Plexiform Structure Research Articles

Urogenital vasculature and local steroid concentrations in the uterine branch of the ovarian vein of the female tammar wallaby (Macropus eugenii).

The urogenital vasculature of the tammar comprises 4 major paired arteries and veins: the ovarian, the cranial urogenital, the caudal urogenital and the internal pudendal artery and vein. The ovarian artery and vein and their uterine branches which supply the ovary, oviduct and uterus, ramify extensively. Each anterior urogenital artery and vein supplies the caudal regions of the ipsilateral uterus, lateral and median vagina and cranial parts of the urogenital sinus. The caudal urogenital arteries and veins supply the urogenital sinus and caudal regions of the bladder. The internal pudendal artery and vein vascularize the cloacal region, with some anastomoses with branches of the external pudendal vessels. Anastomoses connect the uterine branch of the ovarian artery with the uterine branch of the cranial urogenital and cranial branches of the caudal urogenital arteries, and connect the caudal urogenital and the internal pudendal arteries. Anastomotic connections between the left and right arterial supply also occur across the midline of the cervical regions of the uteri and the anterior lateral vaginae. Similar connections are seen in the venous system. The uterine branch of the ovarian artery ramifies extensively very close to the ovary, giving a plexiform arrangement with the ovarian veins, and also with the uterine venous system on the lateral side of each uterus. This plexiform structure provides an anatomical arrangement which could allow a local transfer of ovarian hormones from ovarian vein into the uterine arterial supply, and thence to the ipsilateral uterus. Progesterone concentrations in plasma from the mesometrial side of the uterine branch of the ovarian vein are markedly higher than in tail vein plasma, especially during the 'Day 5 peak' early in pregnancy, and also at full term. There is also a marked decrease in progesterone concentration from all sites immediately before birth as previously reported for peripheral plasma. These results support the suggestion of a countercurrent transfer mechanism, at least for progesterone, and possibly other hormones, between the ovarian vein and uterine artery. Such a local transfer could explain the different morphological responses of the endometria of the two adjacent uteri during pregnancy in macropodid marsupial species.

Fracture properties of bovine tibial bone

Linear elastic fracture mechanics predicts that the fracture stress of precracked materials is dependent on the length of the initial crack and crack tip radius of curvature, as supported by the Griffith and Inglis equations. In order to determine the applicability of these equations and the effects of other variables, tensile specimens of bovine tibia were produced with edge cracks of known dimensions and tested to fracture. Longitudinal sheet tensile specimens were taken from the midposterior diaphysis of bovine tibiae that had been kept frozen in saline soaked towels. Each specimen had a milled gauge length of 25 mm, 16 mm width and 2 mm thickness. All specimen preparation was performed under a saline drip. An edge crack, centered along the gauge length, was milled in the specimen perpendicular to its long axis. The crack lengths used were 4, 6, 8, 10 and 12 mm. The crack tip was formed with drill bits having nominal diameters of 1 32 , 1 16 , and 3 32 in. All the combinations of crack length and crack tip radius were repeated five times for a total of 75 specimens. The testing order was randomly selected. Each specimen was tested in tension to fracture at a constant deformation rate of 7.5 × 10 −3 mm s −1, on an Instron mechanical testing device, and the fracture stress was measured. A linear load-deflection curve to fracture was exhibited by all of the specimens. The weight percent calcium of each specimen was determined by atomic absorption spectrophotometry. Microradiographs were used to determine the fractional void area and to histologically evaluate each bone sample. The weight percent calcium and the fractional void area were found to not significantly influence the fracture stress. A plexiform structure was present throughout the specimens. A two-way analysis of variance found that the fracture stress was dependent on the crack length ( F = 161.79, p < 0.0001) and not on the crack tip radius of curvature ( F = 1.37, p > 0.26). The relationship between the fracture stress and crack length can be expressed as σ frac= 7.12c −1 2 −54.2 MPa which is similar to the Griffith equation. The surface energy, intrinsic flaw size, and an estimate of the opening mode critical stress intensity factor were found to be 3.98 kJm −2, 1.82 mm and 11.2 ± 2.6 MNm −3 2 , respectively.

Arrhythmogenic right ventricular dysplasia a clinical model for the study of chronic ventricular tachycardia.

Arrhythmogenic right ventricular dysplasia (ARVD) is a recently individualised clinical entity which sometimes presents with episodes of ventricular tachycardia (VT). These attacks may be resistant to anti-arrhythmic therapy and new therapeutic approaches have been developed for the treatment of this condition. These new methods are mainly surgical, based on the analysis of the electrical activation of the heart in sinus rhythm and during VT. This approach has increased our understanding of the physiopathology of VT, not only in the context of ARVD, but also in the most commonly encountered clinical setting of VT, after myocardial infarction. Electrophysiological study of the epicardial activation of the dysplastic zones has demonstrated the presence of delayed potentials recorded after the end of the QRS complex. This can be explained by the histopathology of these tissues. ARVD is characterised histologically by partial degeneration of the myocardial wall. Most of the muscle fibers are replaced by fatty tissue in the middle of which some healthy fibers survive. These changes are mainly observed in the intramyocardial and subepicardial layers, the subendocardium being almost normal. Strands of isolated muscle fibers within the non-conducting fatty degeneration may lead to very delayed activation with respect to the adjacent healthy tissues. The propagation of activation is delayed as it passes through this plexiform structure and in the zones adjacent to healthy muscle were reentry phenomena may arise. In ARVD, these changes are mainly located over the right ventricle, so explaining the right ventricular origin of most forms of VT observed in this condition. However, we have also observed a case which suggested an isolated arrhythmogenic left ventricular dysplasia. Epicardial mapping localizes the point of origin of VT in zones situated between the slow and normally conducting tissues. Simple ventriculotomy, a full thickness section of the ventricular wall, at the point of epicardial breakthrough of the VT prevents recurrence in the great majority of patients. The same pathophysiological concepts may be applied to VT complicating myocardial infarction but in this situation the myocardial fibers capable of slowly conducting the activation are isolated within the fibrous tissue in the border zone of the infarct. The point of origin of VT is usually within the interventricular septum with a point of epicardial breakthrough which could be located some distance away. Different surgical techniques have been developed to deal with this condition. Encircling endocardial ventriculotomy isolates the arrhythmogenic zone from the rest of healthy tissues by tracin

Plexiform structures in malignant schwannomas after prenatal exposure to ethylnitrosourea

75 Schwann cell tumors were induced in the offspring of Wistar rats which had been treated intraperitoneally with 15 mg/kg b.w. ethylnitrosourea on the 15th day of pregnancy. Plexiform structures characterized by poorly-developed, distorted and bizarre bundles of nerves were seen in 2 of 33 benign tumors, and in 17 of 42 malignant schwannomas. Since when seen in man similar findings are distinctive of neurofibromatosis, it is suggested that this experiment may offer a model for studying non-inherited forms of neurofibromatosis and, more particularly, the malignant changes often associated with this disease.

The intestine of Triatoma infestans. II. The surface coat of the midgut

The apical surface of the midgut epithelium in fasted Triatoma infestans shows a striated border covered by a surface coat. The electron microscope demonstrates that the surface coat, which has a tubular plexiform structure, is at least four times the height of the microvilli. A trilaminar membrane thinner than the cell membrane covers the apical surface of the epithelial cells and projects as tubular expansions into the lumen of the intestine. The trilaminar membrane ensheathes each microvillus. The intervillus space is occupied by a meshwork of septa continuous with the trilaminar membrane. Cytochemical techniques suggest that the extracellular coating contains glycophospholipids and acid phosphatase.

Cranial venous system and the posterior fossa in spina bifida aperta

A study of the cerebral venous system in children with S.B.A. was undertaken, and this report concerns the gross structure of this structure of this system in the posterior fossa. Noteworthy is the closeness of the torcular to the foramen magnum. The lateral sinuses ran near to the foramen magnum to the sigmoid sinuses. The dura of the posterior fossa consisted of a plexiform structure in which no clear distinction could be made between various sinus systems normally present in the dural layers of the posterior fossa, thus constituting an occipital plexus. The walls of the sinuses were weak and were vulnerable to mechanical pressure. The foramen magnum of the skulls of children with S.B.A. was larger than in normal children. The distance of the torcular to the ventral margin of the foramen magnum was smaller in S.B.A. This distance remained unchanged at least until nine months of age in normal children as well as in children with S.B.A., although there was an increase in size of the foramen magnum in both with advancing age.

Necrotizing and healing pulmonary arteritis in schistosomal cor pulmonale: a retrospective study of ten cases.

SummaryA study was made of the necrotizing and healing arteritis in 10 patients who had developed schistosomal cor pulmonale. The necrotizing vasculitis was classified into two groups: (1) produced directly by the Schistosoma mansoni eggs and of probable allergic origin and (2) not directly related to the presence of eggs and apparently connected with either hypersensitive reactions caused by antigenic substances in the circulating blood or with a nonspecific reaction to hypertension. The widespread healed arteritis is described and an attempt is made to relate the organization and recanalization of hyaline thrombi to the development of plexiform structures.