Lung Defenses
Sunit K. Singh in Human Respiratory Viral Infections, 2014
Epithelials provide a mucosal barrier and contribute to the mucociliary clearance function already mentioned. Lining the luminal surface of the airways, they are attached to neighboring cells by several structures: tight junctions, intermediate junctions, gap junctions, and desmosomes.9 These structures form a barrier between the luminal space and the pulmonary parenchyma. Desmosomes mediate mechanical adhesion of cells to their neighbors and tight junctions completely obliterate the intercellular spaces just below the luminal surface.10 Transport through gap junctions may be a means for the cells to provide their neighbors with defense molecules, such as antioxidants.11 This organization of epithelial cells creates an effective mechanical barrier and allows for polarity in function, thus, maintaining an ionic gradient for bidirectional secretion of many substances.
The Ultrastructure And Pathobiology Of Urinary Bladder Cancer
George T. Bryan, Samuel M. Cohen in The Pathology of Bladder Cancer, 2017
Historically, desmosomes were the first class of cell junctions to be implicated in strong cell-to-cell adhesion.82,103,106 This led to their designation as adherens junctions.123 In all likelihood, all categories of cell junctions are sites of strong intercellular adhesion.82,106 The absolute contribution of each type of cell junction (i.e., occludens, adherens, gap, etc.) to adhesion is technically difficult to measure, especially since several types of junctions are present at the surfaces of most kinds of epithelial cells. Further, the contribution of specific nonjunctional plasma membrane components to cell adhesion under physiological conditions is a matter for speculation at the present time. Ultrastructural observations provide some evidence that the plasma membrane of neighboring epithelial cells are adherent at nonjunctional sites as well as at cell junctions, since the width of the extracellular space tends to remain constant in various physiological states, such as contraction and dilatation of the bladder. On the other hand, cells in epithelia are easily separated by relatively mild perturbations, at nonjunctional sites, but not at cell junctions, indicating that the nonjunctional plasma membranes of neighboring cells are weakly interadherent, at least under artificial conditions.106
The Structure of Odontogenic Cysts
Roger M. Browne in Investigative Pathology of the Odontogenic Cysts, 2019
Ultrastructurally, the epithelial cells demonstrate the same basic organelles as in oral mucosal epithelium, but they lack the orderly progression of changes of the mucosa, as the cells migrate from the basal to the surface layers.67,68 Large numbers of organelles are still present in the surface cells, although histochemical studies indicate a reduction in oxidative enzyme activity towards the epithelial surface.25 Acid phosphatase activity remains largely membrane-bound in the surface layers.24 This relative lack of cellular differentiation is accompanied by a relative lack of blood group reactivity in the cell membranes.28,29,64 Prominent desmosomes are present, although there are wide intercellular spaces, particularly in the presence of inflammation.19 Scanning electron microscopy of the luminal surface of the epithelium reveals channels between the cells, some of which contain polymorphonuclear leukocytes.69,70 The basement membrane has a lamina lucida and lamina densa supported by anchoring fibrils and microfilaments.19
Epithelial integrity, junctional complexes, and biomarkers associated with intestinal functions
Published in Tissue Barriers, 2022
Arash Alizadeh, Peyman Akbari, Johan Garssen, Johanna Fink-Gremmels, Saskia Braber
The lining epithelial cells are connected by multiple protein structures denoted as apical junctional complexes, including tight junctions (TJs), adherens junctions, and desmosomes (Figure 1).13–15 Adherens junctions play a role in initiation and stabilization of cell-cell contacts through a family of intercellular adhesion molecules and consist of transmembrane proteins, including E-cadherin and nectin as well as associated cytoplasmic proteins catenins, which are directly connected to the actin cytoskeleton.16 Desmosomes are patch-like intercellular junctions at the lateral sides of plasma membranes that join adjacent cells together and provide anchoring sites for intermediate filaments.15,17,18 TJ proteins are thought to be the most essential components of these multiple structures and it is now well-established that the mucosal barrier function cannot be maintained without a well-organized pattern of this anastomosing network of sealing strands comprising over 50 proteins. The intercellular space completely disappears at the level of TJs, whereas in adherens junctions and desmosomes, the adjacent membranes are 15–20 nm apart (Figure 1).13,16,17,19,20 Each individual component of the TJ network is structurally and functionally different, but closely interacts with each other to form an efficient and functional barrier.
The value of desmosomal plaque-related markers to distinguish squamous cell carcinoma and adenocarcinoma of the lung
Published in Upsala Journal of Medical Sciences, 2020
Inmaculada Galindo, Mercedes Gómez-Morales, Inés Díaz-Cano, Álvaro Andrades, Mercedes Caba-Molina, María Teresa Miranda-León, Pedro Pablo Medina, Joel Martín-Padron, María Esther Fárez-Vidal
Desmosomes are cell structures specialized for focal cell-to-cell adhesion that are localized in randomly arranged spots on the lateral sides of plasma membranes. They play an important role in providing strength to tissues under mechanical stress, such as the cardiac muscle and epidermis. Besides the constitutive desmosomal plaque proteins desmoplakin and plakoglobin, at least one of the three classical members of the plakophilin (PKP) family is required to form functional desmosomes (12–14). PKP1 is a major desmosomal plaque component that recruits intermediate filaments to sites of cell–cell contact via interaction with desmoplakin. PKPs regulate cellular processes, including protein synthesis and cell growth, proliferation, and migration, and they have been implicated in tumour development (15–21).
AMPK in regulation of apical junctions and barrier function of intestinal epithelium
Published in Tissue Barriers, 2018
Mei-Jun Zhu, Xiaofei Sun, Min Du
Epithelial cells are joined by a series of intercellular junctions and polarized into the apical and the basolateral domains.30,31 The apical domain of epithelial cells is linked with adjacent epithelial cells through TJs and AJs, which are also referred to as apical junctions (Fig. 1). The assembly of apical junctions is indispensable for the formation and maintenance of epithelial barrier integrity.1,32 Desmosomes are intercellular junctions located below AJs on the lateral membrane and link to intermediate filaments to stabilize the epithelial layer and provide mechanical strength to tissues.33,34 On the basolateral membrane, hemidesmosomes connect to intermediate filament and facilitate epithelial cell adhesion to extracellular matrix in the basal lamina.35 In addition, epithelial cells communicate with surrounding cells through gap junctions (Fig. 1) that are composed of connexins and assembled into hexameric pore-forming channels.36
Related Knowledge Centers
- Bladder
- Cadherin
- Cell Adhesion
- Cell Junction
- Desmoglein
- Epithelium
- Cell Membrane
- Cardiac Muscle
- Cell
- Gastrointestinal Wall