Induction and Patterning of the Purkinje Fibre Network

2008 ◽  
pp. 142-156 ◽  
Author(s):  
Takashi Mikawa ◽  
Robert G. Gourdie ◽  
Kimiko Takebayashi-Suzuki ◽  
Nobuyuki Kanzawa ◽  
Jeanette Hyer ◽  
...  
Keyword(s):  
Purkinje Fibre ◽  
Fibre Network

scholarly journals The elastic properties of composites reinforced by a transversely isotropic random fibre-network

2019 ◽  
Vol 208 ◽  
pp. 33-44 ◽  
Author(s):  
Xiude Lin ◽  
Hanxing Zhu ◽  
Xiaoli Yuan ◽  
Zuobin Wang ◽  
Stephane Bordas
Keyword(s):  
Elastic Properties ◽  
Transversely Isotropic ◽  
Fibre Network ◽  
Random Fibre ◽  
Isotropic Random ◽  
Properties Of Composites

scholarly journals Cell–matrix interaction during strain-dependent remodelling of simulated collagen networks

2016 ◽  
Vol 6 (1) ◽  
pp. 20150069 ◽  
Author(s):  
Lazarina Gyoneva ◽  
Carley B. Hovell ◽  
Ryan J. Pewowaruk ◽  
Kevin D. Dorfman ◽  
Yoav Segal ◽  
...  
Keyword(s):  
Mechanical Stability ◽  
Theoretical Work ◽  
Collagen Fibres ◽  
Tissue Remodelling ◽  
Cell Network ◽  
Fibre Network ◽  
Cell Matrix ◽  
A Cell ◽  
Tensional Homeostasis ◽  
Strain Dependent

The importance of tissue remodelling is widely accepted, but the mechanism by which the remodelling process occurs remains poorly understood. At the tissue scale, the concept of tensional homeostasis, in which there exists a target stress for a cell and remodelling functions to move the cell stress towards that target, is an important foundation for much theoretical work. We present here a theoretical model of a cell in parallel with a network to study what factors of the remodelling process help the cell move towards mechanical stability. The cell-network system was deformed and kept at constant stress. Remodelling was modelled by simulating strain-dependent degradation of collagen fibres and four different cases of collagen addition. The model did not lead to complete tensional homeostasis in the range of conditions studied, but it showed how different expressions for deposition and removal of collagen in a fibre network can interact to modulate the cell's ability to shield itself from an imposed stress by remodelling the surroundings. This study also showed how delicate the balance between deposition and removal rates is and how sensitive the remodelling process is to small changes in the remodelling rules.

Cellular and subcellular mechanisms of cardiac pacemaker oscillations

1979 ◽  
Vol 81 (1) ◽  
pp. 205-215
Author(s):  
R. W. Tsien ◽  
R. S. Kass ◽  
R. Weingart
Keyword(s):  
Membrane Potential ◽  
Voltage Clamp ◽  
Surface Membrane ◽  
Cardiac Pacemaker ◽  
Oscillatory Activity ◽  
Purkinje Fibre ◽  
Pacemaker Activity ◽  
Heart Cells ◽  
Control Loop ◽  
Internal Oscillation

Rhythmic oscillations in the membrane potential of heart cells are important in normal cardiac pacemaker activity as well as cardiac arrhythmias. Two fundamentally different mechanisms of oscillatory activity can be distinguished at the cellular and subcellular level. The first mechanism, referred to as a surface membrane oscillator, can be represented by a control loop in which membrane potential changes evoke delayed conductance changes and vice versa. Since the surface membrane potential is a key variable within the control loop, the oscillation can be interrupted at any time by holding the membrane potential constant with a voltage clamp. This mode of oscillation seems to describe spontaneous pacemaker activity in the primary cardiac pacemaker (sinoatrial node) as well as other regions (Purkinje fibre, atrial or ventricular muscle). In all tissues studied so far, the pacemaker depolarization is dominated by the slow shutting-off of an outward current, largely carried by potassium ions. The second mechanism can be called an internal oscillator since it depends upon a subcellular rhythm generator which is largely independent from the surface membrane. Under voltage clamp, the existence of the internal oscillation is revealed by the presence of oscillations in membrane conductance or contractile force which occur even though the membrane potential is held fixed. The two oscillatory mechanisms are not mutually exclusive; the subcellular mechanism can be preferentially enhanced in any given cardiac cell by conditions which elevate intracellular calcium. Such conditions include digitalis intoxication, high Cao, low Nao, low or high Ko, cooling, or rapid stimulation. Several lines of evidence suggest that the subcellular mechanism involves oscillatory variations in myoplasmic calcium, probably due to cycles of Ca uptake and release by the sarcoplasmic reticulum. The detailed nature of the Cai oscillator and its interaction with the surface membrane await further investigation.

Effective anisotropic properties of fibre network sheets

2022 ◽  
pp. 104492
Author(s):  
Massimo Cuomo ◽  
Claude Boutin ◽  
Loredana Contrafatto ◽  
Salvatore Gazzo
Keyword(s):  
Anisotropic Properties ◽  
Fibre Network ◽  
Effective Anisotropic Properties

The spatial distribution and relative abundance of gap-junctional connexin40 and connexin43 correlate to functional properties of components of the cardiac atrioventricular conduction system

1993 ◽  
Vol 105 (4) ◽  
pp. 985-991 ◽  
Author(s):  
R.G. Gourdie ◽  
N.J. Severs ◽  
C.R. Green ◽  
S. Rothery ◽  
P. Germroth ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Relative Abundance ◽  
Atrioventricular Node ◽  
Conduction System ◽  
Atrioventricular Conduction ◽  
Purkinje Fibre ◽  
Purkinje Fibres ◽  
Atrioventricular Bundle ◽  
Junctional Protein ◽  
Gap Junctional

Electrical coupling between heart muscle cells is mediated by specialised regions of sarcolemmal interaction termed gap junctions. In previous work, we have demonstrated that connexin42, a recently identified gap-junctional protein, is present in the specialised conduction tissues of the avian heart. In the present study, the spatial distribution of the mammalian homologue of this protein, connexin40, was examined using immunofluorescence, confocal scanning laser microscopy and quantitative digital image analysis in order to determine whether a parallel distribution occurs in rat. Connexin40 was detected by immunofluorescence in all main components of the atrioventricular conduction system including the atrioventricular node, atrioventricular bundle, and Purkinje fibres. Quantitation revealed that levels of connexin40 immunofluorescence increased along the axis of atrioventricular conduction, rising over 10-fold between atrioventricular node and atrioventricular bundle and a further 10-fold between atrioventricular bundle and Purkinje fibres. Connexin40 and connexin43, the principal gap-junctional protein of the mammalian heart, were co-localised within atrioventricular nodal tissues and Purkinje fibres. By applying a novel photobleach/double-labelling protocol, it was demonstrated that connexin40 and connexin43 are co-localised in precisely the same Purkinje fibre myocytes. A model, integrating data on the spatial distribution and relative abundance of connexin40 and connexin43 in the heart, proposes how myocyte-type-specific patterns of connexin isform expression account for the electrical continuity of cardiac atrioventricular conduction.

Histopathology of pituitary tumours

2011 ◽  
pp. 121-127
Author(s):  
Eva Horvath ◽  
Kalman Kovacs
Keyword(s):  
Mammalian Species ◽  
Cell Types ◽  
Pars Intermedia ◽  
Pars Tuberalis ◽  
Posterior Lobe ◽  
Human Pituitary ◽  
Human Pituitary Gland ◽  
Fibre Network ◽  
Pars Anterior ◽  
A Minor

The human pituitary gland consists of two major components: the adenohypophysis comprising the hormone producing cells of the pars anterior, pars intermedia, and pars tuberalis, and the neurohypophysis, also called pars nervosa or posterior lobe (1). In contrast to most mammalian species, the human gland has no anatomically distinct pars intermedia (2). The exclusively proopiomelanocortin (POMC)-producing cells of the pars intermedia are sandwiched between the anterior and posterior lobes in the majority of mammals, whereas in the human they are incorporated within the pars anterior, thereby constituting the pars distalis (3). The pars tuberalis is a minor upward extension of the adenohypophysis attached to the exterior of the lower pituitary stalk. In this chapter we deal only with adenohypophyseal tumours. Histologically, the adenohypophysis consists of a central median (or mucoid) wedge flanked by the two lateral wings. The hormone-producing cell types are distributed in an uneven, but characteristic manner. The cells are arranged within evenly sized acini surrounded by a delicate but well-defined reticulin fibre network giving the pituitary its distinct architecture (4). In the center of the acini is the long-neglected pituitary follicle composed of the agranular nonendocrine folliculo-stellate cells (5).

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