The locomotor system
C. Simon Herrington in Muir's Textbook of Pathology, 2020
The largest tissue within the body, muscle, accounting for 40% of an average male's weight, is highly organized to contract, produce movement or stability, and do work. Skeletal muscle consists of long multinucleated syncytia formed by the fusion of columns of single cells. The cytoplasm contains bundles of myosin and actin filaments forming contractile myofibrils. The individual subunit is the sarcomere and these are arranged end to end to form muscle fibres. The parallel alignment of actin and myosin bundles gives a characteristic band-like appearance on light microscopy and alternating dark (A, anisotropic) and light (I, isotropic) bands are seen on electron microscopy. A variety of other proteins including α-actinin and dystrophin are found within muscle cells. The individual muscle fibre is surrounded by the endomysium. Fibres are bound into fascicles by the perimysium, whereas the muscle itself is sheathed by the epimysium.
Host Defense II: Acquired Immunity
Constantin A. Bona, Francisco A. Bonilla in Textbook of Immunology, 2019
Perhaps the most direct method for avoiding immune destruction is to isolate oneself from contact with immune recognition elements. For example, some viruses (respiratory syncytial virus, herpes viruses, human immunodeficiency virus, and others) can cause syncytia formation. This permits viral spread to infect new cells without their having to enter the circulation and come into contact with potentially neutralizing antibodies. Other microbes may, in fact, replicate in phagolysosomes and resist intracellular killing (Table 11–I). These entities have evolved mechanisms which protect them from intracellular killing in phagocytes and replicate within the very cells attempting to destroy them. During this time, they are protected from attack by humoral and some cellular immune mechanisms (e.g., ADCC). Some parasites may encyst for varying lengths of time and envelop themselves in dense layers of complex glyco/proteins which resist immune destruction. Finally, intestinal worms are protected from the full force of immune mechanisms by inhabiting the intestinal lumen, and not penetrating further into host tissues.
The Secret of Nin: A Novel Neural-Immunological Network Potentially Integral to Immunologic Function in Human Skin
Brian J. Nickoloff in Dermal Immune System, 2019
Cellular and molecular biologists are becoming increasingly aware of the multiplicity and complexity of interactions that dynamically determine skin cell phenotype and function. For the most part, cells do not work alone, but diverse cell types integrate to form interactive syncytia capable of rapid, efficient, and parsimonious signal recognition and propagation. The NIN hypothesis presented here represents a series of cellular and molecular interactions that spatially unify epidermal cells (Langerhans cells, surrounding cytokine-producing keratinocytes) and dermal cells (mast cells) in vertical dimension; dermal mast cells and endothelial cells are unified via axon plexuses in horizontal dimension. Might such a network be capable of direct propagation of primary proinflammatory signals from epidermis to dermis, and secondary or subsidiary signals from central nervous system to peripheral nervous system? Inflammation so induced could spread radially (as many forms of dermatitis do) via similar mechanisms involving axon/mast cell-elicitied endothelial activation.
COVID-19 during Pregnancy and Postpartum:
Published in Journal of Dietary Supplements, 2022
Sreus A. G. Naidu, Roger A. Clemens, Peter Pressman, Mehreen Zaigham, Kelvin J. A. Davies, A. Satyanarayan Naidu
Macro-pinocytosis and viral uptake: Macro-pinocytosis is exploited by many viral pathogens for cell entry. In SARS CoV, S-protein mediates interaction with receptors on adjacent cells, resulting in cell fusion and syncytium formation. Syncytium formation is a cytopathic effect (plasma membrane changes) consistent with macro-pinocytosis that increases cell-to-cell spreading of the virus (Yamada et al. 2009). Macro-pinocytosis is a type of endocytosis that is morphologically defined by the presence of membranous extensions of outwardly polymerizing actin termed membrane ruffles. Membrane ruffles nonspecific vesicles that surround and internalize fluid cargo into large vesicles or macro-pinosomes (Kerr and Teasdale 2009). An active replicating virus could induce macro-pinocytosis. LF inhibits macro-pinocytosis and impairs viral replication and cell-cell fusion (Freeman et al. 2014).
Suggestions for Combatting COVID-19 by Natural Means in the Absence of Standard Medical Regimens
Published in Journal of the American College of Nutrition, 2021
Harry G. Preuss, Okezie I. Aruoma
When the pandemic arose, Dr. Preuss dug into his files and found some preliminary in vitro work concerning their antiviral potential that had been performed but never published. Some success was discovered for both agents against the lipid encapsulated respiratory syncytial virus (RSV). A viral syncytial assay was established using a HEp-2 culture assay based on the concept that when an RSV infects human lung epithelial cells (monolayer), it replicates and invades the adjoining or surrounding cells. A syncytium is formed when infected cells fuze. These infected centers can be visually examined directly or with a phase contrast microscope. Accordingly, effects of oregano oil and monolaurin in comparison with Ribavirin, an antiviral drug on the infection and the development of syncytia were conducted (Table 2).
Physiology of sweat gland function: The roles of sweating and sweat composition in human health
Published in Temperature, 2019
Figure 2(d) shows the mechanism of ion reabsorption according to the modified Ussing leak-pump model. On the apical membrane of the luminal cells passive influx of Na occurs through amiloride-sensitive epithelial Na channels. Active transport of Na across the basolateral membrane of the basal cells occurs via Na-K-ATPase, which is accompanied by passive efflux of K through K channels on the basolateral membrane. The movement of Cl is largely passive via cystic fibrosis membrane channels (CFTR) on both the apical and basolateral membranes [9,34,35]. The two cell layers are thought to be coupled and behave like a syncytium. The sweat duct also reabsorbs bicarbonate, either directly or through hydrogen ion secretion, but the specific mechanism is unknown [5,8,36,37]. The activity of Na-K-ATPase is influenced by the hormonal control of aldosterone [38]. Overall the rate of Na, Cl, and bicarbonate reabsorption is also flow-dependent, such that higher sweating rates are associated with proportionally lower reabsorption rates resulting in higher final sweat electrolyte concentrations [39,40]. This concept will be covered in more detail in the Effect of sweat flow rate section below.
Related Knowledge Centers
- Action Potential
- Gap Junction
- Multinucleate
- Embryo
- Cell Nucleus
- Cytokinesis
- Cardiac Muscle
- Skeletal Muscle
- Cell
- Coenocyte