transitional epithelial tissues

Examples of transitional epithelial tissues in the following topics:

• Ureters

  • The ureters are two tubes that are made out of smooth muscle and transitional epithelial tissues, which are a type of epithelial tissue that may either be columnar or squamous.
  • The ureteral valves function similarly to the semilunar valves in the veins of the body, but are structurally different, consisting of transverse mucosal epithelial folds.
  • Ureter cancer is often due to a malignant transformation of of the transitional epithelial tissue, which is more vulnerable to developing cancer cells compared to other tissues.

• Types of Epithelial Tissue

  • Epithelial tissue is classified by cell shape and the number of cell layers.
  • Most epithelial tissue is described with two names.
  • For example, simple squamous epithelial tissue describes a single layer of cells that are flat and scale-like in shape.
  • Simple epithelial tissues are generally classified by the shape of their cells.
  • Transitional epithelia are found in tissues that stretch and it can appear to be stratified cuboidal when the tissue is not stretched, or stratified squamous when the organ is distended and the tissue stretches.

• Characteristics of Epithelial Tissue

  • The human body consists of four types of tissue: epithelial, connective, muscular, and nervous.
  • Epithelial tissue covers the body, lines all cavities, and composes the glands.
  • Epithelial tissue is composed of cells laid out in sheets with strong cell-to-cell attachments.
  • The epithelial cells are nourished by substances diffusing from blood vessels in the underlying connective tissue.
  • Epithelial tissues are identified by both the number of layers and the shape of the cells in the upper layers.

• Gastrulation

  • During gastrulation, the embryo develops three germ layers (endoderm, mesoderm, and ectoderm) that differentiate into distinct tissues.
  • Each layer gives rise to specific tissues and organs in the developing embryo.
  • Cells from the epiblast at the primitive streak undergo an epithelial to mesenchymal transition and ingress at the primitive streak to form the germ layers.
  • The ectoderm gives rise to the epidermis, and also to the neural crest and other tissues that will later form the nervous system.
  • The somites form muscle, the cartilage of the ribs and vertebrae, the dermis, the notochord, blood and blood vessels, bone, and connective tissue.

• Epithelial Membranes

  • It consists of an epithelium layer and an underlying lamina propria of loose connective tissue.
  • Most mucous membranes contain stratified squamous or simple columnar epithelial tissue.
  • The epithelial tissue sheet lies directly over the layer of loose connective tissue called lamina propria.
  • The submucosa is the tissue that connects the mucosa to the muscle outside the tube.

• Development of the Peripheral Nervous System

  • The peripheral nervous system develops from two strips of tissue called the neural crest, running lengthwise above the neural tube.
  • At this point the future CNS appears as a cylindrical structure called the neural tube, whereas the future PNS appears as two strips of tissue called the neural crest, running lengthwise above the neural tube.
  • Subsequently, neural crest cells from the roof plate of the neural tube undergo an epithelial to mesenchymal transition, delaminating from the neuroepithelium and migrating through the periphery where they differentiate into varied cell types, including pigment cells and the cells of the peripheral nervous system.

• Glandular Epithelia

  • Epithelium is one of the four basic types of animal tissue, along with connective tissue, muscle tissue, and nervous tissue.
  • Epithelial tissues line the cavities and surfaces of structures throughout the body, and also form many glands.
  • Exocrine and endocrine epithelial cells are highly vascular.
  • Secretion is one major function of epithelial cells .
  • Glands are formed from the invagination / infolding of epithelial cells and subsequent growth in the underlying connective tissue.

• Serosa

  • Serosa consists of a secretory epithelial layer and a thin connective tissue layer that reduce the friction from muscle movement.
  • Serosa is not to be confused with adventitia, a connective tissue layer which binds together structures rather than reducing friction between them.
  • Each serous membrane is composed of a secretory epithelial layer and a connective tissue layer underneath.
  • The epithelial layer, known as mesothelium, consists of a single layer of avascular flat nucleated cells (simple squamous epithelium) which produce the lubricating serous fluid.
  • These cells are bound tightly to the underlying connective tissue.

• Tissues in Levels of Organization

  • Tissues are groups of similar cells that have a common function.
  • The four basic tissue types are epithelial, muscle, connective, and nervous tissue.
  • Each tissue type has a characteristic role in the body:
  • Most organs contain more than one tissue type.
  • Cells form tissues, and tissues form organs.

• Levels of Organization

  • In humans, most cells combine to form tissues, but some cells are found independent of solid tissues and have their own functions.
  • Humans have four different types of basic tissues.
  • Connective tissues such as bone tissue are made up of fibrous cells and give shape and structure to organs.
  • Epithelial tissues make up the outer layers of organs, such as the skin or the outer layer of the stomach.
  • Most organs contain tissues such as parenchyma (used to perform the organ functions),  stroma (connective tissue specific to organs) and epithelial.