epithelium

Examples of epithelium in the following topics:

• Mucosa

  • The mucosa is the innermost layer of the gastrointestinal (GI) tract, composed of simple epithelium cells.
  • It is composed of epithelium cells and a thin connective tissue.
  • The mucosa is made up of three layers: epithelium, lamina propria, and muscularis mucosae.
  • The most variation is seen in the epithelium tissue layer of the mucosa.
  • In the esophagus, the epithelium is stratified, squamous, and non-keratinizing, for protective purposes.

• Types of Epithelial Tissue

  • Simple epithelium consists of a single layer of cells.
  • In this case, the epithelium is described as ciliated pseudostratified epithelium.
  • Stratified epithelium differs from simple epithelium by being multilayered.
  • Squamous epithelium has cells that are wider than they are tall.
  • Columnar epithelium has cells taller than they are wide.

• Characteristics of Epithelial Tissue

  • Epithelia tissue forms boundaries between different environments, and nearly all substances must pass through the epithelium.
  • In its role as an interface tissue, epithelium accomplishes many functions, including:
  • The secretion of sweat, mucus, enzymes, and other products that are delivered by ducts come from the glandular epithelium.
  • There are eight basic types of epithelium: six of them are identified based on both the number of cells and their shape; two of them are named by the type of cell (squamous) found in them.

• Epithelial Membranes

  • The mucous membranes are linings of mostly endodermal origin, covered in epithelium, which are involved in absorption and secretion.
  • It consists of an epithelium layer and an underlying lamina propria of loose connective tissue.

• Anatomy of the Gallbladder

  • There are several different layers of the gallbladder: the mucosa (epithelium and lamina propria), the muscularis, the perimuscular, and the serosa.
  • The epithelium is a thin sheet of cells closest to the inside of the gallbladder.
  • The lamina propria is a thin layer of loose connective tissue, which together with the epithelium forms the mucosa.

• Development of the Integumentary System

  • At 4 weeks gestation, simple ectoderm epithelium forms.
  • Between 4 and 12 weeks, the basal cells divide repeatedly to form the stratified epithelium while the mesoderm forms the blood vessels and connective tissues.
  • Melanoblasts that form melanocytes migrate with neural crests cells to the epithelium and begin producing melanin prior to birth.

• Glandular Epithelia

  • Glandular epithelium contains glands, either exocrine or endocrine, allowing for secretory function.
  • Epithelium is one of the four basic types of animal tissue, along with connective tissue, muscle tissue, and nervous tissue.
  • The exocrine glands secrete their products into a duct that then delivers the product to the lumen of an organ or onto the free surface of the epithelium.

• Skin and Mucosae (Surface Barriers)

  • The most variation is seen in the epithelium.
  • In the esophagus and oropharynx, the epithelium is stratified, squamous and non-keratinising, to protect these areas from harsh or acidic foods.
  • The small intestine epithelium is specialized for absorption, organized into simple columnar epithelium on protruding villi with narrow crypts that have a high surface area.
  • The mucosal epithelium in the nasopharynx is psuedostratified and ciliated, which helps accumulate and remove mucus.
  • Not every pathogen is caught nor inhibited in mucus, and some may infect the mucosal epithelium directly.

• Basement Membranes and Diseases

  • The basement membrane anchors epithelium to the connective tissue beneath it.
  • The basal lamina layer can further be divided into two layers: the clear layer closer to the epithelium is called the lamina lucida, and the dense layer closer to the connective tissue is called the lamina densa.
  • The primary function of the basement membrane is to anchor down the epithelium to its loose connective tissue underneath.
  • The most notable examples of basement membranes are in the glomerular filtration of the kidney, by the fusion of the basal lamina from the endothelium of glomerular capillaries and the basal lamina of the epithelium of the Bowman's capsule; and between lung alveoli and pulmonary capillaries, by the fusion of the basal lamina of the lung alveoli and of the basal lamina of the lung capillaries, which is where oxygen and CO2 diffusion happens.

• Development of Vision

  • The epithelium thickens to form the lens placode.
  • The lens differentiates and invaginates until it pinches off from the epithelium.
  • The optic cup then delaminates into two layers: the neural retina and the retinal pigment epithelium.
  • It is critical for the induction of the retinal pigment epithelium and the optic nerve.
  • The pigmented retina is formed by rods and cones and composed of small cilia typical of the ependymal epithelium of the neural tube.