Contribution Of Mechanical Factors Research Articles

Tension at intercellular junctions is necessary for accurate orientation of cell division in the epithelium plane

The direction in which a cell divides is set by the orientation of its mitotic spindle and is important for determining cell fate, controlling tissue shape, and maintaining tissue architecture. Divisions parallel to the epithelial plane sustain tissue expansion. By contrast, divisions perpendicular to the plane promote tissue stratification and lead to the loss of epithelial cells from the tissue-an event that has been suggested to promote metastasis. Much is known about the molecular machinery involved in orienting the spindle, but less is known about the contribution of mechanical factors, such as tissue tension, in ensuring spindle orientation in the plane of the epithelium. This is important as epithelia are continuously subjected to mechanical stresses. To explore this further, we subjected suspended epithelial monolayers devoid of extracellular matrix to varying levels of tissue tension to study the orientation of cell divisions relative to the tissue plane. This analysis revealed that lowering tissue tension by compressing epithelial monolayers or by inhibiting myosin contractility increased the frequency of out-of-plane divisions. Reciprocally, increasing tissue tension by elevating cell contractility or by tissue stretching restored accurate in-plane cell divisions. Moreover, a characterization of the geometry of cells within these epithelia suggested that spindles can sense tissue tension through its impact on tension at subcellular surfaces, independently of their shape. Overall, these data suggest that accurate spindle orientation in the plane of the epithelium relies on a threshold level of tension at intercellular junctions.

Postpartum Sacral Stress Fracture: An Atypical Case Report.

Sacral stress fractures are common in elderly people. However, sacral stress fracture should be always screened in the differential diagnoses of low back pain during the postpartum period. We present a case of sacral fracture in a thirty-six-year-old woman with low back pain and severe right buttock pain two days after cesarean section delivery of a 3.9 Kg baby. The diagnosis was confirmed by MRI and CT scan, while X-ray was unable to detect the fracture. Contribution of mechanical factors during the cesarean section is not a reasonable cause of sacral fracture. Pregnancy and lactation could be risk factors for sacral stress fracture even in atraumatic delivery such as cesarean section. Our patient had no risk factors for osteoporosis except for pregnancy and lactation. Transient or focal osteoporosis is challenging to assess and it cannot be ruled out even if serum test and mineral density are within the normal range.

TCT-691: Contributions of Mechanical Factors and Biologic Response to Sirolimus- Eluting Stent Thrombosis: Final IVUS Results From the RESTART Registry

TCT-691: Contributions of Mechanical Factors and Biologic Response to Sirolimus- Eluting Stent Thrombosis: Final IVUS Results From the RESTART Registry

Angular Distribution of Slip Steps by Three-Dimensional Polycrystalline Model for Stainless Steel

Localized deformation plays an important role in the initiation of irradiation-assisted stress corrosion cracking, and it can be characterized by the spacing and inclination of slip steps observed on the surface. In order to examine the contribution of mechanical factors (stress) to slipping, the angular distribution of slip steps was evaluated by using a three-dimensional polycrystalline model generated by Voronoi tessellation. An elastic finite element analysis was performed to derive the resolved shear stress (RSS) acting on each slip system. Random crystallographic orientations assigned to each grain caused the microstructural inhomogeneity of local stress due to anisotropic elastic properties. The angular distribution obtained was compared with the experimental results observed in irradiated and deformed stainless steel. It was shown that mechanical factors dominate the slipping behavior of the irradiated stainless steel and that not only RSS but also normal stress acting on the slip plane affects the crystallographic slip. The angular distribution was also evaluated from the maximum Schmid factor of individual grains, in which the inhomogeneous local stress was not taken into account. The angular distributions obtained using RSS and the Schmid factor were almost the same. This suggests that the inhomogeneity of local stress negligibly affects the angular distribution of slip steps, although the change in the local stress in the polycrystalline material is significant.

Postpartum Sacral Stress Fracture

Low-back and buttock pain is a common complaint during pregnancy and the postpartum period and is usually attributable to mechanical lesions of the pelvis. Sacral stress fractures are unusual but important causes that should be considered in differential diagnosis. To date, only eight postpartum sacral stress fractures have been reported in the literature. A 32-yr-old woman presented with low-back and right buttock pain that started 15 days after uneventful cesarean section delivery. Imaging studies revealed a right sacral stress fracture. Lumbar spine and femoral neck bone mineral density were normal and, except for pregnancy and lactation, no risk factors for osteoporosis were identified. There was no history of trauma, excessive weight gain, strenuous physical activity, or contribution of mechanical factors. The question remains whether this is an insufficiency fracture or a fatigue fracture. Clinicians should consider sacral fracture during pregnancy and the postpartum period as a diagnostic possibility in patients with low-back and/or buttock pain.

Simulation of mechanoelectrical coupling in cardiomyocytes under normal and abnormal conditions

Mathematical models of the electromechanical function of cardiomyocytes and muscle duplexes, the simplest mechanically inhomogeneous myocardial systems, are developed. Using these models, the contribution of mechanoelectrical feedbacks to the contractive activity of the myocardium in normal and abnormal conditions is studied. In particular, the influence of the mechanical conditions of contraction on the shape and duration of the action potentials is reproduced and interpreted. In this context, different types of mechanical heterogeneity of the myocardium are analyzed. It is established that this heterogeneity can play a positive or negative role depending on the distribution of heterogeneous properties and on the order the elements of the system are activated. Using the same models, the contribution of mechanical factors to arrhythmogenesis under calcium overload of cardiomyocytes due to the weakening of the sodium-potassium pump is studied. Methods for correction of the contractive activity of cardiomyocytes in the case of such abnormalities are outlined.

Urethral Funlction after Chronic Cauda Equina Lesions in Cats. I. The Contribution of Mechanical Factors and Sympathetic Innervation to Proximal Sphincter Dysfunction

We investigated the contribution of mechanical and sympathetic neural factors to proximal urethral sphincter dysfunction in the cat after chronic sacral rhizotomy. Concomitant vesicostomy prevented a decrease in the urethral pressure profile measured three months post-rhizotomy. Sympathetic influences on basal urethral perfusion pressure were the same in neurally-intact and chronic rhizotomised cats. A significant prazosin-sensitive component of basal urethral perfusion pressure remained after section of all extrinsic urethral innervation in both neurally-intact and chronic cats. Local intra-arterial 6-hydroxydopamine also abolished this component. After rhizotomy, noradrenaline content in the proximal urethra was significantly increased but there was no change in sensitivity to sympathetic stimulation. A small (5% of control) atropine-sensitive and prazosin-resistant constriction was seen only after chronic sacral rhizotomy.We conclude that a mechanical factor associated with bladder expression and not an alteration in sympathetic control is the major factor leading to diminished proximal urethral closure after vesicourethral lower motor neuron lesion. Furthermore, short adrenergic neurons have an important role in the maintenance of urethral pressure in the normal state and after lower motor neuron lesion. (J. Urol., 144: 1022–1028, 1990)

Length changes within isolated frog muscle spindle during and after stretching.

1. The length changes within the frog muscle spindle during stretch have been studied by stroboscopic photomicroscopy. Attention was focused on the length changes within the central reticular zone and these changes were related to the features of the receptor potential.2. It was found that the length changes of the central reticular zone closely followed the applied stretch in time course and magnitude. The results suggest that the length changes of the polar zones are generally similar to those in the central zone.3. There was no evidence of a relative shortening of the central zone in the early phase of maintained stretch, corresponding to the decline of the receptor potential from its dynamic peak to the static level.4. Following release of stretch the central zone returned to its original resting length within a few msec. The rapid return of the spindle was in sharp contrast to the relatively slow exponential decay of the receptor potential. With strong or prolonged stretches the return became slower and resting length was not completely restored until 100-150 msec after release of stretch. No corresponding change in the decay of the receptor potential was seen.5. The results suggest that the early adaptive fall of the receptor potential is not related to differential length changes between the central zone and the polar zones. It seems more likely that the contribution of mechanical factors to the early adaptation of the frog spindle have to be sought at the ultrastructural level.6. The finding that the length changes closely follow the applied stretch suggests that the stimulus in terms of lengthening is transmitted to the endings with little distortion.7. The results suggest that the elastic elements play a dominant role for the transmission of the stimulus to the endings and for the return of the spindle to resting length after release of stretch.