Respiratory epithelium
Encyclopedia
Respiratory epithelium is a type of epithelium
found lining the respiratory tract
, where it serves to moisten and protect the airways. It also functions as a barrier to potential pathogens and foreign particles, preventing infection and tissue injury by action of the mucociliary escalator.
and are, therefore, a single layer of cells, the nuclei are not aligned in the same plane. Hence, it appears as though several layers of cells are present and the epithelium is called pseudostratified.
The majority of cells composing the ciliated pseudostratified columnar epithelium are of three types: a) ciliated cells, b) goblet cells, and c) basal cells. The ciliated cells are columnar epithelial cells with specialized ciliary modifications. Goblet cells, so named because they are shaped like a wine goblet, are columnar epithelial cells that contain membrane-bound mucous granules and secrete mucus, which helps maintain epithelial moisture and traps particulate material and pathogens moving through the airway. The basal cells are small, nearly cuboidal cells thought to have some ability to differentiate into other cells types found within the epithelium. For example, these basal cells respond to injury of the airway epithelium, migrating to cover a site denuded of differentiated epithelial cells, and subsequently differentiating to restore a healthy epithelial cell layer.
Certain parts of the respiratory tract
, such as the oropharynx
, are also subject to the abrasive swallowing of food. To prevent the destruction of the respiratory epithelium in these areas, it changes to stratified squamous epithelium
, which is better suited to the constant sloughing and abrasion. The squamous layer of the oropharynx is continuous with the esophagus
.
containing trapped foreign particles toward the oropharynx
, for either expectoration or swallowing to the stomach where the acidic pH helps to neutralize foreign material and micro-organisms. This system is collectively known as the mucociliary escalator and serves two functions: to keep the lower respiratory tract sterile, and to prevent mucus accumulation in the lungs.
The mucocilliary escalator is vital for the movement of mucus up the respiratory tract to the pharynx. The mucus layer is biphasic with a serous, sol layer in which the cilia beat and, above this, a viscoelastic or gel layer. Due to the viscous properties of this upper mucous layer, the tips of the cilia catch in the layer, which may contain particulate matter, and drag it cranially toward the oropharynx
.
Epithelium
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. Functions of epithelial cells include secretion, selective...
found lining the respiratory tract
Respiratory tract
In humans the respiratory tract is the part of the anatomy involved with the process of respiration.The respiratory tract is divided into 3 segments:*Upper respiratory tract: nose and nasal passages, paranasal sinuses, and throat or pharynx...
, where it serves to moisten and protect the airways. It also functions as a barrier to potential pathogens and foreign particles, preventing infection and tissue injury by action of the mucociliary escalator.
Classification
The respiratory epithelium lining the upper (cranial) airways is classified as ciliated pseudostratified columnar epithelium. This designation is due to the arrangement of the multiple cell types composing the respiratory epithelium. While all cells make contact with the basement membraneBasement membrane
The basement membrane is a thin sheet of fibers that underlies the epithelium, which lines the cavities and surfaces of organs including skin, or the endothelium, which lines the interior surface of blood vessels.- Composition :...
and are, therefore, a single layer of cells, the nuclei are not aligned in the same plane. Hence, it appears as though several layers of cells are present and the epithelium is called pseudostratified.
The majority of cells composing the ciliated pseudostratified columnar epithelium are of three types: a) ciliated cells, b) goblet cells, and c) basal cells. The ciliated cells are columnar epithelial cells with specialized ciliary modifications. Goblet cells, so named because they are shaped like a wine goblet, are columnar epithelial cells that contain membrane-bound mucous granules and secrete mucus, which helps maintain epithelial moisture and traps particulate material and pathogens moving through the airway. The basal cells are small, nearly cuboidal cells thought to have some ability to differentiate into other cells types found within the epithelium. For example, these basal cells respond to injury of the airway epithelium, migrating to cover a site denuded of differentiated epithelial cells, and subsequently differentiating to restore a healthy epithelial cell layer.
Certain parts of the respiratory tract
Respiratory tract
In humans the respiratory tract is the part of the anatomy involved with the process of respiration.The respiratory tract is divided into 3 segments:*Upper respiratory tract: nose and nasal passages, paranasal sinuses, and throat or pharynx...
, such as the oropharynx
Oropharynx
The Oropharynx reaches from the Uvula to the level of the hyoid bone.It opens anteriorly, through the isthmus faucium, into the mouth, while in its lateral wall, between the two palatine arches, is the palatine tonsil....
, are also subject to the abrasive swallowing of food. To prevent the destruction of the respiratory epithelium in these areas, it changes to stratified squamous epithelium
Stratified squamous epithelium
A stratified squamous epithelium consists of squamous epithelial cells arranged in layers upon a basement membrane. Only one layer is in contact with the basement membrane; the other layers adhere to one another to maintain structural integrity...
, which is better suited to the constant sloughing and abrasion. The squamous layer of the oropharynx is continuous with the esophagus
Esophagus
The esophagus is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. During swallowing, food passes from the mouth through the pharynx into the esophagus and travels via peristalsis to the stomach...
.
Mucociliary Escalator
The cilia of the respiratory epithelium beat in concert cranially, effectively moving secreted mucusMucus
In vertebrates, mucus is a slippery secretion produced by, and covering, mucous membranes. Mucous fluid is typically produced from mucous cells found in mucous glands. Mucous cells secrete products that are rich in glycoproteins and water. Mucous fluid may also originate from mixed glands, which...
containing trapped foreign particles toward the oropharynx
Oropharynx
The Oropharynx reaches from the Uvula to the level of the hyoid bone.It opens anteriorly, through the isthmus faucium, into the mouth, while in its lateral wall, between the two palatine arches, is the palatine tonsil....
, for either expectoration or swallowing to the stomach where the acidic pH helps to neutralize foreign material and micro-organisms. This system is collectively known as the mucociliary escalator and serves two functions: to keep the lower respiratory tract sterile, and to prevent mucus accumulation in the lungs.
The mucocilliary escalator is vital for the movement of mucus up the respiratory tract to the pharynx. The mucus layer is biphasic with a serous, sol layer in which the cilia beat and, above this, a viscoelastic or gel layer. Due to the viscous properties of this upper mucous layer, the tips of the cilia catch in the layer, which may contain particulate matter, and drag it cranially toward the oropharynx
Oropharynx
The Oropharynx reaches from the Uvula to the level of the hyoid bone.It opens anteriorly, through the isthmus faucium, into the mouth, while in its lateral wall, between the two palatine arches, is the palatine tonsil....
.