Columnar epithelium in the context of "Epidermis"

The trachea (pl.: tracheae or tracheas), also known as the windpipe, is a cartilaginous tube that connects the larynx to the bronchi of the lungs, allowing the passage of air, and so is present in almost all animals' lungs. The trachea extends from the larynx and branches into the two primary bronchi. At the top of the trachea, the cricoid cartilage attaches it to the larynx. The trachea is formed by a number of horseshoe-shaped rings, joined together vertically by overlying ligaments, and by the trachealis muscle at their ends. The epiglottis closes the opening to the larynx during swallowing.

The trachea begins to form in the second month of embryo development, becoming longer and more fixed in its position over time. Its epithelium is lined with column-shaped cells that have hair-like extensions called cilia, with scattered goblet cells that produce protective mucins. The trachea can be affected by inflammation or infection, usually as a result of a viral illness affecting other parts of the respiratory tract, such as the larynx and bronchi, called croup, that can result in a cough. Infection with bacteria usually affects the trachea only and can cause narrowing or even obstruction. As a major part of the respiratory tract, the trachea, when obstructed, prevents air from entering the lungs; thus, a tracheostomy may be required. Additionally, during surgery, if mechanical ventilation is required during anaesthesia, a tube is inserted into the trachea: this is called tracheal intubation.

The seminal vesicles (also called vesicular glands or seminal glands) are a pair of convoluted tubular accessory glands that lie behind the urinary bladder of male mammals. They secrete fluid that largely composes the semen.

The vesicles are 5–10 cm (2.0–3.9 in) in size, 3–5 cm (1.2–2.0 in) in diameter, and are located between the bladder and the rectum. They have multiple outpouchings, which contain secretory glands, which join together with the vasa deferentia at the ejaculatory ducts. They receive blood from the vesiculodeferential artery, and drain into the vesiculodeferential veins. The glands are lined with column-shaped and cuboidal cells. The vesicles are present in many groups of mammals, but not marsupials, monotremes or carnivores..

Respiratory epithelium, or airway epithelium, is ciliated pseudostratified columnar epithelium a type of columnar epithelium found lining most of the respiratory tract as respiratory mucosa, where it serves to moisten and protect the airways. It is not present in the vocal cords of the larynx, or the oropharynx and laryngopharynx, where instead the epithelium is stratified squamous. It also functions as a barrier to potential pathogens and foreign particles, preventing infection and tissue injury by the secretion of mucus and the action of mucociliary clearance.

The gastric mucosa is the mucous membrane layer that lines the entire stomach. The mucus is secreted by gastric glands, and surface mucous cells in the mucosa to protect the stomach wall from harmful gastric acid, and from digestive enzymes that may start to digest the tissue of the wall. Mucus from the glands is mainly secreted by pyloric glands in the lower region of the stomach, and by a smaller amount in the parietal glands in the body and fundus of the stomach.

The mucosa is studded with millions of gastric pits, which the gastric glands empty into. In humans, it is about one millimetre thick, and its surface is smooth, and soft. It consists of simple secretory columnar epithelium, an underlying supportive layer of loose connective tissue called the lamina propria, and the muscularis mucosae, a thin layer of muscle that separates the mucosa from the underlying submucosa. The gastric mucosa serves as a gastric barrier, reinforced by tight junctions between the epithelial cells.