products. Furthermore, birds are endothermic organisms and the cardiovascular system plays a major role in conserving or removing body heat. The descriptions of the component parts of the circulatory system in this chapter illustrate that these transport requirements are met in a variety of ways in birds inhabiting particular environmental niches. This chapter describes the morphological and functional aspects of the avian heart, circulatory hemodynamics, and the vascular tree. A common thread running through this discussion is that the component parts of the circulation must function in an integrated fashion to ensure tissue oxygen delivery matches tissue demands. This is accomplished through the integrative control of circulation by autoregulatory, humoral, and neural mechanisms. Since the last edition of this book, a significant number of studies have examined the development of cardiovascular control in avian embryos which has expanded our understanding of this system throughout ontogeny. Finally, this chapter examines how the cardiovascular system functions within a complex animal, interacting in complex environments.

ARTERIOVENOUS MALFORMATIONS ARE a heterogeneous group of intra-axial central nervous system vascular lesions consisting of tangles of abnormal arteriovenous connections without intervening capillary beds. The heterogeneity of arteriovenous malformations is described by the Spetzler-Martin grading scale, a scale that also forms the basis for clinical decision making. The microsurgical treatment of appropriately selected supratentorial arteriovenous malformations is based on the tenets of circumferential isolation and transection of arterial feeders, preservation of vessels en passant and surrounding functional neural tissue, and skeletonization and transection of venous drainage.

Accurate characterization of capillary geometry is of the utmost importance for physiological tissue studies such as oxygen transport. We show that 3D microscopy can be used to measure tissue capillary geometry both in normal and disease states. We imaged fluorescently labeled gut mucosa capillary beds of three control rats and three rats 4 hours after i.p. injection of 9 mg/kg endotoxin. We used serial optical sectioning microscopy coupled with deconvolution to reconstruct 3D capillary geometry. Theoretical point spread functions accounting for depth into the specimen resulted in better reconstructions than experimentally measured point spread functions. We next derived the distribution of the shortest distances to the nearest capillary from all extravascular tissue voxels. In normal rats the shortest-distance distributions were remarkably constant despite widely varying capillary geometry. Furthermore, the mean of the shortest-distance distributions increased significantly for endotoxemic rats (4.8 ± 0.4 μm) compared to controls (4.3 ± 0.3 μm, P < 0.05). Hence, serial sectioning microscopy provides an accurate venue for measuring physiologically relevant 3D capillary structure. Microsc. Res. Tech. 61:428–437, 2003. © 2003 Wiley-Liss, Inc.

Cortical blood flow was probed via the motion of red blood cells (RBCs) in individual capillaries that lay as much as 600 μm below the pia matter of primary somatosensory cortex in rat. The flow was quite variable, with a speed of 0.8±0.5 mm/s (mean±S.D.) and a flux of 60±40 RBC/s, averaged over all capillaries and over time. The fluctuations in the flow were dominated by a spectral band near 0.1 Hz. This band coincides with the spectral band of fluctuations previously seen across whole capillary beds with optical [Neuroimage 4 (1996) 183] and f MRI [Mag. Reson. Med. 37 (1997) 511] imaging techniques. Time-locked increases in the flow of red blood cells (RBCs) within individual capillaries were observed in response to stimulation of multiple vibrissae at natural levels of deflection. The magnitude of the stimulus-evoked change in speed was, at most, equal to 20% of the basal speed. This change is comparable to the level of the fluctuations in speed seen in single capillaries. Thus, changes in flow evoked by natural stimuli are largely masked by basal fluctuations. In toto, the results of our study suggest that fluctuations at the level of the microvasculature limit the sensitivity of brain imaging techniques, at least at low frequencies.

We solved the Laplace equation for the radius of an arterial gas embolism (AGE), during and after breath-hold diving. We used a simple three-region diffusion model for the AGE, and applied our results to two types of breath-hold dives: single, very deep competitive-level dives and repetitive shallower breath-hold dives similar to those carried out by indigenous commercial pearl divers in the South Pacific. Because of the effect of surface tension, AGEs tend to dissolve in arterial blood when arteries remote from supersaturated tissue. However if, before fully dissolving, they reach the capillary beds that perfuse the brain and the inner ear, they may become inflated with inert gas that is transferred into them from these contiguous temporarily supersaturated tissues. By using simple kinetic models of cerebral and inner ear tissue, the nitrogen tissue partial pressures during and after the dive(s) were determined. These were used to theoretically calculate AGE growth and dissolution curves for AGEs lodged in capillaries of the brain and inner ear. From these curves it was found that both cerebral and inner ear decompression sickness are expected to occur occasionally in single competitive-level dives. It was also determined from these curves that for the commercial repetitive dives considered, the duration of the surface interval (the time interval separating individual repetitive dives from one another) was a key determinant, as to whether inner ear and/or cerebral decompression sickness arose. Our predictions both for single competitive-level and repetitive commercial breath-hold diving were consistent with what is known about the incidence of cerebral and inner ear decompression sickness in these forms of diving.

This prospective study of 120 autopsy collected human hearts correlates the "Right Ventricle/Left Ventricle" free walls mass ratio and the ventricular mass fraction supplied by the right coronary ("Right Coronary/Ventricular Weight"). Different coloured gel injected through both coronary artery's capillary beds allowed ventricular myocardium separation to obtain the weights. In hearts without hypertrophy, mean +/- standard deviation of the "Right Ventricle/Left Ventricle" mass ratio was 0.54 +/- 0.09 for males and 0.62 +/- 0.23 for females; "Right Coronary/Ventricular Weight" mass ratios were 0.39 +/- 0.08 and 0.39 +/- 0.04, respectively. Mean +/- standard deviation of the "Right Ventricle/Left Ventricle" and "Right Coronary/Ventricular Weight" ratios were 0.37 +/- 0.05 and 0.36 +/- 0.10, respectively in hearts with "Left Ventricle Hypertrophy"; 0.56 +/- 0.07 and 0.38 +/- 0.11 in hearts "Without Hypertrophy"; 0.54 +/- 0.08 and 0.39 +/- 0.08 in hearts with "Biventricular Hypertrophy"; 0.89 +/- 0.16 and 0.49 +/- 0.06 in hearts with "Right Ventricle Hypertrophy". Means and variances are narrower for the "Right Coronary/Ventricular Weight" than that observed for the "Right Ventricle/Left Ventricle" mass ratio. It is due to the special double coronary arrangement in which every artery irrigates both ventricles. These results suggest that the usual pattern of the human coronary arteries' anatomy acts as a buffer for the ventricular mass distribution to be irrigated by both arteries in hypertrophy.

The mammalian ear has an extraordinary capacity to detect very low-level acoustic signals from the environment. Sound pressures as low as a few μPa (−10 dB SPL) can activate cochlear hair cells. To achieve this sensitivity, biological noise has to be minimized including that generated by cardiovascular pulsation. Generally, cardiac pressure changes are transmitted to most peripheral capillary beds; however, such signals within the stria vascularis of the cochlea would be highly disruptive. Not least, it would result in a constant auditory sensation of heartbeat. We investigate special adaptations in cochlear vasculature that serve to attenuate cardiac pulse signals. We describe the structure of tortuous arterioles that feed stria vascularis as seen in corrosion casts of the cochlea. We provide a mathematical model to explain the role of this unique vascular anatomy in dampening pulsatile blood flow to the stria vascularis.

In fixed mouse brain magnetic resonance images, a high prevalence of fixation artifacts have been observed. Of more than 1700 images of fixed brains acquired at our laboratory, fixation artifacts were present in approximately 30%. In this study, two of these artifacts are described and their causes are identified. A hyperintense rim around the brain is observed when using perfusates reconstituted from powder and delivered at a high flow rate. It is proposed that these perfusion conditions cause blockage of the capillary beds and an increase in pressure that ruptures the vessels, resulting in a blister of liquid below the dura mater. Secondly, gray-white matter contrast inversion is observed when too short a fixation time or too low a concentration of fixative is used, resulting in inadequate fixation. The deleterious consequences of these artifacts for quantitative data analysis are discussed, and precautions for their prevention are provided.

A basic pattern is common to the circulation in all fish, including hagfish, elasmobranchs, and bony fish. The fish circulation is a simple loop in which blood, pumped by the heart, passes first through a short arterial system into the gills and then onto a second, more extensive arterial system that supplies the systemic tissues. While the respiratory and systemic circulations lie in series, arterial branching within the gill and systemic circulations create in-parallel vascular arrangements of capillary beds. A well-developed venous system then collects the blood and returns it back to the heart. This article identifies the major arteries and veins of a bony fish and serves as a general anatomical reference of fish vascular nomenclature. The more notable variations in hagfish and elasmobranchs are also described.

A study of the microvasculature of the omentum using corrosion casts was undertaken. The object was to supply information regarding the morphology of the three-dimensional structure of the microvasculature information which may be valuable in understanding the functions of the omentum. Corrosion casts of rat omenta were prepared and studied. Characteristic glomerular-like capillary beds were identified. Some of these beds were densely and others loosely arranged. Two types of capillaries made up these beds, tortuous and straight capillaries. These beds also showed a planate surface giving the impression that they lie directly under the mesothelium.

This chapter deals with a case study, where an elderly man with a history of alcoholism, was found in home, dead from blood loss. Although the victim's body was found between the hall and the bathroom, bloodstains were noted leading to the bedroom, along a hallway, into the bathroom. The victim had been beaten around the face and head. A clinical pathologist made no mention of arterial damage in the autopsy report, but the cause of death was listed as exsanguinations blood loss. Injury occurred to the middle finger of the fight hand, resulting in the finger being mashed at the tip. Although not a commonly recognized source of arterial damage, the tips of the fingers do involve arteriole (very small arterial vessels) that lead into the capillary beds and on to the venous system. There is some pressure involved. This can account for weak arterial distribution from injury to the fingers, and arterial-like projection of drops distributed from squeezing punctures to the fingertips. Initial review of the scene focused on three patterns on the wall near the victim's bed. One pattern was a clearly defined oval whole pattern shape, with randomly distributed spatters of variable sizes, with directions of travel almost perpendicular but showing some orientation toward gravity (directly down). The second small pattern was to the left of the bed near a chair and a third largest pattern next to sheer curtains. A few of the stains had inclusions suggestive of saliva, which would fit the classification of exhalation (expiration, respiratory) distribution.

Histological and scanning electron microscopy (SEM) characteristics of the microvasculature of muscle fibers in the anterior third of the adult rat tongue are described. For light microscopy, the specimens were embedded in paraffin and frontal sections were stained with Picro-Sirius. Thick sections were obtained from Spurr embedded samples and stained with toluidine blue solution. For SEM, specimens were obtained by the corrosion cast method and fractured specimens in dimethyl sulfoxide were observed with high-resolution SEM (HRSEM). The blood vessels, enveloped with a thin layer of connective tissue, had fibers running parallel to the muscular fibers. Capillary arterioles were noted following the endomysium, but their lateral branches often ran at right angles to the fibers. The capillary beds were clearly revealed in transverse sections where the individual capillaries appeared ring-like or elliptical in shape. The nuclei of endothelial cell cores could be seen on the vessel surfaces. Collagen fibers type I and III were noted in the connective tissue and in the fibrous layer of vessels. (J. Oral Sci, 43, 269-275, 2001)

Blood leaving the left ventricle of the heart is distributed to the tissues through the aorta, arteries (large and small), arterioles, and capillaries. Blood is collected from the capillaries via venules, which join repeatedly to form increasingly large veins that finally reach the heart (Figure 1.1). The systemic circulation includes the blood vessels originating from the left ventricle (aorta) and terminating at the right atrium. Pulmonary circulation constitutes the vessels lying between the right ventricle and the left atrium. Vessels are classified according to function: distribution, resistance, exchange, and capacitance or storage. Shunt vessels provide channels that bypass capillary beds. The resistance vessels include small arteries, arterioles, and precapillary sphincters. Capacitance vessels include small and large veins. Capacitance vessels have great capacity to distend. For a similar rise in pressure, capacitance vessels may accommodate 20 times more blood than resistance vessels. Exchange vessels include the capillaries.

A modification of the usual microsphere injection method is presented which is appropriate for rat lung blood flow measurement. The injection of microspheres into the abdominal cava vein, together with the sampling of a reference flow from the right ventricle, allowed to calculate pulmonary blood flows in the same range than the cardiac output. The differences between the two figures (about 30%) are attributed to arterio-venous shunts. The tissue distribution of the microspheres bypassing the lung capillary beds agree with this interpretation.

This chapter describes the normal and the abnormal venous systems. The essential function of veins is to return blood from the peripheral capillary beds to the heart. Veins are constructed to allow flow in one direction only, and this is ensured by their numerous delicate valves. Return against gravity is an essential requirement and most venous problems are related to some form of failure in this due to the inadequacy of valve function or due to the obstruction of flow in major veins. This is the essence of understanding venous disorders. The forces creating or opposing purposeful movement of venous blood are considered first. Gravity is an ever-present force against which the limbs venous system is designed to compete in the upright position. If the valves fail, it is gravity that causes any blood that has been shifted upward to fall back again and this has various effects. In the superficial veins, it may cause visible tortuosity but, much more damaging, the reflux of blood through superficial or deep veins may cause the rapid buildup of an uninterrupted column of blood to the heart with consequent high venous pressure at the ankle. The same force, so malign in the upright position, can be used as a powerful therapeutic measure promoting venous return if the limb is elevated so that the foot is above horizontal and gravity is creating flow in the direction of the heart.

The capillary beds of ten isolated perfused placental cotyledons were examined by injecting microspheres ranging from 2 microgram to more than 20 microgram diameter into the villous circulation. As many as 25 per cent of capillaries may be less than 4 microgram in diameter; there are virtually none whose diameter exceeds 11 microgram and there is no evidence of large diameter vascular shunts.

The role of larval behaviour in successful completion of tissue migration is briefly discussed and it is related to the passive carriage of larvae along the ‘pipes and tubes’ of the host. Larvae of N. brasiliensis were injected into selected portions of the circulatory system and following periods of 5–60 min they were recovered from the blood, liver and lungs. Larvae were also immobilised in 0·4% piperazine, a dosage which permitted recovery in about 60 min. The dispersion of treated larvae was compared with that untreated controls. It was found that larvae were carried very rapidly in the blood stream and that they became lodged in the first capillary bed that they entered. They could not pass through capillary beds without movements (and/or secretions). A decreased number of adults developed after larvae were introduced via a series of routes which required the larvae to pass through an increasing number of ‘hurdles’ to migration.

Morphometric data of the pulmonary veins in the cat right lung are presented. Silicone elastomer casts of the right lungs of five cats were made, measured, counted, and analyzed. The Strahler system is used to describe the branching pattern of the vascular tree. These data are needed for the physicomathematical approach to pulmonary circulation. For all the pulmonary blood vessels lying between the left atrium and the capillary beds, there are a total of 10 orders of vessels in the right upper lobe, 9 orders of vessels in the right middle lobe, and 11 orders of vessels in the right lower lobe. The ratios of the diameters, lengths, and the number of branches in successive orders of vessels are called the diameter, length, and branching ratios, respectively. For the cat pulmonary venous tree, the average branching ratio is 3.521, the average diameter ratio is 1.727, and the average length ratio is 2.402 for vessels of orders 1-3 and 1.532 for vessels of orders 4-10.

The post mortem which was obtained from the tongue of more than ten human adults was examined. The cast of the capillary loops was made by means of injection of acrylic resin via the lingual artery, and then was observed under a scanning electro-microscope. In the filiform papillae the small arteries parallel to the surface of the tongue and make small networks, from which a small branch is given off enters the papillae to be divided into three capillary loops which rise towards the top of papillae. In the circumvallate papillae the small branches rise from networks which are made in the submucosal membrane. The branches give off numerous capillary loops which rise towards the surface of the papillae. The loops decrease in height near the bottom of the groove. The fungiform papillae receives the capillaries from bottom of papillae of capillary beds, and capillary loops are arranged radially towards the surface, and are observed among them.

Unusually high capillary densities, volumes, and surface areas were revealed by morphometric analysis of the hypothalamic paraventricular nuclei (magnocellular and parvocellular division), supraoptic nuclei, and pituitary neural lobe of Long-Evans and Brattleboro rats. Capillaries of the magnocellular division of the paraventricular nucleus were greater in number, but smaller in diameter, than those in the parvocellular division. Expressed per unit area or volume, capillary dimensions in the hypohalamo-neurohypophysial system of Brattleboro rats were the same as in Long-Evans rats.

The regional blood flow to the rat cochlea has been studied using a method which combines the microsphere method with observation of serially-sectioned, plastic-embedded cochleas. Direct quantitation of the microspheres in a reference blood sample and in the different vascular areas of the cochlea allows the analysis of blood flow patterns with respect to the different capillary beds. inner ear, blood flow, microsphere

1. The arterial supply to the atria of the human heart was demonstrated by the Coslett Nixon X-Ray Projection Microscope and the small arteriole and capillary beds examined. 2. The “smooth” portion of the wall of the right atrium revealed an irregular pattern of vessels, while the “rough” part showed parallel arterioles in the musculi pectinati, which supplied numerous clusters of capillaries. 3. The wall of the left atrium possessed circumferentially arranged arterioles, which anastomosed with each other and a circular pattern was demonstrated around the orifices of the pulmonary veins. 4. Arterial vasa were demonstrated in the adventitia of the superior and inferior vena cava in their terminal portions, originating from the arterial plexus in the wall of the right atrium. 5. Measurements of capillary densitities showed that this was greatest in the “rough” portion of the right atrium.

1. Because of the importance of nutrition of the intervertebral disc in relation to its disorders, a detailed study has been made of the neighbouring vasculature of the vertebral body. 2. This has been made possible by an injection technique involving prevention of leakage by freezing with liquid nitrogen. 3. By this method capillary beds are found in the vertebral end-plate cartilage in the adult. A very fine subchondral post-capillary venous network has been demonstrated draining by short vertical tributaries to a much coarser horizontal collecting vein system connecting with the familiar basivertebral system. 4. This arrangement may be of special importance in the nutrition of the intervertebral disc.

We have reviewed the distribution of portal circulations throughout the animal body; they are commoner than is generally supposed. Most portal circulations consist of two serial capillary beds connected by one or more larger vessels. We have called these 'convergent' portal circulations: examples are hepatic portal, placental, hypophysial, renal, ovarian and testicular circulations, as are parts of the lymphatic circulation. A second type of portal circulation, which is less common, consists of two serial capillary beds that are not connected by larger vessels. These we have called 'continuous' portal circulations: adrenal and pancreatic circulations are examples of this type. When a countercurrent concentrating mechanism exists in the body it is always part of the primary or secondary bed of a convergent portal circulation, though some convergent portal circulations are not associated with countercurrent mechanisms.

1. The pulmonary vascular anatomy of the toad, Bufo marinus was studied by scanning electron microscopy of vascular corrosion casts and of tissues prepared for light microscopy. 2. The lung is divided by septa into three orders of alveoli. Arterial branches run in the septa and cannot be observed directly through the lung surface. 3. The capillary bed forms a meshwork over the lumenal surface of septa and lung walls. It is divided into longitudinal zones of arterial distribution; it is broken along primary septal margins into primary alveolar units; within alveoli, it is functionally divided by distortion over circum-alveolar smooth muscle bundles. 4. The capillaries form a network of tubes rather than a perforated sheet of vascular space. Capillary beds on either face of septa are interconnected through the septum. 5. There is no evidence of collateral (“bronchial”) vessels or of anatomically definable shunt vessels. 6. Intrinsic pulmonary arterial branches have a muscular coat.

Fenestrated capillaries are provided with two types of regular discontinuities: fenestrae with negatively charged diaphragms, and transendothelial channels fitted with two diaphragms, of which the luminal one is uncharged. These structures are expected to affect macromolecular exchanges on the basis of size and charge. We have detected variations in the surface density of fenestrations and transendothelial channels (normalized to 1 micron of capillary endothelial profiles in sections) in selected areas of different murine organs, i.e., kidney cortex, duodenal mucosa, and exocrine pancreas. The survey was limited to endothelial segments less than or equal to 400 nm thick, and covered a total length of endothelial profiles of 1180 microns, 730 microns, and 1189 microns in the exocrine pancreas, intestinal mucosa, and kidney cortex, respectively. At least 1000 transendothelial openings were recorded by scoring for easily recognizable fenestrations, transendothelial channels, and unknowns, the latter representing either of the above in grazing sections. The linear density of all transendothelial openings taken together was found to vary among the different capillary beds (kidney cortex greater than intestinal mucosa greater than exocrine pancreas). This same sequence was observed for the linear densities of fenestrations, transendothelial channels, and unknowns considered individually. The values obtained were as follows: kidney cortex, 1.35 fenestrations per micron, 0.25 transendothelial channels per micron, 0.52 unknowns per micron; intestinal mucosa, 0.92 fenestrations per micron, 0.10 transendothelial channels per micron, 0.38 unknowns per micron; exocrine pancreas, 0.58 fenestrations per micron, 0.04 transendothelial channels per micron, 0.27 unknowns per micron. The differences in distribution of transendothelial openings among fenestrated capillary beds probably reflect capillary permeability modulations connected with the functions of these various organs.

The regional blood flow in the cochlea has been studied by mapping the distribution of microspheres in 22 μm thick serial sections of plastic embedded rat and rabbit cochleas. Using a computer-assisted reconstruction technique, a graphic display of the microspheres in each cochlea is obtained. From this display, microspheres may be counted and their distribution may be observed both in relation to the different vascular areas and with respect to the length of the cochlea. This technique, coupled with quantitation of the microspheres in a reference blood sample, offers a method for calculating total and regional cochlear blood flow using non-radioactive microspheres. In addition, this technique allows analysis of blood flow patterns with respect to the different capillary beds along the length of the cochlea. Thus it may be possible to determine if regional blood flow displays a longitudinal gradient, as do other functional, morphologic and biochemical characteristics of the cochlea.

The effects of moderate and severe hypoxia on quantitative regional morphometric indexes of the total and perfused arteriolar and capillary network were studied in the rat brain to determine whether diffusion distances were reduced in hypoxia. Fluorescein isothiocyanate (FITC)-labeled dextran was injected into the femoral vein of conscious control and hypoxic rats. After 20 s, the animal was decapitated and the head was frozen in liquid N2. Sections from eight brain regions were photographed to detect the perfused microvessels and then stained for alkaline phosphatase to visualize the total vascular network. There were significant increases in percent perfused arteriolar and capillary morphology between the two groups of hypoxic animals and control animals. In control rats, the percent of capillaries perfused averaged 45.6 +/- 0.6% (mean +/- SE). In moderate hypoxia 63.4 +/- 1.8% of the vessels were perfused and in severe hypoxia 89.4 +/- 0.1% were perfused. The percentage of arterioles perfused changed similarly. There were no significant differences in any index of total or percent perfused arteriolar or capillary morphometry among the regions within any group. During severe hypoxia, a greater percentage of the capillary reserves was utilized. These results demonstrate a uniform response to hypoxia in the capillary and arteriolar network of the conscious rat brain.

This paper reports the results of a scanning electron microscopy (SEM) study of the vessels in the cochlea of the Mongolian gerhil. Using the microcorrosion technique and SEM we were able to obtain an overall picture of the capillary beds in the cochlea of the gerbil. The vasculature of the inner ear of the gerbil was found to differ from Wistar rats. The different vascular anatomy in comparison with the Wistar rat is discussed.

A measure was made of the perfused capillary surface area per gram of tissue (Sf) in postural, anterior latissimus dorsi (ALD), and locomotor, posterior latissimus dorsi (PLD), skeletal muscles in chickens. The animals were anesthetized with L.A. Thesia and the ALD and PLD muscles were prepared for observation using a modification of the method developed by R. E. Klabunde and P. C. Johnson (1977, Amer. J. Physiol.232, H411–417). Sf was determined from the relationship Sf = πdLθf, where d = capillary diameter, L = capillary length, and θf = number of perfused capillaries per gram. Capillary lengths and diameters were measured directly through the microscope. Estimates of θf were measured in two ways: by a flow method (θQf), and by an histochemical method (θHf). It was observed that the average capillary diameter in PLD was the same as in ALD muscles, but the average capillary length in PLD was two times longer than in ALD muscles. Both the flow and histochemical methods yielded values of θf that gave similar values of Sf for PLD muscles (SQf = 24.7 ± 20.0 cm2/g, SHf = 13.7 ± 14.4 cm2/g), but different values for ALD muscles (SQf = 9.8 ± 6.8 cm2/g, SHf = 42.8 ± 19.1 cm2/g). The difference between SQf and SHf for ALD muscles could be explained by the more irregular and longer perfusion path observed in postural versus locomotor muscle. The flow method appears to underestimate Sf in capillary beds with irregular perfusion paths. The results indicate that only a small fraction of the total capillary bed was perfused in resting skeletal muscle and that SHf for ALD was approximately three times larger than SHf for PLD.

Studies on the vascularization of the cochlea with conventional injection methods that use light microscopy have failed in viewing both the overall three-dimensional picture, as well as the detailed construction of the cochlea vascular blood vessels. This basic shortcoming can be omitted by the use of scanning electron microscopy (SEM) on corrosion casts, which only presently has been introduced. The use of a commercial resin (Mercox) as an injected medium, followed by application of macerating fluids, provides clean and completely filled casts of the cochlea vascular system, which can then be inspected by SEM. This method not only confirms the general findings about cochlea vascularization but gives the opportunity to view the overall picture, as well as the detailed pattern of the intricate cochlear capillary beds.

We examined latex casts of the pulmonary microcirculation with the scanning electron microscope (SEM). Mature rats were anesthetized and ventilated; the pulmonary vasculature was washed out with lactated Ringer solution and then filled with a mixture of Geon latexes. The airways were filled with glutaraldehyde with resulting transmural vascular pressures of 10 cmH2O. After critical-point drying and corrosive removal of the lung tissue, SEM studies of the vascular replicas revealed two distinct patterns of pulmonary microcirculation: 1) sparse, long, tubular capillaries that comprise the thin subpleural layer and appear as “filler” in the peribronchial spaces; and 2) alveolar microcirculation that is composed of tightly matted, intersecting tubules, shorter but of the same diameter as type 1, in spherical array in two layers. The alveolar capillaries at low magnification appear superficially as sheets; however, the detailed morphology is not consistent with the sheet-and-post model. We conclude that the basic component of the pulmonary microcirculation is tubular and not different from other capillary beds except in density.

Horseradish peroxidase was detected in the choroid plexus capillary 5 min after the onset of a 2 1 2 - min injection of 7.5 μl of 40% solution into the cisterna cerebellomedullaris in mice. Venous capillaries in the capillary beds of circumventricular organs including the choroid plexus were indicated as sites of cerebrospinal fluid absorption.

Dog hearts were taken without loss of blood under 3 different conditions: (1) normally beating hearts, (2) hearts that were arrested by potassium chloride for varying lengths of time and (3) potassium chloride-arrested hearts that were reperfused with blood after varying lengths of time. In normal hearts counts of open capillaries containing erythrocytes showed a uniform distribution throughout the right myocardium and a gradient decreasing from the epicardium toward the endocardium in the left myocardium. Potassium chloride-arrested hearts showed a reverse gradient in the left myocardium. In normal hearts, erythrocytes are oriented in capillaries so that their flat sides lie against the nearest myocardial cell. In the arrested hearts, one sees few or no erythrocytes with this orientation. The erythrocytes in the arrested hearts are swollen, rounded, or packed in clumps in the capillaries. Arrested hearts exhibit a weakening of the connective tissue elements of the myocardium, evident upon fixation or on perfusion of the myocardium with blood. The weakening increases as the length of myocardial arrest increases.

The validity of current theories concerning the function of the area postrema ultimately rests on the nature of its microcirculation. Therefore a detailed study of the vasculature of the postremal region was undertaken in the rat. The findings indicate a singular arteriolar supply from branches of the posterior inferior cerebellar arteries. These vessels are caudal, intracranial branches of the vertebral arteries. Networks of enlarged capillaries are prominent features of sections taken through the area postrema. These enlarged capillary channels are re-entrant. At the borders of the structure they are joined by short interconnecting vessels to capillaries of smaller caliber typical of the medullary tissue. The bed is considered to be a portal system because two distinctive, serially connected capillary beds are interposed between artery and vein. No arteriovenous shunts or thoroughfare channels are observed in the rat, contrary to reports of this type of vessel in other species. This microcirculatory pattern would seem to be adequate to current theories of postremal function, which attribute neurosecretory or chemosensory functions to this region.

Publisher Summary An arterio-venous fistula can be defined as an abnormal connection between an artery and vein whose resistance is less than that is offered by the capillary bed which normally connects them. The large arterio-venous fistulae are usually traumatic in origin, whereas the minute fistulae are usually multiple and congenital. The different types of congenital arterio-venous abnormality represent arrest at different stages of the development. The conglomeration of undifferentiated blood vessels in a haemangioma is similar to the primitive network of blood spaces. In later development, when the main vessels are becoming differentiated, many others are obliterated that would otherwise bypass the capillary beds. Failure to obliterate such vessels leads to abnormal arterio-venous connections and is the cause of multiple congenital microscopic arterio-venous fistulae. This chapter discusses the two common types of arterio-venous fistula, the congenital multiple fistulae and the acquired fistula. The clinical features of an acquired fistula depend upon its size and site; however, both the local and the general effects are similar to those described for congenital fistulae.

Injections of various opaque materials including latex, India ink, and silicone rubber were used to examine microscopic sections and whole specimens of the rat submaxillary gland. An excretory duct, several large collecting ducts and a complex system of blood vessels occupy the central areas of the gland, surrounded by connective tissue. A major bifurcation of these central structures occurs approximately 1 3 into the gland. Excretory, collecting and striated ducts are well supplied with a thick capillary network which is connected to an extensive secondary network of metarteriole-sized vessels. Thus, a total of three different strata of blood vessels accompany the excretory and central collecting ducts: (1) the intramural extensive network of capillaries of the ducts themselves, (2) an outermost layer of one, two or three large arteries and veins, and (3) a middle area of intermediate sized vessels (intermediate arteriolar plexus). These latter vessels connect the large vessels with the ductal network, and supply capillaries of the connective tissue in the area and vasa vasorum; this intermediate arteriolar plexus also shows connections between larger vessels which may represent an A-V shunt system. The granular ducts and acini appear to be served by the same capillary bed, which is rather sparse compared to that of the more distal striated, collecting and excretory ducts. These acinar capillary beds are composed of end capillaries of the arteries which accompany the collecting ducts as they enter the lobules, the vessels branching together with the ducts to the most proximal parenchymal areas containing the acini. The venous drainage of these areas also parallels the ducts.

THE appearance of tumor cells in peripheral blood drawn from the antecubital vein in patients with various visceral cancers has been frequently reported.1-3Depending upon the location of the primary tumor or its known secondaries, these cells would have traversed one or more organ vascular beds. Tumor cells are generally larger than the normal formed elements of the blood, a factor of possible importance in their arrest and subsequent development into metastases. Certain tissues and organs, including those of the distribution drained by the antecubital veins, are rarely the site of metastatic implant. It could be inferred from the clinical studies on antecubital vein blood that such tumor cells had either passed through or around the capillary beds of hand and forearm unimpeded and, hence, produced no metastases. There is no evidence, however, that other tumor cells had not entered these capillary beds, lodged, and become nonviable. Three possibilities

Author summary After an ischaemic stroke—one where a clot blocks a major artery in the brain—patients can undergo a procedure where the clot is removed mechanically via a catheter—a thrombectomy. This reopens the blocked vessel, yet some patients don’t achieve blood flow returning to their tissue downstream. One hypothesis for this phenomenon is that the clot fragments into smaller clots (called micro-emboli) which block smaller vessels downstream. However, this can’t be measured in patients due to the inability of clinical imaging resolving the micro-scale. We therefore develop a computational model here, based on experimental thrombectomy data, to quantify the impact of micro-emboli on blood flow in the brain after the removal of a clot. With this model, we found that micro-emboli are a likely contributor to the no-reflow phenomenon after a thrombectomy. Individual blood vessel geometries, clot composition, and thrombectomy technique all impacted the effect of micro-emboli on blood flow and should be taken into consideration to minimise the impact of micro-emboli in the brain. Furthermore, the computational model developed here allows us to now build large-scale models of blood flow in the brain, and hence simulate stroke and the impact of micro-emboli on the entire brain., Many ischaemic stroke patients who have a mechanical removal of their clot (thrombectomy) do not get reperfusion of tissue despite the thrombus being removed. One hypothesis for this ‘no-reperfusion’ phenomenon is micro-emboli fragmenting off the large clot during thrombectomy and occluding smaller blood vessels downstream of the clot location. This is impossible to observe in-vivo and so we here develop an in-silico model based on in-vitro experiments to model the effect of micro-emboli on brain tissue. Through in-vitro experiments we obtain, under a variety of clot consistencies and thrombectomy techniques, micro-emboli distributions post-thrombectomy. Blood flow through the microcirculation is modelled for statistically accurate voxels of brain microvasculature including penetrating arterioles and capillary beds. A novel micro-emboli algorithm, informed by the experimental data, is used to simulate the impact of micro-emboli successively entering the penetrating arterioles and the capillary bed. Scaled-up blood flow parameters–permeability and coupling coefficients–are calculated under various conditions. We find that capillary beds are more susceptible to occlusions than the penetrating arterioles with a 4x greater drop in permeability per volume of vessel occluded. Individual microvascular geometries determine robustness to micro-emboli. Hard clot fragmentation leads to larger micro-emboli and larger drops in blood flow for a given number of micro-emboli. Thrombectomy technique has a large impact on clot fragmentation and hence occlusions in the microvasculature. As such, in-silico modelling of mechanical thrombectomy predicts that clot specific factors, interventional technique, and microvascular geometry strongly influence reperfusion of the brain. Micro-emboli are likely contributory to the phenomenon of no-reperfusion following successful removal of a major clot.