Cells, Tissues and Organs
David Sturgeon in Introduction to Anatomy and Physiology for Healthcare Students, 2018
So far we have looked at the body on an atomic, molecular and a cellular level. In terms of size and complexity, the next functional unit of the body is tissue. Tissue is simply a collection or aggregation of cells acting cooperatively to perform one or more specific function in the body. There are four distinct categories of tissue: epithelial, connective, muscular and nervous. The first type, epithelial, has three important functions: protection, secretion and absorption. The best way to imagine epithelial tissue is as a continuous sheet of cells that cover the outside and the inside surfaces of the body. For example, the skin, the lining of the cardiovascular system, the digestive tract, the urinary tract, the respiratory tract and the reproductive tract are all composed of epithelial cells. Epithelial tissue that covers the outer surfaces of the body (including the mucous membranes of the gastrointestinal and urinary tracts that communicate with the outside of the body) is referred to as epithelium. Whilst epithelial tissue that is only found on inner surfaces of the body, such as within the blood and lymphatic vessels, is known as endothelium. In either case, the cells are arranged in a number of ways. The simplest way to classify them is by shape (Figure 2.7). They can be columnar (like columns – upright), cuboidal (like cubes) or squamous (from the Latin for ‘fish-scale’ – flat). Just pause to remember that they are cells like any other and exhibit exactly the same characteristics discussed above (they have a plasma membrane, nucleus and cytoplasm, etc.).
Tissue is the Issue
Brian Leyland-Jones in Pharmacogenetics of Breast Cancer, 2020
Undoubtedly the solid type of tissue carries the bulk of these issues. Other fluid forms of tissue, however, do have their own share of these issues, of course. Tissue will be defined here as biological material comprising a network of characteristically diverse cells. In essence, blood, urine, surgical resections, biopsies, marrow, lavage, hair, nail, and other specimen taken from a person will be considered as tissue. Turn to any biomedical community member and most, if not all, will have some sort of opinion about tissue. Between the ultimate giver (patients) and ultimate user (laboratorians) lie the challenges. To the patient, care team, and several entities, the tissue is the issue, and to the laboratories, technologists, and the interpreters of results, the issue is really the tissue.
Sample Preparation for Liquid Scintillation Counting
Graham Lappin, Simon Temple in Radiotracers in Drug Development, 2006
There are four basic types of tissue: epithelium, connective tissue, muscle tissue, and nervous tissue. The epithelium is usually the layer of cells that resides closer to the outside world. The outermost layer of skin is composed of dead scaly or platelike epithelial cells. Other examples are the mucous membranes lining the inside of mouths and body cavities. Internally, epithelial cells line the insides of the lungs, the gastrointestinal tract, the reproductive and urinary tracts, and make up the exocrine and endocrine glands. The primary functions of epithelial cells include secretion, absorption and protection. Loose connective tissue holds organs and epi-thelia in place and contains a variety of proteinaceous fibers, including collagen and elastin. Ligaments and tendons are a form of fibrous connective tissue. In most vertebrates, cartilage is found primarily in joints, where it provides cushioning. Muscle cells contain contractile filaments that move past each other, changing size as they do so. The most obvious examples of nervous tissue are the cells forming the brain, spinal cord and peripheral nervous system. The nervous system consists chiefly of two types of cells, neurons and Glia.
Regenerating β cells of the pancreas – potential developments in diabetes treatment
Published in Expert Opinion on Biological Therapy, 2018
The in vivo reprogramming of non-β cells into β cells is an attractive but challenging strategy. Thus far, four types of tissues/cells have been explored in preclinical studies, which include liver cells, GI tract cells, pancreatic exocrine cells, and islet α cells. More remotely related cells require more complicated manipulation of gene expression. For example, liver-to-pancreas transdifferentiation appears to be a progressive and hierarchical process, which needs sequential expression of transcription factors in the order of Pdx1, Pax4, and MafA. The epithelium of antral stomach can be reprogrammed into insulin+ cells by co-expression of Ngn3, Pdx1, and MafA. The acinar cells in pancreas can be reprogrammed into three types of islet cells with different transcription factors, and a combination of Ngn3, Pdx1, and MafA results in acinar-to-β-cell conversion. Transdifferentiating α cells to β cells can be achieved by forced expression of a single transcription factor Pax4 or by inhibition of Arx.
Dysfunction of epithelial permeability barrier induced by HMGB1 in 2.5D cultures of human epithelial cells
Published in Tissue Barriers, 2022
Takashi Kojima, Yuma Shindo, Takumi Konno, Yuki Kodera, Wataru Arai, Maki Miyakawa, Kizuku Ohwada, Hiroki Tanaka, Mitsuhiro Tsujiwaki, Yuji Sakuma, Shin Kikuchi, Tsuyoshi Ohkuni, Kenichi Takano, Atsushi Watanabe, Takayuki Kohno
The airways are broadly classified into conducting and respiratory regions. The conducting airways consist of the trachea, bronchi, and bronchioles, while respiratory regions consist of respiratory bronchioles and alveoli. The conducting airways are lined by a continuous layer of bronchiolar epithelial cells, which act as a first barrier for inhaled materials and play an important role in protection from external pathogens such as bacteria, viruses, chemical substances and allergic components.23,24 On the other hand, alveolar epithelial cells, which are vital for gas exchanges, form a barrier for an air-liquid interface.25 To maintain the air-liquid interface and control gas exchanges, alveolar epithelial cells provide a proper permeability barrier.26 The main characteristic of epithelial tissues is that epithelial cells are arranged in monolayers or stratified layers and tightly adhere to each other. This sheet-like structure provides a barrier function that separates the apical and basolateral compartments of various tissues, and maintains homeostasis.
Novel understanding of high mobility group box-1 in the immunopathogenesis of incisional hernias
Published in Expert Review of Clinical Immunology, 2019
Nicholas K. Larsen, Matthew J. Reilly, Finosh G. Thankam, Robert J. Fitzgibbons, Devendra K. Agrawal
Connective tissue consists of many components which form a supportive network of fibrous components to anchor cells and proteins. Recent evidence has shown that the network can bind growth factors and cytokines to regulate cell function and wound repair [13]. The extracellular matrix (ECM) and connective tissue play an important role in the pathological and physiological components of wound healing. Wound healing is a dynamic and tightly regulated process that associates cellular, molecular, biochemical, and physiological events together, which start immediately after wounding and continues until the complete healing and restitution of the tissue functionality [14]. The wound healing process consists of three phases: inflammatory, proliferative, and remodeling (Figure 1). The ECM has a major role in the latter two. The ECM has classically been considered to be the architectural foundation for cellular support, but current evidence suggests that it also plays a large role in many important cellular functions including proliferation, migration, protein degradation, and apoptosis [14].