Types of surface epithelium

Types of surface epithelium

Surface epithelia cover the external and internal surfaces of the body

Biology

Keywords

epithelial tissues, epithelial tissue, integument, columnar epithelium, squamous epithelium, cuboidal epithelium, mucous membrane, keratinised, non-keratinised, single layer, stratified, ciliated epithelium, endothelium, absorptive surface, keratinous layer, callus, human, animal, biology

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Scenes

Simple squamous

  • basement membrane - An extracellular matrix of tissue that provides a base for epithelial cells.
  • nuclei - The nuclei are flattened and are situated in the centre of cells.
  • flat cells

Simple cuboidal

  • basement membrane - An extracellular matrix of tissue that provides a base for epithelial cells.
  • nuclei - The nuclei are spherical and are situated in the centre of cells.
  • cuboidal cells - Cube-shaped or spherical cells.

Simple columnar

  • basement membrane - An extracellular matrix of tissue that provides a base for epithelial cells.
  • nuclei - The nuclei are elongated and are situated close to the base of the cells.
  • columnar cells

Pseudostratified ciliated columnar

  • basement membrane - An extracellular matrix of tissue that provides a base for epithelial cells.
  • nuclei - The nuclei are typically elongated and arranged at different levels.
  • elongated cells - Every cell is in direct contact with the basement membrane.
  • cilia - Pseudostratified ciliated columnar epithelium is found in the respiratory system. The function of cilia is to clean the airways. Nicotine damages and paralyses these cilia.
  • mucus
  • goblet cell - A glandular cell that secretes the mucus covering the mucous membrane of the respiratory system.

Non-keratinised stratified squamous

  • basement membrane - An extracellular matrix of tissue that provides a base for the bottom row of cells.
  • nuclei - They become flattened towards the top.
  • lower elongated cells - The bottom layer of cells rests on the basement membrane and consists of stem cells, which can divide and create new epithelial cells.
  • upper flat cells - Epithelial cells are pushed towards the surface, meanwhile they become flattened.

Keratinised stratified squamous

  • basement membrane - An extracellular matrix of tissue that provides a base for the bottom row of cells.
  • nuclei - They become flattened towards the top.
  • lower elongated cells - The bottom layer of cells rests on the basement membrane and consists of stem cells, which can divide and create new epithelial cells.
  • upper flat cells - Epithelial cells are pushed towards the surface, meanwhile they become flattened and keratin protein accumulates in them. They undergo apoptosis (programmed cell death) and a keratinous layer is formed.
  • keratinous layer - Near the surface keratin protein collects within the epithelial cells. They undergo apoptosis (programmed cell death). This is how the keratinous layer is formed. This layer plays an important role in mechanical protection: its thickness depends on the external forces it is exposed to. It also protects against chemical agents and pathogens.

Animation

  • basement membrane - An extracellular matrix of tissue that provides a base for epithelial cells.
  • nuclei - The nuclei are flattened and are situated in the centre of cells.
  • flat cells
  • basement membrane - An extracellular matrix of tissue that provides a base for epithelial cells.
  • nuclei - The nuclei are spherical and are situated in the centre of cells.
  • cuboidal cells - Cube-shaped or spherical cells.
  • basement membrane - An extracellular matrix of tissue that provides a base for epithelial cells.
  • nuclei - The nuclei are elongated and are situated close to the base of the cells.
  • columnar cells
  • basement membrane - An extracellular matrix of tissue that provides a base for epithelial cells.
  • nuclei - The nuclei are typically elongated and arranged at different levels.
  • elongated cells - Every cell is in direct contact with the basement membrane.
  • cilia - Pseudostratified ciliated columnar epithelium is found in the respiratory system. The function of cilia is to clean the airways. Nicotine damages and paralyses these cilia.
  • mucus
  • goblet cell - A glandular cell that secretes the mucus covering the mucous membrane of the respiratory system.
  • basement membrane - An extracellular matrix of tissue that provides a base for the bottom row of cells.
  • nuclei - They become flattened towards the top.
  • lower elongated cells - The bottom layer of cells rests on the basement membrane and consists of stem cells, which can divide and create new epithelial cells.
  • upper flat cells - Epithelial cells are pushed towards the surface, meanwhile they become flattened.
  • basement membrane - An extracellular matrix of tissue that provides a base for the bottom row of cells.
  • nuclei - They become flattened towards the top.
  • lower elongated cells - The bottom layer of cells rests on the basement membrane and consists of stem cells, which can divide and create new epithelial cells.
  • upper flat cells - Epithelial cells are pushed towards the surface, meanwhile they become flattened and keratin protein accumulates in them. They undergo apoptosis (programmed cell death) and a keratinous layer is formed.
  • keratinous layer - Near the surface keratin protein collects within the epithelial cells. They undergo apoptosis (programmed cell death). This is how the keratinous layer is formed. This layer plays an important role in mechanical protection: its thickness depends on the external forces it is exposed to. It also protects against chemical agents and pathogens.

Narration

The cells that make up the simple squamous epithelium are flat and irregularly-shaped; they are arranged in one layer on the basement membrane. This thin and vulnerable type of tissue is found in the body where mechanical protection is not needed and where absorption, secretion and filtration occur. Simple squamous epithelium is found for example in the lining of the alveoli in the lungs and in the inner lining of the walls of blood vessels (where it is called the endothelium).

The cells that make up the simple cuboidal epithelium are nearly cube-shaped and arranged in one layer on the basement membrane. Nuclei are located in the centre of the cells. This type of epithelium is found in simple cuboidal epithelia on the surface of the ducts of certain glands, in the lining of renal tubules and on the surface of the ovaries.

The cells that make up the simple columnar epithelium are cylindrical; their elongated nuclei are located near the base of the cell. This type of epithelium is typically found in the epidermis of invertebrates. In the human body, simple columnar epithelium is found in the lining of intestines, where the epithelial cells are covered with microvilli, and in the inner lining of oviducts, where the epithelial cells are ciliated.

Cellular nuclei of the pseudostratified ciliated columnar epithelium are found in several layers, but the cells form a single epithelium with all the cells resting on the basement membrane. Goblet cells that secrete mucus are typically found in this type of tissue.
This tissue lines most of the lower respiratory tract: the mucus and debris are continuously moved up towards the pharynx by the rhythmic movement of cilia. As nicotine paralyses the cilia, the respiratory tract in smokers is not cleaned properly, thus making them cough.

In the non-keratinised stratified squamous epithelium, only the lowest layer of cells rests on the basement membrane. Cells become flattened towards the top. This tissue provides more protection than simple epithelia. As it does not keratinise, it does not prevent cutaneous respiration. It is therefore typically found in the epidermis of fish. In the human body, it is found where mechanical protection is needed: in the mouth cavity and the pharyngeal cavity, in a part of the esophagus, around the anus and in the vagina.

The keratinised stratified squamous epithelium is the most resistant type of epithelial tissue. The elongated cells of the lowest layer divide, producing new epithelial cells that are pushed towards the surface. Meanwhile, they become flattened and keratin protein accumulates within them. They undergo apoptosis (or programmed cell death) and a keratinous layer is formed on the surface.

The thick keratinous layer plays an important role in life on dry land, as it decreases evaporative water loss and increases tissue resistance. However, it prevents cutaneous respiration and it is therefore typically found in animals with well-developed lungs: reptiles, birds and mammals. The epithelium of amphibians is not fully keratinised and does not prevent cutaneous respiration.
Keratinised stratified squamous epithelium constitutes the external layers of our skin. Its thickness depends on the amount of mechanical stress: physical work often causes calluses on the skin of the palm of our hands.

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