epithelial tissue

Examples of epithelial tissue in the following topics:

• Epithelial Tissues

  • Epithelial tissues cover the outer surfaces of the body and the lumen of internal organs; they are classified by shape and number of layers.
  • Epithelial tissues cover the outside of organs and structures in the body.
  • Epithelia composed of a single layer of cells is called simple epithelia; epithelial tissue composed of multiple layers is called stratified epithelia.
  • However, each cell is attached to the base membrane of the tissue and, therefore, they are simple tissues.
  • In other words, the tissue transitions from thick to thin.

• Complex Tissue Structure

  • Animals, besides Parazoa (sponges), are characterized by specialized tissues such as muscle, nerve, connective, and epithelial tissues.
  • In addition, animals possess unique tissues, absent in fungi and plants, which allow coordination (nerve tissue) and motility (muscle tissue).
  • In vertebrates, bone tissue is a type of connective tissue that supports the entire body structure.
  • Epithelial tissues cover, line, protect, and secrete; these tissues include the epidermis of the integument: the lining of the digestive tract and trachea.
  • For example, the evolution of nerve tissues and muscle tissues has resulted in animals' unique ability to rapidly sense and respond to changes in their environment.

• Intercellular Junctions

  • The extracellular matrix allows cellular communication within tissues through conformational changes that induce chemical signals, which ultimately transform activities within the cell.
  • These junctions are typically found in epithelial tissues that line internal organs and cavities and comprise most of the skin.
  • For example, the tight junctions of the epithelial cells lining your urinary bladder prevent urine from leaking out into the extracellular space.
  • Desmosomes act like spot welds between adjacent epithelial cells, connecting them .
  • The cadherins join two adjacent cells together and maintain the cells in a sheet-like formation in organs and tissues that stretch, such as the skin, heart, and muscles.

• Regulating Immune Tolerance

  • MALT is a collection of lymphatic tissue that combines with epithelial tissue lining the mucosa throughout the body .
  • This tissue functions as the immune barrier and immune response in areas of the body in direct contact to the external environment.
  • Foreign particles that make their way to MALT are taken up by absorptive epithelial cells called M cells and delivered to APCs (antigen-presenting cells) located directly below the mucosal tissue.
  • The dendritic cells migrate to an underlying tissue called a Peyer's patch.
  • The activated cells then return to MALT tissue effector sites.

• Organogenesis

  • The ectoderm forms epithelial cells and tissues, as well as neuronal tissues.
  • If the signaling by growth factors were disrupted, then the entire ectoderm would differentiate into neural tissue.
  • The mesoderm that lies on either side of the vertebrate neural tube will develop into the various connective tissues of the animal body .
  • It forms the epithelial lining of the whole of the digestive tube (except part of the mouth and pharynx) and the terminal part of the rectum (which is lined by involutions of the ectoderm).
  • The mesoderm aids in the production of cardiac muscles, skeletal muscle, smooth muscle, tissues within the kidneys, and red blood cells.

• Gene Expression for Spatial Positioning

  • For example, some cells in the ectoderm (the outer tissue layer of the embryo) will express the genes specific to skin cells.
  • The ectoderm forms epithelial cells and tissues, as well as neuronal tissues.
  • If the signaling by growth factors were disrupted, then the entire ectoderm would differentiate into neural tissue.
  • The mesoderm that lies on either side of the vertebrate neural tube will develop into the various connective tissues of the animal body.

• Animal Characterization Based on Features of Embryological Development

  • Most animal species undergo a separation of tissues into germ layers during embryonic development.
  • The ectoderm develops into the outer epithelial covering of the body surface and the central nervous system.
  • The mesoderm, the third germ layer forming between the endoderm and ectoderm in triploblasts, gives rise to all muscle tissues (including the cardiac tissues and muscles of the intestines), connective tissues such as the skeleton and blood cells, and most other visceral organs such as the kidneys and the spleen.
  • Eucoelomates (or coelomates) have a true coelom that arises entirely within the mesoderm germ layer and is lined by an epithelial membrane.
  • The epithelial membrane also lines the organs within the coelom, connecting and holding them in position while allowing them some free motion.

• Cells as the Basic Unit of Life

  • Several cells of one kind that interconnect with each other and perform a shared function form tissues; several tissues combine to form an organ (your stomach, heart, or brain); and several organs make up an organ system (such as the digestive system, circulatory system, or nervous system).
  • For example, epithelial cells protect the surface of the body and cover the organs and body cavities within.

• Cellular Differentiation

  • The cells of the inner cell mass go on to form virtually all of the tissues of the human body.
  • Epithelial stem cells (progenitor cells) that give rise to the various types of skin cells
  • Muscle satellite cells (progenitor cells) that contribute to differentiated muscle tissue
  • The ectoderm ends up forming the skin and the nervous system, the mesoderm forms the bones and muscular tissue, and the endoderm forms the internal organ tissues.

• Mechanics of Cellular Differentation

  • How does a complex organism such as a human develop from a single cell—a fertilized egg—into the vast array of cell types such as nerve cells, muscle cells, and epithelial cells that characterize the adult?
  • The embryonic cells that develop from totipotent stem cells and are precursors to the fundamental tissue layers of the embryo are classified as pluripotent.
  • A pluripotent stem cell is one that has the potential to differentiate into any type of human tissue but cannot support the full development of an organism.
  • One type of adult stem cell is the epithelial stem cell, which gives rise to the keratinocytes (cells that produce keratin, the primary protein in nails and hair) in the multiple layers of epithelial cells in the epidermis of skin.